LIBRARY UNIVERSITY OF CALIFORNIA. Class CLAYS THEIR OCCURRENCE, PROPERTIES, AND USES WITH ESPECIAL REFERENCE TO THOSE OF THE UNITED STATES BY HEIKKICH BIES, PH.D. Professor of Economic Geology in Cornell University ; Fellow Geological Society of America ; Member American Ceramic Society ; Member American Institute of Mining Engineers ; Author of "Economic Geology of the United States " FIRST EDITION FIRST THOUSAND NEW YORK JOHN WILEY & SONS CHAPMAN & HALL, LIMITED 1906 Copyright, 1906 BY HEINRICH RIES ROBtET DROMMOND, PRINTER, NEW YORK PREFACE FEW mineral products have, perhaps, been more extensively treated in the scientific and technical literature than clay, but the published facts are widely scattered, and many of them are not always easily accessible. It has therefore seemed to the author that there is a demand for a comprehensive work on the subject, which may be of value to geologists, chemists, and others interested in clay and its applications. As the title of the work indicates, the subject is treated mainly from the American standpoint, and in the preparation of it the author has drawn freely on his own published reports as well as those of others. The arrangement of the subject-matter of the State descriptions by geologic formations has been selected as permitting the greatest uni- formity of treatment, and those desiring to look up the distribution of any one kind of clay can easily do so by reference to the Index. Credit for information is usually given in foot-notes; but where some particular report has been freely drawn upon, this is indicated by a parenthesis containing the number of the reference in the bibliography following each State. The author wishes to express his thanks to Dr. G. P. Merrill of the United States National Museum for many helpful suggestions received during the course of his work; and to Mr. S. Geijsbeek of Seattle, Wash., for assistance rendered during the compilation of the manuscript. Acknowledgments are similarly due to Professors C. S. Prosser and E. Orton, Jr., of Ohio State University; Prof. H. A. Wheeler and Mr. Lemon Parker of St. Louis, Mo. ; Prof. I. A. Williams, Iowa Geological Survey; Dr. E. A. Smith, Alabama Geological Survey; Dr. G. P. Grims- ley, West Virginia Geological Survey; Dr. W. B. Clark, Maryland Geo- logical Survey; Dr. D. H. Newland, New York Geological Survey; Dr. iii 155021 iv PREFACE H. B. Kummel, New Jersey Geological Survey; and Mr. H. Leigh ton, Cornell University. Dr. W. B. Phillips, former State Geologist of Texas, has kindly given the author permission to publish the facts relating to that State. For the loan of cuts the writer is indebted to the American Clay Machinery Co., Bucyrus, Ohio; Chambers Brothers Co., Philadelphia, Pa.; Henry Martin Machine Co., Lancaster, Pa.; and Bergstrom & Bass, Brooklyn, N. Y. Many others have kindly loaned photographs, and to each of these acknowledgment is made under the respective illustrations. CORNELL UNIVERSITY, ITHACA, N. Y., July, 1906. CONTENTS PAGE PREFACE iii CONTENTS v LIST OF ILLUSTRATIONS xi LIST OF ABBREVIATIONS xvi INDEX - . 469 CHAPTER I ORIGIN OF CLAY. '. 1 Definition, 1; Weathering processes involved, 1; Kaolinization, 3; Kaoliniza- tion by pneumatolysis, 5; Residual clay, 7; Kaolin, 8; Form of residual deposits, 11; Distribution of residual clays, 12; Transported clays, 14; Sedimentary clays, 14; Origin, 14; Structural irregularities in sedimentary clays, 17; Classification of sedimentary clays, 18; Marine clays, 19; Estuarine clays, 19; Swamp and lake clays, 20; Flood-plain and terrace clays, 20; Drift or bowlder clays, 20; /Eolian clays, 23; Classification of clay -deposits, 23; Orton's classification, 23; Wheeler's classification, 24; Ladd's classification, 24; Buckley's classification, 25; E. Orton, Jr.'s, classification, 26; Grimsley and Grout's classification, 26; Ries' classification, 27; Secondary changes in clay-deposits, 28; Mechanical changes, 28; Tilting, folding, faulting, 28; Erosion, 30; Chemical changes, 33; Change of color, 33; Leaching, 35; Softening, 35; Consolidation, 35; Concretions, 35; Formation of shale, 36. CHAPTER II CHEMICAL PROPERTIES OF CLAY 40 Minerals in clay, 40; Hydrous aluminum silicates, 42; Kaolinite, 42; Minerals related to kaolinite, 48; Halloysite, 48; Indianaite, 50; Pholerite, 50; Nacrite, 51; Rectorite, 51; Newtonite, 51; Allophane, 51; Le Chatelier's experiments, 51; Quartz, 52; Feldspar, 53; Mica, 53; Iron ores, 54; Limonite, 54; Hematite, 54; Magnetite, 55; Siderite, 55; Pyrite, 55; Calcite, 55; Gypsum, 56; Rutile, 56; Ilmenite, 56; Glauconite, 57; Dolomite and magnesite, 57; Hornblende and garnet, 57; Vanadates, 57; Tourmaline, 57; Manganese oxides, 58; Vivianite, Vi CONTENTS PAGE 57; Rare elements, 58; The chemical analysis of clays, 58; The ultimate analysis, 58; Interpretation of ultimate analysis. 59; Variation in chemical composition of clays, 60; Variations in the same deposit, 60; Rational analysis, 61; Comparison of ultimate and rational analyses, 62; Method of making ultimate analysis, 64; Method of making rational analysis, 66; Mineral compounds in clay and their chemical effects, 68; Silica, 68; Hydrous silica, 70; Iron oxide, 71; Sources of iron oxide in clays, 71; Effects of iron compounds, 72; Coloring action of iron in unburned clay, 72; Coloring action of iron oxide on burned clay, 72; Fluxing action of iron oxide, 75; Effect of iron oxide on absorptive power and shrinkage of clay, 76; Lime, 76; Effect of lime carbonate in clay, 76; Effect of lime-bearing silicates, 78; Effect of gypsum, 78; Magnesia, 80; Alkalies, 82; Titanium, 84; Effect of titanium, 85; Water in clay, 86; Mechanically combined water, 86; Chemically combined water, 87; Carbonaceous matter, 88; Effects of carbon in clay, 88; Effect of water on black coring, 90; Soluble salts, 90; Origin, 90; Quan- tity of soluble salts in a clay, 92; Prevention of soluble salts, 92; Method of use, 92. CHAPTER III PHYSICAL PROPERTIES OF CLAY 94 Introductory, 94; Plasticity, 94; Definition, 94; Cause of plasticity in clay, 96; Water-of-hydration theory, 96; Texture theory, 96; Plate theory, 97; Inter- locking-grain theory, 98; Ball theory, 99; Colloid theory, 99; Molecular- attraction theories, 103; Effect of bacteria, 104; Weathering clay, 104; The measurement of plasticity, 105; Tests of the wet clay, 105; Tests of the dry clay, 108; Texture, 108; Definition, 108; Mechanical analysis, 108; Methods of separation, 110; Beaker method, 110; Schoene method, 113; Hilgard's elutriator, 114; Centrifugal separator, 115; Relation between composition and texture, 117; Tensile strength, 120; Definition, 120; Practical bearing, 120; Relation to plasticity, 120; Meas- urement of tensile strength, 120; Cause of tensile strength, 123; Shrinkage, 128; Air-shrinkage, 128; Fire-shrinkage, 129; Measurement of shrinkage, 132; Poros- ity, 134; Specific gravity, 136; Determination of specific gravity, 137; Fusibility, 137; Incipient vitrification, 138; Complete vitrification, 138; Viscosity, 138; Effect of chemical composition on fusibility, 139; Homogeneity, 144; Influence of texture, 144; Condition of oxidation, 145; Expression of fusibility, 145; Bischof's formula, 145; Seger's formula, 146; Wheeler's formula, 146; Methods of measuring fusibility, 147; Direct methods, 147; Seger cones, 148; Thermo- electric pyrometer, 153; Wedgewood pyrometer, 154; Lunette optical pyrometer, 154; Classification of clays based on fusibility, 154; Indirect methods, 155; Changes taking place in burning, 156; Dehydration period, 157; Oxidation period, 158; Vitrification period, 159; Effects due to variation in the clay, 159; Loss of volatile products in burning, 161; Color, 161; Color of unburned clay, 161; Color of burned clay, 161; Slaking, 162; Permeability, 163; Absorp- tion, 163. CHAPTER IV KINDS OP CLAYS 165 Kaolins, 165; Chemical composition, 167; Physical tests, 167; Distribution, 167; Ball-clay, 168; Chemical composition, 169; Physical characters, 169; Dis- CONTENTS vii PAGE tribution, 169; Fire-clays, 170; Chemical composition, 170; Effect of silica, 170; Effect of titanium, 177; Physical properties, 177; Analyses of fire-clays, 177; Occurrence and distribution, 177; Uses, 179; Stoneware-clays, 180; Physical properties, 180; Chemical composition, 180; Physical tests, 181; Terra-cotta clays, 182; Sewer-pipe clays, 183; Brick-clays, 185; Common brick, 185; Adobe, . 186; Loess, 186; Pressed brick, 187; Flashing, 189; Enameled brick, 191; Paving- brick clays, 191; Fireproofing and hollow-brick clays, 192; Slip-clays, 193; Miscellaneous kinds of clays, 195; Clays used when burned, 195; Gumbo-clay, 195; Retort-clay, 196; Pot-clay, 196; Ware-clay, 196; Pipe-clay, 196; Sagger- clay, 196; Wad-clay, 197; Portland -cement clay, 197; Clays used in unburned condition, 197; Paper-clays, 197; Mineral paint, 198; Ultramarine manufacture, 199; Polishing and abrasive materials, 199. METHODS OF MINING AND MANUFACTURE 199 Methods of mining, 199; Prospecting for clays, 199; Outcrops, 199; Springs, 200; Ponds, 200; Vegetation, 200; Exploitation of clay-deposits, 203; Adapta- bility of clay for working, 203; Methods of winning the clay, 204; Haulage, 209; Kaolin- mining, 209; Underground workings, 212; Preparation of clay for market, 213; Washing, 213; Details, 213; Air separation, 214; The manufacture of clay products, 217; Uses of clay, 217; Methods of manufacture, 217; Building- brick and paving-brick, 218; Manufacture of brick, 218; Preparation, 218; Crushers, 219; Dry pans, 219; Disintegrators, 219; Rolls, 219; Soak-pits, 220; Ring-pits, 220; Pug-mills, 220; Wet pans, 220; Molding, 220; Soft-mud process, 220; Stiff -mud process, 228; Dry-press and semi -dry- press process, 231; Re-pressing, 232; Drying, 232; Open yards, 232; Pallet driers, 232; Drying tunnels, 232; Floor driers, 236; Burning, 236; Kilns, 236; Up-draft kilns, 236; Down-draft kilns, 239; Continuous kilns, 239; Sewer-pipe manufacture, 240; Drain-tile, 247; Hollow ware for structural work, 247; Manufacture, 251; Conduits, 251; Manu- facture, 251; Fire-brick, 252; Roofing-tile, 254; Terra-cotta, 254; Manufacture, 254; Floor- tile, 258; Wall- tile, 261; Pottery, 262; Classification, 262; Manufac- ture of pottery, 263; Preparation, 264; Weathering and grinding, 264; Washing, 264; Blunging and filter- pressing, 264; Ball-mills, 265; Tempering, 265; Chaser- mills, 265; Pug-mills and hand-wedging, 265; Wedging- tables, 266; Molding, 266; Turning, 266; Jollying or jiggering, 266; Pressing, 269; Casting, 269; Dry- ing, 270; Subsequent steps, 270; Common red earthenware, 270; Yellow and Rockingham ware, 270; Stoneware, 270; White ware and porcelain, 271; Elec- trical porcelain, 275; Sanitary ware, 275; Bath-tubs and wash-tubs, 276. CHAPTER V DISTRIBUTION OF CLAY IN THE UNITED STATES. ALABAMA LOUISIANA 277 Introduction, 277; Statistics of production, 277; Alabama, 278; Archaean and Algonkian, 278; Cambrian and Silurian, 281; Lower Carboniferous, 281; Coal- measures, 281; Cretaceous, 282; Tertiary, 283; Pleistocene, 283; Division of clays by kinds, 283; China clays, 283; Fire-clays, 283; Pottery-clays, 283; Brick- clays, 283; References on Alabama clays, 285; Arkansas, 285; References on Arkansas clays, 286; Arizona, 286; California, 286; References on California viii CONTENTS clays, 289; Colorado, 289; Mesozoic, 290; Pleistocene, 290; References on Colo- rado clays, 290; Connecticut, 293; Residual clays, 293; Pleistocene, 295; Refer- ences on Connecticut clays, 296; Delaware, 296; District of Columbia, 296; Florida, 297; References on Florida clays, 297; Georgia, 298; Palaeozoic area, 298; Pre-Cambrian belt, 298; Coastal plain region, 301; References on Georgia clays, 303; Illinois, 303; Ordovician, 304; Coal-measures, 304; Tertiary clays, 304; Drift-clays, 304; References on Illinois clays, 307; Indiana, 307; Ordovician, 307; Silurian, 307; Devonian, 307; Mississippian or Lower Carboniferous, 307; Residual clays, 307; Shales, 307; Carboniferous, 309; Kaolin or Indianaite, 309; Coal- measure clays and shales, 311; Pleistocene clays, 313; References on Indiana clays, 313; Indian Territory, 315; Iowa, 316; Cambrian, 316; Ordovician, 316; Galena- Trenton, 316; Maquoketa shale, 316; Silurian, 316; Devonian, 318; Carboniferous, 318; Kinderhook, 318; Augusta, 318; Coal-measures, 321; Cre- taceous, 321; Pleistocene, 322; References on Iowa clays, 322; Kansas, 326; Carboniferous, 326; Triassic, 327; Cretaceous, 327; Pleistocene, 327; References on Kansas clays, 327; Kentucky, 328; Ordovician- Devonian, 328; Carboniferous, 328; Lower Carboniferous, 328; Coal-measures, 329; Tertiary, 329; Recent clays, 329; References on Kentucky clays, 330; Louisiana, 331; References on Louisiana clays, 332. CHAPTER VI MAINE NORTH CAROLINA 333 Maine, New Hampshire, and Vermont, 333; References on Vermont clays, 334; Maryland, 334; Algonkian clays, 334; Silurian shales, 335; Devonian shales, 335; Carboniferous shales, 335; Mauch Chunk, 335; Pottsville, 335; Allegany, 336; Conemaugh, 336; Cretaceous and Jura-Trias clays, 336; Patuxent, 336; Arundel formation, 337; Patapsco formation, 337; Rari tan formation, 337; Tertiary clays, 337; Pleistocene, 337; References on Maryland clays, 339; Massachusetts, 340; Residual clays, 340; Cretaceous and Tertiary clays, 341; Pleistocene clays, 341; References on Massachusetts clays, 342; Michigan, 342; Silurian, 342; Hudson Rivrer, 342; Devonian, 345; Hamilton shales, 345; Marshall series, 345; Car- boniferous, 345; Michigan shales, 345; Coldwater shales, 346; Pleistocene, 346; References on Michigan clays, 347; Minnesota, 348; Residual clays, 348; Trans- ported clays, 348; Pre-Cambrian, 348; Ordovician, 348; Cretaceous, 348; Pleis- tocene, 351; Loess-deposits, 351; References on Minnesota clays, 351; Mississippi, 352; References on Mississippi clays, 352; Missouri, 352; Palaeozoic limestone clays, 354; Kaolins, 354; Flint-clays, 354; Ball-clays, 355; Stoneware clays, 355; Coal-measures, 356; Plastic fire-clays, 356; Stoneware-clays, 359; Impure shales, 359; Tertiary, 360; Pleistocene, 360; Loess clays, 360; Glacial clays, 360; Allu- vial clays, 360; References on Missouri clays, 360; Nebraska. 362; Carboniferous, 362; Cretaceous, 363; Loess and alluvium, 363; References on Nebraska clays, 364; New Jersey, 364; Cambrian and Ordovician, 364; Triassic, 364; Cretaceous, 366; Lower Cretaceous clay series, 366; Clay -marl series, 370; Tertiary, 370; Pleistocene clays, 371; References on New Jersey clays, 373; New Mexico, 373; New York, 375; Residual clays, 375; Palaeozoic shales, 375; Hudson River shale, 376; Niagara shale, 376; Medina shale, 376; Clinton shales, 376; Salina shale, CONTENTS ix 376; Hamilton shale, 376; Portage shale, 376; Chemung shale, 376- Crete* m/"" and Tertiary clays, 378; Pleistocene clays, 378; References on New York clav 382; North Carolina, 382; Residual clays, 385; Sedimentary clays 385- Ref ences on North Carolina clays, 388. CHAPTER VH NORTH DAKOTA TO WYOMING North Dakota, 389; Cretaceous, 389; Benton and Niobrara, 389; Pierre 389- Fox Hills, 389; Laramie and Tertiary, 389; Pleistocene, 390; References on North Dakota clays, 390; Ohio, 390; Ordovician and Silurian, 390; Devonian, 392; Lower Carboniferous, 392; Coal measures, 392; Pottsville formation, 393; Sharon shales, 393; Quakertown clay and shale, 393; Lower Mercer clay and shale, 394- Upper Mercer clay and shale, 394; Mount Savage clay, 394; Allegheny or Lower Coal-measures, 394; Putnam Hill or Brookville clay, 394; Ferriferous or Vanport limestone and clays, 395; Lower Kittanning clay and shale, 395; Middle Kittan- ning clay, 397; Lower Freeport clay, 397; Upper Freeport clay and shale, 397; Conemaugh or Lower Barren Measures, 398; Monongahela or Upper Productive Measures, 398; Dunkard or Upper Barren Measures, 398; Pleistocene, 398; Refer- ences on Ohio clays, 399; Oklahoma Territory, 400; Pennsylvania, 401; Residual clays, 401; Silurian and Devonian shales, 402; Carboniferous, 402; Pottsville, 402; Mercer or Alton fire-clay, 402; Sharon upper coal fire-clay, 405; Savage Mountain fire-clay, 405; Allegheny or Lower Productive Measures, 405; Brookville clay, 405; Clarion clay, 406; Ferriferous coal under-clay, 406; Lower Kittanning fire-clay, 406; Middle Kittanning clay, 407; Upper Kittanning clay, 407; Lower Freeport clay, 408; Upper Freeport limestone clay or Bolivar fire-clay, 411; Upper Freeport clay, 411; Conemaugh formation or Lower Barren Measures, 411; Monon- gahela group or Upper Coal-measures, 413; Pleistocene clays, 413; References on Pennsylvania clays, 414; Rhode Island, 415; References on Rhode Island clays, 415; South Carolina, 415, Residual clays, 415; Coastal plain clays, 415; South Dakota, 419; References on South Dakota clays, 420; Tennessee. 420, Pre- Cam- brian clays, 421; Palaeozoic residual clays, 421; Carboniferous, 421; Tertiary, 422; Alluvial clays. 423; References on Tennessee clays, 424; Texas, 424, Car- boniferous clays, 426; Cretaceous clays, 426; Lower Cretaceous, 426; Upper Cre- taceous, 426; Woodbine formation, 427; Eagle Ford formation, 427; Taylor- Navarro formation. 427; Tertiary clays, 428; Lignitic, 428; Marine beds, 431; Pleistocene, 431; References on Texas clays, 433; Utah, 434; Virginia, 434; Residual clays, 434; Carboniferous, 437; Triassic, 437; Tertiary, 437; Pleisto cene, 437; References on Virginia clays, 441; Washington, 441; Clay shales, 441; Residual clays, 441; Glacial clays, 441; References on Washington clays, 441; West Virginia, 442; Silurian, 442; Devonian, 442; Lower Carboniferous, 442; Mauch Chunk shales, 442; Carboniferous, 442; Pottsville series, 442; Allegheny series, 445; Clarion clay, 445; Kittanning clays, 445; Upper Freeport clay, 446; Conemaugh series, 446; Monongahela series, 446; Dunkard or Permo Carbonifer- ous, 449; Pleistocene, 449; References on West Virginia clays, 451; Wisconsin, 451; Residual clays, 452; Pre-Cambrian residuals, 452; Potsdam shales, 452; Ordovician limestone residuals, 452; Sedimentary clays, 452; Hudson River CONTENTS PAGE shale, 452; Pleistocene clays, 455; Lacustrine deposits, 455; Estuarine clays, 455; Glacial clays, 455; References on Wisconsin clays, 457; Wyoming, 457; Bentonite, 457; References on Wyoming clays, 459. CHAPTER VIII FULLERS' EARTH 460 Properties, 460; Distribution in the United States, 461; Georgia Florida, 461; South Carolina, North Carolina, and Virginia, 462; New York, 462; Arkansas, 462; South Dakota, 462; California, 462; Mining and uses, 466; Production, 467. LIST OF ILLUSTRATIONS PLATE PAGE I. Bank of residual clay at Christiansburg, Va., showing uneven surface of underlying limestone 9 II Fig. 1. Section showing beds of stratified clay overlain by glacial drift . . 15 Fig. 2. Bank of clay showing white sand on right, passing into a black clay on the left 15 III. Fig. 1. Deposit of stony glacial clay 21 Fig. 2. Clay-pit in lignitic Tertiary formation, Athens, Texas. Shows gently dipping layers 21 IV. Fig. 1. Clay -bank showing carbonate of iron concretions, Reynolds bank, Anne Arundel County, Md 37 Fig. 2. Clay concretions 37 V. Fig. 1. Photomicrograph of kaolinite 43 Fig. 2. Washed kaolin 43 VI. Photomicrograph of indianaite 45 VII. Fig. 1. Section showing coal-bed underlain by fire-clay 171 Fig. 2. Entrance to drift in fire-clay seam, which is overlain by limestone 171 VIII. Showing method of working clay in a rectangular pit 201 IX. Fig. 1. Digging clay by means of open pits. At the top of the bank, in the background, a workman is driving a wedge into the clay in order to break it off. The clay is hauled to the yards in carts 207 Fig. 2. Removing the overburden from a shale- bed by hydraulicking. . . 207 X. Fig. 1. View showing portion of sand- troughs, settling- tanks, and dry- ing-racks at a kaolin washing-plant 215 Fig. 2. Filter press for removing water from washed or blunged clays. The portion at the left end has been emptied and the leaves of clay taken from it are on the car. The workman is just removing a leaf of clay from the press 215 XI. Fig. 1. Dry pan used for grinding hard clays, shale, and brick 221 Fig. 2. Ring-pit for mixing clays 221 XII. Fig. 1. Wet pan for grinding and mixing clays or shales 225 Fig. 2. Cutting table of stiff- mud brick machine 225 XIII. Dry-press brick machine 233 xii LIST OF ILLUSTRATIONS PLATE PAGE XIV. Fig. 1. A steam-power re-press. The bricks on belt are being brought from the stiff-mud machine 237 Fig. 2. Setting brick for a scove-kiln 237 XV. Fig. 1. Side view of a scove-kiln for burning common brick, exterior daubed with wet clay. The firing-holes are shown at bottom of one side 241 Fig. 2. Down-draft kilns 241 XVI. Fig. 1. Interior view of circular down-draft kiln 243 M?. 2. Height continuous kiln 243 XVII. Fig. 1. Molding 30-in. sewer- pipe in pipe press 249 Fig. 2. Some forms of fireproofing made by stiff-mud machine 249 XVIIL Fig. 1. Roofing-tile press for molding interlocking tile 255 Fig. 2. Modeling terra-cotta objects 255 XIX. Fig. 1. View showing method of setting terra-cotta in kiln for burning. . 259 Fig. 2. Partial interior view of a pottery kiln, showing saggers in which white wares are burned 259 XX. Bergstrom & Bass tile-press 267 XXI. Views illustrating the process of turning jars 273 XXII. Dipping biscuit- ware into the glazing tubs 279 XXIII. Fig. 1. Pit of Carboniferous shale, near Birmingham, Ala 287 Fig. 2. Tertiary clays (lone formation) used for brick, terra-cotta, etc., Lincoln 287 XXTV. Fig. 1. Tertiary clays used for common brick, Los Angeles, Cal 291 Fig. 2. View of fire-clay pits, Golden, Colo. The good clay has been taken out, the worthless sandy beds left standing 291 XXV. Fig. 1. Kaolin- pit at West Cornwall, Conn 299 Fig. 2. White clay and sands of Cretaceous age, overlain by Tertiary beds, Rich Hill, near Knoxville, Ga 299 XXVI. Fig. 1. Carboniferous shale used for paving-brick, Galesburg, 111. The excavating is done with a steam shovel 305 Fig. 2. View in Knobstone-shale pit, Crawfordsville, Ind 305 XXVTI. Fig. 1. Carboniferous shale for paving-blocks, near Veedersburg, Ind.. . 319 Fig. 2 Cretaceous shale, Sioux City, la 319 XXVIII. Fig. 1. Loess-bank, Muscatine, la 321 Fig. 2. Bank of Devonian shale used for paving-brick, Cumberland, Md. 321 XXIX. Fig. 1. Coldwater (Carboniferous) shales at White Rock, near Forest- ville, Mich 343 Fig. 2. Carboniferous shale, used for paving-brick, Flushing, Mich 343 XXX. Fig. 1. Deposit of calcareous glacial clay, Ionia, Mich 349 Fig. 2. Cretaceous stoneware-clay, Red Wing, Minn 349 XXXI. Fig. 1. Photo of shaft-house and crushing-house at fire-clay mine, St. Louis 357 Fig. 2. Pit of Raritan (Cretaceous) clays, Woodbridge, N. J 357 XXXII. Fig. 1. Clay-loam deposit of shallow character, west of Mount Holly, N. J 367 Fig. 2. Pleistocene brick-clay, Little Ferry, N. J 367 XXXIII. Fig. 1. Bank of Chemung shale, used for brick, Corning, N. Y 379 Fig. 2. Bank of Pleistocene clay, overlain by sand, Roseton, N. Y 379 LIST OF ILLUSTRATIONS xiii PLATE PAGE XXXIV. Fig. 1. Kaolin-mine, near Webster, N. C., showing mining of kaolin by circular pits 383 Fig. 2. Bank of Carboniferous shale near Akron, Ohio 383 XXXV. Fig. 1. Kaolin-deposit at Upper Mill, Mount Holly Springs, Pa 403 Fig. 2. White sedimentary clay, Aiken area, S. C 403 XXXVI. Bolivar flint-clay, Bolivar, Pa. This clay is about 22 feet thick and overlain by impure clay, coal, and sandstone 409 XXXVII. Fig. 1. Beds of Cretaceous fire-clay, southwest of Rapid City, S. Dak.. . 417 Fig. 2. General view of valley at Thurber, Texas, underlain by Carbon- iferous paving-brick shale 417 XXXVIII. Fig. 1. Bank of sewer- pipe clay in Lignitic (Tertiary) formation, Sas- pamco, Texas. Shows electric system of haulage 429 Fig. 2. Pit in Beaumont clay, Houston, Texas. The walls of the pit are a very sandy clay underlying the other 429 XXXIX. Fig. 1. View of kaolin-pit near Oak Level, Va. The ferruginous clay walls are clearly contrasted to the white kaolin 435 Fig. 2. General view of kaolin washing-plant near Oak Level, Va. The crude clay is washed down the trough from the mine 435 XL. Fig. 1. Section showing diatomaceous earth (Miocene) overlain by Pleistocene clay. Dotted line shows the boundary 439 Fig. 2. Pleistocene brick and tile-clay underlying terrace, Oldfield on James River, Va 439 XLI. Fig. 1. Red-burning brick-clay bank at Freeman, Wash 443 Fig. 2. Shale-bed of Mahoning horizon, Charleston, W. Va. The shale is blue and red with some fire-clay mixed through it 443 XLII. Shale-pit of High Grade Shale Brick Co., Clarksburg, W. Va. Coal- streak near top is the redstone coal of Monongahela series 447 XLIII. Fig. 1. Pit of estuarine clay, Fort Atkinson, Wis. The flat area is underlain by clay, while the surrounding low hills are of sand 453 Fig. 2. Pleistocene clay, Milwaukee, Wis. The mound in middle of pit is sand and is left standing 453 XLIV. Fig. 1. Fullers' earth pit, Quincy, Fla. Behind it are the drying-floors. 463 Fig. 2. Outcrop of Fullers' earth, northeast of Fairburn, S. Dak 463 no. PAGE 1. Section showing the passage of the fully formed residual clay on the surface into the solid bed-rock below. A, clay; B, clay and partly decomposed rock; C, bed-rock below, passing upward into rock fragments with a little clay. ... 7 2. Generalized section showing three possible occurrences of kaolin in a glaciated country. 1, limestone; 2, mica schist; 3, pegmatite; 4, feldspathic quartzite; 5, dark gneiss; 6, light granite; 7, dark granite; 8, kaolin, protected from glacial erosion. Arrow indicates direction of ice movement 13 3. Generalized section showing how beds may vary both horizontally and vertically. 18 4. Section showing uneven boundary of two clay-beds, due to erosion of one before deposition of the other 18 5. Section of folded beds, with crest worn away, exposing different layers 29 6 Section showing strata broken by parallel fault-planes 29 7. Strata broken by fault-plane of low inclination 30 8. Section of horizontal strata, with only the top one exposed at the surface 30 xiv LIST OF ILLUSTRATIONS FIG. PAGE 9. Section showing how horizontal beds are exposed along the sides of a valley. ... 31 10. Section of inclined beds 31 11. Section of vertical beds. The width of outcrop is the same as the actual width of the bed 31 12. Horizontal beds with several layers exposed by wearing down of the land surface. 32 13. Inclined strata, showing rise of the bed above the sea-level, when followed up the slope or dip 32 14. Outcrops of a clay on two sides of a hill and its probable extension into the sam^. 32 15. Section showing how weathering penetrates a clay-bed, particularly along roots, cracks, and joint planes 34 16. Section showing weathered (yellow) clay where the overburden is least 34 17. Section showing occurrence of concretions in certain layers 36 18. Curve showing effect of titanium on fusibility of clay 85 19. Changes in burning a black clay to a buff -colored brick. The lightest one was not removed from kiln until all the carbon was burned off 89 20. Schoene's apparatus for mechanical analysis of clay 113 21. Hilgard's apparatus for making mechanical analyses 114 22. Centrifugal separator for mechanical analyses 116 23. Drawing showing particles of a Cape May clay 117 24. Drawing of an Alloway clay 118 25. Grains of sand in a Clay Marl I, M, mica; Q, quartz; F y feldspar; L, lignite 119 26. Drawing showing bunches of kaolinite (?) plates in a ball-clay from Edgar, Fla. 119 27. Outline and dimensions of a briquette for testing the tensile strength of a clay. . 120 28. Riehle machine for testing tensile strength 121 29. Fairbanks tensile- strength machine. N, clips for holding briquettes; P, screw for applying strain to balance- lever C; F, bucket to hold shot fed in through / from the hopper K; J, automatic cut-off 122 30. Curve showing relation between fineness of grain of non-plastic material and tensile strength of clay mixtures 124 31. Curves showing relation of texture to tensile strength 126 32. Seger's volumeter for determining porosity and specific gravity 133 33. Diagram showing effect of silica on the fusion-point when mixed with alumina and with kaolin, from Seger's experiments 141 34. Seger cones used for determining heat effects in kilns. Nos. 7 and 8 were com- pletely melted; No. 10 was slightly softened; No. 12 was unaffected; No. 9 was bent completely over, but not melted. The fusing-point of cone 9 was reached 148 35. Section of kiln showing method of placing Seger cones 152 36. Map showing kaolin and ball-clay deposits of United States east of the Mississippi River 166 37. Diagram showing effects of silica on fusibility of kaolin 174 38. Formation of spring due to ground- water following a clay-layer 200 39. Formation of a spring due to a layer of cemented sand 200 40. Formation of a pond due to a clay- bed beneath a depression. 200 41. Section of pit working in Middlesex district 206 42. Pug-mill for tempering clay 223 43. A soft-mud brick-machine 227 LIST OF ILLUSTRATIONS XV FIG. PAGE 44. Manufacture of brick by stiff- mud process 229 45. Tunnels for drying bricks and other structural clay-products 235 46. Side elevation of sewer-pipe press 245 47. Front elevation of sewer-pipe press 246 48. Graphic representation of composition and fusibility of some domestic fire-brick. 253 49. Section across Connecticut Valley, showing relations of the clays and other Pleis- tocene deposits. 294 50. Map of a portion of Georgia, showing location of clay -works in coastal plain area. 302 51. Map of Indiana, showing a real distribution of Goal-measure shales and Knob- stone shales 308 52. Section near Glen Mine, Coal Bluff, Ind., showing association of coals under clays, etc 311 53. Map of Iowa, showing distribution of clay- bearing formations, and location of clay- and shale-pits 317 54. Map of Missouri, showing distribution of clay- bearing formations, and location of clay-pits 353 55. Map showing distribution of Missouri kaolins 354 56. Section of a Missouri flint-clay deposit. 355 57. Map of New Jersey, showing distribution of important clay-bearing formations. 365 58. Map of Northeastern States, showing distribution of clay- bearing formations. . . 377 59. Map of Ohio, showing distribution of clay- and shale-bearing formations 391 60. Section of Barren Measures opposite Steubenville, Ohio 396 61. Vertical sections near New Brighton, Pa. 408 62. Section of Barren Measures in Pittsburg region, Pennsylvania 412 63. Map of eastern Texas, showing distribution of clay- bearing formations. 425 64. Map of Wisconsin, showing distribution of clay- bearing formations 451 65. Map of Benton formation in Wyoming 459 LIST OF ABBREVIATIONS USED Amer. Geol. f American Geologist. Amer. Jour. Sci. = American Journal of Science. Ann. des M ines = Annales des Mines de Paris. Bdhm. Ges. Wiss. = Bohmische Gesellschaf t fiir Wissenschaften. Bull. Geol. Soc. Amer. = Bulletin Geological Society of America. Comptes rend. Comptes rendus de la Academie des Sciences de Paris. Dingl. polyt. Jour. = Dingler's Polytechnisches Journal. Jour. Geol. = Journal of Geology. Jour. prak. Chem. = Journal iiir praktische Chemie. M in. Mag. = Mineralogical Magazine. Min. Tasch. = Mineralogisches Taschenbuch. Naturhist. Ver. J?o7w = ]S T aturhistorischen Vereins Bonn. Neues Jahrb. = Neues Jahrbuch fiir Mineralogie, Geologie und Palaeontologie. Pogg. Ann. = Poggendorfs Annalen. Phil. Trans. =- Philosophical Transactions. Quart. Jour. Chem. Soc. = Quarterly Journal of the Chemical Society of London. Royal Agric. Soc. Jour. = Journal of the Royal Agricultural Society of London. Seger Ges. Schrift. = Seger's Gesammelte Schriften. Syst. Min. = Dana's System of Mineralogy = Tscherm. Mitth. = Tschermak's Mineralogische und Petrographische Mittheilungen. Trans. Amer. Ceram. Soc. = Transactions American Ceramic Society. Trans. Amer. Inst. Min. Eng. = Transactions American Institute Mining Engineers. Trans. Eng. Cer. Soc. = Transactions English Ceramic Society. Trans. N. Y. Acad. Sci. = Transactions New York Academy of Sciences. Zeitschr. anorg. Chem. = Zeitschrift fur anorganische Chemie. Zettschr. d. d. Geol. Ges. = Zeitschrift der deutschen Geologischen Gesellschaft. Zeitschr. f. Kryst. u. Min. = Zeitschrift fiir Krystallographie und Mineralogie. Zeitschr. prak. Geol. = Zeitschrift fiir praktische Geologie. xvi or THF UNIVERSITY OF CLAYS THEIR OCCURRENCE, PROPERTIES, AND USES CHAPTER I ORIGIN OF CLAY Definition. Clay is the term applied to those earthy materials occurring in nature whose most prominent property is that of plasticity when wet. On this account they can be molded into almost any desired shape, which is retained when dry. Furthermore, if heated to redness, or higher, the material becomes hard and rock-like. Physically, clay is made up of a number of small particles mostly of mineral character, ranging from grains of coarse sand to those which are of microscopic size, or under one one-thousandth of a millimeter in diameter. Minera- logically, it consists (1) of many different mineral fragments, some of them fresh, but others in all stages of decay, and representing chemically many different compounds, such as oxides, carbonates, silicates, hydrox- ides, etc.; (2) of colloidal material which might be of either organic or mineral character. 1 These points are discussed in more detail, however, on a later page (see Minerals in Clays, Physical properties and Chemical composition). Weathering processes involved. Clays are always of secondary ori- gin and result primarily from the decomposition of other rocks, very frequently from rocks containing feldspar, so that for this reason many writers have intimated that it was always derived from feldspathic rocks. There are some rock species, however, that contain no feldspar (such as serpentine), and others with very little (as some gabbros), which, on weathering, produce some of the most plastic clays known. 1 H. Ries, Md. Geol. Surv., IV, 251, 1902; A. S. Cushman, Jour. Amer. Chem. Soc., XXV, 5. 2 CLAYS In order to trace the changes' occurring in the formation of clay we may take the case of a rock like granite. When such a mass of rock is exposed to the weather, minute cracks are formed in it, due to the rock expanding when heated by the sun and contracting when cooled at night, or they may be joint planes formed by the contraction of the rock as it cooled from a molten condition. Into these cracks the rain-water percolates and, when it freezes in cold weather, it expands, thereby exerting a prying action, which further opens the fissures, or may even wedge off fragments of the rock. Plant-roots force their way into these cracks, and, as they expand, supplement the action of the frost, thus further aiding in the breaking up of the mass. This process alone, if kept up, may reduce the rock to a mass of small angular fragments, or even a mass of sand. The rock having been opened up by disintegrate forces, the silicates are next attacked by the surface-waters, although those exposed on the surface of the stone may already have begun to change. It has usually been supposed that the decomposition of the silicates in the rock, such as feldspar, is caused chiefly by the dissolved carbon dioxide, which is probably always present in the percolating waters, and this view was advanced by Forschammer as early as 1835, 1 as well as by other writers later; 2 but, as pointed out by Cameron and Bell, 3 this is very doubtful, in view of the fact that many of the minerals found in rocks are known to be soluble in water alone, although their solution may take place but slowly. The water, moreover, is believed to react with or hydrolyze them, as is shown by the fact that an alkaline reaction can be obtained with phenolphthalein, after treating powdered minerals with water free from dissolved carbon dioxide. The rate of solubility varies, of course, with the different minerals ,. the magnesium-bearing micas being more soluble than muscovite, and albite more so than orthoclase, with oligoclase between. 4 Clarke 5 found that muscovite, lepidolite, phlogopite, orthoclase, oligoclase, albite, leu- cite nephelite, cancrinite spodumene, scapolite, and many zeolites, all dissolve in water, giving an alkaline reaction, and the same has been shown of others. 6 1 Pogg. Ann., XXXV, p. 354, 1835. 'Rogers, Amer. Jour. Sci.. V, p. 404, 1848; Bischof, Naturhist. Ver. Bonn, XII, p. 308, 1855; Daubree, Compt. ren., LXIV, p. 339, 1867; Miller, Tscherm. Mitth., 1877, p. 31. 3 Bur. of Soils, Bull. 30, p. 16, 1905. 4 Merrill, Rocks, Rock-weathering and Soils, p. 234, 1897. 6 U. S. Geol. Surv., Bull. 167, p. 156, 1900. 6 See Bull. 30, Bur. of Soils, for numerous references on this subject. ORIGIN OF CLAY 3 The action of water on orthoclase is assumed to be somewhat accord- ing to the following formula l : The potassium hydrate thus formed may unite with carbon dioxide to form either a carbonate or bicarbonate of potash, or it is possible that it may unite with other acids, forming salts more soluble than the orthoclase in the hydrolyzed acid. The HAlSi 3 Os formed is apparently unstable, and may lose some of its quartz, resulting in the formation of kaolinite, pyrophyllite, or dia- spore, but the first of these appears to be more commonly formed in the weathering of feldspar. Kaolinization. This alteration of the feldspar is termed kaolinization, and the mineral kaolinite is always of secondary character. The changes which take place in the alteration of several species of feldspar may be given as follows : SiO 2 A1 2 3 K 2 O H 2 % Orthoclase 64.86 18.29 16.85 100.00 Lost 43.24 16.85 60.09 Taken up 6.45 6.45 Kaolinite 21.62 18.29 6.45 46.36 Albite Si0 2 68.81 A1 2 3 19.40 Na 2 11.79 H 2 % 100.00 Lost 45.87 11.79 57.66 Taken up 6.85 6.85 Kaolinite 22.94 19.40 6.85 49.10 Anorthite SiO 2 43.30 A1 2 3 36.63 CaO 20.07 H 2 O % 100.00 Lost 20 07 20.07 Taken up 12.92 12.92 Kaolinite 43.30 36.63 12.92 92.85 It will be seen from this that both the orthoclase and plagioclase might yield kaolinite; in fact the plagioclase varieties decompose more readily than orthoclase. 2 Vogt 3 has recorded an occurrence of kaolin near Josingfjord, atEker- 1 Cameron and Bell, 1. c., p. 18. 2 Ries, Kaolins and fire-clays of Europe, U. S. Geol. Surv., 19th Ann. Rept., pt. VI (ctd.), p. 377, 1898; Leimberg, Zeitsch, d. d. Geol. Ges., Vol. 35, 1883; Rosier, Neues Jahr., Beil. Bd. XV, 2d Heft, p. 231. 3 Amer. Inst. Min. Eng., Trans., XXXI, p. 151, 1902. CLAYS sund-Soggendal, Norway, which is formed from labradorite, the different stages in the change being indicated by the following analyses : Labra- dorite. Labradorite partly kaoli- nized. Massive kaolin, more or less pure. Kao- litiito I II I II III IV V Silica (SiO 2 ) Alumina (A^Oa) Iron oxide (Fe2Oa) . . Lime (CaO) Magnesia (MgO) Potash (KijO) Soda (Na 2 O) Water (HaO) 54.5 27.0 2 5 9.0 10 1 5.0 50 03 28 60 1.62 4 21 2.95 [ 1 00 11 90 49.16 29 60 1.88 3.47 1.67 undet. 13 63 48.16 29.45 3.40 .68 .49 undet. 16.38 48.06 f 38.57 1 } undet J 12.95 47.83 1 34 . 53 1 1.70 1 .48 } .59 J undet 13 76 47 72 37.40 1.59 .23 .11 44 .76 11.66 46 85 46.50 37.56 39 56 1.00 tr. tr. [ undet 1 14 44 13.94 Total 100 6 100.31 (99.41) (99.01) (99 58) (98.89) 99.91 (99 85) 100 00 Prof. Vogt believes that the kaolinization here is due to the action of carbonic-acid waters, because calcite occasionally occurs with the kaolin- However, from what has been said on page 2, the presence of this min- eral would not necessarily show that the acid above mentioned had assisted in the decomposition of the feldspar, but simply that it had united with the lime set free during the breaking up of the labradorite. While it is probable that other silicates, such as hornblende or augite, yield a hydrous aluminum silicate, it is not known that it is kaolinite, 1 but their decomposition no doubt proceeds in a manner similar to that of feldspar. Vogt, 2 on the other hand, states that hornblende, augite, beryl, topaz, etc., are known to be occasionally converted into kaolinite, but gives no evidence. Quartz, although apparently resistent, is not left untouched, for it too is slightly soluble, but, aside from that originally present in the rock, silica may have been liberated during the decomposition of some of the silicates, such as feldspar. It has been found that in soils, and the same may be said of clays, quartz has accumulated in relatively large proportions. It may be present as quartz, amygdaloidal silica, or perhaps other forms. There is, however, a tendency for it to be gradually changed over into other forms of quartz through solution and redeposition. 3 1 Merrill, Rocks, Rock-weathering and Soils, p. 21, 1897. 2 Problems in the Geology of Ore Deposits, Trans. Amer. Inst. Min. Eng., XXXI, p. 151, 1902. 3 Hayes, Bull. Geol. Soc. Amer., VIII, p. 213, 1897, and Jour. Geol., V, p. 319, 1897. ORIGIN OF CLAY 5 While there is undoubtedly lack of absolute proof that other silicates than feldspar yield kaolinite, all clays appear to contain a variable amount of some hydrated silicate of aluminum, which may be present in some quantity, since it is a highly insoluble natural compound; and even though the statement is frequently made that this silicate is the mineral kaolinite, the fact is at times somewhat difficult of proof; indeed the evidence is clearly against it in some cases. This hydrated aluminum silicate is- sometimes referred to as the clay substance or clay base. 1 Kaolinization by pneumatolysis. Aside from the kaolinization of feldspar by the ordinary processes of weathering it seems possible, and even probable, that its decomposition may have been brought about by the action of mineralizing vapors, as at Cornwall, Eng., where it was found that the feldspar of the granite on both sides of the tin veins had been kaolinized. This change is attributed to the action of fluoric vapors, whose presence is pretty clearly indicated by the finding of such minerals as tourmaline and topaz. That such a process is possible is shown by J. H. Collins, 2 who ex- posed feldspar to the action of hydrofluoric acid. The feldspar, accord- ing to Mr. Collins, was converted into hydrated silicate of alumina, mixed with soluble fluoride of potassium, while pure silica was deposited on the sides of the tube. With such treatment the orthoclase yielded more readily than either albite or oligoclase. The following analyses show the effect of 96 hours' treatment of orthoclase with hydrofluoric acid at 60 F.: I. II. III. Silica (SiO 8 ) 63.70 49.20 44.10 Alumina (A1 2 O 3 ) 19-76 35.12 40.25 Potash (K.O) 13.61 .12 .25 Soda (Na 2 O) 2.26 tr. tr. Ferric oxide (Fe 2 O 3 ) .71 tr. tr. Water (H 2 O) tr. 14.20 15.01 100.04 98.64 99.61 I is the original feldspar. II is inner layer of altered feldspar. Ill is outer layer of altered feldspar. 1 The term is now rather loosely used, however, and in impure clays includes practically all of the very finest particles. 2 Min. Mag., 1887, VII, p. 213. ^ CLAYS From the analysis it will be seen that the composition of the outer layer simply approximates that of kaolinite. The artificial clay thus produced, when examined under the micro- scope, resembled washed kaolin. It shoxved no hexagonal scales, but contained a number of minute colorless cubes which are supposed to be fluorspar. The theory advanced by Mr. Collins was earlier suggested by Von Buch and Daubree. 1 The former early observed the constant occurrence of kaolin with minerals containing fluorin, and suggested that the kaolin of Halle, dermany, owed its origin to hydrofluoric acid. 2 Daubree considered that the kaolin near St. Austell in Cornwall, 3 Central France, and the Erzgebirge must have had a similar origin. The formation of kaolin by other causes than surface agencies has loeen referred to by B. von Inkey and Semper as a product of propyliti- zation in some cases. 4 Cross and Penrose 5 have sought to suggest a pneumatolytic origin for the kaolin found in some of the Cripple Creek, Colo., mines, but Ransome and Lindgren 6 have rather disputed this. If Mr. Collins' theory be correct, the kaolin deposits should extend to great depths, but if the kaolinization be due to weathering, then we should encounter undecomposed feldspar at the limit to which weather- ing has reached. In Cornwall the kaolin mines, which are probably the largest in the world, have reached a depth of over 400 feet without the "kaolin giving out, while at Zettlitz in Bohemia a similar depth has been proven with the same result. The latter locality is one of thermal ac- tivity. In these two instances the theory just mentioned seems to be Tery reasonable. There are many localities, however, where the kaolin decreases with the depth, passing into the undecomposed feldspar, as is the case, for example, in North Carolina, where the fresh feldspar is met at a depth of 60 to 120 feet, in Pennsylvania, and also in Delaware. IVIore recently Rosier 7 has advanced the view, on w r hat seems to the writer rather insufficient evidence, that the kaolinization of feldspars is never 1 Annales des mines, XX, 1841. 2 Min. Tasch., 1824. The writer can state from personal examination that the Halle kaolins were formed by ordinary weathering. 3 Etudes synthetiques de Geologic Experimental, 1879. 4 Nagyag u. seine Lagerstatten, Budapest, 1885. 5 U. S. Geol. Surv., 16th Ann. Kept., Pt. IT, p. 160. 6 U. S. Geol. Surv., Bull. 254, p. 21, 1904. 7 H. Rosier Beitrase zur kenntniss der Kaolinlagerstatten, Neues Jahrb. f. Min., eol. u. Pal., XV. Beilage-Band, 2d Heft. pp. 231-393. ORIGIN OF CLAY 7 due to atmospheric action, but to post-volcanic pneurruitolytic and pneumatohydatogeriic processes. The very fact that many of our kaolins pass into undecomposed feld- spar or feldspathic rock when the limit of weathering is reached shows the incorrectness of such a broad statement. 1 Residual Clay Where the clay is thus found overlying the rock from which it was formed, it is termed a residual clay, because it represents the residue of rock decay, and its grains are more or less insoluble. If now a granite which is composed chiefly of feldspar decays under weathering action, the rock will be converted into a clayey mass, with quartz and mica scattered through it. Remembering that the weather- ing began at trhe surface and has been going on there for a longer period than in deeper portions of the rock, we should expect to find, on digging downward from the surface, (.4) a layer of fully formed clay, (B) below this a poorly defined zone containing clsy and some partially decomposed rock fragments, (0) a third zone, with some clay and many rock fragments, grading downward into the solid bed-rock. (Fig. 1.) In other words. FIG. 1. Section showing the passage of the fully formed residual clay on the sur- face into the solid bed-rock below. A, clay; B, clay and partly decomposed rock; C, bed-rock below, passing upward into rock fragments with a little clay. there is usually a gradual transition from the fully formed clay at the surface into the parent rock beneath. The only exception to this is found in clays derived from limestone, where the passage from dry to rock is 1 In this connection, see G. P. Merrill, What Constitutes a Clay, Amer. Geol. XXX, Nov. 1902, and H. Ries, Origin of Kaolin, Trans. Amer. Ceramic Soc., II, p. 93, 1900. 8 CLAYS sudden. The reason for this is that the change from limestone into clay does not take place in the same manner as granite. Limestone consists of carbonate of lime, or carbonate of lime and magnesia, with a variable quantity of clay impurities, so that when the weathering agents attack the rock, the carbonates are dissolved out by the surface-waters, and the insoluble clay impurities are left behind as a mantle on the undis- solved rock, the change from rock to clay being, therefore, a sudden one, and not due to a gradual breaking down of the minerals in the rock, as in the case of granite. Kaolin. A residual clay derived from a rock composed entirely of feldspar, or one containing little or no iron oxide, is usually white and therefore termed a kaolin; deposits of this type may contain a high percentage of the mineral kaolinite, 1 this being assumed because, after cashing the sand out of such materials, the silica, alumina, and water in the remaining portion are in much the same ratios as in kaolinite, although, as previously mentioned, other aluminous silicates may at times be present. A clay made up entirely of kaolinite is sometimes termed a "pure" clay, but since the term clay refers to a physical condition and not a definite chemical composition, it would perhaps be more correct to term kaolin the simplest form of clay. There are clays made up almost entirely of other hydrous aluminum silicates than kaolinite, which are also termed kaolins, as the indianaite of Indiana, or the halloysite of Alabama. A deposit of pure kaolinite has not thus far been found in nature though some very nearly pure occurrences are known. While the term kaolin is sometimes applied to any residual clay, the writer believes that this designation should be restricted to white-burning residual clays, a usage which is wide-spread but has not become universal. The name kaolin is a corruption of the Chinese Raiding, which means high ridge, and is the name of a hill near Jauchau Fu, where the mineral is obtained. 2 In this connection it is interesting to note that, according to Richt- hofen, 3 the rock from which the King-te-chin porcelain is made is not true kaolin, but a hard jade-like greenish rock which occurs between beds of slate. He states: "This rock is reduced, by stamping, to a white powder, of which the finest portion is ingeniously and repeatedly sep- 1 The terms kaolinite, referring to the mineral, and kaolin, referring to the rock mass, are often carelessly confused even by scientific writers, although there seems to be little excuse for so doing. 2 Dana, System of Min., 1892, p. 687. s Amer. Jour. Sci., 1871, p. 180. OS las S 3 73 o S J ORIGIN OF CLAY 11 arated. This is then molded into small bricks. The Chinese distinguish chiefly two kinds of this material. Either of them is sold in King-te-chin in the shape of bricks, and as either is a white earth, they offer no visible differences. They are made at different places, in the manner described, by pounding hard rock, but the aspect of the rock is nearly alike in both cases. For one of these two kinds of material the place Kaoling ('high ridge') was in ancient times in high repute, and, though it has lost its prestige since centuries, the Chinese still designate by the name 'Kao- ling' the kind of earth which was formerly derived from there, but is now prepared in other places. The application of the name by Berzelius to porcelain earth was made on the erroneous supposition that the white earth which he received from a member of one of the embassies (I think Lord Amherst) occurred naturally in this state. The second kind of material bears the name Pe-tun-tse ('white clay')." The following analyses 1 show the average composition of (I) the natural material from King-te-chin, such as is used in the manufacture of the finest porcelain; (II) that from the same locality used in the so- called blue Canton ware; (III) that of the English Cornwall stone; (IV) washed kaolin from St. Yrieux, France; and (V) washed kaolin rom Hockessin, Del. I. II. III. IV. V. Silica (SiO 2 ) 73.55 73.55 73.57 48.68 48.73 Alumina (A1 2 O 3 ) 21.09 18.98 16.47 36.92 37.02 Ferric oxide (Fe 2 O 3 ) .27 .79 Lime (CaO) 2.55 1.58 1.17 .16 Magnesia (MgO) .15 1.08 .21 .52 .11 Potash (K,0) .461 - 84 5g / .41 .Soda(Na 2 0) 2.09/ 1-04 Water (H 2 O) 2.62 1.96 2.45 13.13 12.83 Total 99.62 99.70 99.98 99.83 100.00 The above analyses show a most striking difference between the two washed kaolins and the Chinese clay and Cornwall stone. Form of residual deposits. The form of a residual clay deposit, which is also variable, depends on the shape of the parent rock. Where the residual clay has been derived from a great mass of granite or other clay-yielding rock, the deposit may form a mantle covering a consider- able area. On the other hand, some rocks, such as pegmatites (feldspar and quartz), occur in veins, that is, in masses having but small width as compared with their length, and in this case the outcrop of residual clay along the surface will form a narrow belt. 1 G. P. Merrill, Non-metallic Minerals, p. 224, 1901. 12 CLAYS Clay derived from a rock containing much iron oxide will be yellow red, or brown, depending on the iron compounds present. Between the white clays and the brilliantly colored ones others are found represent- ing all intermediate stages, so that residual clays vary widely in their color. The depth of a deposit of residual clay will depend on climatic con- ditions, character of the parent rock, topography, and location. Rock decay proceeds very slowly, and in the case of most rocks the rate of decay is not to be measured in months or years, but rather in centuries. Only a few rocks, such as some shales or other soft rocks, change to clay in an easily measurable time. With other things equal, rock decay proceeds more rapidly in a moist climate, and consequently it is in such regions that the greatest thickness of residual materials is to be looked for. The thickness might also be affected by the character of the parent rock, whether composed of easily weathering minerals or not. Where the slope is gentle or the surface flat, much of the residual clay will re- main after being formed, but on steep slopes it will soon wash away. In some cases the residual materials are washed but a short distance and accumulate on a flat or very gentle slope at the foot of the steeper one, forming a deposit not greatly different from the original ones, al- though they are not, strictly speaking, residual clays. Distribution of residual clays. Residual clays, usually of ferruginous character, are found in many portions of the United States, but reach their maximum development in that portion lying east of the Mississippi and south of the southern margin of the ice-sheet of the glacial epoch. North of the terminal moraine they are found only in protected situa- tions (Fig. 2) or non-glaciated areas. Thus, for example, an important area of residual clay, derived from limestone, is found in the driftless area of Wisconsin. 1 This is a silty clay in its upper part, and a tough jointed clay below, while scattered through it are numerous cherty fragments. A second type of residual clay occurring in Wisconsin is that found underlying the Potsdam sandstone and has been derived from the pre- Cambrian crystallines. It represents probably the geologically oldest residual clay found in the United States. The general character of these residuals is much the same whatever the parent rock. Nearly all are ferruginous-, and contain angular mineral particles, as well as more or less decomposed ones, from which the more soluble constituents have been leached out. The colors range usually from brown or red to yellow. In the Piedmont and Appalachian areas *~Chamberlin and Salisbury, 6th Ann. Rep. U. S. Geol. Surv., p. 240, 1885. ORIGIN OF CLAY 13 of the Southern States they often attain great thickness and are widely used for brickmaking. 1 In rare cases they are formed from rocks run- FIG. 2. Generalized section showing three possible occurrences of kaolin in a glaciated country. 1, limestone; 2, mica schist; 3, pegmatite; 4, feldspathic quartzite; 5, dark gneiss; 6, light granite; 7, dark granite; 8, kaolin, pro- tected from glacial erosion. Arrow indicates direction of ice-movement. (After Laughlin, Conn. Geol. and Nat. Hist. Surv., Bull. 4, p. 70, 1905.) ning low in iron, such as pegmatite veins, and then the clay is whitish in color. The following analyses 2 represent the composition of several residual clays : ANALYSES OF RESIDUAL CLAYS Constituents I. II. III. IV. V. VI. VII. VIIL IX. X SiO 2 71.13 49.90 53.09 49.13 55,42 40.127 39.55 66.27 77.24 55 39 A1 2 3 ...... 12.50 18.64 21.43 20.08 22.17 13.75 28.76 15.25 26.17 20 16 FeoO 3 ..... FeO 5.52 .45 17.19 .27 8.53 .86 11.04 .93 j- 8.30 12.315 16 80 6.97 7 76 8 79 TiO 2 .45 .28 .16 .13 .64 P 2 5 .02 .03 .03 .04 .626 .10 " .07 '".14 '".04 MnO .04 ,01 .03 .06 CaO .85 .93 .95 1.22 ".15 3. sis '.37 '".24 ".*iB .51 MgO 38 .73 1.43 1.92 1.45 .479 .59 43 .38 1 27 Na 2 O .... . 2.19 .80 1.45 1.33 .17 .006 tr. .40 .29 79 K 2 O 1.61 .93 .83 1.60 2.32 .118 tr. .86 4.41 4 03 H 2 O *4.63 *10 46 *10.79 *11.72 *9.86 t27.441 13.26 8.2 7.38 C0 2 .43 .30 .29 .39 2.251 C .19 .34 .22 1 09 100.39 100 50 109 09 100.68 99 84 100.631 100.07 98.69 99.27 98.30 * Contains hydrogen and organic matter. Dried at 100 C. t Contains 11.21 per cent of organic matter. Nos. I, II, III, and IV are limestone residuals from southern Wiscon- sin. Nos. I and II are from the same vertical section, I being 4J feet from the surface, and II 8J, and in contact with the underlying lime- 1 G. P. Merrill, Rocks, Rock-weathering, and Soils, p. 301; I. C. Russell, U. S... Geol. Surv., Bull. 52, 1884-85; H. Ries; U. S. Geol. Surv., Prof. Pap. 11. 2 G. P. Merrill, Rocks, Rock-weathering, and Soils, p. 306. 14 CLAYS stone. Nos. Ill and IV are similarly related, III being 3 feet from .the surface, and IV 4^ feet, the lower sample lying on the unchanged rock. "The larger percentages of silica, in samples from nearest surface, are due to higher state of decomposition, the soluble portions having been more largely removed. The presence of larger percentages of alkalies in these same samples indicates that these salts existed in the form of silicates which have resisted the decomposing influences, and remain mechanically included in the residues/' No. V represents a residual from the Knox dolomite at Morristown, Ala.; VI is a red earth formed by decay of Bermuda coralline limestone; VII is a diabase residual from Wades- boro, N. C.; VIII a gabbro subsoil from Maryland; IX a Trenton lime- stone residual from Hagerstown, Md.; and X a Triassic limestone residual. The texture of some of the above residual soils has been determined as follows 1 : MECHANICAL ANALYSES or RESIDUAL CLAYS Diameter of particles, mm. Name. I. II. III. IV. V. 2-1 Fine gravel . 54 17 00 00 19 1- 5 Coarse sand .32 .00 .23 26 1 80 5-25 Medium sand .72 .15 1.29 .18 3 12 25-1 Fine sand .62 .25 4.03 .66 6 96 .1 -.05 05 - 01 Very fine sand Silt 4.03 36.02 2.34 19.04 11.57 38.97 6.73 47.32 8.76 34 92 01 - 005 Fine silt 14.99 20.88 8.84 10.04 12 14 005- 0001 Clay . 41.24 51.77 32.70 34.90 28 82 Total mineral matter Org. matter, water, loss 88.48 1 52 94.60 5 40 97.63 2 37 94.44 5 56 96.71 3 29 100. 100. 100. 100. 100. TRANSPORTED CLAYS Sedimentary clays Origin. As mentioned above, residual clays rarely remain on steep slopes, but are washed away by rain-storms into streams and carried off by these to lower and sometimes distant areas. By this means residual clays possibly of different character may be washed down into the same stream and become mixed together. This process of wash and trans- portation can be seen in any abandoned clay bank, where the clay of the slopes is washed down and spread out over the bottom of the pit. 1 M. Whitney, Maryland Agricult. Exper. Sta., Bull. 21, 1893. PLATE 11 FIG. 1. Section showing beds of stratified clay overlain by glacial drift. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 440.) FIG. 2. Bank of clay showing white sand on right, passing into a black clay on the left. (After Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 12, 1904.) 15 ORIGIN OF CLAY 17 As long as the stream maintains its velocity it will carry the clay in suspension, but if its velocity be checked, so that the water becomes quiet and free from currents, the particles begin to settle on the bottom, forming a clay layer of variable extent and thickness. This may be added to from time to time, and to such a deposit the name of sedimentary clay is applied. All sedimentary clays are stratified or made up of layers, this being due to the fact that one layer of sediment is laid down on top of another (Plate II, Fig. 1). If there were absolutely no difference in the character of the material deposited, it would form one thick homo- .geneous bed, but there is usually more or less variation, a layer of very fine material being laid down at one time and a layer of coarser material on top of it, or vice versa. These layers may also vary in thickness, and since there is less cohesion between unlike particles, the two layers will tend to separate along their line of contact. As the finer material can only be deposited in quiet water, and coarse material in disturbed waters, so from the character of the deposit we can read much regarding the conditions under which it was formed. If, therefore, in the same bank alternating layers of sand, clay, and gravel are found, it indicates a change from disturbed to quiet water, and still later rapid currents over the spot in which these materials were deposited. The commonest evidence of current deposition is seen in the cross-bedded structure of some sand beds where the layers dip in many different directions, due to shifting currents which have deposited the sand in inclined layers. The beds of thinly stratified or laminated sands and clays found in many of the Cretaceous and Tertiary deposits of the coastal plain are another example of rapid changes in the conditions of deposition. Sedimentary clays can be distinguished from residual clays chiefly by their stratification, and also by the fact that they commonly bear no direct relation to the underlying rock on which they may rest. Structural irregularities in sedimentary clays. All sedimentary clays resemble each other in being stratified, but, aside from this, they may show marked irregularities in structure. Thus, any one bed, if followed from point to point, may show varia- tions in thickness, pinching or narrowing in one place and thickening or swelling in others, as shown in Fig. 3. In digging clay the miner often finds streaks of sand extending through the deposit and cutting through several different layers, these having been caused by the filling of channels cut in the clay deposits by streams after the elevation of the former to dry land. Occasionally a bed of clay may be extensively worn away or corraded by currents subsequent to 18 CLAYS its deposition, leaving its upper surface very uneven, and on this an entirely different kind of material may be deposited, covering the earlier - Fireclay Sandy clay //^r-^-- ;:~^r : . \- ' r--- ~ ; ' ~T- L '. --^-- _ ,- - Bed Rock FIG. 3. Generalized section showing how beds may vary both horizontally and vertically. bed, and filling the depressions in its surface. If the erosion has been deep, adjoining pits dug at the same level may find clay in one case and sand in the other (Fig. 4). Such irregularities are known to occur in both clays and shales. FIG. 4. Section showing uneven boundary of two clay beds, due to erosion of one before deposition of the other. While in many instances the changes in the deposit are clearly visible to the naked eye, variations may also occur, due to the same cause, which would only show on burning. Thus, for example, the so-called retort- clay, found in the Woodb ridge region of New Jersey, is similar in its plastic qualities wherever found, but the shrinkage of that found in the different pits is not always the same, because it varies in fineness from place to place. It may also vary in color. CLASSIFICATION OF SEDIMENTARY CLAYS The general character of sedimentary clays is more or less influenced by the locality and conditions of deposition, which enables us, there- fore, to divide them into the following classes: ORIGIN OF CLAY 19 Marine clays. This class includes those sedimentary clays deposited on the ocean bottom, where the water is quiet. They have, therefore, been laid down at some distance from the shore, since nearer the land, where the water is shallower and disturbed, only coarser materials can be deposited. Beds of clay of this type may be of vast extent and great thickness, but will naturally show some variation, horizontally at least, because the different rivers flowing into the sea usually bring down different classes of material. Thus, one stream may carry the wash from an area of iron-stained clay, and another the drainage from an area of white or light-colored clay. As a sediment spread out over the bottom, the areas of deposition might overlap, and there would thus be formed an intermediate zone made up of a mixture of the two sediments. This would show itself later as horizontal transition from one kind of clay to another. These changes may occur gradually, or at other times within the distance of a few feet (Plate II, Fig. 2). The laminations produced by vertical changes are shown in Plato II, ^ig. 1. The most persistent beds of this class are found in the rocks of the Silurian, Devonian, and Carboniferous systems, but beds of considerable horizontal extent are at times found in the Mesozoic formations. Estuarine clays. These form a second type of some importance in certain areas. They represent bodies of clay laid down in shallow arms of the sea, and are consequently found in areas that are comparatively long and narrow, with the deposits showing a tendency towards basin shapes. If strong currents enter the estuary from its upper end, the settling of the clay mud may be prevented, except in areas of quiet water in recesses of the bay shore. Or, if the estuary is supplied by one stream at its head, and this of low velocity, the finer clays will be found at a point most distant from the mouth of the river. In such cases we should anticipate an increase in coarseness of the clay bed or series of beds as they are followed from what was formerly the old shore line up to the mouth of the former river that brought down the sediment. Estuarine clays often show sandy laminations, and are not infre- quently associated with shore marshes, due to the gradual filling up of the estuary and the growth of plants on the mud flats thus formed. The clays of the Hackensack region of New Jersey and those of the Hudson Valley of New York are good examples of estuarine deposits, formed at the close of the glacial period, when the region around the Palisades stood somewhat lower in respect to sea-level than at present. 1 1 Report on Glacial Geology, N. J. Geol. Survey, Vol. V, p. 196; and N. Y, State Museum, Bull. 35, p. 576. 20 CLAYS Swamp and lake clays. Swamp and lake clays constitute a third class of deposits, which have been formed in basin-shaped depressions occupied by lakes or swamps. They represent a common type, of vari- able extent and thickness, but all agree in being more or less basin- shaped. They not infrequently show alternating beds of clay and sand, the latter in such thin laminae as to be readily overlooked, but causing the clay layers to split apart easily. Many of the lake clays are directly or indirectly of glacial origin, having been laid down in basins or hollows along the margin of the continental ice-sheet, or else in valleys that have been dammed up by the accumulation of a mass of drift across them. This wall of drift serves to obstruct the drainage in the valley, thus giving rise to a lake, in which the clay has been deposited. Clay beds of this type are extremely abundant in all glaciated regions. They are usually surface deposits, 1 often highly plastic, and more or less impure. Their chief use is for common brick and earthenware, and they are rarely of refractory character. Flood-plain and terrace clays. Many rivers, especially in broad val- leys, are bordered by a terrace or plain, there being sometimes two or more, extending like a series of shelves, or steps, up the valley side. The lowest of these is often covered by the river during periods of high water, and is consequently termed the flood-plain. In such times much clayey sediment is added to the surface of this flood-terrace, and thus a flood- plain clay deposit may be built up. Owing to the fact that there is usually some current setting along over the plain when it is overflowed, the finest sediments cannot settle down, except in protected spots, and consequently most terrace clays are rather sandy, with here and there pockets of fine, plastic clay. They also frequently contain more or less organic matter. Along its inner edge the terrace may be covered by a mixture of clay, sand, and stones, washed down from neighboring slopes. Where several terraces are found it indicates that the stream was formerly at the higher levels, and has cut down its bed, each terrace representing a former flood-plain. Even alorig the same stream, however, the clays of the several terraces may vary widely in their character, those of one terrace being perhaps suitable for pottery, and those of the sec- ond being available only for common brick and tile. Examples of such clays are to be found in most regions. Drift or bowlder clays. In that portion of the United States formerly covered by the continental ice-sheet there are occasional deposits of clay formed directly by the glacier. These are usually tough, dense, gritty 1 Not necessarily thin. PLATE III FIG. 1. Deposit of stony glacial clay. (After H. Ries, N. 3. Geol. Surv. Fin. Kept., VI, p. 128.) FIG. 2. Clay pit in Lignitic Tertiary formation, Athens, Tex. Shows gently dipping layers. (Photo by H. Ries, 1903.) 21 ORIGIN OF CLAY 23 clays, often containing many stones (PL III, Fig. 1). The material deposited by the ice (till) was usually too stony and sandy to serve as clay, although often known as bowlder clay. Locally, however, although the ice-transported material has been largely ground to a fine rock flour, the bowlder clay is plastic enough and not too full of stones for use. Such deposits are mostly of limited extent, impure, and of little value. In addition to this type of clay formed directly by the ice, there were clays deposited in lakes or along flood-plains by the streams issuing from the glacier. These were composed of material derived from the ice, but since they were deposited by water they were stratified, and may properly be classed as lacustrine, estuarine, or flood-plain clays of glacial age. Bowlder clays, although abundantly distributed, are often too stony to be of much value for the manufacture of clay products. JEolian clays. In many parts of the West there is found a silty, often calcareous clay, termed the loess. This, although commonly a water deposit, may at times have been formed by wind action. It could there- fore properly be classed as transported clay, and would also show a strati- fied structure. CLASSIFICATION OF CLAY DEPOSITS Clays may be classified according to their origin, chemical and physi- cal properties, or uses. To the geologist the first is, perhaps, the most important, to the technologist the second and third are of more interest. Several such classifications have appeared in the United States in the last few years, most of them based primarily on genetic features, and sometimes secondarily on the properties of the clay. They include the following: Orton's classification. 1 High-grade clays. (50 per cent or more kaolin) with silica. Low-grade clays. (10 to 70 per cent kaolin with no- table per cent fluxing elements. 1. Kaolin. 2. China-clay. 3. Porcelain-clay. 4. Fire-clay (hard). 5. Fire-clay (plastic). 16. Potter's, clay. 1. Argillaceous shale Paving-block. 2. Ferruginous shale Pressed brick. 3. Siliceous clays Sewer-pipe and paving-block. 4. Tile-clays. 5. Brick-clays. 6. Calcareous shales Brick. Ohio Geol. Survey, VII, p. 52. '24 CLAYS Quality is made the basis of division in the above. Nos. 1,2, and 4 of the first group are practically the same, and the subdivisions of group 2 are not always distinct. The term kaolin is used incorrectly, kaolinite .being intended instead. Wheeler's classification. 1 1. Whiteware clays. Kaolin. China-clay. Ball-clay. 2. Refractory clays. Plastic fire-clay. Flint-clay. Refractory shale. 3. Pottery- clays. 4. Vitrifying clays. Paving-brick clay and shale. Sewer- pipe clay and shale. Roofing-tile clay and shale. 5. Brick-clays. Common-brick clay and shale. Terra-cotta clay and shale. Drain- tile clay and shale. 6. Gumbo clays Burnt-ballast clay. 7. Slip-clays. The qualities or uses of the materials are here again employed as bases for subdivision. Such a classification is somewhat unsatisfactory, for the reason that one kind of clay might be used for several purposes. Ladd's classification. 2 Indigenous. A. Kaolins. (a) Superficial sheets. (6) Pockets, (c) Veins. Foreign or transported. A. Sedimentary. 1 Mo. Geol. Surv., XI, p. 25, 1897. 2 Ga. Geol. Surv., Bull. 6 A, p. 12, 1898, ORIGIN OF CLAY 25 (a) Marine. 1. Pelagic (deposited in deeper water). 2. Littoral (deposited near shore). (b) Lacustrine (deposited in fresh-water lakes). (c) Stream. 1. Flood-plain. 2. Delta. B. Meta-sedimentary. C. Residual. D. Unassorted. Under the Indigenous are included those clays formed by the decay of feldspar and other aluminous silicates in place. The Foreign or trans- ported embrace all sedimentary deposits. The meta-sedimentary clays are chemical products resulting from the decomposition of other trans- ported materials, such as volcanic tuffs, pumfce ; etc. The residual clays include the insoluble residue left by the dissolving of limestones, while under unassorted are included the glacial ones. The term kaolin, as here used, includes all residual clays, except those derived from limestones, and, since it is not restricted to white-burning ones, its use is unfortunate. Furthermore, the placing of limestone re- siduals in a separate class seems a rather fine distinction. Delta clays hardly seem of sufficient importance to warrant being placed in a separate class, and are rare. Buckley's classification. 1 I. Residual derived from A. Granitic or Gneissoid Rocks. B. Basic igneous rocks. C. Limestone or dolomite. D. Slate or shale. E. Sandstone. II. Transported by A. Gravity assisted by water. Deposits near the heads and along the slopes of ravines. B. Ice. Deposits resulting mainly from the melting of the ice of the glacial epoch. C. Water. Marine. Lacustrine. Stream. 1 Wis. Geol. Surv.,-Bull. Vll, Pt I, p. 14. CLAYS D. Wind. Loess. E. Orton Jr.'s classification. 1 A. Primary or residual clays. I. Entirely decomposed feldspathic rock. Kaolin or china clay. II. Partially decomposed feldspathic rock. English Cornwall stone. Porzellanerde of the Germans. B. Secondary or transported clays. 1. Deposited in still water, (a) Fire-clays. Highly refractory. Flint fire-clay. Plastic fire-clay. Moderately refractory. No. 2 fire-clay. Stoneware-clay. Sewer- pipe clay. (6) Shales. Slaty shales. Bituminous shales. Clay shales. II. Deposited from running water. Alluvium. Sandy clay. Loam. III. Deposited by glacial action. Leached Whitish or red bowlder clay. Unleached Blue bowlder clay. IV. Deposited by winds. Loess. Grimsley and Grout's classification. 2 I. Residual clays. 1. Kaolin. 2. China- or porcelain-clay. 1 Quoted by Beyer and Williams, la. Geol. Surv., XIV. p. 40, 1904. 3 W. Va. Geol. Surv., Vol. Ill, p. 70. 1906, ORIGIN OF CLAY 27 II. Transported clays. A. Refractory (fluxing impurities low). 3. Flint fire-clay. 4. Plastic fire-clay. B. Semi-refractory clay (fluxing impurities medium). 5. Paving-brick clay and shale. 6. Sewer-pipe clay and shale. 7. Roofing- tile clay and shale. 8. Stoneware-clay and shale. C. Non-refractory (fluxing impurities high). 9. Pottery clay. (a) Ball-clay. (b) Flower- pot clay. 10. Brick- and tile-clay and shale. (a) Ornamental brick-clay and shale. (b) Terra -co tta clay and shale. (c) Ornamental tile-clay and shale. (d) Common-brick and tile clay and shale. 11. Gumbo ballast-clay. 12. Slip-clay. Ries' classification. The following classification suggested by the author is an amplification of one proposed by him some years ago 1 : A. Residual clays. (By decomposition of rocks in situ.) I. Kaolins or china-clays. (White-burning.) (a) Veins, derived from pegmatite. (b) Blanket deposits, derived from extensive areas of igneous or metamorphic rocks. (c) Pockets in limestone, as indianaite. II. Red-burning residuals, derived from different kinds of rocks. B. Colluvial clays, representing deposits formed by wash from the fore- going and of either refractory or non-refractory character. C. Transported clays. I. Deposited in water. (a) Marine clays or shales. Deposits often of great extent. White-burning clays. Bpll-clays. Fire-clays or shales. Buff burning. Impure clays or shales, j T alcareous - ( Non-calcareous. 1 Md. Geol. Surv., IV. 28 CLAYS (6) Lacustrine clays. (Deposited in lakes or swamps.) Fire-clays or shales. Impure clays or shales, red-burning. Calcareous clays, usually of surface character. (c) Flood-plain clays. Usually impure and sandy. (d) Estuarine clays. (Deposited in estuaries.) Mostly impure and finely laminated. II. Glacial clays, found in the drift, and often stony. May be either red- or cream-burning. III. Wind-formed deposits (some loess). IV. Chemical deposits. (Some flint-clays.) SECONDARY CHANGES IN CLAY DEPOSITS Changes often take place in clays subsequent to their deposition. These may be local or wide-spread, and in many cases either greatly im- prove the deposit or render it worthless. The marked effect of some of these changes is often well seen in some clay beds of which only a por- tion has been altered. These secondary changes are of two kinds, viz., mechanical and chemical. MECHANICAL CHANGES Tilting, folding, faulting. In the uplifting of beds of clay or shale, subsequent to their deposition, the amount of elevation is rarely the same at all points over a large area, so that the beds frequently show a variable degree of tilting. If the uplift is accompanied by folding of the rocks, the dip of the beds may be quite steep. Thus, for example, the Cre- taceous and Tertiary clay-bearing formations of the Atlantic and Gulf coastal plain show a gentle dip to the southeast and south (PI. Ill, Fig. 2), while the Devonian shales of southern New York dip to the south. At Golden, Colo. (PI. XXIV, Fig. 2), the Cretaceous fire-clays often have a dip of as much as 90. Beds of clay and shale sometimes show folds or undulations. In the case of consolidated, or hard beds these may be due to lateral pressure, caused by movements in the earth's crust, while in soft beds the cause is frequently local. Many clay deposits in the Northern States show a local folding caused by the shoving action of the ice-sheet during the glacial period. Such folds, however, are of minor account and affect only a few beds. Where beds of clay are gently folded into arches (anticlinal folds) ORIGIN OF CLAY 29 and troughs (synclinal folds) each bed slopes or dips away from the axis of an anticlinal fold and towards the axis of a synclinal fold, but if fol- FIG. 5. Section of folded beds, with crest worn away, exposing different layers. (After Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 18, 1904.) lowed parallel to the axis it will remain at the same level, provided the axis itself is horizontal. Where a bed is not sufficiently elastic to bend under pressure it breaks, and if, at the same time, the beds on opposite sides of the break slip past each other, faulting is said to occur. When the breaking sur- face or fault-plane is at a low angle one portion of the bed may be thrust FIG. 6. Section showing strata broken by parallel fault-planes. (After Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 15, 1904.) over the other for some distance. In other cases the displacement may amount to but a few inches. Figs. 6 and 7 represent sections in faulted strata, and in these- it will be noticed that every bed terminates abruptly 30 CLAYS at the fault-plane, its continuation on the other side being at a higher or lower level. Displacements of this type are somewhat rare in surface FIG. 7. Strata broken by fault-plane of low inclination. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 15, 1904.) clays, and if occurring, the throw is not apt to exceed a few feet. In the shales of pre-Pleistocene age the amount of displacement is sometimes much greater. Both tilting and folding exert an important influence on the form and extent of the outcropping beds. Where no tilting has occurred, that is, where the beds are flat, only one bed, the upper one of the section, will be exposed at the surface, where the latter is level (Fig. 8), and lower FIG. 8. Section of horizontal strata, with only the top one exposed at the surface. beds will be . exposed only where stream-valleys have been carved (Fig. 9). If the beds are tilted (Figs. 10 and 11) or folded, and the crests of the folds worn off (Fig. 5), then the different beds will outcrop on the surface as parallel bands, whose width of outcrop will decrease with an increase in the amount of dip (Figs. 10 and 11). Erosion. All land areas are being constantly attacked by the weather. ing agents (frost, rain, etc.). The effect of this is to disintegrate the sur- ORIGIN OF CLAY 31 face rocks and wash away the loose fragments and grains. This brings about a general sculpturing of the surface, forming hills and valleys, FIG. 9. Horizontal beds, with several layers exposed by wearing down of the land surface. (After Ries, N. J. Geol. Surv., Fm. Kept., VI, p. 18, 1904.) the former representing those parts of the rock formations which have not yet been worn away. The effect of this is to cause phenomena or FIG. 10. Section showing outcropping of tilted strata. conditions which may at first sight appear puzzling, but are neverthe- less quite simple when the cause of them is understood. FIG. 11. Section of vertical beds. The width of outcrop is the same as the actual width of the bed. (See also PI. XXIV, Fig. 2.) Let us take, for example, a section of horizontal clay beds which originally covered an extensive area and were interstratified with sand 32 CLAYS beds. In Figs. 8 and 12, beds 1 and 3 may be taken to represent the clays. In Fig. 8 we have indicated the surface as it originally was, and in Fig. 12 the outline as it appears after the land has been exposed to weather- FIG. 12. Horizontal beds with several layers exposed by wearing down of the land surface. ing and erosion for an extended period. Here we see that the upper bed is left only on the highest hills and has been removed over a large area, while No. 2 caps the smaller knolls, and No. 3 outcrops in the sides of FIG. 13. Inclined strata, showing rise of the bed above sea-level, when followed up the slope or dip. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 19, 1904.) the deeper valleys. Many small areas of clay thus represent all that is left of a formerly extensive bed. If the beds had a uniform dip, the conditions may be as indicated in FIG. 14. Outcrops of a clay bed on two sides of a hill and its probable extension into the same. (After Ries, N. J. Geol. Surv. Fin. Rept., VI.) Fig. 13. Here bed 1 appears at the summit of two hills, a and 6, but its rise carries it, if extended, above the summit of hill c, which is capped by bed 2. If one did not know that the beds rose in that direction, it might ORIGIN OF CLAY 33 be assumed that bed 1 passed into bed 2, because they are at the same level. This dipping of the layers, or beds, sometimes accounts for the great dissimilarity of beds at the same level in adjoining pits. Where a bed of clay is found outcropping at the same level on two sides of a hill it is reasonable to assume that it probably extends from one side to the other, but it is not safe to predict it with certainty, for, as has been mentioned above, clay beds may thin out within a short distance. Furthermore, the overlying material, or overburden, will become thicker towards the center or summit of the hill, so that even if present the clay may be economically unworkable (Fig. 14). CHEMICAL CHANGES Nearly all clay deposits are frequently changed superficially, at least, by the weather or by percolating surface-waters. The changes are chiefly chemical and can be grouped under the following heads : Change of color. Leaching. Softening. Consolidation. Change of color. Most clay outcrops which have been exposed to the weather for some time show various tints of yellow or brown. This coloration, or rather discoloration, is due to the oxidation, or rusting, of the iron oxide which the clay contains. This iron compound is usually found in the clay as an original constituent of some mineral, and rusts out as the result of weathering, so that the depth to which the weathering has penetrated the material can often be told by the color. The lower limit of this is commonly not only irregular, but the distance to which it extends from the surface depends on the character of the deposits, sandy open clays being affected to a greater depth than dense ones. The dis- coloration of a clay due to weathering does not always originate within the material itself, for in many instances, especially where the clay is open and porous, the water seeping into the clay may bring in the iron oxide from another layer, and distribute it irregularly through the lower clay. The changes of color noticed in clay are not in every case to be taken as evidence of weathering, for in many instances the difference in color is due to differences in chemical composition. Many clays are colored black at one point by carbonaceous matter, whereas a short distance off the same bed may be white or light gray, due to a smaller quantity of carbonaceous material. In many of the Lower Cretaceous clays of New Jersey, for example, there is often a change from blue to red and white 34 CLAYS mottled, and from this into red clay. This is not the result of weathering, but is due to local variations in the iron-oxide contents of the different layers. Discoloration caused by weathering can usually be distinguished from differences in color of a primary character in that the former begins at the surface and works its way into the clay, penetrating to a greater FIG. 15. Section showing how weathering penetrates a clay bed, particularly along roots, cracks, and joint-planes. (After Ries.) distance along planes of stratification or fissures, and even following plant-roots as shown in Fig. 15. Where the clay deposit outcrops on the top and side of a hill it does not follow that, because the whole cliff face is discolored, the weather will have penetrated to this level from the surface, but indicates simply that the weathering is working inward from all exposed surfaces. The over- '- ~ ~_ JH _j- _. _ ~~ "_ "Yellow Clay - - - - Blue Clay Blue-Clay FIG. 16. Section showing weathered (yellow) clay where the overburden is least. /does not appreciate the important bearing which it may have on the I behavior of his material. Some unweathered clays crack badly in dry- Vjng or burning, but weathering seems to mellow and loosen them, as well burden often plays an important role in the weathering of clay, for the greater its thickness the less will the clay under it be affected. This fact is one which the clay-worker probably often overlooks, and therefore ORIGIN OF CLAY 35 as to increase their plasticity, so that the tendency to crack is sometimes either diminished or destroyed. If a clay which is being worked shows this tendency, it will be advisable to search for some part of the deposit which is weathered, and if the clay is covered by a variable thickness of overburden, the most weathered part will be found usually under the thinnest stripping, as shown in Fig. 16. Leaching. More or less surface-water seeps into all clays, and in some cases drains off at lower levels. Such waters contain small quantities of carbonic acid which readily dissolves some minerals, most prominent among them carbonate of lime. In some areas, therefore, where cal- careous clays occur, it is not uncommon to find that the upper layers of the deposit contain less lime carbonate than the lower ones, due to this solvent action of the percolating waters, and residual clays from lime- stone contain little or no lime carbonate. Softening. Most weathering processes break up the clay deposits, either by disintegration or by leaching out some soluble constituents that served as a bonding or cementing material, thus mellowing the out- crop, and many manufacturers recognize the beneficial effect which weathering has on their clay. They consequently sometimes spread it on the ground after it is mined and allow it to slake for several months or, in some cases, several years. The effect of this is to disintegrate thoroughly the clay, render it more plastic, and break up many injurious minerals, such as pyrite. Although mentioned under Chemical Changes it will be seen that the process of softening is partly a physical one. Consolidation. This change is found to have taken place in a few deposits, and is due to the formation of limonite crusts in the clay. At times these may form at a few points in the deposit, or only along certain layers, but in other instances they have originated in all parts of the mass, both along the stratification-planes, as well as in every joint or crack. They thus permeate the clay deposit with such a network of rusty, sandstone-like chunks, nodules, and strips as to seriously interfere with the digging of the clay, and requiring powerful machinery to break up the hard parts. Concretions. In some deposits the Hmonite or siderite (carbonate of iron) collects around nuclei, 1 such as pebbles or grains of sand, and grows into more or less symmetrical ball-like concretions, which, if large ? can be avoided or thrown out in mining. These are most abundant in the weathered portions of the clay (Fig. 17). They are not to be con- 1 The way in which natural physical forces act to bring about this segregation of chemical compounds of the same kind is not yet satisfactorily explained, although it is a common phenomenon. 36 CLAYS lused, however, with the nodules and lumps of pyrite that are found throughout some clay beds, and are of yellow color and glistening metal- lic lustre. These latter, although of secondary origin, are not necessarily due -to weathering. In many calcareous clays concretions (PI. IV, Fig. 2) are specially abundant, being found not uncommonly along lines of stratification. Many of the drift-clays, though free from lime, show concretionary lumps, .and in some deposits they have been formed by the deposition of lime FIG. 17. Section showing occurrence of concretions in certain layers. carbonate around tree-roots. In this case they would be closely asso- ciated with weathering. Formation of shale. Many sedimentary clays, specially those of ma- rine origin, after their formation are covered up by many hundred feet of other sediments, due to continued deposition on a sinking ocean bot- tom. It will be easily understood that the weight of this great thickness of overlying sediment will tend to consolidate the clay by pressure, con- verting it into a firm rock-like mass, termed shale. That the cohesion of the particles is due mostly to pressure alone is evidenced by the fact that grinding the shale and mixing it with water will develop as much plasticity as is found in many surface clays. An additional hardening has, however, taken place in many shales, due to the deposition of min- eral matter around the grains, as a result of which they become more firmly bound together. In regions where mountain-making processes have been active and folding of the rocks has taken place, heat and pressure have been de- veloped, and the effect of this has sometimes been to transform or metamorphose the shale into slate or even mica-schist (when the meta- morphism is intense), both of which are devoid of any plasticity when ground. The shales utilized for clay products in different parts of the o 8.S ^ r ^ T ORIGIN OF CLAY 39 country show a wide variation in their plasticity. Those of the Carbon- iferous, much used in the Central States, are often highly plastic, while the red shales of the Triassic formation of New Jersey are in most cases consolidated sandy clay, but, with one exception, all those examined are of poor plasticity and very low fusibility. The Hudson River slates, found over a large area of New Jersey, New York, and Pennsylvania, owe their low plasticity partly to a slight metamorphism, and partly to the deposition of cement around the grains. CHAPTER II CHEMICAL PROPERTIES OF CLAY MINERALS IN CLAY THE complex mineralogical character of clay has been referred to on an earlier page, and a microscopic examination or chemical analysis of a few impure clays will convince one of this fact. Nevertheless the statement is often made in print that clay is a hydrated silicate of alumina of the formula Al 2 03,2Si02+2H 2 0, con- sequently of definite chemical composition and with a formula corre- sponding to that of the mineral kaolinite. That this explanation is clearly improbable can be seen by examin- ing any series of clay analyses, few of which will reduce to such a formula. Equally sweeping and incorrect is the statement that kaolinite is the basis of all clays, and that they are therefore to be regarded as a mixture of kaolinite with other minerals Many clays no doubt contain a variable amount of kaolinite, 1 but there are others, consisting almost entirely of silica, alumina, and water, which clearly do not correspond to the formula of the mineral above mentioned (see H alloy site and Pholerite) , and in impure clays it becomes a matter of some difficulty to prove beyond a doubt whether the hydrous aluminum silicate present is kaolinite or some other mineral. 2 We may even express reasonable doubt regarding the necessary presence of kaolinite for the development of plastic qualities in the mass. The flint-clays of Missouri (many of which correspond closely to pholerite in composition) when finely ground possess some plasticity. The Edwards County, Texas, kaolin has even more plasticity, a tensile strength of 159 Ibs. per sq. in., and an air shrinkage of 6.2, and yet it 1 Kaolins of commerce and ball clays. 2 This fact has also been emphasized by G. P. Merrill, Non-metallic Minerals, p. 217 1904. 40 CHEMICAL PROPERTIES OF CLAY 41 dees not correspond exactly to the formula of kaolinite, but stands intermediate between halloysite and kaolinite. Wheeler has described an halloysite from Missouri 1 which is slightly plastic even when ground to pass 20 mesh, and has an average tensile strength of 38 Ibs. per sq. in. The number of different minerals present in a clay is often no doubt large and depends partly on the mineralogical composition of the rock or rocks from which the clay has been derived, and partly on the extent to which the mineral grains in the clay have been destroyed by weather- ing; but in any case the identification of mineral species is rendered rather difficult, chiefly because of the extreme fineness of the grains, and partly because these are often surrounded by decomposition products. More attention has been given to the mineralogy of soils than of clays, but since the former are in many cases nothing more than surface clays, what is true of the one is more or less so of the other. Chamberlin and Salisbury, 2 in studying the residuals of the Wis- consin driftless area, were abk to identify such minerals as plagio- clase, orthoclase, biotite, muscovite, hornblende, augite, magnetite, and quartz, while Ladd, in studying the Georgia Cretaceous clays, 3 has noted kaolinite, feldspar, quartz, muscovite, biotite, magnetite, titanite, limonite, calcite, and prochlorite. In the Wisconsin materials Buckley 4 records finding quartz, feldspar, mica, calcite, dolomite, and iron oxide. The Leda clays of Canada 5 show quartz, orthoclase, plagioclase. mica, tourmaline, pyroxene, chlorite, and hornblende. In the study of soils perhaps the largest number of species have been determined by Delage and Lagatu, 6 who include in their list calcite, quartz, biotite, muscovite, sericite, orthoclase, oligoclase, zircon, tour- maline, amphibole, apatite, andalusite, titanite, microcline, limonite, hematite, chlorite, augite, etc. The more important of these may be referred to in more than a passing manner. 1 Mo. Geol. Surv., XI, p. 186, 1896. 2 U. S. Geol. Surv., 6th Ann. Rept., 245. 3 Amer. Geol., XXIII, p. 240, 1899. 4 Wis. Geol. and Nat. Hist. Surv., Bull. VII, Pt. I. 6 Merrill, Rocks, Rock-weathering, and Soils, p. 335. e Ann. de Pe"cole nationale d'agriculture de Montpellier, VI, pp. 200-220, 1905; also Comptes rend., CXXXIX, p. 1044, 1904. See also F. Steinriede, Anleitung zur mineralogischen Bodenanalyse, Halle, 1889; Dumont, Comp. rend., CXL, p. 1111, 1905; Tebier, ibid.., CVIII, p. 1071, 1889; and Cameron and Bell, Bur. of Soils, Bull. 30, p. 11, 1905, and Bull. 22, p. 12, 1903. 42 CLAYS Hydrous Aluminum Silicates Kaolinite. This mineral is a hydrated silicate of alumina, repre- sented by the formula .11203,28102,21120, which corresponds to a composition of Silica (Si0 2 ), 46.3 per cent; Alumina (A1 2 O 3 ), 39.8 per cent; Water (H 2 0), 13.9 per cent. It is sometimes referred to as clay substance, and is that portion of the clay which is soluble in hot sul- phuric acid and sodium carbonate. It is a white, pearly mineral, crystal- lizing in the monoclinic system, the crystals presenting the form of small hexagonal plates (PL V, Fig. 1) with a hardness of 2-2.5 and a specific gravity of 2.2-2.6. It is naturally white in color, and a mass of it is plastic when wet, but very slightly so. According to Rosenbusch 1 its index of refraction is the same as that of Canada balsam; the double refraction is strong. A negative bisectrix emerges from the face, of the plate, and the axial plane bisects the acute prism angle. The optical behavior is therefore very similar to that of muscovite, and it can only be distinguished with certainty from colorless mica by chemical reaction to prove the absence of alkali; its specific gravity cannot be used to advantage because of the mica- ceous form of both minerals. It has naturally been assumed by most writers that kaolinite was a widely distributed mineral in clays, but when we come to sift the evi- dence of its presence comparatively little is to be found. A microscopic examination even of the white clays free from im- purities rarely reveals the presence of the hexagonal kaolinite scales, although the little vermiculite-like bunches of plates of this mineral may be present (Fig. 26); but still even these are rarely seen in the more impure clays, and the theory of the universal presence of kaolinite in clay is probably traceable to the fact that many white clays, after having the sand washed out, often approach kaolinite in composition. 2 The occurrence of kaolinite in crystals has been noted from the National Belle mine, Red Mountain, Colo., 3 by Dick from Anglesey, 4 as well as by several other writers. 5 Many kaolins show the bunches of kaolinite plates referred to above, 1 Physiography of Rock-making Minerals, Iddings' translation, 1889, p. 320. 2 H. Ries, Ala. Geol. Survey, Bull. 6, p. 41, 1900. 3 H. Reusch, Jahrb. f. Min., 1887, II, p. 70. 4 A. Dick, Min. Mag., 1876, VIII, p. 15. 5 Safarik, Bohm. Ges. Wiss., 16th Feb., 1870; Knop, Neues Jahr. Min., etc.. 1859, p. 595; Johnson and Blake, Amer. Jour. Sci., ii, XLII, pp. 351 and 867. PLATE V FIG. 1. Photo-micrograph of kaolinite. (After Merrill, Non-metallic Minerals.)) FIG. 2. Washed kaolin. (After Merrill.) 43 PLATE VI Photo-micrograph of indianaite, showing coarseness of grain. 45 CHEMICAL PROPERTIES OF CLAY 47 and the separation of these by grinding was said by Cook 1 to increase the plasticity. Kaolinite is always of secondary origin, and although in most cases it has probably been derived from feldspar, its derivation from numerous other minerals has been recorded, although unaccompanied by proof. Thus Rosier 2 states that the formation of kaolinite from scapolite, leucite, nepheline, sodalite, hauyne, analcite, topaz, etc., is chemically possible, but not proven. The same may be said in part regarding the statements of Van Hise, 3 who lists andalusite, anorthoclase, biotite, cyanite, epidote, leucite, microcline, nephelite, orthoclase, plagioclase, scapolite, sillimanite, soda- lite, topaz, zoisite, and garnet as the primary mineral. He gives the formula for the kaolinization of feldspar as follows : 2K AlSi 3 O 8 + 2H 2 O + CO 2 = H 4 Al 2 Si 2 09 + 4SiO 2 + K 2 C0 3 . Van Hise calculates that the decrease in volume, supposing the freed silica as quartz, and the potassium carbonate dissolved, is 12.57%. If all the silica were dissolved (which is unlikely), then the volume de- crease would be 54.44%. Pure kaolin is highly refractory, but a slight addition of fusible im- purities lowers its refractoriness. Many kaolins contain very minute scales of white mica which it would be difficult to distinguish under the microscope from kaolinite; and since white mica in a very finely divided condition is not unlike kaolinite in its plasticity, as shown by the experiments of Vogt, its presence may be of no influence, unless there is an appreciable amount of it. The following quotation 4 exhibits those experiments : "Mr. Vogt considers that the plasticity which clays have is chiefly due to the hydrated silicate of alumina or kaolinite. Experiments which he made show that the kaolinite is not the only substance which remains in suspension for a long period. For his trials he took quartz from Limousin, orthoclase from Norway, and a potash mica. All three were ground very fine, and then washed in a current of slightly ammoniacal water. The washed materials were then allowed to stand. After 24 hours each of the liquids was as opalescent as if it had washed clay in suspension. After nine days the turbidity still remained, but was less 1 Clays of New Jersey, N. J. Geol. Surv., 1878. 2 l.c. 3 Treatise on Metamorphism, p. 352. 4 Thonindustrie-Zeitung, 1893, p. 140; also Compt. rend., Acad. Sci., Paris, CX, p. 1199, 1890. 48 CLAYS marked. At the end of this time the supernatant liquid was ladled off of each, and a few drops of hydrochloric acid added to it. The suspended materials coagulated and settled, and the precipitate was collected, dried, and weighed. The mica which had remained in suspension during the nine days was very fine; still the particles glittered in the light. The addition of hydrochloric acid caused the instant settling of the par- ticles, which was also noted by the cessation of the glittering. The settlings of mica from 1 liter of water amounted to 0.15 gram. This fine-grained mica possessed a plasticity almost equal to that of the kaolin. "From the decanted liquid of the feldspar the hydrochloric acid brought down about 0.4 gram of this mineral per liter, while of the quartz only 0.1 gram of sediment was obtained. "A very plastic clay from Dreux was treated in the same manner, and after nine days a precipitate of 0.56 gram was brought down. "From these experiments we see that in washing kaolin it is impos- sible to free it entirely from quartz, feldspar, and mica, if they are present in a finely divided condition." Minerals related to Kaolinite These include several species, all hydrated silicates of alumina. Some of these have been found in crystals and are very probably good species, but others are known only in an amorphous condition, which may tend to suggest some doubt as to their validity; in fact Johnson and Blake 1 suggested that the name kaolinite should include all the associated species mentioned below, and that the term kaolin be retained for the "more or less impure commercial article," but this usage seems too comprehensive, especially since some of those hydrous aluminum silicates mentioned below seem to have a definite formula distinctly different from that of kaolinite proper. These associated species to- gether with their characters are given by Dana as follows : Halloysite. A massive, clay-like or earthy mineral with a con- choidal fracture and showing little or no plasticity; hardness 1-2; specific gravity 2.0-2.20; luster somewhat pearly to waxy or dull; color white, grayish, greenish, yellowish, and reddish; translucent to opaque, sometimes becoming translucent or even transparent in water, with an increase of one fifth in weight. It is a hydrous silicate of alumina like kaolinite, but amorphous and containing more water; the amount is somewhat uncertain, but according to Le Chatelier the composition 1 Amer. Jour. Sci., ii, XL1I, p. 351. CHEMICAL PROPERTIES OF CLAY 49 ^~ . is probably 2H 2 0,Al 2 O3,2SiO 2 +aq, or silica 43.5%, alumina 36.9%, water 19.6% = 100. It is not uncommon in the kaolin deposits around Valleyhead, Dekalb County, Ala., 1 where it occurs as veins in the kaolin, but no analysis of the material is available. A deposit has been described by Wheeler 2 from five miles southwest of Aurora, Mo. The material is a white porcelain-like clay, which is more or less stained or intermixed with yellow clay. It is massive, compact, hard, and of low plasticity. It fuses completely at 2600 F. and has the following composition : ANALYSIS OF MISSOURI HALLOYSITE Silica (SiO 2 ) ............................................ 44.12 Alumina (A^OJ ........................................ 37.02 Ferric oxide (Fe 2 O 3 ) .......... ............................ 33 Lime (CaO) ..................................... . . : ..... 19 Alkalies (Na 2 O,K 2 O) ..................................... 24 Water (H 2 O) ................................ ........... 18,48 Total .............................................. 100.38 This analysis it will be seen agrees closely with the theoretic com- position of this mineral given above. G. P. Merrill 3 has also noted its occurrence in small quantities asso- ciated with kaolin, in narrow veins in the decomposing gneissic rock near Stone Mountain, Ga. The following three analyses 4 represent the composition of halloysite from different localities: ANALYSES OF HALLOYSITE I. II. III. Silica (SiOJ 39.30 40.70 42.91 Alumina (Al 2 Og) 38.52 38.40 38.40 Lime (CaO) 0.75 0.60 0.60 Magnesia (MgO) 0.83 1.50 1.5 Ferric oxide (Fe Og) 1 42 Manganese 0.25 Water 19 34 18 00 18 00 100.41 99.20 101.41 I. Elgin, Scotland. II. Steinbruck, Styria. III. Detroit Mine, Mono Lake. Calif. 1 Gibson, Geol. Surv. of Ala., Report on Murphrees Valley, 1893, p. 121. 2 Mo. Geol. Surv., XI, p. 186, 1896. 3 Non-metallic Minerals, p. 225. 4 Ibid. 50 CLAYS The kaolin found near Leaky, Edwards County, Tex./ appears to be of intermediate composition between kaolinite and halloysite, and may be a mixture of the two. Indianaite. This is a whitish residual clay found in Lawrence County, Ind. (see Indiana clays), which is placed under halloysite by Dana, 2 and called allophane in the Indiana 3 Survey report. The two following analyses show its composition, No. I being given by Dana, and No. II by the Indiana Survey: ANALYSES OF INDIANAITE I.* II. III. IV. Silica (SiO,,) 43 25 44 75 43 5 46 3 Alumina (Al 2 Og) 39.92 38.69 36 9 39 8 Ferric oxide (Fe,O 3 ) .95 Lime (CaO) Magnesia (MgO) } .69 f .37. 1 .30 Potash (K O) } f 12 Soda (Na O) \ .59 1 23 Water (H O) 15 52 15 17 19 6 13 9 * The moisture has been left out. and the analysis recalculated to 100 per cent. While the percentage of combined water in this material is higher than in kaolinite, and the silica lower, still they approach no more closely to those given for halloysite than they differ from similar constituents of kaolinite, No. Ill representing the composition of the former, and No. IV of the latter, placed there for purposes of comparison. Pholerite. This term was first applied by Guillemin in 1825 4 to a pure white pearly substance, occurring in the form of small hexagonal scales, soft and friable to the touch, adherent to the tongue, and giving a plastic mass with water. Similar occurrences were noted later by J. L. Smith 5 in 1859, by A. Knop, 6 and by L. L. Koninck. 7 The composition of pholerite is: Silica (Si02) 39.3, alumina (A1 2 O 3 ) 45, water (H 2 0) 15.7, which corresponds to a chemical formula of 2Al 2 O 3 ,3Si0 3 ,4H 2 0. Dana 8 classes this under kaolinite, and gives halloysite as a separate 1 See description of Texas clays. 2 System of Mineralogy, 688, 1892. 3 Ind. Geol. Surv., 29th Ann. Kept. 4 Ann, des Mines, XI, p. 489. 6 Amer. Jour. Sci., ii, XI, p. 58. 6 Neues Jahrb. Min., 1859; also Johnson and Blake, Amer. Jour. Sci., XLIIL p. 361, 1867. 7 Zeitschr. f. Kryst. u. Min., II, p. 661. 8 Syst. Min., 1893, p. 685. CHEMICAL PROPERTIES OF CLAY 51 species, but, in view of the fact that the pholerite has been found in crystalline form and the halloysite not, this hardly seems reasonable. So far as the author is aware no crystallized pholerite has been described from the United States, but Wheeler has pointed to its probable presence in some of the Missouri flint-clays, 1 in which the silica-alumina ratio ranged from 0.94 to 1.15. Now, since this ratio in kaolinite is 1.16 and in pholerite 0.81, it seems quite probable that in some at least of the Missouri clays there is a mixture of kaolinite and pholerite present. Cook in his report on the New Jersey clays 2 gives 32 analyses in which the combined silica has been separated from the sand, and of these 21 seem to indicate the presence of some pholerite, their silica- alumina ratio ranging from 0.94 to 1.15. If this explanation is correct, then pholerite is no doubt present in many other fire-clays, and perhaps even some kaolins. The writer has questioned whether the presence of bauxite with the kaolinite might not give a mixture with a high alumina percentage similar to that shown by pholerite. Nacrite, according to Johnson and Blake, 3 is identical with pholerite. Rectorite. 4 Monoclinic. In leaves or plates resembling mountain- leather; hardness less than that of talc; feels soapy; luster pearly; color pure white, sometimes stained red with iron oxide. Composition : HAlSiO* or Al 2 O3,2Si02,H 2 = silica 50.0, alumina 42.5, water 7.5. Newtonite. 5 Rhombohedral. In soft, compact masses, resembling kaolinite. Color white. Its composition is H 8 Al 2 Si2On + water, or Al 2 O3,2SiO2,5H 2 = silica 38.5, alumina 32.7, water 28.8. Sp. gr. 2.37. Allophane. Amorphous. As incrustations which are usually thin, with mammillary surface. Occasionally almost pulverulent. Fracture imperfectly conchoidal and shining to earthy. Very brittle. Color variable. Translucent. Hardness 3. Sp. gr. 1.85-1.89. A hydrous aluminum silicate, Al 2 SiO 5 +5H 2 O= silica 23.8, alumina 40.5, water 35.7. Other species listed by Dana in the kaolinite group are cimolite, montmorillonite, pyrophyllite, colly rite, and schrotterite. Le Chatelier's Experiments. H. Le Chatelier, 6 in studying the action of heat on certain clays, emphasized the fact that the hydrated aluminum silicates, in spite of their common occurrence and their industrial import- 1 Mo. Geol. Surv., XI, p. 50, 1897. 2 N. J. Geol. Surv., 1878. 3 I.e. 4 Brackett and Williams, Amer. Jour. Sci., XLII, p. 16, 1891. 5 Ibid. 8 Compt. rend., CIV, p. 1443, 1887; also Ding, polyt, Jour., CCLXV, p. 94, 1887.. 52 CLAYS ance, are little known as regards their chemical constitution. They generally form mixtures so complex that analysis alone furnishes no precise data as to their nature, and he suggests that by studying the temperature of dehydration of these bodies, it may be possible to iden- tify a small number of chemical species, and to distinguish the presence of each of them in different mixtures. Le Chatelier states that if a small quantity of clay is rapidly heated there occurs at the moment of de- hydration a retardation in the rise of temperature, and this point may be utilized for establishing a distinction between the various hydrated aluminum silicates. As a result of his experiments he recognized the following groups: 1. Halloysite (2Si0 2 ,Al 2 3 ,2H 2 0+Aq). Shows a retardation in the rate of rise of the temperature between 150 and 200 C., a second one at 700 C., followed by a sudden acceleration at 1000 C. 2. Allophane (SiO 2 ,Al 2 03+Aq). Retardation between 150 and 220 C., and acceleration at 1000 C. 3. Kaolin (2SiO 2 ,Al 2 O 3 ,2H 2 0). Shows retardation towards 770 C., and a slight acceleration towards 1000 C. 4. Pyrophyllite (4SiO 2 ,Al 2 O 3 ,H 2 0). The first distinct retardation occurs at 700 C., and a second, but less-evident one, at 850 C. 5. Montmorillonite (4Si0 2 ,Al 2 C)3,H 2 + Aq). First retardation at about 200 C., a second at 770 C., and a third less-marked one at 950 C. Other Minerals Quartz. This mineral whose formula is Si0 2 is found in at least small quantities in nearly every clay, whether residual or sedimentary, but the grains are rarely large enough to be seen with the naked eye. They are translucent or transparent, usually of angular form in residual clays and rounded in sedimentary ones, on account of the rolling they have received while being washed along the river channel to the sea, or dashed about by the waves on the beach previous to their deposition in deeper, quiet water. The quartz grains may be colorless, but are more often colored superficially red or yellow by iron oxide. Nodular masses of amorphous silica, termed chert or flint, are found in some clays. These are not uncommon in many residual clays of the Southeastern States, and quartz pebbles are by no means rare in many sedimentary clays of Mesozoic or Pleistocene age; indeed, most of the sand-grains found in the coarse, gritty surface clays of sedimentary character are quartz. This mineral also forms most of the hard pebbles found in the :so-called "feldspar" beds of the Woodbridge district of New Jersey. 1 ' Ries and Kiimmel, N. J. Geol. Surv., Fin. Kept., VI, p. 468, 1904. CHEMICAL PROPERTIES OF CLAY Both quartz and flint are highly refractory, being fusible only at cone 35 of the Seger series (see Fusibility, Chap. Ill), but the presence of other minerals in the clay may exert a fluxing action and cause the quartz to soften at a much lower temperature. The amount of quartz in clays varies from under one per cent in some kaolins or fire-clays to over 50 or 60 per cent in some very sandy brick-clays. Feldspar. This mineral is nearly as abundant in some clays as quartz, but, owing to the ease with which it decomposes, the grains are rarely as large. When fresh and undecomposed the grains have a bright luster, and split off with flat surfaces or cleavages. Feldspar is slightly softer than quartz, and while the latter, as already mentioned, scratches glass, the former will not. There are several species of feldspar, which vary somewhat in their chemical composition, and are known by different names, as shown below. COMPOSITION OF FELDSPARS Feldspar Species. Chemical Composition. SiO 2 . A1 2 3 . K 2 O Na 2 O. CaO. Orthoclase 64.70 68 62 53 43 18.40 20 24 30 37 16.90 12 9 4 12 5 13 20 Albite Oligoclase La/bra,dorit6 Anorthito The fusing-point of feldspar is about cone 9 (see Seger Cones, under Fusibility), but the different species vary somewhat in their melting- points. The feldspar grains may, however, begin to flux with other in- gredients of the clay at a much lower temperature. (See under Alkalies.) Mica. This is one of the few minerals in clay that can be easily detected with the naked eye, for it occurs commonly in the form of thin, scaly particles whose bright, shining surface renders them very con- spicuous, even when small. Very few clays are entirely free from mica, even in their washed condition, for, on account of the light scaly char- acter of the mineral, it floats off with the clay particles. Some clays are highly micaceous, but such are rarely of much commercial value. There are several species of mica, all of rather complex composition, but all silicates of alumina, with other bases. Two of the commonest 54 CLAYS species are the white mica or muscovite, H 3 KAl 3 (Si04)3 = (Si 45.2, A1 2 O 3 38,5, K 2 11.8, H 2 O 4.5), and the black mica or biotite (H 1 K) 2 (Mg,Fe)2(Al,Fe)2(Si0 4 )3. Of these two, the muscovite is the most abundant in clay, because it is not readily attacked by the weathering agents. The biotite, on the other hand, decomposes much more rapidly on account of the iron oxide which it contains. Other species of the mica group are no doubt present in some clays. The effect of mica in burning is mentioned under Alkalies. Lepidolite occurs in some clays, as evidenced by the small amounts of lithia which have been occasionally noted. 1 Iron Ores. This title includes a series of iron compounds which are sometimes grouped under the above heading, because they are the same ones that serve as ores of iron when found in sufficiently concentrated form. The mineral species included under this head are: Limonite <2Fe 2 O 3 ,3H 2 O=Fe 2 O 3 85.5%, H 2 14.5%), hematite (Fe 2 3 ), magnetite (Fe 3 O 4 ), siderite (FeC0 3 =FeO 62.1%, C0 2 37.9%). Limonite. This mineral occurs in clays in a variety of forms, and is often widely distributed in them, its presence when in a finely divided condition being shown by the yellow or brown color of the material. When the clay is uniformly colored the limonite is evenly distributed through it, sometimes forming a mere film on the surface of the grains; at other times it is collected into small rusty grains, or again forms concretionary masses of spherical or irregular shape; in still other clays it is found in the form of stringers and crusts, extending through the clay in many directions. The concretions are often especially abundant in some weathered clays. At times they take the shape of thick-walled cylindrical bodies which have apparently formed around plant-roots. The beds of sandstone found in many of the sand and gravel deposits associated with some clays are caused by limonite cementing the sand- grains together. Limonite concretions can often be removed by hand-picking. If left in the clay, they cause fused blotches which are unsightly and some- times even cause splitting of the ware. Limonite is most abundant in surface clays, especially those which are of sandy character or sufficiently porous to admit the oxidizing waters from the surface. It is also found quite frequently in the weath- ered outcrops of many shales. Hematite, the oxide of iron, is of a red color and may be found in clays, but it changes readily to limonite on exposure to the air and in the presence of moisture. 1 N. W. Lord, Amer. Inst. Min. Eng., Trans,, XII, 505. CHEMICAL PROPERTIES OF CLAY 55 Magnetite, the magnetic oxide of iron, forms black magnetic .grains, and, while not common, is sometimes found when the material is examined microscopically. Like the hematite, it changes to limonite. Siderite, the carbonate of iron, may occur in clay in the following forms: 1. As concretionary masses known as clay-ironstones, ranging in size from a fraction of an inch to several feet in diameter! They are very abundant in some Carboniferous shales, and are often strung out in lines parallel with the stratification of the clay. If near the surface, the siderite concretions often change to limonite. 2. In the form of crystalline grains, scattered through the clay and rarely visible to the naked eye. 3. As a film coating other minerals in the clay. This min- eral will also change to limonite if exposed to the weather. When iron carbonate is in a finely divided condition and evenly distributed through the clay it may give it a blue or slate-gray color. Siderite may be present in some surface clays, but it is probably of greatest importance in shales, notably those associated with coal-seams, and may occur in either finely divided (disseminated) or concretionary form. Pyrite (FeS 2 =Fe 46.6%, S 53.4%). This mineral, which is not uncommon in some clays, can be often seen by the naked eye, and is known to the clay-miners in some districts as sulphur. It has a yellow color, metallic luster, and occurs in large lumps, small grains or cubes, or again in flat rosette-like forms. Not infrequently it is formed on or around lumps of lignite, showing quite clearly that the carbonaceous matter has reduced some iron sulphate present to sulphide. It is a familiar object to all clay-miners of the Raritan district of New Jersey, and abundant also in many Carboniferous clays. When exposed to the weather pyrite alters rather easily, first to the sulphate of iron and then to limonite. Clays containing pyrite are not, as a rule, desired by the clay-worker, and in mining the pyritic material is rejected. Pyrite may be found in almost any clay or shale, but owing to the ease with which it is converted into limonite its formation or permanence in surface clays is rare. Calcite (CaC0 3 = CaO 56.00%, C0 2 44.00 %) .This mineral, when abundant, is found chiefly in clays of recent geological age, but some shales also contain considerable quantities of it. It can be easily de- tected, for it dissolves rapidly in weak acids, and effervesces violently upon the application of a drop of muriatic acid or even vinegar. It is 56 CLAYS rarely present in grains large enough to be seen with the naked eye, but has been detected with the microscope. 1 In some clays calcite, as well as some other minerals, may form con- cretions. Many of the lacustrine and glacial clays found in Wisconsin and Michigan contain large quantities of lime carbonate, and some of those found in other states are highly calcareous. The flood-plain clays mentioned under Texas often carry a high percentage of carbonate of lime. Gypsum (CaS0 4 ,2H 2 0=CaO 32.6%, S0 3 46.5%, H 2 20.9%).- It is doubtful whether this mineral is widely distributed in clays, but it is true that some deposits contain large quantities of it. It may occur in a finely divided condition, or in the form of crystals, plates, or fibrous masses of selenite. The Salina shales of New York frequently contain large plates of nearly clear selenite, while some clays of the southern Atlantic coastal plain exhibit fine crystals of it. Its softness, pearly luster, and trans- parency render its identification easy when the pieces are of macroscopic size. When heated to a temperature of 250 C. (482 F.) the gypsum loses its water of combination, and when burned to a still higher tem- perature the sulphuric acid passes off. Rutile (Ti0 2 =Ti 60%, O 40%) is presumed to be of wide-spread occurrence in clays, because titanium is usually found on chemical analy- sis when proper tests are made. Rutile grains can be seen under the microscope in many fire-clays, and the analyses frequently show the presence of titanium oxide to the extent of two per cent or more. The presence of this mineral, however, is unfortunately too commonly ignored in the analysis of clay, and yet, as will be shown later, its effect on the fusibility of clay is such that it should not be neglected in the higher grades at least. It occurs mostly in the form of bristle-like crystals. No systematic study of their occurrence in clay has ever been taken up. The writer has observed them in some of the Staten Island, N. Y., clays, and reference has been made to them from time to time by other writers. 2 Hmenite (TiFe 2 03) probably occurs in clays, but as far as the writer is aware its presence has not been definitely mentioned. If present, it would probably be in part altered to leucoxene Hmenite is most likely to occur in those clays which have been derived from soda-rich and basic eruptive rocks. 1 Wheeler, Mo. Geol. Surv., XI; Buckley, Wis. Geol. and Nat. Hist. Survey, Bull. VII, Pt. I. 2 See J. J. H. Teall, Min. Mag., Ill, 201; G. E. Ladd, Amer. Geol., XXIII, 240, 1899. CHEMICAL PROPERTIES OF CLAY 57 Glauconite, a hydrous silicate of potash and iron, is a common ingredient of some clays. Its composition is often somewhat variable, and it may contain other ingredients as impurities. Thus a sample from New Jersey analyzed: 1 Silica 50.70%, alumina 8.03%, iron oxide 22.50%, magnesia 2.16%, lime 1.11%, potash 5.80%, soda 0.75%, water 8.95%. It is an easily fusible mineral, and hence a high percentage of it is not desired in a clay. It is found in the Clay Marl formations of the New Jersey Cretaceous, 2 and in the Eocene formations of Mary- land 3 and other coastal-plain states. Dolomite and Magnesite. Dolomite (CaMgCO 3 = CaO 30.4%, MgO 21.7%,C0 2 47.8%) and magnesite (MgC0 3 = MgO 47.6%,C0 2 52.4%) may both occur in clay. They are soft minerals resembling calcite, and either alone is highly refractory, but when mixed with other minerals they exert a fluxing action, although not at so low a temperature as lime. In some residual clays derived from dolomitic limestone the grains of the dolomite are clearly visible in those portions of the mass in which disintegration has not proceeded very far. Hornblende and Garnet. These are both silicate minerals of com- plex composition, which are probably abundant in many impure clays, but their grains are rarely larger than microscopic size. Both are easily fusible, and weather readily on account of the iron oxide in them, and therefore impart a deep-red color to clays formed from rocks in which they are a prominent constituent. Garnet in fair-sized grains has been noted by the writer in some of the North Carolina kaolins. Vanadiates, though not common in clays, may cause discoloration. In Germany they have been found in clays associated with the lignites, and also in some fire-clays, 4 but in this country, so far as the writer is aware, they have never been investigated. Clays containing soluble vanadiates, if not burned at a sufficiently high temperature, will show on the surfa.ce of the ware a green discoloration which, though it can be washed off with water, will continue to return as long as any of the salt is left in the brick. Vanadiates may be rendered insoluble by burning the clay to a point of vitrification. 5 Tourmaline. Since this mineral is not an uncommon constituent of many pegmatite veins, it is sometimes found in kaolins derived from pegmatites. Large crystals of tourmaline are frequently found in the kaolin of Henry County, Virginia. 1 N. J. Geol. Surv., Fin. Kept., VI, p. 46, 1904. 4 Seger, Ges. Schrift, p. 301. 2 Ibid., p. 151. 5 Ibid. 3 Md. Geol. Surv., Eocene, p. 52, 1901. 58 CLAYS Manganese oxides. These occur in many clays in small amounts, and when determined are found to rarely exceed one per cent. In some residual clays the manganese has been sufficiently concentrated to be worth collecting. Vivianite (Fe 2 P 2 O 8 -f8H 2 O = FeO 43%, P 2 5 28.3%, H 2 O 28.7%) has not been described as a common constituent of clay. It has been noted in certain Pleistocene clays of Maryland, 1 in which it occurs as small blue spots. It is not known what effect large quantities of it might have on the clay. Rare elements. Even such rare elements as cerium, yttrium, and beryllium oxides have been determined in some clays. 2 THE CHEMICAL ANALYSIS OF CLAYS There are two methods of quantitatively analyzing clays. One of these is termed the ultimate analysis, the other is known as the rational analysis. The ultimate analysis. In this method of analysis, which is the one usually employed, the various ingredients of a clay are considered to exist as oxides, although they may really be present in much more com- plex forms. Thus, for example, calcium carbonate (CaCO 3 ), if it were present, is not expressed as such, but instead it is considered as broken up into carbon dioxide (C0 2 ) and lime (CaO), with the percentage of each given separately. The sum of these two percentages would, how- ever, be equal to the amount of lime carbonate present. While the ultimate analysis, therefore, fails to indicate definitely what compounds are present in the clay, still there are many facts to be gained from it. The ultimate analysis of a clay might be expressed as follows: Silica (SiO 2 ) Alumina (A1 2 O 3 ) Ferric oxide .... (Fe 2 O 3 ) Lime (CaO) Fluxing impurities Magnesia ....... (MgO) Alkalies., j ( Soda ........... (Na 2 0) Titanic oxide. . . (TiO 2 ) Sulphur trioxide.(S0 3 ) Carbon dioxide. . (CO 2 ) Water ......... (H 2 O) 1 Md. Geol. Surv., IV, 228, 1902. 2 J. R. Strohecker, Jour, prakt. Chem. (2), XXXIII, p. 132; Abs. Jour. Chem. Soc., L, p. 314, 1886. CHEMICAL PROPERTIES OF CLAY 59 In most analyses the first seven of these and the last one are usually determined. The percentage of carbon dioxide is small, except in very calcareous clays, and therefore commonly remains undetermined. Titanic oxide is rarely looked for, except in fire-clays, and even here its presence is frequently neglected. Since the sulphur trioxide, carbon dioxide, and water are volatile at a red heat, they are often determined collectively and expressed as "loss on ignition." If carbonaceous matter, such as lignite, is present, this also will burn off at redness. To separate these four, special methods are necessary, but they are rarely applied, and in fact are not very necessary except in calcareous clays or highly car- bonaceous ones. The loss on ignition in the majority of dry l clays is chiefly chemically combined water. The ferric oxide, lime, magnesia, potash, and soda are termed the fluxing impurities, and their effects are discussed under the head of Iron, Lime, Magnesia, etc., and also under Fusibility in Chapter III. All clays contain a small but variable amount of moisture in their pores, which can be driven off at 100 C. (212 F.). In order, therefore, to obtain results that can be easily compared, it is desirable to make the analysis on a moisture-free sample which has been previously dried in a hot-air bath. This is unfortunately not universally done. Interpretation of ultimate analysis. The facts obtainable from the ultimate analysis of a clay are the following: 1. The purity of the clay, showing the proportions of silica, alumina, combined water, and fluxing impurities. High-grade clays show a per- centage of silica, alumina, and water approaching quite closely to those of kaolinite. 2. The refractoriness of the clay; for, other things being equal, the greater the total sum of fluxing impurities, the more fusible the clay. 3. The color to which the clay burns. This may be judged approxi- mately, for clays with several per cent or more of ferric oxide will burn red, provided the iron is evenly and finely distributed in the clay, and there is no excess of lime or alumina. The above conditions will be affected by a reducing atmosphere in burning, or the presence of sul- phur in the fire gases. 2 4. The quantity of water. Clays with a large amount of chemically combined water sometimes exhibit a tendency to crack in burning, and may also show high shrinkage. If a hydrous aluminum silicate of a composition closely resembling kaolinite is the only mineral present containing chemically combined water the percentage of the latter will 1 This means dried at 100 C. until their weight is constant. See under Moisture. 2 See Lime and Iron in this chapter. 60 CLAYS be approximately one third that of the percentage of alumina, but if the clay contains much limonite or hydrous silica the percentage of chemically combined water may be much higher. 5. Excess of silica. A large excess of silica indicates a sandy clay. If present in the analysis of a fire-clay it indicates only moderate refrac- toriness. 6. The quantity of organic matter. If this is determined separately, and it is present to the extent of several per cent, it would require slow burning during the oxidation period if the clay was dense. 7. The presence of several per cent of both lime (CaO) and carbon dioxide (CO 2 ) in the clay indicates that it is quite calcareous. Variation in chemical composition of clays. The variation in the ultimate composition of clays is well brought out by the following analyses : ANALYSES SHOWING VARIATION IN COMPOSITION OF CLAYS L ! H. III. IV V, VI. VII. VIII. IX, X. SUica (SiO 2 ) 46 3 39 8 13.9 45.70 40.61 1.39 .45 .09 2.82 '8.98 .35 57.62 24.00 1.9 1.2 .7 :! 2 io 5 2.7 35 59.92 27.56 1.03 tr. tr. j .64 '9.70 *: 12 68.62 14.98 4.16 'i.'48 1.09 3.36 3.55 2.78 82.45 10.92 1.08 . 22 .96 {::! 1.00 2.4 54.64 14.62 5.69 'o.!6 2.90 5.89 '3:74 .85 4.80 38.07 9.46 2.70 15.84 8.50 2.76 J2.49 20.46 90.00 4.60 1.44 . . .10 .10 Jtr. 1 tr. .70 (3 04 47.92 14 40 3 60 .... 12.30 1.08 1.20 1 50 1 22 4.85- '9.50- 1.44 1.34 Ferric oxide (Fe 2 O 3 ) . . . Ferrous oxide (FeO). . Lime (CaO) Magnesia (MgO) Potash (K2O) Soda (Na 2 O) Titanic oxide (TiO 2 ). . Water (H 2 O) Moisture Carbon dioxide (CO 2 ). .. Sulphur trioxide (SO 3 ). Organic matter Manganous oxide ( MnO) .64 ".'76 Total 100.00 100.39J100.07 99.97 100.66 99 . 03 99.06 100. 2S 99. 98; 100. 35- I. Kaolinite. II. Kaolin, Webster, N. Ca. III. Plastic fire-clay, St. Louis, Mo. IV, Flint fire-clay, Salines ville, O. V. Loess-clay, Guthrie Centre, la. VI. Rusk, Cherokee County, Tex. VII. Brick shale, Mason City, la. VIII. Calcareous clay, Milwaukee, Wis. IX. Sandy brick-clay, Colmesneil, Tex. X. Blue shale-clay, Ferris, Tex. Variations in the same deposit. Similar differences may not infre- quently be shown by the different layers of any one bank, as the follow- ing analyses indicate: ANALYSES SHOWING VARIATIONS IN THE SAME DEPOSIT 59.' 10 28.84 Silica (SiO 2 ) Alumina (A1 2 O 3 ) ^o . * Ferric oxide (Fe 2 O 3 ) 1 . 00 Lime (CaO) Magnesia (MgO) Potash (K.,O). Soda (Na 2 O) Titanium oxide (TiO.,) Water (H 2 O) .70 none trace trace .87 9.30 99.81 98.6 99.8, CHEMICAL PROPERTIES OF CLAY 61 Rational analysis. 1 This method has for its object the determination of the percentage of the different mineral compounds present, such as quartz, feldspar, kaolinite, etc., and gives us a much better conception of the true character of the material. Most kaolins and other high-grade clays consist chiefly of kaolinite (or some similar hydrous aluminum silicate), quartz, and feldspar, the first forming most of the finest par- ticles of the mass, while the balance is quartz, feldspar, and perhaps some mica. The finest particles are known as the clay substance, which may be looked upon as having the properties of kaolinite. Now, as each of these three compounds of the kaolin clay substance, quartz, and feldspar have characteristic properties, the kaolin will vary in its behavior according as one or the other of these constituents predominates or tends to increase. As to the characters of the three, quartz is of high refractoriness and practically non-plastic, has very little shrinkage, and is of low tensile strength; feldspar is easily fusible, and alone has little plasticity; kao- linite is plastic and quite refractory, but shrinks considerably in burning. The mica, if extremely fine, may serve as a flux, and even alone is not refractory. It is less plastic than the kaolinite, and, when the percentage of it does not exceed 1 or 2 per cent, it can be neglected. To illustrate the value of a rational analysis we can take the following example: Porcelain is made- from a mixture of clay, quartz, and feldspar. Sup- pose that a manufacturer of porcelain is using a clay of the following rational composition: Clay substance 67. 82% Quartz 30 . 93 Feldspar 1 .25 If now to 100 parts of this there are added 50 parts of feldspar, it would give a mixture whose composition is: Clay substance 45 . 21% Quartz 20.62 Feldspar 34. 17 If, however, it became necessary to substitute for the one in use a new clay which had a composition of: Clay substance 66.33% Quartz 15.61 Feldspar 18.91 1 The method is described in the Manual of Ceramic Calculations, issued by the American Ceramic Society. See also Langenbeck, Chemistry of Pottery, 1895, p. 8. 62 CLAYS and added the same quantity of it as we did of the old clay, it would change the rational analysis of the body to the following proportions: Clay substance 44 . 22% Quartz 10.41 Feldspar 45 . 98 Such an increase of feldspar, as shown by this formula, would greatly increase the fusibility and shrinkage of the mixture; but, knowing the rational composition of the new clay, it would be easy, by making a simple calculation, to ascertain how much quartz and feldspar should be added to bring the mixture back to its normal composition. The rational composition of a clay can be determined from an ulti- mate analysis, but the process of analysis and calculation becomes much more complex. The rational analysis is, furthermore, useful only in connection with mixtures of the better grades of clay, in which the varia- tion of the ingredients can only be within comparatively narrow limits. For ordinary purposes the ultimate analysis is of greater value. Comparison of ultimate and rational analyses. 1 If we compare the ultimate and rational analyses of a series of clays we find that two clays which agree closely in their ultimate composition may differ markedly in their rational composition and vice versa, as shown in the table on page 63. In this table Nos. I and II represent two clays which agree very closely in. their ultimate composition, but their rational analyses differ by 6 per cent in their clay substance, 12 per cent in quartz, and nearly 19 per cent in feldspar. Nos. Ill and V, and X and XII also illustrate this point. In Nos. VI and VII, one a German and the other a North Carolina kaolin, the ultimate analyses are very closely alike, and the rational analyses also agree very well. This is frequently the case when the clay substance is very high, between 96 and 100 per cent, as in Nos. IX and XL A third case would be presented if the rationals agreed but the ulti- mates did not, but such instances seem to be much less common. 1 Ries, Amer. Inst. Min. Eng., Trans., XXVIII, p. 160, 1899. CHEMICAL PROPERTIES OF CLAY 63 hH ^S :^^S5 c^ X I> O5 . i 1 -^ Tfl O co * oo I-H -* oo t^ CM CO O(M rH (M Tt< CO -II 8 M > 03 88^^.888 I>Tp TH "** 'COCO Tjl CO i-H 8 8 J O CO 00 00 00 CO CM i-H O rH CO O 00 CO > J z 5 CO CO rH i-H IOCO r-l 1 rH T-( 00 "* CO IO t> iO -^ CO O -^ ^O CO i > g Tf rH CO CO 'O 05 CO 00 00 00 1C CO CO s rjn CO rH 00 CO CM ^O O "* t^ O O C5 CO I-H O (M s H Sc^ 8 O rH Tt< t>. i 1 00 O Tt< iO i-H IO O O5 00 ^ (N CO rH 00 CO CM 8 ::;:::* i 13 U? ; ^ i|5| aag^rfS slg,l^>. U|i H! rH O CM t>- "* b- OO a SJ2 CO CM Oi 00 i 00 Oi r-l 10 10 oo 10 co O5 l>- 00 CM Ci O5 t>- CO O5O CM CM CO O 10000 Ot rH CM N^ CO rHrH CO CO O5 CO 1C 00 CO rH i 1 CO ' 8 .8 5 ST. ^ OH o W3 y \*fA .ss^ss. 3 ^^i > ;fl c CQO^Or!^^3Q < . h*H ?M C^ JU j^ *Tl ^^ 64 CLAYS Method of making Ultimate Analysis The method employed in making the ultimate analysis is usually that outlined below. Moisture. Two grams are heated in a platinum crucible at 100 C. until they show a constant weight. The loss is reported as moisture. Loss on ignition (combined water, and sometimes organic matter, etc.) . The crucible and clay are heated with a blast-lamp until there is no further loss in weight. Alkalies. This same portion of clay, which has been used for deter- mining moisture and loss, is treated with concentrated sulphuric and hydrofluoric acids until it is completely decomposed. The acids are evaporated off by heating upon the sand-bath. The cooled crucible is washed out with boiling water to which several drops of hydrochloric acid have been added. The solution after being made up to about five hundred cubic centimeters is boiled, one-half gram ammonium oxalate added, and made alkaline with ammonium hydroxide; the boiling is continued until but a faint odor of ammonia remains. The precipitate is allowed to settle and is separated from the liquid by filtering and washed three times with boiling water. The filtrate is evaporated to dryness and ignited to drive off ammonium salts. The residue is treated with five cubic centimeters of boiling water, two or three cubic centi- meters of saturated ammonium carbonate solution are added, and the whole is filtered into a weighed crucible or dish. The precipitate is washed three or four times with boiling water and the filtrate evaporated to dryness. Five drops of sulphuric acid are added to the residue, and then the crucible or dish is brought to a red heat, cooled in a desiccator, and the alkalies are weighed as sulphates. To separate the alkalies, the sulphates are dissolved in hot water, acidified with hydrochloric acid, sufficient platinum chloride added to convert both the sodium and potassium salts into double chlorides; the liquid is evaporated to a syrup upon a water-bath, eighty per cent alco- hol added, and filtered through a Gooch crucible or upon a tared filter- paper. The precipitate is thoroughly washed with eighty per cent alcohol, dried at 100 C.,and weighed; the potassium oxide is calculated from the double chloride of potassium and platinum. When magnesium was present to as much as one half of one per cent the magnesium hydroxide was precipitated with barium hydroxide solution, and the barium in turn removed by ammonium carbonate. When the amount of magnesium was less than the amount named, this portion of the ordinary process was not regarded as necessary. CHEMICAL PROPERTIES OF CLAY 65 Silica. Two grams of clay are mixed with ten grams of sodium car- bonate and one-half gram of potassium nitrate and brought to a calm fusion in a platinum crucible over the blast-lamp. The melt removed from the crucible is treated with an excess of hydrochloric acid and evaporated in a casserole to dry ness upon a water-bath, and heated in an air-bath at 110 C. until all the hydrochloric acid is driven off. Di- lute hydrochloric acid is added to the casserole now, and the solution brought to boiling and rapidly filtered. The silica is washed thoroughly with boiling water and then ignited in a platinum crucible, weighed, and moistened with concentrated sulphuric acid. Hydrofluoric acid is cau- tiously added until all the silica has disappeared. The solution is evap- orated to dryness upon a sand-bath, ignited, and weighed. The differ- ence in weight is silica. The residue may contain iron, alumina, and titanium. Iron Sesquioxide. The filtrate from the silica is divided into equal portions. To one portion in a reducing-flask are added metallic zinc and sulphuric acid. After reduction and filtration to free the liquid from undissolved zinc and carbon, the iron is determined by titration with a standard solution of potassium permanganate. Aluminum Oxide. To the second portion, which must be brought to boiling, ammonium hydroxide is added in slight excess, the boiling continued from two to five minutes, the precipitate allowed to settle and then caught upon the filter, all the chlorides being washed out with boiling water. The precipitate is ignited and weighed as a mixture of aluminium oxide and iron sesquioxide. The amount of iron sesquioxide already found is taken from this and the remainder reported as alumina. Calcium Oxide. The filtrate from the precipitate of iron and alumin- ium hydroxides is concentrated to about two hundred cubic centimeters, and the calcium precipitated in a hot solution by adding one gram of ammonium oxalate. The precipitate is allowed to settle during twelve hours, filtered, and washed with hot water, ignited, and weighed as cal- cium oxide. When the calcium is present in no table, amounts, the oxide is converted into the sulphate and weighed as such. Magnesium Oxide. The filtrate from the calcium oxalate precipitate is concentrated to about one hundred cubic centimeters, cooled, and the magnesium precipitated by means of hydrogen disodium phosphate in a strongly alkaline hydroxide solution. The magnesium ammonium phosphate, after standing overnight, is caught upon an ashless filter, washed with water containing at least five per cent ammonium hydroxide, burned, and weighed as magnesium pyrophosphate. 66 CLAYS Titanic Oxide. One-half gram clay is fused with five grams potas- sium bisulphate and one gram sodium fluoride in a spacious platinum crucible. The melt is dissolved in five per cent sulphuric acid. Hydro- gen dioxide is added to an aliquot part and the tint compared with that obtained from a standard solution of titanium sulphate. A simpler plan is to fuse the ignited alumina and iron oxides with potassium bisulphate, dissolve this in warm water, a little sulphuric acid, and then titrate with permanganate for ferric oxide. This same solu- tion can, after the disappearance of the permanganate color, be treated with hydrogen peroxide as outlined above. Sulphur (total present). The sulphur is determined by fusing one- half gram of clay with a mixture of sodium carbonate, five parts, and potassium nitrate, one part. The melt is brought into solution with hydrochloric acid. The silica is separated by evaporation, heating, re- solution, and subsequent filtration. Hydrochloric acid is added to the filtrate to at least five per cent, and the sulphuric acid is precipitated by adding barium chloride in sufficient excess, all solutions being boil- ing hot. The barium sulphate is filtered off and washed with hot water, burned, and weighed as such. Ferrous Oxide is determined by fusing one-half gram with five grams sodium carbonate, the clay being well covered with the carbonate, the top being upon the crucible. The melt is dissolved in a mixture of di- lute hydrochloric and sulphuric acids in an atmosphere of carbon dioxide. The ferrous iron is determined at once by titration with a standard potassium permanganate solution. Method of making Rational Analysis This may be made in several ways, two of which are given. 1. The first consists in separating the "insoluble residue" in the clay, as follows: Two grams of the material are digested with twenty cubic centimeters of dilute sulphuric acid for six or eight hours on a sand-bath, the excess of acid being finally driven off. One cubic centimeter of concentrated hydrochloric acid is now added and boiling water. The insoluble portion is filtered off, and after being thoroughly washed with boiling water is digested in fifteen cubic cen- timeters of boiling sodium hydroxide of ten per cent strength. Twenty- five cubic centimeters of hot water are added and the solution filtered through the same filter-paper, the residue being washed five or six times with boiling water. The residue is now treated with hydrochloric acid in the same manner and washed upon the filter-paper, until free from hydrochloric acid, is burned and weighed as insoluble residue. CHEMICAL PROPERTIES OF CLAY 67 The alumina found in the portion insoluble in sulphuric acid and sodium hydroxide is multiplied by 3.51. This factor has been found to represent the average ratio between alumina and silica in orthoclase feldspar; therefore the product just obtained represents the amount of silica that would be present in undecomposed feldspar. The sum of this silica with the alumina, ferric oxide, and alkalies equals the "feld- spathic detritus." The difference between silica as calculated for feld- spar and the total silica in the insoluble portion represents the " quartz " or "free sand." The difference between that portion of the sample insoluble in sulphuric acid and sodium hydroxide and the total repre- sents the "clay substance." 2. A second method, and one used in Germany, 1 is conducted as fol- lows: After five grams of clay are weighed and placed in a 200 c.c. Erlen- meyer flask, 100-150 c.c. of water and 2 c.c. of sodium hydrate are added, and the contents boiled, covering the flask with a small glass funnel. The contents of the flask are allowed to cool, and 25 c.c. of sulphuric acid is added. Continue the boiling until ths fumes of the acid begin to be driven off the flask. As a result of the reactions which have taken place the calcium carbonate has been changed to calcium sulphate, the aluminum silicate has been converted into aluminum sulphate and silicic acid, while the quartz and feldspar remain. Water is added to the flask and most of the sulphuric acid and aluminum sulphate washed out of the residue by decantation. In washing by decantation the water which is decanted should be placed upon a filter-paper, for the reason that, should any of the residue be removed from the flask, it can be returned by making a hole in the filter and washing back into the flask. After washing by decantation the contents of the flask are treated with hydrochloric acid (100 c.c.) and boiled. Decant off the liquid and add sodium hydroxide (100 c.c.), boil and decant. Repeat the above process with hydrochloric acid and sodium hydrate. The residue is then transferred to a filter and washed with dilute hydrochloric acid (1 to 20). The filter with contents is transferred to a platinum crucible and weight determined. The contents of the crucible are treated with a few drops of sul- phuric acid and small quantities of hydrofluoric acid, evaporated to dryness in the water-bath, ignited, weighed, and from the loss calculate 1 Ladenburg, Handworterbuch der Chemie, 12, p. 15. 68 CLAYS and determine aluminum, iron, etc. From the aluminum found in the residue the feldspar is calculated, 1 part of alumina (aluminum oxide) = 5.41 of feldspar. Although, as pointed out above, the rational analysis is an invalu- able aid to the investigator of high-grade clays, still the methods em- ployed are far from satisfactory or accurate, for in the treatment of the clay with concentrated sulphuric acid the feldspar does not remain un- attacked, 1 and the mica may also be decomposed. This fact led Buckley 2 to adopt the following method for the Wis- consin clays, which are usually impure and often of highly feldspathic character. "The feldspar and kaolinite were calculated from the ulti- mate analysis, using the following percentage compositions of feldspar: K 2 0, 16.9; A1 2 3 , 18.4; 6Si0 2 , 64.7; and Na 2 O, 11.8; A1 2 O 3 , 19.5; 6Si0 2 , 68.7; and kaolinite as A1 2 O 3 , 39.5; 2SiO 2 , 46.5; 2H 2 O, 14; as given by Dana. 3 "All the potash and soda were figured to feldspar. The alumina required for the feldspar was deducted from the total alumina, and the difference was taken as the starting-point from which to figure the kao- linite substance. The difference between the total silica (Si0 2 ) and that required by both feldspar and kaolin gives the quartz and the silica in silicates other than those mentioned." MINERAL COMPOUNDS IX CLAY AND THEIR CHEMICAL EFFECTS All the constituents of clay influence its behavior in one way or another, their effect being often noticeable when only small amounts are present. Their influence can perhaps be best discussed individually. Silica 4 This is present in clay in two different forms, namely, uncombined as silica or quartz and in silicates, of which there are several. Of these one of the most important is the mineral kaolinite, which probably occurs in all clays, and is termed the clay base or clay substance. The other silicates include feldspar, mica, glauconite, hornblende, garnet, etc. These two modes of occurrence of silica, however, are not always dis- tinguished in the ultimate analysis of a clay, but when this is done they are commonly designated as "free " and "combined" silica, the former 1 Langenbeck, Chemistry of Pottery, pp. 3-12. 2 Wis. Geol. and Nat. Hist. Surv., Bull. 7, Pt. I, p. 267, 1901. 8 Text-book of Mineralogy, pp. 371, 377, and 481. 4 See also description of the minerals quartz, feldspar, kaolinite, and mica above. CHEMICAL PROPERTIES OF CLAY 69 referring to all silica except that contained in the kaolinite, which is indicated by the latter term. This is an unfortunate custom, for the silica in silicates is, properly speaking, combined silica, just as much as that contained in kaolinite. A better practice is to use the term sand to include quartz and silicate minerals other than kaolinite, which are not decomposable by sulphuric acid. In the majority of analyses, how- ever, the silica from both groups of minerals is expressed collectively as "total" silica. The percentage of both quartz and total silica found in clays varies between wide limits, as can be seen from the following examples. Wheeler gives a minimum 1 of 5 per cent in the flint-clays, and the sand percentage as 20 to 43 per cent in the St. Louis clays, and 20 to 50 per cent in the loess-clays. Twenty-seven samples of Alabama clays analyzed by the writer contained from 5 to 50 per cent of insoluble residue, mostly quartz. 2 In seventy North Carolina clays 3 the insoluble sand ranged from 15.15 to 70.43 per cent. The following table 4 gives the variation of total silica in several classes of clays, the results being obtained from several hundred analyses: AMOUNT OF SILICA IN CLAYS Kind of clay. Per cent of total silica. Min. Max. Aver. Brick-clays . . .... 34.35 45.06 34.40 32.44 90.877 86.98 96.79 81.18 59.27 45.83 54.304 55.44 Pottery-clays Fire-clays Kaolins The free silica or quartz is one of the commonest constituents of clay, and ranges in size from particles sufficiently large to be visible to the eye down to the smallest grains of silt. With the exception of kaolinite, all of the silica-bearing minerals mentioned above are of rather sandy or silty character, and, therefore, their effect on the plasticity and shrinkage will be similar to that of quartz. In burning the clay, however, the general tendency of all is to affect the shrinkage and also the fusibility of the clay, but their behavior is in the latter respect more individual. 1 Mo. Geol. Surv., Vol. XI, p. 54. 2 Ala. Geol. Surv., Bull. 6,1900. 3 N. C. Geol. Surv., Bull. 13, p. 24, 1898. 4 Bull. N. Y. State Museum, No. 35, p. 525. 70 CLAYS Sand (quartz and silicates) is an important antishrinkage agent, which greatly diminishes the air-shrinkage, plasticity, and tensile strength of clay, its effect in this respect increasing with the coarseness of the material; clays containing a high percentage of very finely divided sand (silt) may absorb considerable water in mixing, but show a low air- shrinkage. The brickmaker recognizes the value of the effects men- tioned above and adds sand or loam to his clay, and the potter brings about similar results in his mixture by the use of ground-flint. It is thought by some that because of the refractoriness of quartz its addition to any clay will raise its fusion-point, but this is true only of those clays containing a high percentage of common fluxes and silica and which are burned at low temperatures. Its effect on highly alum- inous low-flux clays reduces their refractoriness. In considering the effects of sand in the burning of clays, it must be first stated that the quartz and silicates fuse at different tempera- tures. A very sandy clay will, therefore, have a low fire-shrinkage as long as none of the sand-grains fuse, but when fusion begins a shrinkage of the mass occurs. We should, therefore, expect a low fire-shrinkage to continue to a higher temperature in a clay whose sand -grains are refractory. Of the different minerals to be included under sand the glauconite is the most easily fusible, followed by hornblende and garnet, mica (if very fine grained), feldspar, and quartz. The glauconite would, there- fore, other things being equal, act as an antishrinkage agent only at low temperatures. Variation in the size of the grain may affect these results, but this point is discussed under Fusibility (Chapter III). Hydrous silica. From the observations of W. H. Zimmer 1 it would appear that some kaolins carry hydrated silicic acid. In a kaolin of the composition : Silica (SiO 2 ) 57.00 Alumina (A1 2 O 3 ) ' 24.85 Ferric oxide (Fe 2 O 3 ) 25 Lime (CaO) 05 Water (H 2 O) 17.81 he found that the rational analysis showed only 0.05 per cent not de- composed by sulphuric acid, which would lead one to suppose that the clay was a pure kaolin. The analysis, however, disproved this, and led to the conclusion that there must be free hydrated silicic acid. His 1 Trans. Amer. Cer. Soc., Ill, p. 25, 1901. CHEMICAL PROPERTIES OF CLAY 71 experiments with this clay, and with artificial mixtures containing silicic acid, showed that the presence of any important quantity of free hy- drated silicic acid in a clay tends: 1. To produce an increase of translucency over that obtained where the silica used is all quartzitic at equal temperatures; 2, to bring about an improvement in color; 3, to increase the shrinkage both in air and in fire; 4, to produce a lowering of the temperature at which vitrification occurs; 5, a tendency to warp in drying; 6, a tendency to form a hard coating on the surface of the clay or ware, due to the deposition of H 2 Si0 3 from water used in making wares plastic. Iron Oxide Sources of iron oxide in clays. Iron oxide is one of the commonest ingredients of clay, and a number of different mineral species may serve as sources of it, the most important of which are grouped below: Hydrous oxide, limonite; oxides, hematite, magnetite; silicates, biotite, glauconite (greensand), hornblende, garnet, etc.; sulphides, pyrite; carbonates, siderite. In some, such as the oxides, the iron is combined only with oxygen, and is better prepared to enter into chemical combination with other elements in the clay when fusion begins. In the case of the sulphides and carbonates, on the contrary, the volatile elements, namely, the sul- phuric-acid gas of the pyrite and the carbonic-acid gas of the siderite, have to be driven off before the iron contained in them is ready to enter into similar union. In the silicates the iron is chemically combined with silica and several bases, forming mixtures of rather complex composition and all of them of low fusibility, particularly the glauconite. Several of these silicates are easily decomposed by the action of the weather, and the iron oxide which they contain combines with water to form limonite. This is usually in a finely divided condition, so that its color- ing action is quite effective. The range of ferric oxide, as determined from a number of published clay analyses, is as follows : 1 AMOUNT OF FERRIC OXIDE IN CLAYS Kind of clay. Min. Max. Aver. Brick-clays 0.126 32.12 5.311 Fire-clays 0.01 7.24 1 .506 1 Bull. N. Y. State Museum, No. 35, p. 520. 72 CLAYS Effects of iron compounds. Iron is the great coloring agent of both burned and unburned clays. It may also serve as a flux and even affect the absorption and shrinkage of the material. Coloring act on of iron in unburned clay. Many clays show a yellow or brown coloration due to the presence of limonite, and a red coloration due to hematite; magnetite is rarely present in sufficient quantity to color the clay; siderite or pyrite may color it gray, and it is probable that the green color of many clays is caused by the presence of silicate of iron, this being specially true of glauconitic ones. The intensity of color is not always an indication of the amount of iron present, since the same quantity of iron may, for example, color a sandy clay more intensely than a fine-grained one, provided both are nearly free from carbonaceous matter; the latter, if present in sufficient quantity, may even mask the iron coloration completely. The coloring action will, moreover, be effective only when the iron is evenly distributed through a clay in an extremely fine form. It is probable that the limonite color- ing clays is present in an amorphous or non-crystalline form, and forms a coating on the surface of the grains. Coloring action of iron oxide on burned clay. All of the iron ores will in burning change to the red or ferric oxide, provided a sufficient supply of oxygen is able to enter the pores of the clay before it is vit- rified; if vitrification occurs the iron oxide enters into the formation of silicates of complex composition. The color and depth of shade pro- duced by the iron will, however, depend on first, the amount of iron in the clay; second, the temperature of burning; third, condition of the iron oxide, and fourth, the condition of the kiln atmosphere. 1. Clay free from iron oxide burns white. If a small quantity, say 1 per cent, is present a slightly yellowish tinge may be imparted to the burned material, but an increase in the iron contents to 2 or 3 per cent often produces a buff product, while 4 or 5 per cent of iron oxide in many cases makes the clay burn red. There seem, how r ever, to be not a few exceptions to the above statements. Thus we find that the white-burning clays carry from a few hundredths per cent to over 1 per cent of iron oxide, 1 the more ferruginous containing more iron than the purer grades of buff-burning clays. Again, among the buff-burning clays we find some with an iron-oxide content of 4 or 5 per cent, an amount equal to that contained in some red-burning ones. The facts would therefore seem to indicate that the color of the burned clay is not influenced solely by the quantity of iron present. 1 Seger's Collected Writings, Translation, I, p. 109; also Orton, Trans. Amer. Ceram. Soc., V, p. 380. CHEMICAL PROPERTIES OF CLAY 73 Seger has divided the buff-burning clays into two groups, namely, (1) those of such high iron contents as to burn red normally, but which are sufficiently calcareous to enable the lime to destroy the red iron color and form a yellow compound of iron and lime, and (2) those low in iron and high in alumina, which would normally burn pale red, but develop a yellow color due to the formation of an alumina-iron compound. He thus believes that the red coloration of the iron is destroyed by similar causes, but on account of the lime being a stronger or more active base than the alumina it is able to take care of a greater quantity of iron. Orton 1 has argued against the effect of alumina, claiming that if this were true synthetic mixtures should easily give the buff color which, in his experience, it is not possible to produce. As he states, there is a great uniformity in the color of buff-burning clays, while their iron- alumina ratios fluctuate greatly; some fire-clays containing 40 per cent of alumina and 0.5 per cent iron, and yielding a good buff product, while others with 15 to 20 per cent alumina and 2.5 per cent iron burn to almost exactly the same tint. On the other hand, some clays with about the same alumina and iron content burn red. It would seem, therefore, as if the cause of this buff-burning quality must be sought for in some other direction. The evenness of color is apparently closely connected with the physi- cal condition of the iron oxide, that in colloidal form giving a uniformity of shade not obtainable by the admixture of very finely ground material. 2. If a clay is heated at successively higher temperatures, it is found that, other things being equal, the color usually deepens as the tempera- ture rises. Thus, if a clay containing 4 per cent of iron oxide is burned at a low temperature it will be pale red, and harder firing will be neces- sary to develop a good brick red, which will pass into a deep red and then reddish purple. Seger explained the successive shades of red by assuming that the iron oxide increased in density with rising temperature. The brilliancy of the color appears to be influenced by the texture, as the more sandy clays can be heated to a higher temperature, without destruction of the red color, than the more aluminous ones. Alkalies also appear to diminish the brightness of the iron coloration. 2 3. Among the oxides of iron two kinds are recognized, known respec- tively as the ferrous oxide (FeO) and ferric oxide (Fe 2 O 3 ) . In the former 1 Trans. Amer. Ceram. Soc., V, p. 389, 1903. 2 Ries, N. Y. State Mus., Bull. 35, 515, 1900; Orton, Trans. Amer. Ceram. Soc., V, p. 414, 1903. 74 CLAYS we see one part of iron united with one of oxygen, w r hile in the latter one part of iron is combined with one and one-half parts of oxygen. The ferric oxide, therefore, contains more oxygen per unit of iron than the ferrous salt, and represents a higher stage of oxidation. In the limonite and hematite the iron is in the ferric form, representing a higher stage of oxidation. In magnetite both ferrous and ferric iron are present, but in siderite the ferrous iron alone occurs. In the ultimate analysis the iron is usually determined as ferric oxide, no effort being made to find out the quantity present in the ferrous form, although if there is any reason to suspect that much of the latter exists it should be determined. Iron passes rather readily from the ferric to the ferrous form and vice versa. Thus, if there is a deficit of oxygen in the inside of the kiln the iron does not get enough oxygen and the ferrous compound results, but the latter changes rapidly to the ferric condition if sufficient air carrying oxygen is admitted. The necessity for recognizing these two forms of iron oxide is because they affect the color of the clay differently. Ferrous oxide alone is said to produce a green color when burned, while ferric oxide alone may give purple or red, and mixtures of the two pro- duce yellow, cherry red, violet, blue, and black. 1 Seger 2 found that combinations of ferric oxide with silica produced a yellow or red color in the burned clay. We may thus get a variation in the color produced in burning clay, depending on the character of oxidation of the iron or by mixtures of the two oxides. 3 Moreover, in the burning of ferruginous clays it is usually desirable to get the iron thoroughly oxidized to prevent trouble in the later stages of burning. To accomplish this the iron must be freed of any sulphur or carbon dioxide which may be combined with it, and other volatile or combustible elements in the clay must be driven off, so as to allow the oxidizing gases to enter the clay and unite with any ferrous iron that may be present. Sulphide of iron (pyrite) loses half its sulphur at a red heat, and the balance will, under oxidizing conditions, pass off probably by 900 C., while siderite or ferrous carbonate loses its carbon dioxide between 400 and 500 C.; magnesium carbonate and calcium carbonate lose their CO 2 at about 500 C. and 800 to 900 C. respectively. Carbonaceous matter, if present, must also be carefully burned off. If the clay con- tains much volatile or combustible matter the burning must proceed 1 Keramic, p. 256. 2 Notizblatt, p. 16, 1874. 8 See "Flashing of Brick," under Burning. CHEMICAL PROPERTIES OF CLAY 75 slowly below 1000 C., in order to remove it and allow the iron to get oxidized while the clay is still porous. After oxidation the clays will show a more brilliant iron color than they do at the end of the dehydration period. They are also harder and show a slight decrease in volume. If the clay has been improperly oxidized it shows later when vitri- fication is reached, by the ferrous oxide in the center of the brick forming a fusible silicate which melts and evolves gases that swell up the ware. In some cases improper oxidation is shown by the presence of a black core in the center of the brick. Fine-grained clays are more difficult to oxidize than coarse-grained ones, because of the small size of their pores, and grog is, therefore, added at times to open the grain of the material. 4. Since the stage of oxidation of the iron is dependent on the quan- tity of air it receives during burning, the condition of the kiln atmos- phere is of great importance. If there is a deficiency of oxygen in the kiln, so that the iron oxide, if present, is reduced to the ferrous condition, the fire is said to be reducing. If, on the contrary, there is an excess of oxygen, so that ferric oxides are formed, the fire is said to be oxidizing. These various conditions are often used by the manufacturer to produce certain shades or color-effects in his ware. Thus, for example, the manu- facturer of flashed brick produces the beautiful shading on the surface of his product by having a reducing atmosphere in his kiln followed by an oxidizing one. The potter aims to reduce the yellow tint in his white ware by cooling the kiln as quickly as possible to prevent the iron from oxidizing. Fluxing action of iron oxide. Iron oxide is a fluxing impurity, lower- ing the fusing-point of a clay, and this effect will be more pronounced if the iron is in a ferrous condition or if silica is present. In burning a clay .at low temperatures the hydrous ferric oxide (limonite) loses its water of hydration. Heating the clay to vitrification in a reducing atmosphere is believed to produce a ferrous silicate, which is seen on the brown, black, or greenish glassy portion of the surface of paving brick and unglazed sewer-pipe. 1 When well-vitrified bricks show a red color it is thought by some that the iron oxide is merely dissolved in the vitri- iied mass and has not entered into combination, i A low iron content is, therefore, desirable in refractory clays, and the average of a number of analyses of these shows it to be 1.3 per cent. Brick-clays, which are usually easily fusible, contain from 3 to 7 per cent of iron oxide. i 1 la. Geol. Surv., XIV, 59, 1904. 76 CLAYS Effect of iron oxide on absorptive power and shrinkage of clay. So far as the writer is aware no experiments have been made to discover the increased absorptive power of a clay containing limonite, although the clay soils show that the quantity of water absorbed is greater with limonite present. This greater absorptive power may be accompanied by an increased shrinkage. The fire-shrinkage might also be great, because of the increased loss of combined water due to the presence of limonite. 1 Lime Lime is found in many clays, and in the low-grade ones may be present in large quantities. Quite a large number of minerals may serve as sources of lime in clays, but all fall into one of the three following groups: 1. Carbonates. Calcite, dolomite. 2. Silicates containing lime, such as feldspar and garnet. 3. Sulphates. Gypsum. Whenever the ultimate analysis of clay shows several per cent of lime (CaO) it is usually there as an ingredient of lime carbonate (CaCO 3 ), and in such cases its presence can be easily detected by putting a drop of muriatic acid or vinegar on the clay. 2 When present in this form it is apt to be finely divided, although it may occur as concretions or lime- stone pebbles, or as cylindrical bodies along rootlets. The feldspars are the commonest source of lime among the silicates, oligoclase and anorthite being the usual lime-bearing varieties, but the amount of lime present in silicates is usually very low. When lime is present as an ingredient of silicate minerals, such as those mentioned above, its presence cannot be detected with muriatic acid. Gypsum, which is found in a few clays, is often of secondary char- acter, having been formed by the action of sulphuric acid on lime-bearing minerals in the clay. Since these three groups of minerals behave some- what differently their effects will be discussed separately. Effect of lime carbonate on clay. Lime is probably most effective in the form of the carbonate, and if finely divided is an active flux. When clays containing it are burned, they not only lose their chemically com- bined water but also their carbon dioxide; but while the water of hyclra- tion passes off between 450 C. (842 F.) and 600 C. (1112 F.) the car- bon dioxide (C0 2 ) does not seem to go off until between 600 C. (1112 F.) and 725 C. (1562 F.). In fact, it more probably passes off between 1 See tests under Fire-shrinkage, Chap. III. 2 See Minerals in Clay, Calcite. CHEMICAL PROPERTIES OF CLAY 77 850 C. (1562 F.) 1 and 900 C. (1652 F.). The result of driving off this gas, in addition to the chemically combined water, is to leave cal- careous clays more porous than other clays up to the beginning of fusion. 2 If the burning is carried only far enough to drive off the carbonic- acid gas, the result will be that the quicklime thus formed will absorb moisture from the air and slake. No injury may result from this if the lime is in a finely divided condition and uniformly distributed through the brick, but if, on the contrary, it is present in the form of lumps, the slaking and accompanying swelling of these may split the brick. If, however, the temperature is raised higher than is required simply to drive off the carbon dioxide, and if some of the mineral particles soften, a chemical reaction begins between the lime, iron, and some of the silica and alumina of the clay, the result being the formation within the clay of a new silicate of very complex composition. The effects of this com- bination are several: In the first place, the lime tends to destroy the red coloring of the iron and imparts instead a buff color to the burned clay. Seger found that this bleaching action, if we may call it such, is most marked when the percentage of lime is three times that of the iron. It should be remembered, however, that all buff-burning clays are not calcareous, and that a clay containing a low percentage of iron oxide may also give a buff body. Another effect of lime, if present in sufficient quantity, is to cause the clay to soften rapidly, thereby sometimes draw- ing the points of incipient fusion and viscosity within 41.6 C. (75 F.) of each other. This rapid softening of calcareous clays is one of the main objections to their use, and on this account also it is not usually safe to attempt the manufacture of vitrified products from them, but, as mentioned under Magnesia, the presence of several per cent of the latter substance will counteract this. It has also been found possible to increase the interval between the points of incipient fusion and viscosity by the addition of quartz and feldspar. 3 Many erroneous statements are found in books regarding the allow- able limit of lime in clays, some writers putting it as low as 3 per cent; still a good building brick can be made from a clay containing as much as 20 or 25 per cent of lime carbonate, provided it is in a finely divided condition, 4 and a vitrified ware is not attempted. If, however, 1 Bourry, Treatise on Ceramic Industries, p. 103; also Kennedy, Trans. Amer. Cer. Soc., IV, p. 146. 2 Some bricks made from calcareous clays and burned at cones 1 to 3 show over 30 per cent absorption. 3 The Collected Writings of H. Seger, Vol. I, p. 336. 4 For analyses and uses of calcareous clays see H. Ries, Clays and Shales of 78 CLAYS that quantity of lime is contained in the clay in the form of pebbles, then much damage may result from bursting of the bricks, when the lumps of burned lime slake by absorbing moisture from the air. Clays containing a high percentage of lime carbonate are used hi the United States, especially in Michigan, Wisconsin, and Illinois, for making common bricks, common earthenware, roofing-tile, and some terra- cotta, and the highly calcareous character of some brick-clays is shown by the following analyses. Of these No. II is the most calcareous that the writer has ever examined. ANALYSES OF CALCAREOUS CLAYS I. II. Silica (SiO 2 ) 44.15 18.62 Alumina (A1 2 O 3 ) 10 - 3 - 23 Ferric oxide (Fe 2 O 3 ) 4 - 08 J- 26 Lime (CaO) 13.30 41 .30 Magnesia (MgO) 1 1 .50 .42 Potash (K 2 0) 1.55 {gone Soda (Na 2 O) By difif. 2.42 Water (H 2 O) 12.13 Carbon dioxide (CO,,) 11.34 32.50 Organic matter 1 . 95 Total 100.00 99.75 Total fluxes 20.43 42.98 I. Ionia, Mich. A. N. Clark, Anal. Mich. Geol. Surv., VIII, Pt. I, p. 53. II. Seguin, Tex. O. H. Palm, Analyst. Effect of lime-bearing silicates. The effect of these is much less pronounced than that of lime carbonate. They contain no volatile ele- ments, and hence do not affect the shrinkage to the extent that lime carbonate does. They serve as fluxes, 1 but do not cause a rapid soften- ing of the clay. Effect of gypsum. Gypsum in clay has probably often been formed by sulphuric acid, liberated by the decomposition of iron pyrite, acting on lime carbonate. Lime, if present in the form of gypsum, seems to behave differently from lime in the form of carbonate, although few clays contain large percentages of it. Gypsum, as already shown, 2 is a hydrous sulphate of lime. In cal- Michigan, Mich. Geol. Surv., VIII, Pt. I; and E. R. Buckley, Clays and Clay Indus- tries of Wis., Wis. Geol. Surv., Bull. 2, Economic Series. 1 See also under Alkalies. 2 Chapter III, Minerals in Clay. CHEMICAL PROPERTIES OF CLAY 79 cining gypsum for making plaster of Paris, the chemically combined water is driven off at 250 C., but only a portion of the sulphuric acid is driven off at a low red heat, the balance passing off at a much higher temperature. To illustrate this a mixture 1 consisting of 75 per cent of a white-burning clay and 25 per cent of nearly pure white gypsum was made up. This mixture contained 15.11 per cent of combined water and 11.65 per cent of sulphur trioxide (S0 3 ), and was burned at a number of different temperatures with the following results: TABLE SHOWING Loss IN WEIGHT BY BURNING Temperature. Loss in weight, per cent. Sample No. 1. Sample No. 2. 860 C (1580 F ) 11.60% 13.18% 19.93% 23.15% 23.21% 11.50% 12.59% 19.58% 23.05% 23.11% 1000 C (1832 F ) 1 100 (2012 F ) 1200 C (2192 F.) 1300 C (2372 F.) These figures show that at 860 C. the loss had not exceeded the amount of combined water contained in the mass; at 1000 C. the loss was not equal to the sum of the water contained in the clay and gypsum; a large loss occurred between 1100 and 1200 C., while between the latter temperature and 1300 C. the loss was exceedingly small. Therefore, even at 1300 C., or slightly above the theoretic melting-point of cone 8, there was still over 3 per cent of what would be considered volatile ma- terial remaining in the mixture. It is presumed that this represents sulphur trioxide which has not been driven off. The presence of silica is said to facilitate the decomposition of the calcium sulphate, and the evolution of the SO 3 is thought to cause some of the swelling or blistering seen in some wares after burning. The range of lime, as determined from a series of clay analyses, is as follows: 2 AMOUNT OP LIME IN CLAYS Kind of day. Min. Max. Aver. 0.024 15.38 1.513 0.011 9.90 1.098 0.03 15.27 0.655 tr. 2.58 0.47 1 N. J. Geol. Surv., VI, p. 63, 1904. 2 Bull. N. Y. State Museum, No. 35, p. 523. Owing to an error in the analysis of one of the brick-clays, the averages in this table have been recalculated. 80 CLAYS Magnesia Magnesia (MgO) rarely occurs in clay in larger quantities than 1 per cent. When present, its source may be any one of several classes of compounds, that is, silicates, carbonates, and sulphates. In the majority of clays the silicates, no doubt, form the most im- portant source, and minerals of this type carrying magnesia are the black mica or biotite, hornblende, chlorite, and pyroxene. These are scaly or bladed minerals, of more or less complex composition, and con- taining from 15 per cent to 25 per cent of magnesia. The biotite mica decomposes readily, and, its chemical combination being thus destroyed, the magnesia is set free, probably in the form of a soluble compound, which may be retained in the pores of the clay. Hornblende is probably not an uncommon constituent of some clays, especially in those which are highly stained by iron, and have been derived from dark-colored igneous rocks. Like biotite, it alters rather rapidly on exposure to the weather. Dolomite, the double carbonate of lime and magnesia, is no doubt present in some clays, and would then serve as a source of mag- nesia. Magnesium sulphate, or Epsom salts, probably occurs sparingly in clays, and might form a white coating either on the surface of clay spread out to weather, or else on the ware in drying. It is most likely to occur in those clays which contain pyrite, the sulphide of iron (FeS 2 ), for the decomposition of the latter would yield sulphuric acid, which, by attacking any magnesium carbonate in the clay, might form magnesium sulphate. This substance has a characteristic bitter taste. On heating, both magnesium carbonate and dolomite lose their CC>2 be- tween 400 C. and 600 C. Magnesia was for many years regarded as similar to lime in its fluxing action. The experiments of Mackler l have indicated, however, that its effect was quite different. In order to prove this point he selected a clay which was free from lime or magnesia, and in its raw and burned condition had the composi- tion shown at top of page 81. To one hundred parts by weight of this clay, either lime or magnesium carbonate was added in the proportions given in the second table on page 81, the percentages given in parenthesis representing the quantity of lime or magnesia contained in the amount of carbonate added. The physical tests of these mixtures are also given. It will be seen here that the effect of magnesia was quite different 1 Thonindustrie-Zeitung, Vol. XXVI, p. 706, 1904. CHEMICAL PROPERTIES OF CLAY 81 Loss on ignition Silica (SiO 2 ) Alumina (AlgOg) Ferric oxide (Fe 2 O 3 ). . Lime (CaO) Magnesia (MgO) Alkalies (Na 2 O, K 2 O) ANALYSIS OF CLAY USED BY MACKLER Raw. , 7.07 63.25 22.97 4.98 Burned. 68.06 24.72 5.36 2.07 100.34 from that exerted by the lime. The mixtures containing magnesia did not vitrify suddenly, as did the limy clays ; nor did the magnesia exert as strong a bleaching action on the iron, and the points of incipient fusion and viscosity were also separated. PHYSICAL TESTS ON MACKLER'S MIXTURES 1 i 83 M a ' ti Fire-shrinkage cone numbers. t/3 c *4-f C 5- 38 M t& 1903. 3 Phil. Trans. (1861), p. 183. Quoted by Cushman, I.e. 100 . CLAYS complexes which possess a submicroscopical, web-like, porous formation, one of the distinguishing characteristics of which is the peculiar relation to and dependency on water which they exhibit. The water-content of these hydrogels varies continually with the temperature and the vapor pressure of the atmosphere in which they find themselves. Dried at high temperatures up to a certain critical point, they will lose nearly all their water, only to take it back again eagerly when allowed to cool in free air or in moist atmospheres. This dehydration and rehydration can be repeated indefinitely, unless the temperature of drying is carried too high, when the faculty is gradually lost and finally destroyed. "The water thus absorbed is denominated 'micellian 7 water, and differs from hygroscopic water in the ordinary sense of the word. It is absorbed into the particles of a powder of an inorganic hydrogel without changing the physical appearance when under the microscope, while hygroscopic water is usually absorbed on the particles producing a distinct appearance of wetness." Among the ingredients of clay which might assume a colloidal form are aluminum hydroxide, iron oxide, hydrated silicic acid, and organic matter. Some clays undoubtedly contain large amounts of colloids, but in others, as in many common clays, it is claimed that there is but a small proportion of ingredients which are capable of assuming the colloid state by the action of the water alone. 1 Schlossing 2 states that in all kaolins there are finely crystalline substances and colloidal ones, which latter he separated by treatment with ammoniacal water, and found them to be singly refracting, globular aggregates, but Kasai, 3 on the other hand, disputed the existence of colloidal matter, for he finds that the apparently colloidal bodies of Zettlitz kaolin are doubly refracting. Still later P. Rohland 4 suggested the colloidal nature of plasticity, while Van der Bellen 5 a little later expressed a similar view. Lucas 6 in commenting on Rohland's observation calls attention to the fact that Zettlitz kaolin must have some colloidal matter because it flows freely through a die, and regards as significant the fact that a non-plastic crystalline powder will, under pressure, allow the water to be squeezed out, and will only form a plastic mass when tragacanth is mixed with it. 1 la. Geol. Surv., XIV, p. 90, 1904. 2 Comp. rend. 1874, LXXIX, pp. 376 and 473. 3 Die Wasserhaltigen Aluminum Silikate. Diss. Munchen, 1896. 4 Zeitschrift fur anorganische Chemie, Vol. XXXI, Ft. I, p. 158, 1902. 5 Chem. Zeit., XXXVI, 1903. e Geol. Centralbl. f. Min., Geol. u. Pal., No. 2, p. 33, 1906. PHYSICAL PROPERTIES OF CLAY 101 The theory of Olchewsky that plasticity was due to the spongy porous nature of the smallest particles, which by reason of pressure arrange themselves into a sort of felt, may be regarded as admitting the presence of colloidal matter, but of more definite character are the statements of Arons 1 and Bischof, who suggest that plasticity was no doubt due to some special form of hydrated aluminum silicate, \\hile Seger 2 remarks further that there is probably some effective molecular arrangement, which was already fixed in the structure of the parent rock. In this country the colloid theory seems to have received little atten- tion. In studying the clays of Maryland the author 3 noted the presence of what he assumed were colloidal bodies in the highly plastic clays, and the subject has been followed up in greater detail by Cushman, 4 who believes that plasticity is due to a "colloid condition of the fine particles, or of some proportion of the particles which go to make up the clay mass. These amorphous inorganic particles possess a sub- microscopic structure. They absorb water eagerly, and gradually assume the coherent condition which causes in the wet mass the quality we call plasticity." In order to prove the existence of colloids in clays, Cushman 5 pre- pared some silicic acid. This jelly dries rapidly to a powder, which is hydrated and loses or gains water with changes in the moisture content of the atmosphere in which it stands, but if heated above 1000 C. it loses its absorptive power. Hydrated colloid alumina was also prepared artificially. On mixing the former with clay 6 it was found that the silicic acid increased the binding power and shrinkage but not the plasticity; while the alumina increased the plasticity but not the shrinkage or binding power. A mixture of the two, prepared by adding sodium silicate (water glass) to the solution of alum, 7 showed that its addition to a clay increased both its binding power and plasticity. Ries 8 found that the addition of one per cent gallotannic acid to a 1 Dammer, Chem. Tech., 1. 2 Tonindustrie-Zeitung, p. 37, 1877. 3 Md. Geol. Surv., Vol. IV T p. 251. 4 Jour. Amer. Chem. Soc., XXX, p. 5. s Trans. Amer. Cer. Soc., VI, p. 7. 1904. 6 The percentage added is not given. 7 The suggested formula of this mixture is XAl 2 O 3 >YSiO 2 ,ZH 2 O. 8 Trans. Amer. Cer. Soc., VI, p. 44, 1904. 102 CLAYS clay appeared not only to increase its plasticity but also its binding power. Grout by using a dilute solution of agar-agar for tempering two clays found that 0.08 per cent increased their plasticity approximately 60 and 36 per cent respectively. He dried the same mass, mixed it with water, filtered off the latter, and tested the clear filtrate for soluble salts, but got no jelly, which was probably due to the fact, overlooked by him, that the clay adsorbs the colloidal material. (See Adsorption.) Alumina cream was then tried instead of agar-agar, and it was found that it took 3 per cent of the former to raise the plasticity as much as 0.08 per cent of the latter; furthermore, after air-drying, powdering, and remixing, the plasticity of the mass dropped to its original figure. Grout consequently argues that since plastic clays are not injured by air-drying, it is evident that "such colloids as alumina cream do not explain plasticity, and that some colloid is required which will soften in water after air-drying, a type which is extremely rare in the inorganic kingdom." He says further: "The suggestion of Cushman, that a hydrated silicate of alumina could be precipitated so as to give the desired properties, has been carefully tried, but all resulted exactly as alumina cream." Grout, moreover, questions the value of detecting colloids by staining with rnethylene blue, since he finds that most clays contain from 1 to 5 per cent of grains which will take a stain from rnethylene blue, gentian violet, eosine, or fuchsine. Both fresh and dried silicic-acid jelly he states take the stain, but the latter acts like quartz in decreasing the plasticity. Weathering, he further claims, does not increase the number of grains capable of taking the stain. It would appear from what has been said that most clays contain (1) both non-plastic bodies or grains, of either crystalline or amorphous character, and (2) colloids, which appear to at least influence the plasticity. If the colloids are the main cause of plasticity, this fact is not proven definitely either by showing their presence in the clay or by demon- strating that their addition to an already plastic clay increases its plasticity. On the contrary, it would seem necessary to add them to some fine- grained mineral aggregate of exceedingly low 7 plastic qualities, and by this addition be able to change it into a thoroughly plastic mass. A mass of colloidal material by itself does not show the solidity and '.cohesiveness which a strongly plastic clay does. It is as if it lacked PHYSICAL PROPERTIES OF CLAY 103 some strengthening internal structure, such as a mass of mineral grains might supply. Molecular-attraction theories. Several writers, to be referred to below, have inclined to the theory that the plasticity of clay was due to molecular attraction between the clay particles themselves or between the clay grains and water surrounding them. Ladd, 1 as a result of his work on the Georgia clays, advocates the theory that the mutual attraction between water and clay particles, and surface tension of the water-films, may exert an important influence in determining plasticity. The affinity of the clay particles for water will, however, vary with their chemical nature; 2 and particles of the same material have a varying affinity, under different conditions not now well understood. Moreover, salts and organic matter, in solution, modify the value of the surface tension of the liquid, the former generally increasing, the latter decreasing. This latter seems an important point for all clays containing a variable quantity of soluble matter. The importance of molecular attraction between the clay substance and water was looked on by Zschokke 3 as an important cause of plasticity, he having pointed out that since clay particles are plastic bodies, they have greater attraction for water than non-plastic grains such as sand, and that therefore the grains will be surrounded by a thicker film of water than sand-grains would be. The addition of an excess of water separates the clay-grains so far that they are no longer able to attract each other, and the mass loses much of its cohesiveness. Moreover it is thought that the absorption of the water into the pores of the clay is accompanied by a superficial alteration of the clay particles, giving them a gelatinous coating, which permits them to change their form and at the same time keep in close contact; a point which is rather corroborated by the experiments of Cushman 4 and Mellor. 5 He finally suggests that plas- ticity must be dependent on (1) the size of the smallest particles; (2) the form and character of the surface; and (3) other peculiar properties possibly of a molecular character. Grout, 6 reasoning along somewhat similar lines, believes that the chief cause of plasticity is the molecular attraction depending on the 1 Ga. Geol. Surv., Bull. 6a, p. 29, 1898. 2 Whitney, U. S. Dept. of Agric., Bull. No. 4, 1892; Briggs, ibid., Bull. 10, 1897. 3 1. c. 4 Bull. U. S. Dept. Agric., 92, 1905. 8 Trans. Eng. Ceram. Soc., V, Pt. I, p. 72, 1905-6. * W. Va. Geol. Surv., Ill, p. 54, 1906. 104 CLAYS chemical constitution of molecules, but that it may be improved by the addition to the clay of colloids such as tannin, etc., or such solutions as ammonia, alum, etc. While several of these theories plate structure, colloids, and molec- ular-attraction theory have much to commend, still there seem to be serious objections in many cases against their being the sole cause of plasticity. It is urged that many clays show little or no plate structure, and yet the evidence of Vogt (p. 47), Cook (p. 98), and Wheeler (p. 98) certainly indicate that it must at least be a factor governing the plastic qualities of many clays. Although the colloid theory may be discarded by some, still the experiments of Cushman (p. 101), Ries (p. 101), and Grout (p. 102) point to its importance. The examination of any extensive series of clays hardly seems to bear out the theory that any one of the causes suggested is the sole one, but rather that plasticity is dependent on a combination of them. Effect of bacteria. Aging a clay mixture, that is, allowing it to lie in cellars for six months or a year, appears to improve its plasticity, and it has been suggested that this is due to bacterial action. Bacteria are not uncommon in clay, and the prevalent one, according to Stover, 1 is believed to be bacillus sulphureus, whose development is facilitated by a temperature of 37 to 38 C. Seger, although not referring to bacteria, stated that in the aging of a clay an acid was gradually developed by organic decomposition, which destroyed the alkalinity of the mass and was supposed to be responsible for the improvement in plasticity. Since bacteria are known to exist in clays, they may add organic colloids (protoplasm) to it, and thereby increase its plasticity. 2 Weathering clay. It is a well-known fact that weathering a clay often increases its plasticity, but this might be due to several causes, such as mechanical disintegration of the mass by frost, water soaking, the oxidation of organic matter, or to the production of colloids by hydrolysis or bacterial action. Grinding may sometimes improve the plasticity as much as weath- ering. 1 Trans. Amer. Cer. Soc., IV, p. 185, 1902. 2 W. Va. Geol. Surv., Ill, p. 47, 1906. PHYSICAL PROPERTIES OF CLAY 105 The Measurement of Plasticity Clays vary widely in their plasticity, ranging from those which are very lean or low in plasticity to those which are very fat or of high plas- ticity. Clay technologists have for a long time been searching for a satis- factory means of measuring the plasticity of clays, but this seems to be as difficult to find as the true cause of this peculiar property. The methods which have been developed fall into two classes, namely, tests of the wet clay and tests of the dry clay, the former being probably the more logical. Tests of the wet clay. The commonest and most practical of these consists in feeling the clay between the fingers. It is not entirely satisfactory, but about the only one that can be used in the field, and, on the whole, gives us an important clue to the workability of the clay. Bischof 1 suggested forcing the wet clay through a cylindrical die, and measuring the length of the pencil extruded before it broke of its own weight, and a similar method has been advised by E. C. Stover, 2 but there are serious objections to this, because the clay should be worked up into its most plastic condition before testing, and there is no means of determining accurately when the condition of maximum plasticity has been reached. The use of the Vicat needle has also been suggested, the operation consisting in forcing a needle into the plastic clay by the pressure of a known weight. Langenbeck 3 states that the proper consistency is reached when the needle under a weight of 300 grams penetrates to a depth of four centimeters in five minutes. The same principle is involved in Ladd's test, which consists in suspending a plumb-bob from one arm of a balance and allowing it to settle into the moist clay for a given period. 4 Both these methods suppose that the more water a clay requires for mixing the higher its plasticity, an assumption not altogether correct. Another method suggested by Ladd 5 consists in having two small sheet-iron troughs with perforated bottoms, in the center of which are set test-tube brushes, so placed that the ends of the brushes touch 1 Die feuerfesten Thone, p. 84. 2 Trans. Amer. Cer. Soc. VII, p. 397, 1905. 8 Chemistry of Pottery, p. 19. 4 Ga. Geol. Surv., Bull. 6a, p. 51, 1898. 5 Ibid., p. 52, 1898. 106 CLAYS when the ends of the troughs are in contact. The dry clay is sifted into the brushes and water absorbed from below until the point of saturation is reached. The pull required to tear the column of clay between the brushes is measured by placing weights on a scale-pan attached to one of the troughs until the two separate. The criticism urged against this method is that it gives little informa- tion regarding the plasticity, but measures the strength of the clay through different degrees of saturation. 1 A somewhat detailed investigation is that of Zschokke. 2 According to him, it is necessary, in testing the plasticity of a clay, to consider (1) its property of deformability; (2) its degree of cohesion; (3) its stickiness or adhesiveness. The degree of deformability was first tested by molding the thoroughly worked clay into cylinders 60 mm. high and 30 mm. in diameter, and subjecting these to pressure applied at the ends until cracks appeared, but this was found to be unsatisfactory, as some lean sandy clays were deformed more than highly plastic ones. A more satisfactory method consisted in placing these freshly molded cylinders in a specially designed machine and pulling them in two. The amount of expansion showed the degree of deformability, while the force required to pull the cylinder in two showed the tensile strength. The product of the two Zschokke terms the plasticity coefficient. It was found that higher figures were obtained by stretching the bar rapidly, or by a succession of short rapid strokes. The following figures illustrate these points. RUPTURE EXPERIMENTS Slow pull. Jerky pull. Per cent No. of sample. Tensile strength kgm. per Deforma- bility H in per cent. Plasticity coefficient 13 L Tensile strength /? kgm. per Deforma- bility A in per cent. Plasticity coefficient 0L H 2 reg. sq. cm. 269 .63 70 44.1 1.73 127 220 29.8 250 .48 28.6 13.7 1.52 97 147 22.9 631 .42 18.4 7.7 .96 91 87 26.0 901 .36 17.4 6.3 .93 82 76 21.8 705 .27 33.4 9. .86 94 81 20.8 507 .25 20. 5. .96 90 86 20.8 702 .20 8.6 1.7 .76 73 55 23.9 636 .08 5. .4 .20 5 1 21.8 1 la. Geol. Surv., Vol. XIV, p. 100, 1904. 2 I.e. PHYSICAL PROPERTIES OF CLAY 107 Commenting on the results of his tests, Zschokke states that in very plastic clays there appears to be a slight amount of elasticity, so that it is necessary to distinguish between elastic and permanent changes of form. The reason for the change of shape, without rupture under pressure, is considered to be as follows: Given two moist sand-grains in contact. Since these are not plastic bodies, they have but little absorptive power for water, and are therefore covered by but a thin film of the latter. If these two grains are slowly drawn apart, the water film binding them together is soon ruptured. On the other hand two moist-clay particles will be surrounded by a thicker layer of water because of their greater attraction for it, and these two can be separated much farther without rupturing the mass. Now the cylinder of moist clay can be considered as being composed of a great number of clay particles surrounded by water, and the smaller the size, and greater the number of particles of clay substance in the mass, the more intimate will be the attraction between clay and water. With an increase in texture, and corresponding decrease in water-content and cohesion, there will be a depression of the tensile strength. While an excess of water may depress the tensile strength of the soft clay, still very plastic clays, although showing higher cohesiveness than lean ones, have a higher strength, which Zschokke believes indicates that there is an intimate relation, of either chemical or physical character, between the clay substance and admixed water. Grout, 1 in his work on the West Virginia clays, arrived at conclusions somewhat similar to those of Zschokke. 2 He considers that plasticity may be considered as involving two variable factors, viz., (1) amount of possible flow before rupture, and (2) resistance to flow or deformation. Plasticity, he says, " increases in direct proportion to each of these fac- tors, and is therefore equal to the product." He measured the plasticity by carefully mixing and tempering the clay, and then forced it into a thin-walled metal cylinder three fourths inch in diameter. A plunger forced the clay through this die, and the bar of clay was cut into two-inch lengths. These small cylinders were placed vertically under a movable plate and pressure applied, the amount necessary to compress it one half centimeter being taken as the measure of resistance to flow or deforma- tion. 1 W. Va. Geol. Surv., Ill, p. 40, 1906. 2 I.e. 108 CLAYS The cylinder was then further compressed until the appearance of cracks at about 45 degrees to the vertical line, and this was considered the point of fracture. Vertical cracks, due to tension as the cylinder "expanded; were disregarded, and an irregular swelling of the cylinder under pressure was an indication that the mass was not uniform." The amount of flow was measured by the increase in area of the head of the cylinder. The resistance to flow was found to be more satisfactorily measured by use of a Vicat needle; a needle of seven square mm. (J in.) was used, and weight determined which was necessary to cause the needle to sink three centimeters in \ min. Tests of dry clay. Of the dry methods, the tensile-strength test is the best known. It is made by molding the wet clay into briquettes, and testing the tensile strength of these when dry, this strength being expressed in Ibs. per sq. in. The objection to this method is the assump- tion that the plasticity of a clay stands in direct relation to its tensile strength, which is incorrect. Bischof x suggested using a set of mixtures of a standard clay with varying amounts of sand. Each of these is rubbed with the fingers, and the amount of dust that can be rubbed off is noted. The clay to be tested is similarly rubbed, and rated with the one of the standard series which has lost a similar amount by rubbing. The method is crude and inaccurate. Texture Definition. By the texture of a clay is meant its size of grain or fineness, and since this exerts an important influence on the physical properties, such as plasticity, shrinkage, porosity, fusibility, etc., it should receive more than passing consideration. Many clays contain sand- grains of sufficient size to be visible to the naked eye, but the majority of clay particles are too small to be seen without the aid of a microscope, and are therefore so small that it becomes impossible to separate them with sieves. In testing the texture of a clay, it is perhaps of sufficient importance for practical purposes to determine the per cent of any sample that will pass through a sieve of 100 or 150 meshes to the inch, since, in the preparation of clays for the market by the washing process, they are not required to pass through a screen any finer than the one above mentioned. Mechanical analysis. If it is desired to measure the size of all the grains found in the clay, some more delicate method of separation becomes 1 Die leuerfesten Thone, p. 88. PHYSICAL PROPERTIES OF CLAY 109 necessary, and in order to do this it is essential that the mass of clay should be first thoroughly disintegrated and the grains separated from each other. This is best done by shaking the clay for a long time in water. 1 For this purpose the bottles used in sterilizing milk for infants are very convenient. Twenty grams of clay are weighed out and washed into such a bottle and the latter about half filled with distilled water. The bottle is closed with a rubber stopper and put into a shaking-machine. A convenient form consists of a box with compartments for holding four tiers of bottles lying on their sides, allowing four bottles in each compartment. This box is supported by chains, attached to the corners, hanging from brackets above. It is fastened by rubber bands to the table below, to steady it, and a guide-rod is fastened to the bottom, which works between two uprights to give a true lateral motion to the box. The box is then moved rapidly back and forth by a crank, with a throw of about 5 inches, at a rate of about 170 revolutions per minute. This gives a very good motion to the liquids in the bottles and keeps the clay constantly agitated. Motion may be imparted to the shaker by a water-motor or other suitable power. The shaking is continued for from one to two days, according to the nature of the sample, the heavier clays requiring the longer time. When shaking is stopped, the contents of the bottles are washed into beakers, and the sediment, which quickly subsides, is examined with the microscope. If the disintegration is not complete, a small amount of pestling with the rubber-tipped pestle will finish it. Usually sandy clays are very thoroughly disintegrated after being shaken a day, while clay soils frequently require pestling after having been shaken for two days. When clean, the grains should show sharp outlines under the micro- scope, being as a rule quite transparent. Adhering particles make them appear rounded and more or less deeply colored and the outlines indistinct. When pestling alone is resorted to for the disintegration of the material, it may require from fifteen minutes to an hour or more, depending upon the nature of the sample. 1 U. S. Dept. of Agric., Bur. of Soils, Bull. 4, p. 9, 1896. 110 CLAYS Methods of Separation Beaker method. This method suggested by Whitney is simple,. but somewhat inconvenient on account of the large amount of water required. Its operation is as follows: l "The thoroughly disintegrated clay is transferred to a 3-inch beaker, which we may call S. This is filled with water and thoroughly stirred. It is then allowed to settle until all solid particles larger than 0.05 mm. have subsided. This is determined by taking a sample of the turbid liquid from near the bottom of the beaker by lowering a small tube, with the top closed by the finger, to a point just above the sediment, then removing the finger for an instant and letting the liquid enter the tube, closing the tube with the finger again and withdrawing the sample. A drop of this is placed upon a microscope slide, a cover-glass placed over it, and the particles examined by a good microscope containing an eyepiece micrometer. It is convenient to use a 1-inch eyepiece and a three-fourths and one-fifth inch objective. "When the particles larger than 0.05 have subsided, the turbid liquid is carefully decanted into a larger beaker, M. This turbid liquid contains silt, fine silt, and clay, but no sand if the separation has been properly timed. The sediment in S consists of sand, containing, still some silt, fine silt, and clay. This is stirred up with water and again allowed to settle until all the grains of sand have subsided, when the turbid liquid is again decanted into M. This operation is continued until an examination of the sediment in B shows that all particles smaller than 0.05 mm. have been removed. The contents of this beaker B are then washed into a small porcelain dish and evaporated to dryness on the water-bath. When dry this sand may be gently ignited to burn off the organic matter, and when cool it is sifted through a series of sieves which will be described further on. "It is often convenient in separating the silt, fine silt, and clay from the sand to decant before the last portions of sand have settled. This hastens the operation of separating the fine and the coarse material, especially where there is a large mass of sand and but little fine material to be removed. In this case, the turbid liquid which is decanted is put into a separate beaker, and the sand which has been poured off is recovered by a further decantation, and when free from all fine material it is added to the sand in the porcelain dish while the latter is evaporating to dryness. The turbid liquid in the breaker M. is thoroughly stirred 1 U. S. Dept. Agric., Bur. of Soils, Bull. 4, p. 10, 1896. . PHYSICAL PROPERTIES OF CLAY 111 and allowed to settle until a drop taken from near the bottom of the the beaker contains no solid particles larger than 0.01 mm., equal to two spaces of the eyepiece micrometer using the --inch objective. The turbid liquid, containing only fine silt and clay in suspension, is then carefully decanted into another beaker, P. The sediment remaining in M is again stirred up with water and allowed to settle, and decanted as before. This operation is continued until all particles smaller than 0.01 mm. have been washed out of the sediment in the beaker. Care must be taken in pouring off the turbid liquid that none of the silt goes over, or if it does it must be recovered and added to that in beaker M at some later stage of the operation. The sediment remaining in beaker M should contain nothing larger than 0.05 nor smaller than 0.01, if the separation has been carefully and completely made. This is washed into a platinum dish, evaporated to dry ness on the water- bath, ignited at a low red heat, cooled in a desiccator, and finally weighed. " The sediment in beaker P containing fine silt and clay is stirred up with water and allowed to settle until everything larger than 0.005 mm. has subsided, as determined by a microscopic examination as before. The turbid liquid, containing only ' clay ' or material finer than 0.005 mm. equal to one space of the micrometer, is then decanted into a larger beaker, C, of 1 or 2 liters capacity, and the sediment in P repeatedly washed until all of the clay has been removed. When this has been accomplished, the sediment is washed into a platinum dish, evaporated to dryness, ignited, and weighed. " The clay water usually amounts to a number of liters, and to prevent it accumulating to any great extent it is the practice in this Division to measure it in a liter flask and take 100 cc. from each liter to evaporate to dryness. The remainder of the clay solution is thrown away. When the liter flask is full to the mark with the clay solution, care must be taken to thoroughly mix it before taking out the tenth part to be evapo- rated to dryness. The successive 100 cc. of clay water are poured into a beaker and evaporated in a platinum dish as rapidly as possible. When this clay water has been evaporated to dryness, the sediment is ignited and weighed and the weight multiplied by ten to give the total amount of fine material in the original sample. 11 In the course of the analysis, several of these grades may be separated at once, to facilitate the operation, by the use of additional beakers. It is best to transfer material into smaller beakers as the quantity becomes less in being freed from the finer particles, as this materially hastens the time required for the material to subside. 112 CLAYS " The sand which was separated in the beginning of the operation and dried and ignited in the porcelain dish is sifted through a series of sieves of the following dimensions: Three round brass sieves 4 inches in diameter are used, which fit into each other and into a cup at the bottom. The top sieve has circular holes 2 mm. in diameter, the second has similar holes 1 mm. in diameter, and the third has holes 0.5 mm. in diameter. These grades are sifted in a very short time. " The material which passes through the lower sieve is then sifted through two grades of bolting-cloth Nos. 5 and 13 having square holes approximately 0.25 and 0.1 mm. in linear dimensions. This sifting requires quite a long time, on account of the fineness of the spaces through which the particles have to pass. It can conveniently be done upon the shaker which is used for the disintegration of the original sample. The two pieces of bolting-cloth can be fitted into conveniently arranged brass rings, and the samples should be shaken for an hour or two on this shaker. 11 Each of these grades of sand are weighed without previous drying, as the amount of hygroscopic moisture is usually inappreciable. " The operation of" mechanical analysis is frequently made tedious and sometimes impossible by flocculation. If any tendency to this is discovered, vigorous stirring should be resorted to, arid this can best be done with one of the improved forms of egg-beaters found in the market. A small trace of ammonia also assists in overcoming this tendency to flocculation, but it should be added very cautiously, as an excess of ammonia will cause many soils to flocculate. If the sediments are left standing for a length of time, flocculation is liable to occur, and it is very important that the work should be pushed along as rapidly as possible. The operator will find by experience that while waiting for one sediment to subside he may be decanting into extra beakers, which in time may be added to the proper beaker. " The water used in the mechanical analysis should be distilled, if possible, but clear river, well, or hydrant water may be used. In case distilled water is not available, the solid matter in suspension or in solution in the water used should be determined by evaporating 500 cc. of the water to dryness, and igniting and weighing the residue. Allowance should then be made for this residue in the clay determination. " Eight or ten samples can be started at once and can be pushed through about as readily as a single sample. It is not advisable, however, to attempt to carry on more than this number, because the proper attention cannot be given to the beakers. A fresh set of samples may be started on the shaker, however, a day or two before the last set is finished. PHYSICAL PROPERTIES OF CLAY 113 It requires from six to ten days to complete the analyses of a set of samples, if close attention is^given to the decantations. " Schoene method. A second method consists in separating the pebbles and coarse-sand particles cut of the disintegrated clay by means of sieves, and then placing the finer portion in a tube where it is exposed to an upward current of water. Since the carrying power of the current will increase with its veloc- ity, a current of water rising very slowly in the tube will carry off only the finest particles, while the heavier ones remain behind. If the velocity of the current be kept at this speed, it will finally become clear when all the finest particles are carried off. A form of apparatus used for this purpose is the Schoene elutriator shown in Fig. 20. The apparatus consists of the separating funnel A, which at the bottom ends is a bent tube, and is connected at the top with a narrow tube 1 meter long. This latter is Z-shaped and has an opening at L, ] .5 mm. in diameter. The grains of the clay to be separated are first disintegrated by boiling and then placed in the funnel A. Water is then run in from the reservoir D FIG. 20. Schoene's apparatus for me- and the supply regulated by the chanical analysis of clay, stopcock E, so that there is always a definite velocity in the funnel A. The rapidity of flow depends on the amount of water entering the funnel per second. Knowing the amount of water and the cross-section of A, the velocity is equal to the quantity divided by the cross-section. The quantity is measured by allowing it to run into a measuring-vessel for a definite length of time, care being taken that the level of the water in k remains constant. In this way the flow per second can be calculated. The velocity of the flow can be told by the height to \vhich the water backs up in the tube k. This has to be determined in calibrating the instrument. 114 CLAYS To every velocity there corresponds a size of grain determined by calculations, and five sizes are made, as fellows: 1. Clay substance, including particles removed by a flow of 0.18 mm. per second. Maximum diameter 0.01 mm. 2. Silt, including grains removed by a flow of 0.70 mm. per second. Maximum diameter 0.025. 3. Dust-sand, including particles removed by a flow of 1.5 mm. per second. Maximum size 0.04 mm. 4. Residue remaining in funnel, called fine sand. Diameter 0.04 to 0.2 mm. 5. Coarse sand, everything larger than 0.2 mm. This form of apparatus is much used in Germany, and but little in the United States. An objection which has been urged against it is that, on account of the funnel-shaped character of the vessel A, counter- currents are set up, which interfere with accurate results. FIG. 21. Hilgard's apparatus for making mechanical analyses. Hilgard's elutriator. E. W. Hilgard devised the form of apparatus shown in Fig. 21 for overcoming the defects of Schoene's separator. It is known as Hilgard's Churn Elutriator. It consists of an upright glass cylinder, 300 mm. in height and 45 mm. in diameter; this cylinder is united at its lower end to a brass cup-shaped funnel, crossed by a horizontal axis furnished with four wings; this churn is separated from the cylinder by a wire screen with meshes 0.8 mm. in diameter. The churn is worked by any convenient motor-power; about 500 revolutions per minute is the speed required when separating the two finest groups of particles, but for the other separations a smaller velocity will suffice. PHYSICAL PROPERTIES OF CLAY 115 The lower end of the brass funnel is fixed into a conical test-glass, which is in connection with the water-supply. The water is supplied from a reservoir maintained at a constant level. The lever opening the water- tap moves over a graduated arc, on which are marked the positions of the lever which yield supplies of water, giving the required velocities in the glass cylinder. The apparatus being half filled with water and the churn in motion, the sediment is introduced, and the water-current adjusted to the low- est velocity, 0.25 mm. per second; this current is continued till the water ceases to remove any more matter. The operation requires many hours for its completion. The object of the churn is to break up the aggregations of fine particles which are very apt to form. Should any be seen on the sides of the cylinder, the apparatus must be stopped, and the flocks detached with a feather. The water leaving the cylinder is conducted by a tube nearly to the bottom of a tall, wide vessel, from the top of which the water runs to waste. The receiving vessel being much wider than the separating cylinder, the upward current of water in it is too slow for any of the solid matter carried into it to escape. When no more particles are removed by the current moving 0.25 mm. per second, the regulator is changed, and the velocity of the current increased to 0.5 mm. per second. When the second group of particles has been in this way removed, the velocity of the current is again doubled, and this mode of proceeding is continued till the last separation, with a velocity of 64 mm. per second, is completed. With velocities above 4 mm. per second, the churn may be dispensed with. The work gets more rapid as the higher velocities are reached. When the apparatus is in action day and night, the separations will be completed in three or four days. Soft, filtered water should be used in all the operations. A most serious objection to the three methods just described is the time required for making an analysis, and the quantity of water con- sumed. Centrifugal separator. The most satisfactory method is that known as the centrifugal method. The apparatus (Fig. 22) used consists of a fan-motor 1 placed with the armature shaft in a vertical position. This carries a framework with eight test-tube holders, trunnioned so that they can swing outward and upwards as the frame revolves. The disintegrated sample in suspension in water is placed in these tubes, and twirled at a high speed for several minutes. As a result of this, all particles except the finest clay grains are thrown to the bot- 1 For complete description, see Bulletin No. 64, Bureau of Soils, Dept. of Agri- culture, Washington, 1900. 116 CLAYS torn of the tube by centrifugal force. These are decanted off, the tubes refilled with water, and the sediment again stirred up. A second twirling of the tubes, either at a lower speed or for a shorter period, precipitates everything except the fine silt, which is then also decanted off. The subsequent sizes are then separated from each other partly by settling and partly by sieves. FIG. 22. Centrifugal separator for mechanical analysis. (Photo loaned by Bureau of Soils.) The different sizes which can be so separated and their dimensions are shown in the table below: TABLE SHOWING SIZE OF GRAINS OF SAND, SILT, AND CLAY Size of diameters. Conventional name. Inches. 1. Gravel 1/12 -1/25 2. Coarse sand 1/25 -1/50 3. Medium sand 1/50 -1/100 4. Fine sand 1/100-1/250 5. Very fine sand 1/250-1/500 6. Silt 1/500-1/2500 7. Fine silt 1/2500-1/5000 8. Clay 1/5000-1/25000 If a raw clay is examined under the microscope to be composed of a number of different-sized grains. Millimeters. 2-1 1-0.5 0.5-0.25 0.25-0.1 0.1-0.05 0.05-0.01 0.10-0.005 0.005-0.001 it is usually seen These may show PHYSICAL PROPERTIES OF CLAY 117 a wide range of sizes as given in Fig. 23, which represents a gritty clay from the Cape May formation of New Jersey. In other clays, such as those of the Alloway formation in the same State, there is often m "* *\. ** \ o oO ^ a o^ o^ 1 FIG. 23. Drawing showing particles of a Cape May clay, enlarged 362 diameters. (After Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 109, 1904.) less variation in the size of the grains (Fig. 24), the grains in the latter being bunched together more than in the former. Fig. 25 represents several grains of sand from a sample of Clay Marl I, which have been separated by the mechanical analysis and enlarged 115 diameters; they consist of quartz (Q), mica (M), feldspar (F), and lignite (L), the cloudiness of the feldspar being due to partial kaolinization. Relation between composition and texture. Few analyses have been published showing the chemical composition of the different-sized grains in a clay. Recently Grimsley and Grout have analyzed the mechanical sepa- rations of 16 samples of clay with the following results: 1 1 W. Va. Geol., Ill, p. 61, 1906. 118 CLAYS Sizes in mm. 00 to 0.001 0.001 to 0.005 0.005 to 0.02 . 02 to 0.15 0.15 up Silica (SiO 2 ) . . . 44 08 54 54 70 30 81 16 73 63 Alumina (A1 2 O 3 ) 28 16 23 00 16 04 9 76 13 01 Ferric oxide (Fe 2 O 3 ) 7 94 5 91 3 21 2 13 4 71 Ferrous oxide (FeO) 99 99 63 40 18 Lime (CaO) . "76 82 72 31 .47 Magnesia (MgO) 1.36 l76~2 .80 .39 .48 Potash (K 2 O) 3~05 3.31 2.14 1.78 .93 Soda (Na 2 O) 00 .29 .45 .56 .00 Moisture 2 80 1 10 56 ~35 .87 Ignition, loss 10.86 7.79 4.33 2.59 4.40 Titanic oxide (TiO 2 ) .84 1.12 1.08 .78 .60 / p , 8< * b go 3 >A o g tOo o tfS? {700 a n V?o^>Q oQ&c^ o o :o o s* o o ^ FIG. 24. Drawing of the Alloway, N. J., clay, enlarged 362 diameters. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 110, 1904.) As might be expected, these analyses show a higher percentage of silica in the coarser grains, still the increase is not a steady one, but none of the other ingredients show either an increase or decrease from PHYSICAL PROPERTIES OF CLAY 119 FIG. 25. Drawing of sand-grains in a New Jersey clay marl, enlarged 115 diam- eters. M, mica; Q, quartz; F, feldspar; L, lignite. (After Ries, N. J. Geol. Surv., Fin. Rept., VI, p. Ill, 1904.) FIG. 26. Drawing showing bunches of kaolinite (?) plates in a ball-clay from Edr-ar, Fla., enlarged 362 diameters. (After Ries, Md. Geol. Surv., IV.) 120 CLAYS coarse to fine. The maxima are in each case underscored. The appre- ciable titanium percentage in even the coarser grains is of interest, although it is not known in what form the titanium occurs therein. Tensile Strength Definition. The tensile strength of a clay is the resistance which it offers to rupture or being pulled apart when air-dried. Practical bearing.. The tensile strength is an important property, and has a practical bearing on problems connected with the handling molding, and drying of the ware, since a high strength enables the clay to withstand the shocks and strains of handling. Through it, also, the clay is able to carry a large quantity of non-plastic material, such as flint or feldspar, ground bricks, etc. Relation to plasticity. Although it was formerly believed by many that tensile strength and plasticity were closely related, this view is no longer generally accepted. High tensile strength and high plas- ticity often go together, but a clay low in tensile strength may have high plasticity and vice versa. Measurement of tensile strength. The tensile strength is measured by molding the thoroughly kneaded clay into briquettes, of the form and dimensions shown in Fig. 27, and, when thoroughly air-dried, pulling them apart in a suitable testing-machine. The cross-section of the briquettes when molded is 1 square inch, and, after being formed, they are allowed to dry first in the air and then in a hot-air bath at a temperature of 100 C. (212 F.). When thus thoroughly dried the briquette is placed in a machine, in which its two ends are held in a pair of brass clips, and is subjected to an increasing tension until it breaks into two. The type of machine used is of either type shown in Figs. 28 and 29. Theoretically the briquette should break at its smallest cross-sec- tion with a smooth, straight fracture, and when this does not occur it is due FIG. 27. Outline and dimensions either to a flaw in the briquette or because of a briquette for testing the the clipg tend to cut into the c i ay In tensile strength of a clay. such event the briquette breaks across one end, and to prevent this it is necessary to put some soft material, PHYSICAL PROPERTIES OF CLAY 121 such as asbestos, pasteboard, or rubber between the inner surface of the clip jaws and the sides of the briquette. If the briquettes are molded and dried with care, the variation in the breaking strength of the individual briquettes should not vary more than 15 or 20 per cent, but with some very plastic clays it is extremely difficult to keep the variation within these limits. FIG. 28. Richie" tensile-strength machine. Great care has to be exercised in filling the briquette molds, in order to prevent flaws in the piece, and the best method consists in cutting a lump of the tempered clay of approximately the shape and size of the mold, and then pounding it in from both sides with the hands. Wheeler 1 advocates filling the mold by pressing in separate small pieces of wet clay with the fingers, the object of this being to avoid air-bubbles and prevent laminations in the briquette; but some have obected to this, on the ground that it is difficult to make the separate pieces of clay amalgamate. Since the briquettes of any one clay will always show more or less variation, at least 10 or 12 should be tested in order to get a fair aver- age. The author's experience has shown that the greatest variation usually appears in clays of high tensile strength, in which the fracture nearly always occurred in the head, indicating that the briquettes broke before the limit of their strength was reached. The tensile strength of clay briquettes is expressed in pounds per square inch; but, sirce 1 Mo. Geol. Surv., Vol. XI, p. 111. 122 CLAYS the briquette shrinks in drying, the strength actually obtained in test- ing will be less than that for a square inch, and the result must be increased in proportion to the amount the brick has shrunk. FIG. 29. Fairbanks tensile-strength machine. N, clips for holding briquettes; P, screw for applying strain to balance-lever C; F, bucket to hold shot fed in through / from the hopper K\ J , automatic cut-off. Clays vary widely in their tensile strength, ranging from but a few pounds up to over 400, and even in clays of the same class a wide vari- ation is not uncommon, as the following approximate figures will show: Kaolins Fire-clays. . . . Brick-clays. . . Pottery-clays. Minimum. Maximum. 20 60 (Flint-clays) 150 50 300 50 250 Wheeler 1 in testing 135 Missouri clays found that their tensile strength ranged from an average of 8 to 380 Ibs. per square inch, dis- tributed among the several kinds as follows: Kind. Flint-clays ... , Range. , 8 to 50 Average 20 Kaolins 12 to 20 20 Fire clays and pottery-clays 50 to 284 150 Shales . 87 to 192 120 Gumbo 275 to 410 340 Loess . . 97 to 354 150 1 Mo. Geol. Surv., XI, p. 111. PHYSICAL PROPERTIES OF CLAY 123 Beyer and Williams 1 give a range of from 46 to 319 Ibs. per square inch for the Iowa clays. The range in strength determined by the writer for the Texas clays was as follows: Fire clays 46 to 277 Stoneware clays 66 to 320 Calcareous clays 119 to 366 Sandy brick clays 77 to 455 Semi-refractory brick clays 161 to 329 Red- or brown-burning brick clays 74 to 487 while in the New Jersey clays 2 the extremes were 20 and 453 Ibs. per square inch. When any series of clays is tested, it is found that both the very sandy ones and very fine-grained ones often have a low tensile strength, although there are marked exceptions to both these cases. Cause of tensile strength. In order to get satisfactory and reliable results, great care is necessary in molding and drying the briquettes, it being claimed by some that fine-grained clays will show an abnormally low strength unless dried very slowly. Experiments by Orton 3 seem to bear out this fact. Five series of the same clay were tested by him as follows: Average Series. Rate of drying. tensile strength, Ibs. per sq. in. 1 Quickest, severest drying 182 . 49 2 Somewhat slower 178 . 17 3 Still slower 176.13 4 Very slow indeed 204 . 80 5 Artificial conditions 205 . 53 The fifth series was placed in a tightly closed jar with calcium chloride. With such a variation existing in the tensile strength of clays, it becomes a matter of importance to know the cause of this variation. It is a well-known fact that all clays shrink in drying, and that this shrinkage is accompanied by a drawing together of the particles. Indeed, some clays shrink to such a hard mass as to suggest a close interlocking of the grains, which, it seems to the writer, may be the explanation of the tensile strength shown; that is to say, those clays in which the inter- 1 la. Geol. Surv., XIV, p. 83, 1904. 2 N. J. Geol. Surv., Final Report, Vol. VI, p. 85, 1904. Trans. Amer. Cer. Soc., Vol. Ill, p. 202, 1901. 124 CLAYS locking of the particles is the tightest will show the highest tensile strengtn and vice versa. If this is true it becomes necessary to determine, if possible, what arrangement or size of particles produces the tightest and strongest structure. E. Orton, Jr., 1 attempted to determine the effect of the fineness of grain on the tensile strength of clays by taking a very fine-grained clay and mixing different sizes of sands with it, the sand being obtained by grinding and screening vitrified bricks. His conclusions were " (1) that the tensile strength of mixtures of a plastic ball-clay with equal quantities of non-plastic sands will vary inversely with the diameter of the grains of 90 80 70 60 50 40 Diameter of grains in terras of the largest. 30 20 10 Largest size =100 FIG. 30. Curve showing relation between fineness of grain of non-plastic material and tensile strength of clay mixtures. (After Orton, Trans. Amer. Cer. Soc., III.) the sand from grains of 0.04 inch down to the finest sizes obtainable. (2) That the non-plastic ingredients of clay influence its tensile strength inversely as the diameter of their grains, and fine-grained clays will, other things being equal, possess the greatest tensile strength." In other words, the coarser the grains of sand the less the tensile strength of the mixture containing them. The results of these tests are shown graphically in Fig. 30. 1 Transactions American Ceramic Society, Vol. II, p. 100, and Vol. Ill, p. 198. PHYSICAL PROPERTIES OF CLAY 125 A series of tests on natural mixtures of varying texture were under- taken by the writer in connection with a study of the New Jersey clays. 1 Five samples were selected at random as follows: 1. A very plastic, slightly gritty, dense, red-burning clay from the Alloway formation, with an average tensile strength of 453 pounds per square inch. 2. A Pleistocene clay of gritty, plastic character, but not as dense as the previous one. Its average tensile strength was 297 pounds per square inch. 3. A gritty, plastic clay from the Cape May formation, with an aver- age tensile strength of 289 pounds per square inch. 4. A Raritan clay of black color and sandy, micaceous character, with an average tensile strength of 105 pounds per square inch. 5. A soft, powdery, washed ball clay from the Raritan. It was plastic to the feel, with very little grit, and a tensile strength of under 20 pounds per square inch. The percentage of the sizes in each of the 5 samples is shown in the following table: MECHANICAL ANALYSES OF SOME NEW JERSEY CLAYS Conventional names. I. Lab. No. 680. II Lab. No. 659. III. Lab. No. 645. IV- Lab. No. 615. V. Lab. No. 723. Clay substance . . 59.00% 44.00% 22.00% 30 . 645% 87 . 96% Fine silt 11.00 7.11 5.66 14.21 6.95 Silt and fine sand 14.70 24.35 26.55 5.585 3.00 Medium sand ... 3.50 7.80 11 45 6 400 1.00 g anc l 11.40 16.35 33 44 42 950 99.60 99.61 99.10 99.790 98.91 These figures seem to throw some light on the relation of the texture to the tensile strength, but, while highly suggestive, are not to be taken as final. The results of these tests are also shown graphically in the table (Fig. 31), in which the horizontal lines represent percentages. Of the 6 columns, the first 5 represent the grain sizes and the sixth the tensile strength. Taking No. 5 of the above table of analyses we find that it contains 87.96 per cent of clay substance. This point is plotted in the first column. The point representing the percentage of fine silt is then plotted in the next column, and so on with the other sizes. These points are then N. J. Geol. Surv., Final Report, Vol. VI, p. 87, 1904. 126 CLAYS connected with a curved line. In the same way the percentages of the different sizes of grains of the other samples were plotted and connected by curved lines. The lines are drawn in different ways, so that those representing the different clays can be more readily distinguished at a glance. From a study of this table it is seen that the clay having the FIG. 31. Curves showing relation of texture to tensile strength. (After Ries ? N. J. Geol. Surv., Fin. Kept., VI, p. 89, 1904.) lowest tensile strength (No. 5) contains a very high percentage of the finest clay particles, furfhermore, the clay having the second lowest tensile strength (No. 4) contains the largest percentage of sand (42.9 per cent). From this it appears that an excess of either coarse or fine grains lowers the tensile strength. On the other hand, in those clays having the highest tensile strength the percentages of fine, medium, and PHYSICAL PROPERTIES OF CLAY 127 coarse particles are more nearly equal. This is perhaps what might be expected, for if the tensile strength is due to the interlocking of the grains, a mixture of different sizes would fit together more closely than if particles of one size predominated, as in Nos. 4 and 5 of the table, It is rather difficult, however, to compare these results with Orton's, as in his artificial mixtures the non-plastic particles were of uniform size, while in the natural mixtures a variety of sizes existed. Beyer and Williams * reached somewhat similar conclusions at about the same time, their work on the mechanical analyses of the loess-clays indicating that the clays showing the highest tensile strength were the ones in which there was the most evenly proportioned amounts of the sizes of the grains represented, therefore those possessing a large propor- tion of excessively fine particles or those running high in some inter- mediate size of grain are weaker. The following mechanical analyses made by them indicate this : MECHANICAL ANALYSES OF IOWA LOESS CLAYS Size of clay particles. ell Clay. Loss at 230. Above .lto.05 mm. .05 to .01 mm. .01 to .003 Below .003 Total per cent. if. 3.3 incl. incl. incl. mm. >% <$ Besley, Council Bluffs, top clay 1.55 3.44 22.10 49.11 13.44 10.35 99.99 149 Gethman, Gladbrook . 2.59 5:19 22 .46 32.04 14.15 23.55 99.98 279 Besley, Council Bluffs, bottom clay 2.04 1.62 25.26 29.72 17.85 23. 74 100.23 244 If the theory of interlockment is true, then it should be possible to make a mixture of two clays whose tensile strength is higher than that of either of the clays alone or vice versa. The writer 2 has noted a case of two clays from near Asbury Park, N. J. One of these was a slightly gritty, black clay, with an average tensile strength of 182 Ibs. per square inch. The other was a plastic loam, whose average tensile strength was 137 Ibs. per sq. in. A mixture of the two in equal proportions, however, had an average tensile strength of 258 Ibs. per sq. in. Another clay from a different formation had an average tensile strength of 108 Ibs. per sq. in., while a mixture of equal parts of this clay and a 1 la. Geol. Surv., Vol. XIV, p. 102, 1904. 2 N. J. Geol. Surv., Final Report, Vol. VI, p. 90, 1904. 128 CLAYS somewhat coarse sand had a tensile strength of but 65 Ibs. per sq. in., the decrease being evidently due to the excess of sand. Shrinkage All clays shrink in drying and burning, the former loss being termed the air-shrinkage and the latter the fire-shrinkage. Air-shrinkage. In a clay which is perfectly dry all the grains are in contact, but between them there will be a variable amount of pore- space depending on the texture of the clay. The volume of this pore- space is indicated somewhat by the quantity of water that will be absorbed without the clay changing its volume, this water filling in the space between the grains. It may be termed pore water. The presence of more water than is required to fill the spaces between the grains produces a swelling of the mass, and in this condition each grain is regarded as being surrounded by a film of water; but while the grains still mutually attract each other the attraction is less than in the dry clay, and the mass yields readily to pressure. An excess, how- ever, separates the clay particles to such an extent that the clay softens and runs. A clay will therefore continue to swell as water is added to it, until the amount becomes too great to permit it to retain its shape. Some clays absorb very little water, while others take up a large quantity, and G. P. Merrill 1 mentions one from Wyoming which when placed in a measuring-flask absorbed and retained sufficient water to increase its bulk eightfold. When a clay has been mixed with water and set aside to dry evap- oration of the moisture commences and the particles of clay draw closer together, causing a shrinkage of the mass. This will continue until all the particles come in contact, but since they do not fit together perfectly there will still be some pore-spaces left between the grains, and these will hold moisture which cannot be driven off except by heating at 100 C. The air-shrinkage may therefore cease before all the water has passed off. The amount of air-shrinkage is usually low in sandy clays, at times being under 1 per cent in coarsely sandy ones, while it is high in very plastic clays or in some very fine-grained ones, reaching at times as much as 12 or 15 per cent. Five or six per cent is about the average seen in the manufacture of clay products. 1 The Non-metallic Minerals, p. 233. Or THF "NIVERSITY OF PHYSICAL PROPERTIES OF CLAY All clays requiring a high percentage of water in mixing do not show a high air-shrinkage. The air-shrinkage of a clay will not only vary with the amount of water added, but also with the texture of the materials. Sand or materials of a sandy nature counteract the shrinkage, and are frequently added for this purpose, but, since they also render the mixture more porous, they facilitate the drying as well, permitting the water to escape more readily, and reducing the danger from crack- ing. If the sand added to dilute the shrinkage is refractory it also aids the clay in retaining its shape during burning. The effect of sand on a clay is well seen from the following experi- ment with a clay from Herbertsville, N. J. 1 Clay. . Per cent water required. 32.6 Per cent air- shrinkage. 5.3 Tensile strength, Ibs. per sq. in. 108 Clav + 50% sand. . 15.6 3.3 65 From the above it is seen that the addition of 50 per cent of sharp sand reduced the amount of water required a little over one half. The air-shrinkage was reduced 37.73 per cent, but it was accompanied by a loss in the tensile strength of nearly 40 per cent. Fire-shrinkage. All clays shrink during some stage of the burning operation, even though they may expand slightly at certain tempera- tures. The fire-shrinkage, like the air-shrinkage, varies within wide limits, the amount depending partly on the quantity of volatile ele- ments, such as combined water, organic matter, and carbon dioxide, and partly on the texture and fusibility. Fire-shrinkage begins at a dull-red heat, or about the point at which chemically combined water begins to pass off, and reaches its maxi- mum when the clay vitrifies, but does not increase uniformly up to that point. The clay worker, however, always tries to get a low fire shrinkage, using a mixture of clays if necessary. After the expulsion of the volatile elements the clay is left in a por- ous condition, until the fire-shrinkage recommences. In the table 2 on the next page there are given the results of a series of tests made on eight different clays, which were burned at tempera- tures 100 C. apart from 500 C. (932 F.) up to 1100 C. (2012 F.) inclusive. 2 1 N. J. Geol. Surv., Final Report, Vol. VI, p. 92, 1904. 2 Ibid., p. 94, 1904. 130 CLAYS TABLE SHOWING PROGRESSIVE SHRINKAGE AND Loss OF WEIGHT AT DIFFERENT TEMPERATURES 6 i o^o 600 C. 700 C. 800 C. 900 C. 1000 C. 1100C. jf a 1112 F. 1292 F. 1472 F 1652 F. 1832 F. 2012 F. c j 3 1 " 1 be * to i 1 60 _c bj 1 "o .Sf 1 1 1 1 03 1 Is 1 la 8 1 g 8 N L L 3 ^ c 8-c i| !! i| ^ 1 a r r J - ~ " | 5 - pT " * 648 9.0 2 69 6.38 1.72 0.3 0.70 .0 0.88 0.56 0.19 0.7 0.38 4.0 655 4.6 1.36 6.10 1.38 0.0 0.55 .0 0.33 0.33 0.12 0.7 0.21 2.4 663 5.3 1.50 4.24 1.37 0.7 0.35 .3 0.05 0.27 + 0.06 0.0 0.19 1.3 665 7.0 1.43 8.65 1.07 0.3 0.48 .0 0.39 0.12 0.10 2.7 0.00 12.6 696 5.6 3.48 9.42 2.61 0.4 1.61 .0 0.46 0.33 0.14 1.3 0.22 4.7 703 1.0 0.63 2.52 1.05 0.0 0.26 .0 0.10 0.02 0.09 1.4 0.03 0.0 717 8.0 3.29 5 . 32 1.70 0.3 0.83 .0 0.41 0.49 0.34 1.3 0.24 4.0 728 2.0 0.70 3.23 1.03 0.6 0.61 .0 0.22 0.15 0.10 1.3 0.12 2.7 Explanation of table. The clays tested were the following: 648. Fat, black, micaceous clay, of Clay Marl I from Maple Shade, N. J. 655. A clay marl. Exact locality unknown. 663. A Pleistocene clay from Vineland, N. J. 665. A yellow, finely gritty, Cohansey clay, heavily stained with limonite from Toms River, N. J. 696. Black, Asbury clay from west of Asbury Park, N. J. 703. Sandy, Raritan clay from near Fish House, N. J. 717. A very plastic clay from Clay Marl III, south of Woodbury, N.J. 728. Hudson River shale from Port Murray, N. J. The bricklets had been standing in a warm room for several weeks, and, although they appeared perfectly dry, they were placed in a hot- air bath and kept at a temperature of 110 C. for a day, being weighed both before and after. This drove off the moisture remaining in the pores, and the resulting loss in weight indicated in the third column of the above table shows the quantity of moisture that may remain in a brick after the air-shrinkage has ceased. It is least in the sandy, lean clays and highest in the black one, which is colored by organic matter. The second column indicates the per cent of air-shrinkage, calculated upon the length of a freshly molded bricklet. The fourth column, headed 500 C. (932 F.), gives the loss in weight from the thoroughly dried PHYSICAL PROPERTIES OF CLAY 131 condition up to 500 C., calculated on the weight of the air-dried sample. The following columns give the additional loss in weight for. each 100 C. (180 F.), as well as the fire-shrinkage taking place in this temperature interval. From an inspection of the table it is seen that most of the volatile substances, such as the chemically combined water contained in the hydrous aluminum silicate, mica, or limonite, and organic matter, pass off before 500 C. (932 F.), and that an additional appreciable amount is expelled between 500 C. and 600 C. Between 600 C. (1112 F.) and 1100 C. (2012 F.) there was a small but steady loss, while in one case (No. 663) there was even a gain in weight at 1000 C. (1832 F.). Two samples, Nos. 696 and 665, showed a high loss at 500 C. and 600 C., as compared with the others, but this was due to the former containing considerable organic matter, and the latter having a very high percentage of limonite, which would supply an additional quantity of chemically combined water. The amount of fire-shrinkage shown by these samples is equally interesting, for it is seen that, although the loss in weight between 500 C. (932 F.) and 900 C. (1652 F.) is considerable, still there is little or even no shrinkage, so that, after the volatile elements have been driven off, the clay must be very porous, and remains so until the fire-shrinkage begins again. From the table it will be seen that, with one exception, no shrinkage occurred between 600 C. (1112 F.) and 900 C. (1652 F.); but between 900 C. (1652 F.) and 1000 C. (1832 F.), all except No. 663 decreased in size, and there was an additional but greater shrinkage between 1000 C. (1832 F.) and 1100 C. (2012 F.). None of the brick'ets became steel-hard, that is, sufficiently hard to resist scratch- ing with a knife, until 1000 C. (1832 F.), or even 1100 C. (2012 F.). In the case of those burning red, a good red coloration began to appear at 1000 C. (1832 F.). From this it can be seen, and this is a fact already known, that, up to 600 C. (1112 F.), a clay should be heated slowly; but from that point up to 1000 C. the tempera- ture can be raised quite rapidly, unless much carbonaceous matter is present. The gradual burning-off of this carbon is well shown in Fig. 19, which represents a series of bricks taken from a kiln at regular intervals as the burning proceeded. Further heating should be done slowly, as the shrinkage recommences at the last-mentioned temperature. Wheeler l claims that the most potent factor in fire-shrinkage is the size of grain : the finer it is, the greater the fire-shrinkage. 1 Mo. Geol. Surv., Vol. XI, p. 121, 1897. 132 CLAYS Since many clays, when used alone, shrink to such an extent as to cause much loss from warping and cracking, it is necessary to add mate- rials which of themselves have no fire-shrinkage, and so decrease the shrinkage of the mixture in burning. Sand or sandy clays are the materials most commonly used for this purpose, but ground bricks (grog), and even coke or graphite, may be employed. These materials serve not only to decrease the shrinkage in drying and burning, but also tend to prevent blistering in an easily fusible ferruginous clay when hard- fired. They furthermore add to the porosity of the ware, and thus facilitate the escape of the moisture in drying and in the early stages of burning, as well as enabling the product to withstand sudden changes of temperature. If sand is added for this purpose, it may act as a flux at high temperatures, and this action will be the more intense the finer its grain. Large particles of grog are undesirable, especially if they are angular in form, because, in burning, the clay shrinks around them, and the sharp edges, serving as a wedge, open cracks in the clay, which may expand to an injurious degree. Large pebbles will do the same, and at many common brickyards it is not uncommon to see bricks split open during the burning, because of some large quartz-pebble left in the clay, as the result of improper screening of the tempering sand. For common brick, the type of sand used does not make much difference, as long as it is clean; but if sand is to be added to fire-brick mixtures, it should be coarse, clean, quartz-sand. Burned clay-grog is more desirable than sand for high-grade wares, since it does not affect the fusibility of the clay, or swell with an increase of temperature as sand does, but precau- tion should be taken to burn the clay to its limit of shrinkage before using it. Measurement of shrinkage. A knowledge of the air- and fire-shrink- age of a clay is of vital importance to the manufacturer of clay-products, since, in order to produce a burned ware of the required dimensions, he must know the air- and fire-shrinkage of his raw clays. The shrinkage of a clay may be expressed linearly or cubically. The former is given in percentage terms of the original length of the ware, and is easily determined by direct measurement. To deter- mine the cubical shrinkage in drying, it is necessary to carefully determine the volume of clay when moist and again when dry, while the difference in volume between the latter and that of the burned clay gives the cubic fire-shrinkage. Determination of volume. The change in volume, to be determined for getting the cubic shrinkage, is measured by means of a Seger volu- PHYSICAL PROPERTIES OF CLAY 133 meter (Fig. 32). This consists of a four-litre, wide-mouthed, glass-stop- pered jar. A circular opening in the center of the stopper is fitted with the ground- end of a short glass tube m, which ex- pands above into a bulb b, and is again contracted above it. The jar has a glass stopcock e near its base, which is connected above with a burette a of 125 c.c. capacity, and graduated to tenths. The upper end of the burette also widens to a bulb /, from the top of which there extends a bent tube for the attachment of a rubber, this tube being used to draw the liquid into the burette. When the stopcock in the lower part of the burette is open, and the liquid filled in jar up to the mark on the small glass tube m, the liquid stands at the zero-point in the burette. The method of using the apparatus, together with the results obtained on a number of Iowa clays, was as follows: 1 " To use the volumeter for determining the volume of clay, it is filled with oil, ordinary kerosene with a specific gravity of 0.8 (which must be accurately known) FlG - 32. Seger's volumeter, for having been found to give satisfactory determinin S P 8 ^ and spe. J cific gravity, results. " After filling the jar the burette is drawn full of the liquid by suc- tion through the rubber tube, and held full by turning the burette- valve or by means of a pinch-cock on the rubber. The stopper is now removed and the test-piece of the clay, which is still plastic and per- meated with water, is carefully wiped dry of the coating film and put in. The test-pieces, which were approximately 3 inches long, were allowed to dry till, on picking up a piece endwise between the thumb and finger, the middle portion did not sag. This point was noted care- fully and all samples were treated in this regard exactly the same. Care is taken not to spatter any of the liquid in placing the block of clay la. Geol. Survey, Vol. XIV, p. 107. 1904. 134 CLAYS in the jar. In order to prevent this, and to avoid breaking or other- wise marring the test-piece by dropping it into the vessel, a small wooden float or support by which the clay may be carefully let down into the liquid is advantageous. This float is conveniently made with a small eye or hook near each end so that it may be handled by reaching in with two stiff bent-wire rods. Some such arrangement as this is found quite necessary in handling raw clays, but can be dispensed with when the clays are burned. The stopper is now replaced, and by releasing the pinch-cock d oil from the burette is allowed to flow back into the jar until it stands at the mark on the short tube. " The volume of the clay is then indicated by the height of the liquid in the burette above the zero mark. The piece of clay is taken out and placed to dry while the volumeter is again filled to the zero points to be ready for the next test. " When dry the clay is heated to 230 F. to expel all hygroscopic moisture and after weighing it is placed in a vessel of oil until saturated. This is found to require from three to six hours for small test-pieces of approximately 3X1JX1J inches. When saturated the piece is again weighed and its volume measured as before. Having now the wet and dry volumes, the percentages of cubical shrinkage in drying are easily calculated. " In measuring fire-shrinkage the same test-pieces were employed that were made use of in determining drying shrinkage. They were placed in a small muffle-furnace and burned to a temperature of 700 to 800 C. By burning at this heat dehydration and oxidation of the clay were completed. It is about the temperature at which common, porous red-building brick is burned. For the large number of clays vitrification has not yet begun at this heat, and they are left in the most porous condition attained during any part of the burning process. " The results of a number of determinations made on Iowa clays r giving the cubic air- and fire-shrinkage, as well as the porosity of the dried and burned clay, are tabulated on page 135. It will be seen from the above table that in two cases there was a slight expansion of the mass, as indicated by the minus fire-shrinkage. Porosity The porosity of a clay may be defined as the volume of the pore- space between the clay particles, expressed in percentages of the total volume of the clay, and depends on the shape and size of the particles making up the mass. The maximum porosity would be found in a PHYSICAL PROPERTIES OF CLAY 135 POROSITY AND CUBIC SHRINKAGE OF IOWA CLAYS Clay. Porosity of un burned clay. Porosity of burned clay. Cubic air- shrinkage. Cubic fire- shrinkage. Flint Brick Co bottom, of bank 30 04 26 94 9.44 1 99 Flint Brick Co middle of bank 23 00 24 74 23 34 1 82 Flint Brick Co., top of bank 17.31 22.31 26.23 4 24 Corey Pressed Brick Co., red-burning 30.10 33.24 16.94 2 37 Corey Pressed Brick Co buff-burning 28 10 29 59 27 00 2 91 Colesburg Potters' Clay 28.36 25.51 18 25 5 92 Granite Brick Co top stratum 23.00 25.57 4 86 -2 88 American Brick & Tile Co., plastic shale 26.71 29.77 30.46 32.66 21.52 6 83 0.00 -2 47 clay made up entirely of spherical grains of the same size, but such clays are practically unknown. On the contrary, all clays, so far as known, are made up of a mixture of sizes, which greatly reduces the porosity. In general we may say, however, that increasing fineness means increasing pore-space. The rapidity with which a clay absorbs water is not to be regarded as a criterion of its porosity, for two clays of the same porosity may differ in grain, on which account the coarse-grained one will absorb water more rapidly than the fine-grained one. The porosity of a clay is of importance, because it influences the behavior of it towards water, heat, etc. These effects may be sum- marized as follows: Porosity influences the amount of water which a clay will absorb, or the amount required to make them plastic, and this will in turn influence the air-shrinkage. The possible rate of safe drying depends on the amount of water absorbed and the facility with which it can escape; large pores per- mitting the water to escape rapidly. Small pores, on the other hand, retard both the absorption and evaporation of the water. In the burned clay, too, the porosity has to be considered, for all clays after burning are more or less porous unless burned to vitrification. In most clay products a low porosity is desirable in order to increase its resistance to the weather. If a product is very porous, it will absorb considerable water, which on freezing expands. If the pores are large, the pressure exerted by the expanding water on freezing will be relieved by the exudation of small ice crystals from the pores, and no harm results. If, on the other hand, the pores are small, this cannot occur, and a sufficient pressure may be exerted from the contained ice to dis- integrate the mass. With close-textured clays the porosity may be so small that not enough water can enter to cause any harm. 136 CLAYS The porosity of the clay in either its raw or burned condition is determined by means of a Seger volumeter described under Shrinkage. The porosity percentage is determined by the formula 7 in which F = volume of dry test-piece; 2 ' 6 Si 2 ) 1256 fiRO )0.5 PbO) * a AlaUs ^1.0 B 2 O 3 ) ............ 1>Z5b . 2 Q4 A10 ^2.8 SiO 2 ) 13 Al2Us H-0 B 2 O 3 J ............ i>61 O. 5 PbO) ' 23 H-0 B 2 .a 2 Afi^AlO - 014 JO. 5 PbOj ' 6> Ai2 3 H-0 B 2 3 ^0.5Na 9 O) n? A10 ^3.4 SiO 2 013 jo.5 Pboi - 7 A1? 3 no B 2 o 3 , 10 .a 2 ) ft 7r . A10 ^3.5 SiO 2 012 JO. 5 Pbol ' 5 Ai2 3 U-0 B 2 3 ^0.5Na 2 O^ ft8 A , ^3.6 SiO 2 011 JO. 5 PbO^ Ala 3 H-0 B 2 3 OQ ^0.3 K 2 0) 0.2 Fe 2 3 J3.55 SiO 2 ) x 778 09 JO. 7 CaO^ 0.3 A1 2 3 )0.45 B 2 O 3 ) ..... ^0.3 K 2 0) 0.2 Fe 2 3 ^3.60 SiO 2 ) 08 JO. 7 CaOi 0.3 A1 2 3 ^0.40 B 2 O 3 ^ 0.3 K 2 O) 0.2 Fe 2 O 3 ^3.75 O. 7 Caol 0.3 Al 2 b ? 770 .a. 2 ) nfi A10 }3.2 SiO 2 ) , 472 015 JO. 5 PbOJ Al2 3 H-0 B 2 3 J ............ lj47 0.2 Fe 2 3 ^3.50 SiO 2 ) x 742 95Q 0.3 A1 2 3 J0.50 B 2 OJ ............ *' 74 __ J0.3 K 2 O) 0.2 Fe 2 O 3 ^3.65 SiO 2 ) 1 850 , 7 JO. 7 CaOi 0.3 A1 2 3 )0.35 B 2 O 3 ) ............ ^0.3 K 2 O) 0.2 Fe 2 3 ^3.70 SiO 2 ) 1 886 , 6 JO. 7 CaO^ 0.3 A1 2 3 J0.30 B 2 O 3 ( ............ 150 CLAYS COMPOSITION AND FUSING-POINTS OF SEGER CONES (Continued) No. of Composition. -^ n S-P<>int.^ Cone. * V 1 )0.3 K 2 0) 0.2 Fe 2 3 J3.8Q SiOJ , gr - 8 1 070 4 JO. 7 CaOJ 0.3 A1 2 3 )0.20 B 2 O 3 J ^ nq }0.3 K 2 0) 0.2 Fe,0 3 ^3.85 SiO 2 ) l g94 1 090 3 JO. 7 do\ 0.3 A1 2 3 ^0.15B 2 3 ^ 1)9J 1)U9 )0.3 K 2 0) 0.2 Fe 2 3 J3.90 SiO 2 ) 0.3 A1 2 3 J0.10 B 2 O 3 ^ Si S8 S:S Si J0.3 K,O) 0.05 Fe 2 3 } 4 SiQ 2174 3 J0.7 CaOS 0.45 A1 2 O 3 } 4 lUa 2 ' 1/4 4 !n'? n~ 2 nl - 5 Al 2 O 3 4SiO 2 2,210 1,210 ^ U . i UaL> ) 5 |2:? &8| - 5 A1 '3 5Si 2 2 ' 246 i' 230 6 |g'| ^Q] 0.6 Al 2 3 6Si0 2 ..' 2,282 1,250 7 ]^; 3 ^3] 0.7 Al 2 3 7Si0 2 2,318 1,270 8 )^; 3 ^g] 0.8 Al 2 3 8Si0 2 2,354 1,290 9 07 n Q 2 X! - 9 Al 2 O 3 9SiO 2 2,390 1,310 10 ' 7 Q 1.0 Al 2 3 10Si0 2 ...... ....... ....... 2,426 1,330 ? CaOJ 1>2 A1 2 3 12Si 2 .................... 2 >462 1,350 12 '| ^Q] 1.4 Al 2 3 14Si0 2 . ................... 2,498 1,370 13 JQ-J CaOJ 1>6 A1 2 3 16Si0 2 .................... 2,534 1,390 14 )o!7 CaOJ 1-8 Al 2 3 18Si0 2 .................... 2,570 ,1,410 15 |{5;| JQJ 2.1 Al 2 3 21SiO ? .................... 2,606 1,430 16 |o!7 Ca'oj 2 ' 4 A1 2 3 2 4Si0 2 .................... 2,642 1,450 17 |g'J g| 2.7 Al 2 3 27Si0 2 .................... 2,678 1,470 18 |g'J gjgj 3.1 Al 2 3 3lSi0 2 .................... 2,714 1,490 19 |o!7 CaOJ 3 ' 5 A1 2 3 35Si0 2 .................... 2,750 1,510 PHYSICAL PROPERTIES OF CLAY 151 COMPOSITION AND FU8ING-POINTS OF SEGER CONES (Continued) Composition. '-Fusing-point. F . C. $0.3 K 2 O| )0.7 CaO$ 3.9 Al,O 3 39SiO 2 2,786 1.530 $0.3 K.,0) (0.7 CaO$ 4.4 Al 2 O 3 44SiO 2 2,822 1,550 $0.3 K 2 O) )0.7 CaO$ 4.9 Al,O 3 49SiO 2 2,858 1,570 $0.3 K.,0) JO. 7 CaO$ 5.4 Al,O 3 54SiO 2 . 2,894 1,590 $0.3 K 2 0) }0.7 CaO$ 6.0 Al,O,60SiO 2 , 2,930 1,610 $0.3 K,O) )0.7 CaO$ 6.6 Al,O 3 66SiO 2 . . , 2,966 1,630 $0.3 K 2 0) JO. 7 CaO$ 7.2 Al 2 O 3 72SiO 2 3,002 1,650 }0\7 CaO$ 20 Al.,O 3 200SiO 2 3,038 1,670 A1 2 O 3 10 SiO, 3,074 1,690 A1 2 O 3 8 SiO ? 3,110 1,710 A1 2 O 3 6 SiO, 3,146 1,730 A1 2 0, 5 SiO, 3,182 1,750 A1 2 O 3 4 SiO, 3,218 1,770 A1 2 O 3 3 SiO, 3,254 1,790 A1 2 O 3 2.5 SiO, 3,290 1,810 A1 2 O 3 2 Si0 2 3,326 1,830 A1 2 3 1.5 SiO 2 3,362 1,850 3,398 1,880 3 434 L910 3,470 1,940 No. of Cone. 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 In actual use they are placed in the kiln at a point where they can be watched through a peep-hole (Fig. 35), but at the same time will not receive the direct touch of the flame from the fuel. It is always well to put two or more cones of different .numbers in the kiln, so that warning can be had, not only of the end point of firing but also of the rapidity with which the temperature is rising. In determining the proper cone to use in burning any kind of ware, several cones are put in the kiln, as, for example, numbers .08, 1 and 5. If .08 and 1 are bent over in burning and 5 is not affected the tem- perature of the kiln is between J and 5. The next time numbers 2, 3, and 4 are put in, and 2 and 3 may be fused, but 4 remains unaffected, indicating that the temperature reached the fusing-point of 3. While the temperature of fusion of each cone is given in the pre- ceding table, it must not be understood that these cones are for measur- 152 CLAYS ing temperature, but rather for measuring pyrochemical effects. Thus if certain changes are produced in a clay at the fusing-point of cone 5, the same changes can be reproduced at the fusion-point of this cone, although the actual temperature of fusion may vary somewhat, due to variation in the condition of the kiln atmosphere. As a matter of fact, however, repeated tests with a thermoelectric pyrometer demon- strate that the cones commonly fuse close to the theoretic temperatures. Manufacturers occasionally claim that the cones are unreliable and not satisfactory, forgetting that their misuse may often be the true FIG. 35. Section of kiln showing method of placing Seger cones. reason for irregularities in their behavior. It is unnecessary, perhaps, to state that certain reasonable precautions should be taken in using these test-pieces. The cones are commonly fastened to a brick with a piece of wet clay, and should be set in a vertical position. After being placed in a position where they can be easily seen through a peep- hole, the latter should not be opened widely during the burning, lest a cold draft strike the cones, and a skin form on its surface and inter- fere with its bending. If the heat is raised too rapidly, the cones which contain much iron swell and blister and do not bend over, so that the best results are obtained by the slow softening of the cone under a gradually rising temperature. Aside from this, however, trouble has been experienced with cones Nos. 010 to 3, which may act irregularly PHYSICAL PROPERTIES OF CLAY 153 if exposed for any length of time to sulphurous fumes from the fuel, as in burning in some muffle-kilns, where there is not a free circula- tion of air in the muffle. The sulphuric acid appears to cause a vola- tilization of the boracic acid, and unite with the lime in the exterior of the cone, forming a hard skin of less fusible character than the interior; which melts while the outside is still hard. It has been suggested that the composition of these members of the cone series be changed. 1 One set of cones cannot be used to regulate an entire kiln, but several sets should be placed in different portions of the same. One advantage possessed by a cone over trial-pieces is that the cone can be watched through a small peep-hole, while a larger opening must be made to draw out the trial-pieces. If the cones are heated too rapidly, those con- taining a large percentage of iron are apt to blister. Zimmer 2 has pointed out that with slow firing in a large biscuit- kiln the cones 1-9 reached a melting-point of 25 to 30 C. lower than those placed in a small trial-kiln, whose temperature increased faster, but since it is heat effects and not degrees of temperature that we are measuring, this makes no difference. The cone numbers used in the different branches of the clay-work- ing industry in the United States are approximately as follows: Common brick 012-01 Hard-burned, common brick 1-2 Buff front brick 5-9 Hollow blocks and fireproofing 03- 1 Terra cotta 02- 7 Conduits 7-8 White earthenware 8-9 Fire bricks 5-18 Porcelain 11-13 Red earthenware 010-05 Stoneware 6- 8 Thermoelectric pyrometer. This pyrometer is one of the best instruments for measuring temperatures. It is based on the principle of generating an electric current by the heating of a thermopile or ther- moelectric couple consisting of two wires, one of platinum and the other of an alloy of 90 per cent platinum and 10 per cent rhodium. These two are fastened together at one end, while the two free ends are carried to a galvanometer which measures the intensity of the cur- rent. That portion of the wires which is inserted into the furnace or 1 Trans. Amer. Cer. Soc., Vol. II, p. 60, and III, p. 180. 2 Ibid., Vol. I, p. 23. 154 CLAYS . kiln is placed within two porcelain tubes, one of the latter being smaller and sliding within the other in order to insulate the wires from each other. The larger tube has a closed end to protect the wires from the action of the fire-gases. The shortest tubes put on the market are about 15 inches long, while the longest are 54 inches. To measure the temperature of a furnace or kiln the tube containing the wires is placed in it either before starting the fire, or else during the burning. If the latter method is adopted, the tube must be intro- duced very slowly, to prevent its being cracked by sudden heating. The degrees of temperature are measured by the amount of deflection of the needle of the galvanometer. Thermoelectric pyrometers are useful for measuring the rate at which the temperature of a kiln is rising, or for detecting fluctuations in the same. It is not necessary to place the galvanometer near the kiln, for it can be kept in the office some rods away. This pyrometer is not to be used as a substitute for Seger cones ; but to supplement them The more modern forms have an automatic recording-device. As at present put on the market the thermoelectric pyrometer costs about $180, and the price, delicacy of the instrument, and lack of realiza- tion of its importance have all tended to restrict its use. However, many of the larger clay-working plants are adopting it, as it is better than other forms of pyrometer for general use and probably more accu- rate. It can be used up to 1600 C. (2912 F.). Wedgewood pyrometer. This pyrometer, which has been used from time to time in ceramic establishments, depends on the shrinkage of clay cylinders, whose contraction is supposed to be proportionate to the temperature to which they are exposed. Their behavior is unreliable. Lunette optical pyrometer. This consists of a small telescope con- taining a quartz plate between two Nicol prisms. When looking at a heatod body through it one of the prisms is revolved until the red color changes to yellow, then green, and lastly blue. The angle of rotation necessary to extinguish the red is measured, and the temperature deter- mined by this means. It is only approximate in its recording action and rather unsatisfactory in its work. Classification of clays based on fusibility. 1 The fact that different clays fuse at different temperatures makes it possible to divide them into several different groups, the divisions being based on the degree of refractoriness of the material. Such a grouping, however, is more or less arbitrary, since no sharp natural lines can be drawn between the different groups, and it is to be expected that no grouping pro- 1 N. J. Geol. Surv., Fin. Kept., VI, p. 100. PHYSICAL PROPERTIES OF CLAY 155 posed will meet with universal approval. The following classification was adopted by the author in studying the New Jersey fire-clays: 1. Highly refractory clays, those whose fusing-point is above cone 33. Only the best of the so-called No. 1 fire-clays belong to this class. 2. Refractory clays, those whose fusion-point ranges from cone 31- 33 inclusive. This group includes some of the New Jersey No. 1, as well as some No. 2 fire-clays. 3. Semi-refractory clays, those whose fusion-point lies between cones 27 and 30 inclusive. 4. Clays of low refractoriness, those whose fusion-point lies between cones 20 and 26 inclusive. 5. Non-refractory clays, fusing below cone 20. Indirect methods. There are several indirect methods of deter- mining temperatures, but that of Bischof 1 is perhaps the best known. This consists in increasing the refractoriness of weighed samples by adding to them increasing quantities of an intimate mixture of equal parts of chemically pure silica and alumina, and heating them with a prism of Saarau fire-clay (whose fusing-point is Seger cone 36) to above the melting-point of wrought iron. The amount of the mixture required to tone the clay up to the same refractoriness as the standard indi. cates its quality. It was used by Bischof chiefly for refractory clays- Hofman and Demond 2 tried the method of mixing various samples of fire-clays with varying proportions of calcium carbonate, and cal- cium carbonate and silica, to render them fusible at temperatures below the melting-point of platinum, while common brick-clays were mixed with alumina and silica to decrease their fusibility, the object being to arrive at a standard temperature at which both refractory and fusible clays could be tested. The results obtained at first were very satisfactory, but subsequent ones did not result as was desirep and the method had to be abandoned. More recently, however, this method has been tried by J. L. Newell and G. A. Rockwell with much better results. 3 In these last experi- ments the Seger cone 26 was used as a standard, as it was regarded as forming the line between refractory and non-refractory clays, the non- refractory ones being toned up until they showed the same behavior in the fire as cone 26. The amount of toner added then gave an idea how far the clay stood below the lower limit of refractoriness. The silica used in the experiments was quartz, ground to pass a 1 Dingler's Polyt. Jour., Vol. CXCVI, pp. 438, 525, and CXCVIII, p. 396. 2 Trans. Amer. Inst. Min. Engrs., XXV, p. 3, 1896. 3 Ibid., XXVIII, p. 435, 1899. 156 CLAYS 100-mesh sieve and purified by boiling in nitrohydrochloric acid. It had 99.88 per cent silica. The alumina contained 98.48 A1 2 O 3 . The method followed was to weigh out samples of 1 gram of the clay to be tested and mix them severally with 0.1, 0.2, 0.3, etc., grams of the silica-alumina mixture. The samples were then tested in the Deville furnace. The following table gives the results of the experiments just described, the clays being arranged in the order of their refractoriness, and in each case the amount of flux being given that was required to raise the fusing-point to that of cone 26 of Seger. ANALYSES OF CLAYS AND RESULTS OF TESTS Sample No. 26 l 25 1 3 1 22 ! 241 231 19822 SiO 2 Per cent. 64.10 Per cent. 55.60 Per cent. 57 10 Per cent. 57 45 Per cent. 57 15 Per cent. 49 30 Per cent. 43 94 ALO, 21.79 24.34 21 29 21 06 20 26 24 00 11 17 H 2 O comb 6 05 6.75 6 00 5 90 5 50 9 40 3 90 Total 91.94 86.69 84 39 84 41 82 91 82 70 59 01 Fe,O, . 2.51 6.11 7 31 7 54 7 54 8 40 3 81 CaO 10 43 29 29 90 56 11 64 MgO 58 77 1 53 1 22 1 6? 1 60 4 17 K 2 O 2 62 3 00 3 44 3 27 3 05 3 91 2 90 Na 2 O 03 09 61 39 58 17 71 Total 5 84 10 40 13 18 12 71 13 69 14 64 23 23 Moisture 1 10 2 65 1 30 1 90 2 70 1 20 15 66 3 Grand total 98 88 99 74 98 87 99 02 99 30 98 54 98 OO 4 Stiffening ingredient, % 20 40 60 80 80 100 180 1 N. W. Lord anal. 2 E. Orton, Jr., anal. 3 Includes CO 2 . * Includes P 2 O 5 0.10%. Changes Taking Place in Burning The changes which occur in burning are of two kinds, chemical and physical, the two being more or less closely related; in fact the physical effects are often the results of chemical changes. While the chemical changes are much the same for all clays, still they vary greatly in degree. The temperature at which many of these occur is also fairly constant, but may be influenced somewhat by the composition of the clay and the fire-gases. The changes which occur in burning may be roughly divided into three stages, termed the periods of dehydration, oxidation, and vitri- PHYSICAL PROPERTIES OF CLAY 157 fication, each of which are characterized by certain reactions, but there is no sharp dividing-line between the different ones, the changes of one stage beginning before those of the preceding stage are completed. Dehydration period. In the beginning of burning the last traces of moisture are driven off. This vapor, which is termed water-smoke or steam by the brick-maker, is simply the moisture which has been retained in the pores of the clay. Its expulsion results in a slight loss of weight. The driving out of the moisture is facilitated by raising the heat slowly, and by allowing sufficient draft to pass through the kiln in which the clay is being burned. Raising the temperature too fast expels the steam too quickly and causes a popping of the brick. On the other hand, a stopping or retardation of the draft results in a saturation of the kiln atmosphere with moisture, and its depo- sition on the surface of the ware, producing the effect known as "scumming" or " whitewashing." This is caused in this way: All bituminous coals contain some sulphur, which on burning is given off in the form of sulphurous gas, and is then absorbed by the con- densed moisture on the surface of the ware. The acid solution thus formed attacks certain salts (especially lime) in the clay, forming soluble sulphates, which are left as a white scum on the surface of the ware when the moisture evaporates. Sulphur in a dry atmosphere would cause but little harm. It is therefore desirable to use a fuel for dehy- dration which contains as little water and sulphur as possible. This is often a difficult matter, for most soft coal has much of both, and wood contains water. Coke and charcoal are good, but their use is not always economically practicable. From the point at which the water evaporates, up to 450 C. (842 F.), there is practically no change, unless gypsum is present, and this will lose most of its chemically combined water between 300 C. (572 F.) and 400 C. (762 F.). The amount of loss in this manner is usually small as to be negligible, but at this point the expulsion of the chemi- cally combined water begins and is practically complete by 700 C. (1292 F.), that is, it begins at a very dull red and is completed at a bright-red heat. Before the dehydration of the water is completed, however, other gases begin to pass off, including CO 2 from lime and iron carbonates, sulphur from pyrite, 1 and gases produced by the combustion of carbon- aceous matter in the clay, but all of these may not have passed off after the dehydration of the clay is ended. Moreover the expulsion 1 Pyrite loses only a portion of its sulphur at this temperature, the v balance passing off later. 158 CLAYS of some of them requires the presence of oxygen, so that the periods of dehydration and oxidation overlap. Oxidation period. In the oxidation process, which may begin at a comparatively low temperature, as low as 500 C. (932 F.), and is probably completed by 900 C. (1652 F.), the following changes take place: 1. The oxidation or burning off of the combustible matter. 2. The expulsion of the remaining sulphur from pyrite. 3. The driving off of carbon dioxide. 4. The oxidation of any ferrous iron to the ferric condition. Two things should be borne in mind in this connection: 1. Oxidation may be accomplished without the aid of heat, the process going on slowly when the clay is exposed to the weather: In this case both FeS 2 and FeCOs may be changed to the oxide, and even organic matter may be partly eliminated. 2. The porosity of the clay materially affects the process, a loose, open-textured clay allowing these changes to take place more readily than a close-textured, fine-grained one, which retards the entrance of the oxidizing gases into the mass. Grog is sometimes added to open the grain. From this we can see that the presence of much air mixed with the fuel-gases facilitates the removal of combustible elements in the clay, especially organic matter. Since air carrying oxygen is necessary to help in removing them, it follows that the clay must be sufficiently porous to allow the air to penetrate it. Now if the expulsion of the water in the clay is retarded, thereby keeping the pores of the clay more or less closed up, it may retard the expulsion of other gases, some of which may be retained in the clay, until the rising temperature has. sealed up the pores by vitrification. Thus imprisoned, and subjected to a rising temperature, they may by expansion bloat the ware. As pointed out by Beyer and Williams, 1 it is not definitely known what gases become thus imprisoned, but they may be C0 2 , or S0 2 , and some have suggested that oxygen liberated by the reduction of iron to the ferrous condition may also aid in bloating or blistering the ware. In burning bricks, for example, if the ware is raised to a vitrifying heat before oxidation is complete, the iron in the central part of the mass remains in a ferrous condition, forms a black core, which if the heating continues becomes slaggy. Any imprisoned carbonaceous matter will become finally decomposed, and the expanding gases swell up tha clay in their efforts to escape. 1 la. Geol. Surv., XIV, p. 278, 1904. PHYSICAL PROPERTIES OF CLAY 159 During the temperature interval in which dehydration and oxida- tion occur there are few or no reactions going on between the clay particles, but as the temperature of vitrification is approached chemi- cal union occurs between the different minerals in the clay, and as it- goes on involves an increasing number of elements in the reactions, which become exceedingly complex. The clay, if red-burning, will show a much brighter color at the end of the oxidation period. Vitrification period. In this stage texture plays an important role (see under Fusibility), for in finer-grained clays chemical reactions are more wide-spread and take place more easily than in coarse-grained ones. Increasing density of the clay and increasing homogeneity of the mass produce similar effects. These chemical reactions result in the formation of silicates of ex- ceedingly complex character. The temperature of vitrification is exceedingly variable, being as low as 900 C. (1652 F.) or 1000 C. (1832 F.) in some clays, while in others it may be 1200 C. (2192 F.) or even higher. After the clay is completely vitrified a further rise of temperature causes it to swell, soften still more, and finally run. We may therefore summarize the effects of heating as follows: 1. Loss of volatile substances present, such as water, carbon dioxide, and sulphur trioxide, the volatilization of these leaving the clay more or less porous. 2. Oxidation of ferrous to ferric compounds, if oxygen is present. 3. A shrinkage of the mass, by further heating. 4. Hardening of the clay due to fusion of some, at least, of tn particles. 5. Increasing density with rising temperature, the maximum being reached at the vitrifying point of the clay. 6. Complete softening of the mass. Effects due to variation in the clay. Burned clays may be of many different colors. Although the majority of clays contain sufficient iron oxide to burn red, nevertheless it is not safe to predict, from the color of the raw clay, the shade that it will burn, since some bright red or yellow clays may yield a buff brick. If considerable iron oxide is present, 4 to 5 per cent, the brick usually burns red, unless much lime or alumina is also present. If only 2 to 3 per cent or under, the clay may- burn white or buff. An excess of lime in the clay will, however, counter- act the effect of the iron oxide and yield a buff brick, but a brick owing 160 CLAYS its buff color to this cause will not stand as much fire as one which owes its buff color simply to a low percentage of iron oxide. Where a clay is mottled, as red and white for instance, the colors of the different spots will retain their individuality most plainly after burning, unless the clay is thoroughly mixed. Many clays contain lumps of whitish clay, much tougher than the rest of the mass. These resist disintegration in the tempering-machines, so that after burning they can be plainly seen, as white spots in the red ground of the brick. ANALYSES SHOWING DIFFERENCE BETWEEN RAW AND BURNED CLAY I. II. III. IV. V. VI, VII. Silica (SiO 2 ) Alumina (A1 2 O 3 ) Ferric oxide (Fe 2 O 3 ). . . Lime (CaO) Magnesia (MgO) Potash (K O) 74.03 17.10 .57 .10 22 .'30 .60 1.36 6.15 78.5 21.3 tr. .5 .3 with A1 2 3 none 74.04 15.15 .50 .50 .27 .42 1.12 1.31 6.00 73.94 20.47 1.80 1.08 1.16 .61 .64 .83 49.45 17.11 3.45 12.67 1.77 .13 .21 .70 4.84 7.10 2.00 56.6 20.4 6.2 11.7 1.4 1.5 1.4 with A1 2 3 .5 none none none 56.5 20.2 6.1 11.6 1.8 1.5 1.3 with A1 2 O 3 none none none none 99.1 Soda (Na O) Titanium oxide (TiO 2 ). Water (H 2 O) Carbon dioxide (CO 2 ). . . Sulphur trioxide (SO 3 ). . P errous oxide Total 100.43 101.1 99.31 100 . 53 99.43 99.7 Total fluxes 1.79 2.81 5.27 18.23 I. Fire-clay from six miles southeast of Sulphur Springs, Tex. O. H. Palm, analyst. II. Brick from same. S. H. Worrell, analyst. III. Fire-clay, Athens, Tex. O. H. Palm, analyst. IV. Fire-brick, Athens, Tex. O. H. Palm, analyst. V. Brick shale, Ferris, Tex. O. H. Palm, analyst. VI Brick from same. O. H. Palm, analyst. VII. Hard-burned brick. O. H. Palm, analyst. The normal iron coloration may often be destroyed by the effects of the fire-gases. When these are reducing in their action (i.e., taking a part of the oxygen from the ferric compounds and reducing them to ferrous compounds) the red color may be converted to gray, or even bluish blade, if the reduction is sufficient, so that in some districts the bricks, on account of lack of air in the kilns and carbonaceous matter in the clay, do not burn a very bright red. Moreover, other things being equal, the higher the temperature at which a clay is burned, the deeper will be its color. The surface coloration of a burned brick may often be different from the interior. This is due to several causes. (1) Soluble salts may accumulate on the surface, sometimes causing a white coating PHYSICAL PROPERTIES OF CLAY 161 because they have been drawn out by the evaporation of the water during the drying on the brick. 1 (2) The deposition of foreign sub- stances by the fire-gases may cause a colored glaze. This is especially seen on the ends of arch-brick, and on the bag walls of a down-draft kiln, where the particles of ash carried up from the fires stick to the surface of the hot brick and cause a fluxing action. (3) If the clay contains much lime carbonate, and there is much sulphur in the coal, the latter may unite with the lime, forming sulphate of lime, and thereby prevent the combination of the lime and iron. In this case the center of the brick, not being thus affected by the gases, may show a buff color, whereas the outside has another tint. Loss of volatile products in burning. The analyses (see table on p. 160) giving the composition of several clays, and the bricks made from them, are interesting in showing the loss of the volatile products in burning. Color Color of unburned clay. An unburned clay owes its color commonly to some iron compound or carbonaceous matter, more rarely manganese. A clay free from any of these is white. Carbonaceous matter will color a clay blue, gray, black, or even purplish, depending on the quantity present, 3 per cent being prob- ably sufficient to produce a deep black; clays in actual use having some- times as much as 10 per cent. Iron oxide colors a clay yellow, brown, or red, depending on the form of oxide present. The greenish color may be due to the silicate of iron, and in some clay marls of the Cretaceous it is caused by the mineral glauconite. The iron coloration is, however, often concealed by the black coloration due to carbonaceous matter, and it is sometimes more or less difficult to make even an approximate estimate of the iron content in a clay from its color. Thus, for example, two clays have been noted by the writer 2 which were nearly of the same color and had respectively 3.12 and 12.40 per cent of ferric oxide. There is often a marked difference in color between the wet and the dry clay, in fact such a difference at times as to make one doubt that they are the same material. The dry clay is usually of a lighter tint. Color of burned clay. The color of a raw or unburned clay is not always an indication of the color it will be when burned. Red clays 1 See " Soluble Salts in Clays," pp. 90 et seq. 2 N. J. Geol. Surv., Final Report, Vol. VI, p. 112, 1C04. 162 CLAYS usually burn red; deep-yellow clays may burn buff or red; chocolate ones commonly burn red or reddish brown; white clays burn white or yellowish white; and gray or black ones may burn red, buff, or white. Green ones usually change to red on firing. Calcareous clays are often either red, yellow, or gray, and may burn red at first, but turn cream, yellow, or buff as vitrification is approached, and show a greenish yel- low at viscosity. An excess of alumina seems to exert a bleaching effect similar to that of lime. The vitrification of ferruginous clays yields browns, greens, and blacks, due to the formation of ferrous silicates. 1 Seger states that the colors which a burned clay may show depend on: 1. The quantity of iron oxide contained in the clay. 2. The other constituents of the clay accompanying the iron (see Alumina and Lime). 3. The composition of the fire-gases during the burning. 4. The degree of vitrification. 5. The temperature at which the clay is burned. The same author has attempted to classify clays according to their color-burning qualities as follows: 2 Group. Character of clay. Color after burning. 1 2 3 4 High in alumina and low in iron High in alumina and moderate iron contents Low in alumina and high in iron Low in alumina and high in iron and lime White, or nearly so Pale yellow to pale buff Red Cream or yellow Slaking When a lump of raw clay or shale is immersed under water' it falls to pieces or slakes, the process ceasing only when the clay has broken down to a fine powdery mass. The time required for this varies from a few minutes in the case of soft porous clays to several weeks for tough shales, and some may be incompletely disintegrated even after that. The slaking property is one of some practical importance, as easily slaking clays temper more readily, or if the material is to be washed, it disintegrates more rapidly in the log-washer. 1 la. Geol. Surv., Vol. XIV, p. 59, 1904. 2 Seger's Collected Writings, Vol. I, p. 109. PHYSICAL PROPERTIES OF CLAY 163 Permeability An interesting series of experiments has been made by W. Spring, 1 who finds that clay when under pressure and confined so that it cannot expand on wetting is nearly impervious to water; under such condi- tions it will only soak up enough water to fill the pores. The percent- age of water thus absorbed may range from as low as 3.37 per cent in glass-pot clays to 24.56 per cent in some loams. Wet clay under pres- sure will part with its water even though the mass be entirely sur- rounded by that liquid. Adsorption By this term is meant the power which a clay has of removing solid substances from solutions with which it is in contact. More than fifty years ago T. Way 2 noticed that clays, and soils with a clay base, possessed extraordinary powers for absorbing water, but that in addition the clay substance exhibited greater facility for absorbing the bases contained in certain salts which were dissolved, in water. This action was also selective, certain bases and substances being held so that they could not be washed out again. Bourry 3 states that kaolins do not absorb more than 2 per cent of calcium carbonate from a solution, while plastic clays can absorb from 10 to 20 per cent of it. More recently Dr. Hirsch 4 has made a number of experiments to test the amount of dissolved salts which a clay can absorb when stirred up in a solution. He found that clays and kaolins absorb some of the dissolved salt, because after settling the superna- tant liquid had a lower concentration than it did before; but sand and burned clay do not show this power, while feldspar and marble possess it to some extent. The amount of salt thus absorbed was independent of the time, and the removal of the salt ceased with the settling of the clay. It is, however, dependent on the kind of clay and kind of salt and the degree of concentration. Thus barium, lead, and aluminum compounds were removed in considerable quantities, while strontium, magnesium, and calcium salts were absorbed to a less degree. The 1 Ann. de la Soc. geol. de Belg., XXVIII, 1901. 2 Royal Ag. Soc. Jour., XI, 1880. Quoted by Cushman, Trans. Amer. Cer. Soc., VI, p. 7, 1904. 3 Treatise on Ceramic Industries, p. 54, 1901. 4 Thonindustrie-Zeitung, No. 26, 1904. 164 CLAYS acid of the salt seems to influence the result appreciably. Chlorides, nitrates, and acetates are absorbed more than sulphates, but alkali salts, except the carbonates, are not. The higher the concentration of the solution the greater the quantity of salt absorbed, although in a weak solution all of the salt may be carried down. The conditions are more complicated in the presence of several salts; thus the absorp- tion of barium chloride is decreased by the presence of alkali salts, acids and bases, and entirely prevented by aluminum chloride. Sul- phates are absorbed in the presence of caustic alkalies and acids, while the alkali chlorides seem to be lacking in effect. Experiments by the author l have also shown that some tannins, as gallo-tannic acid, are absorbed by clay, a clear filtrate from a mix- ture of gallo-tannic acid and clay giving no reaction with ferric chloride. In this connection it is of interest to refer to the observations of Ivohler, 2 who finds that clays, among other substances, have the power -of abstracting metallic oxides from solutions which are filtered through .them. E. C. Sullivan, 3 in experimenting along these lines, found that when a solution containing 100 cc. of water with 252 grains of copper as the sulphate was shaken up with powdered orthoclase, albite, shale, or microcline, it was found that there was a remarkable interchange of bases instead of absorption. The copper entered the silicates, and an exact molecular equivalent of the K 2 O, Na 2 O, CaO, MgO, or MnO went into solution. The feldspar proved much more efficient than kaolin, and removed from 60 to 100 per cent of the copper from the liquid. 1 Trans. Amer. Ceram. Soc., VI, p. 44, 1906. 2 Adsorptionsprozesse als Faktoren der Lagerstattenbildung und Lithogenesis Zeitschr. fur prakt. Geologie, Feb. 1903, p. 49. 3 The Chemistry of Ore Deposition, Jour. Amer. Chem. Soc., XX VII, p. 976 and Economic Geology, I, p. 67, 1905. CHAPTER IV KINDS OF CLAYS IN this chapter it is proposed to give briefly the characters of the clays employed for different purposes, beginning with the highest grades. Kaolins This term as commonly used, and it seems to the author the cor- rect way to use it, refers to those white-burning clays of residual char- acter, 1 which are composed mostly of silica, alumina, and chemically combined water, and have a very low percentage of fluxing impurities, especially iron. In this country they have been formed chiefly by the weathering of pegmatite veins, and in rarer instances from feld- spathic quartzites, 2 limestone, 3 and talcose schists. 4 There are some other occurrences, as those of Edwards County, Texas, and the indi- anaite of Indiana, 5 whose exact origin does not seem satisfactorily proven. In Europe they have been formed by the alteration (in most cases probably by weathering) of other rock types, especially granite and quartz-porphyry. The mode of origin of kaolin, and changes accompanying same, have been discussed on another page (p. 8), and it need simply be repeated here that kaolins formed by weathering will grade downward into the parent rock, while the depth of those caused by fluoric action will depend on the depth of the parent rock and the extent of the path through it of the kaolinizing vapors. 1 The white-burning sedimentary clays found in the coastal plain area of the Southern Atlantic States are at times termed kaolins, but it would seem wiser, per- haps, to term these plastic kaolins to distinguish them from the residual ones. 2 H. Ries, Private publication of the Kaolin Co., Cornwall, Conn. 3 Wheeler, Mo. Geol. Surv., XI, p. 162, 1896. 4 Hopkins, Ann. Kept. Pa. State College, 1898-99. B Blatchley, Ind. Dept. Geol. and Nat. Res., XXIX, p. 55, 1904. 165 166 CLAYS Most kaolins as mined are rather siliceous, but in their washed con- dition approach closely to the composition of kaolinite, from which it has been sometimes argued that kaolins are composed chiefly of kaolinite MAP SHOWING DISTRIBUTION OF KAOLIN AND BALL-CLAY DEPOSITS IN EASTERN UNITED STATES LEGEND Kaolin Deposits *Ball Clay Deposits FIG. 36. Map showing kaolin and ball-clay deposits of United States, east of the Mississippi River. (After H. Ries, U. S. Geol. Surv. Prof. Pap. 11, p. 284, 1903.) and quartz. The author himself held this view for some time, but now feels that it is not safe to make such a broad statement. The incorrectness of this theory becomes apparent if we examine any series of kaolin analyses, from which it can be seen that the alumina- silica ratio is often higher than that required for kaolinite, and this KINDS OF CLAYS 167 seems best accounted for on the supposition that some of- the other hydrous aluminum silicates, such as pholerite or halloysite, are present. Again, a washed kaolin might have as much as 20 per cent white mica, and yet on analysis show a composition approaching rather closely to that of kaolinite. All of these minerals kaolinite, pholerite, halloysite, and muscovite are decomposed by treatment with hot sulphuric acid, and therefore reported in the rational analysis as clay substance. This is unfortunate, because mica is not refractory and should not therefore be grouped with the other three. There is also the possibility that in some highly aluminous kaolins some aluminum hydroxide, such as bauxite orgibbsite, might be present. Chemical composition. The analyses shown on page 168 of both native and foreign kaolins, will give some idea of their composition. All of these are washed samples with the exception of No. I. A com- parison of analyses I and II will therefore show the beneficial effects of washing. It will be noticed that all of these analyses show a small percentage of alkalies, due probably to the presence of some undecomposed feldspar or muscovite. Physical tests. When tested physically they all show a low air- shrinkage, low tensile strength, are white-burning, and usually highly refractory. The following tests bring out these points well: 1. Kaolin from Harris Clay Company, Webster, N. C. Works up with 42 per cent of water to a lean mass. Air-shrinkage, 6 per cent; fire-shrinkage at cone 9, 4 per cent; average tensile strength, 22 pounds per square inch; fuses about cone 33. 1 2. Kaolin from Glen Allen, Mo. Requires 23.2 per cent of water to work it up to a lean paste whose air-shrinkage is 4 per cent and fire- shrinkage, at 2500 F., 8.4 per cent; average tensile strength, 12 pounds per square inch; incipient fusion, 2200 F.; vitrification at 2500 F. 2 3. Kaolin, Oak Level, Henry County, Va. Water required, 48.4 per cent; plasticity and tensile strength, low; air-shrinkage, 1.6 per cent; fire-shrinkage, cone 9, 8 per cent, with absorption 36.08 per cent; fusion-point above cone, 27. Distribution. The known workable deposits of kaolin found in the United States are all located east of the Mississippi River, with the exception of those found in Missouri, Utah, and Texas. The last- named two are not worked. The distribution of those east of the 1 N. C. Geol. Surv., Bull. 13, p. 59, 1897. 2 Mo. Geol. Surv., XI, p. 578. 168 CLAYS Mississippi River is shown in Fig. 36, and the Missouri deposits in Fig. 56. Reference is made to their occurrence undei the state descrip- tions in Chapters VI and VII. ANALYSES OF KAOLINS I. II. III. IV. V. VI. Silica (SiO 2 ) 62.40 45.78 46.28 73.80 46.50 72.30 Alumina (A1 2 O 3 ) 26.51 36.46 36.25 17.30 37.40 18.94 Ferric oxide (Fe Oo) 1 14 28 1 644 35 80 40 Ferrous oxide (FeO) 1 08 Lime (CaO) 57 50 192 tr. 68 Magnesia (MgO) . 01 .04 .321 1 18 39 Potash (K 2 O) . 1 f 1 69 2 49 \ , Soda (Na 2 O) . . J .98 .25 1 .85 .20 jl.l .42 Titanium oxide (TiO 2 ) Water (H 2 O) 8.80 13.40 13.535 4.69 12.49 7.04 Moisture .25 2.05 Total 100.66 99.84 100.763 100.01 98.29 100.17 VII. VIII. IX. X. XI. Silica (SiO ) 45 44 46 38 48 26 46 87 47 71 Alumina (Al O 3 ) 40 30 39 76 37 64 38 00 36 78 Ferric oxide (Fe O 3 ) 54 79 46 89 Ferrous oxide (FeO) Lime (CaO) tr. .44 06 tr Magnesia (MgO) . tr. 05 tr. .35 Potash (K 2 O) f tr. 1.80 Soda (Na 2 O) 1 .38 .20 j 1.56 1.22 2.58 Titanium oxide (TiO 2 ) .28 Water (H 2 O) 13 9 10.26 12.02 12.70 13.03 Moisture Total. 100 56 99.96 100.00 100.03 100.10 I. Webster, N. C. Crude kaolin. N. C. Geol. Surv., Bull. 13, p. 62, 1897. II. Webster, N. C. Washed kaolin. Ibid. III. Brandywine Summit, Pa. Hopkins, Pa. State Coll., App. Kept., 1898-99, p. 36. IV. Upper Mill, Pa. T. C. Hopkins, Ann. Kept., Pa. State Coll., 1899-1900, p. 11. V. West Cornwall, Conn. H. Ries, Anal. VI. Glen Allen, Mo. Mo. Geol. Surv., XI, p. 562, 1896. VII. Leaky, Edwards County, Texas. O. H. Palm, Anal. VIII. Oak Level, Henry County, Va. Analyzed by Va. Geol. Surv. IX. Cornwall, Eng. . 1 X. Zettlitz, Bohemia [ U. S. Geol. Surv., Prof. Pap. 11, p. 39, 1903. XI. Co ussac- Bonne val, France J Kaolins after washing are used in the manufacture of white ware, porcelain, floor and wall tiles, paper manufacture, and as an ingre- dient of slips and glazes. Ball-clay This includes those white-burning plastic clays of sedimentary character which are extensively used as a necessary .ingredient of white- ware mixtures in order to give the body sufficient plasticity and bond- KINDS OF CLAYS 169 ing power. They must therefore contain little or no iron oxide, and possess good plasticity and tensile strength. Refractoriness is desir- able, but those imported vitrify at cone 8, while the native ones require a much higher heat for vitrification. Some ball-clays as those of Florida require washing before shipment to market. Chemical composition. The following table gives the composition of several American ball-clays, as well as that of an English ball-clay: ANALYSES OF BALL-CLAYS I. II. III. IV. V. Silica (SiO 2 ) . 46 11 45 57 56 40 45 97 48 99 Alumina (A1 2 O 3 ) 39 55 38 87 30 00 36 35 32 11 Ferric oxide (Fe 2 O 3 ). . 35 1 14 1 08 Ferrous oxide (FeO). . 2 34 Lime (CaO) tr. 40 1 14 43 Magnesia (MgO) 13 11 tr. 1 09 22 Potash (K 2 O) 16 3 261 f 3 31 Soda (Na 2 O) 00 2 01 J 1.84 Titanium oxide (TiO 2 ) i 26 1 30 Sulphur trioxide (SO 3 ) 07 Water (H,O) 13 78 \ / 7 93 12 36 9 63 Moisture ( 14.10 Total 101 19 101 25 100 00 99 83 97 03 I. Edgar, Fla. U. S. Geol. Surv., Prof. Pap. 11, p. 39. II. Woodbridge, N. J. N. J. Geol. Surv., Fin. Kept. VI, p. 443. III. Mayfield, Ky. U. S. Geol. Surv., Prof. Pap. 11, p. 39. IV. Regina, Mo. Mo. Geol. Surv., XI, p. 566, 1896. V. "Poole" clay, Wareham, Eng. Physical characters. The physical properties of some of the well- known ball-clays used in this country are as follows: Edgar, Fla. Very plastic; average tensile strength, 150 pounds per square inch; total shrinkage at cone 9, 15 per cent. Woodbridge, N. J. Water required, 33 per cent; plasticity, fair; air-shrinkage, 3.4 per cent; average tensile strength, 33 pounds per square inch. At cone 10, fire-shrinkage 16.6 per cent and absorption 0.22 per cent; fusion-point, cone 34. Distribution. The number of known localities in the United States at which ball-clays occur is small, and are shown in Figs. 36 and 55. They are obtained from the Tertiary (Florida, Kentucky, Tennessee) and Cretaceous (New Jersey) formations, and in residual deposits derived from Palaeozoic limestones (Missouri). 170 CLAYS Fire-clays The term fire-clay, properly speaking, refers to those clays capable of withstanding a high degreee of heat, but it is unfortunately most loosely used by American clay-workers, and many plastic materials which have absolutely no claim to refractoriness are included under this head. It is to be greatly regretted that no standard of refractori- ness has been adopted in the United States, nor for that matter in Europe, although the use of the term is probably less abused there than here. In the author's opinion no clay should be classed as a fire-clay unless its fusion-point is higher than that of cone 27. Aside from refractoriness, which is the most important property of a fire-clay and the one possessed by all true ones, they vary widely, showing great differences in plasticity, density, shrinkage, tensile strength, and color. Since the resistance of a fire-clay to heat is governed pri- marily by ire chemical composition and secondarily by its texture, it may be well to consider first the former property. Chemical composition Fire-clays contain practically all the sub- stances usually determined by the ultimate analysis (p. 58), but in every good fire-clay the total percentage of certain fluxing impurities, such as ferric oxide, lime, magnesia, and alkalies, is small. This is necessarily the case, since, if the fluxing impurities were present in large quan- tities, the clay would fuse at comparatively low temperatures and could not be classed as refractory. Effect of silica. It is found, however, that clays running low in fluxes but high in silica may also show poor refractoriness. If we compare two fire-clays of low-flux contents, but high silica in one case and low silica in the other, it is found that, other things being equal, the high-silica clay is less refractory than the other. This indicates that a high percentage of silica, as well as a high percentage of the fluxes mentioned above, diminishes the refractoriness of the clay. We might, therefore, term the iron oxide, lime, magnesia, and alkalies low- temperature fluxes and the silica a high-temperature flux. In any fire-clay some of the silica is combined chemically with the alumina and water, forming a hydrous aluminum silicate which for convenience of discussion we assume is kaolinite, 1 while the balance is probably there in the form of quartz. 2 If kaolinite alone is heated, 1 It probably is in most fire-clays. 2 There cannot be many silicate minerals, such as feldspar, mica, etc., in a fire- clay, otherwise the percentage of alkalies, magnesia, lime, and iron oxide would be higher than it usually is, so that the balance of the silica must be quartz. PLATE VII Impure clay Coal Fire-clay p IG i Section showing fire-clay underlying coal-seam. The upper clay above coal is of impure character. (Photo loaned by Robinson Clay-product Com- pany.) FIG. 2. Fire-clay underlying Lower Mercer limestone, Union Furnace, O. (Photo by B. S. Fisher.) 171 KINDS OF CLAYS 173 its refractoriness is found to be high, for its fusion-point is the same as cone 36 of the Seger series, and the refractoriness of quartz or silica alone is nearly as high, but if these two minerals are mixed together in varying proportions, then the fusion-point of the mixtures will in every case be lower than that of either silica or kaolinite alone. This fact was pointed out some years ago by Seger, 1 who made up a series of mixtures of alumina and silica, and kaolin and silica. In the former series of mixtures the quantity of alumina in each case was the same, but the amount of silica was increased. Starting with 1 part of alumina to 1 of silica by volume (91.5 of alumina to 8.5 of silica by weight 2 ), a mixture, the fusion-point of which was the same as that of cone 37, he found that the refractoriness decreased until a mixture of 1 part alumina to 17 parts of silica (10 alumina to 90 silica by weight) was reached. The fusing-point of this mixture was cone 29. A fur- ther increase in the amount of silica caused the refractoriness to rise steadily. This shows that silica added to alumina in certain propor- tions acts as a flux at high temperatures. If now silica is mixed with kaolinite in the same manner, a similar lowering of the refractoriness of the body takes place down to a cer- tain point beyond which the fusion-point again rises. These experi- ments of Seger are shown graphically in Fig. 33, in which the horizontal lines represent the different cone numbers from 26 to 38 inclusive. The divisions on the lower line represent percentages of alumina or kaolin measured above the line, 100 per cent being at the left end, and per- centages of silica measured below the line, 100 per cent being at the right end. The solid curve represents the mixtures of silica and alumina, while the dotted curve represents mixtures of kaolin and silica. An inspection of these curves shows quite clearly how an increase in the percentage of silica up to a certain point causes a dropping of the fusion- point, but that a further increase in the silica contents raises it again, although not quite as high as it originally was. It will be seen from a comparison of these two curves that the kao- linite-silica mixtures have lower refractoriness than the pure silica-alu- mina mixtures. This effect of silica has not always been understood by fire-brick manufacturers, many believing that sand added to the refrac- toriness of a clay in burning. While this is indeed true in the case of 1 bc-^or, Gesammelte Schriften, p. 434, 1896. Amer. Ceram. Soc., Translation, I, p. 545. 2 What is meant here is parts by volume which would not be the same as parts by weight, because the two substances have different specific weights, hence 1 alu- mina to 1 silica per volume would be 91.5 per cent alumina to 8.5 silica by weight. 174 CLAYS brick-clays, it is to be remembered that common brick is burned at at a much lower temperature than that at which alumina and silica unite. Recent tests made on a series of fire-clays from New Jersey 1 agreed with Seger's results in a general way but not exactly, the plotted fusion- points forming a curve on which corresponding points were somewhat lower than those on Seger's. In order to test his experiments a series of mixtures of a white- burning clay (having practically the composition of kaolinite) and finely ground quartz were made up and their fusion-points tested in. the Deville furnace. These results were plotted in a curve (Fig. 37) > Cone No. 30 35 34 33 32 31 30 29 28 27 26 25 21 Kaolin 100 1 *^1 IX Kaolin a id Silica X X X X \ V XII XVIII 9 \ I \ \ X XV I ^^ XIV 1 f 8 8 ) 7 ) 6 9 5 4 3 2 ) 10 10 20 30 10 50 GO 70 80 90 10( FIG. 37. Diagram showing effects of silica on fusibility of kaolin. (After Ries, N. J. Geol. Surv., Fin. Kept. VI, p. 313, 1904.) which in its general form agrees with that of Seger, but shows lower cones of fusion for corresponding mixtures. The results obtained with New Jersey clays seem to agree more closely with this curve than they did with Seger's. (Fig. 33.) Applying the facts obtained from these experiments to a study of fire-clays it would seem that, other things being equal, those fire- clays will be the most refractory which contain the lowest percentage of fluxing impurities, such as iron, lime, magnesia, and alkalies, and the smallest quantity of sand or silica not in combination with the alumina of kaolinite, or some other hydrous aluminum silicate. 1 N. J. Geol. Surv., Fin. Kept., VI, p. 314, 1904. KINDS OF CLAYS 175 The following analyses and fusion-tests made on a series of New Jersey clays are of interest as showing the relation of the composition to the fusing-point. ANALYSES OF SOME NEW JERSEY FIRE-CLAYS 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. g 3 . M ox 1 1 fusion. O Jo w^ 1 'S'M 9i .so ^o J 55 8 i5 '# Is S>S as Is | 3 I 3 1 a a -3 02 1 6 I. 50.60 34. 3i 0.78 tr. tr. tr. 1.62 12.90 87.20 10.65 0.78 34 + II. 51.56 33.13 0.78 0.12 1.91 12.50 83.94 13.25 0.90 34 + III. 68.67 21.46 0.78 1.35 1.34 6.40 52.82 43.71 2.13 27 with IV. 67.26 23.36 1.63 0.25 .... 0.65 Al ? 3 6.94 57.47 40.09 2.53 27 with V. 45.76 39.05 tr. 0.95 0.04 A1 2 3 14.46 98.93 0.24 0.9 34 + VT. 69.78 19.86 0.62 1.24 1.96 6.54 49.50 46.68 i.se 30 with VII. 40.64 41. K 3.27 0.65 Al,0 8 14.74 96.57 3.92 29 I. No. 1 fire-clay, M. D. Valentine & Bro. (Loc. 14), Woodbridge. II. No. 1 fire-clay, Anness & Potter (Loc. 6), Woodbridge. III. Top sandy clay, Anness & Potter (Loc. 6), Woodbridge. IV. Fire-mortar clay, Maurer & Son (Loc. 24), Woodbridge., V. Ware clay, W. H. Cutter (Loc. 29), Woodbridge. VI. No. 1 sandy clay, McHose Bros. (Loc. 45), Florida Grove. VII. No. 1 blue fire-clay, J. R. Grossman (Loc. 65), Burt Creek. * Exclusive of titanium. This probably stands intermediate between silica and the other fluxes in its fluxing power, but nearest to silica. "In this table the second to ninth columns inclusive represent the determinations made in the ultimate analysis. A partial analysis only of some of the samples was available, and in these cases the difference between the sum of the substances determined and 100 was taken as representing the sum of the lime, magnesia, and alkalies. The clay base given in the tenth column was obtained by considering the alumina to be contained in kaolinite, figuring the amount of silica necessary to unite with it, and adding the combined water to it; the total of the three then represents the clay base. 1 The difference between the silica neces- sary to combine with the alumina and form the clay base and the total silica was considered as representing the free silica. The twelfth column 1 The amount of water present as an ingredient of limonite is so small in these cases that it can be neglected. 176 CLAYS represents the sum of the iron oxide, lime, magnesia, and alkalies. The last column gives the cone of fusion. "Examining the percentages given we see that in the first analysis the percentage of clay base is 87.20 per cent and silica 10.65 per cent, while the total fluxes are 0.78 per cent. Comparing these percentages with the curve (Fig. 37), we see that a mixture of 90 per cent kaolinite and 10 per cent silica (IX), which is close to the composition of clay No. I of the table, melted at cone 34, so that the 0.78 per cent fluxes probably exert little influence. " Again, in the third analysis, the percentage of clay base or kaolinite is 52.82 per cent and that of the silica 43.71 per cent; from the curve in Fig. 37 such a mixture would fuse at approximately cone 29. But we have here in addition to the silica 2.13 per cent total fluxes, so that we should expect the clay to fuse at a still lower cone. By actual test the fusion-point was found to be cone 27, so that evidently both the free silica and fluxes present force down the fusing-point and the facts cor- respond to the theory. "No. IV of the table of analyses behaves similarly to No. Ill, and No. V has a high fusing-point, on account of its high percentage of clay substance and low amount of fluxes. "In the case of No. VI we find that, leaving the fluxes out of considera- tion, a mixture of kaolinite and silica in the proportions shown in this clay should fuse at about cone 30, and the amount of lime, magnesia, alkalies, and titanium oxide given in the analysis should lower the fusion- point to at least cone 29 or even 28. As it is, the fusion-point as deter- mined is cone 30, and there is an apparent disagreement between theory and the facts. This is probably explainable by the fact that the clay is a very sandy one, and, therefore, since much of the silica is in the form of coarse grains, it is not able to enter into active chemical union with the clay base. In any event this sample illustrates the fact that the fusion-point of a clay cannot be determined solely from a chemical analysis. No. VII owes its low refractoriness to a high content of total fluxes and not to high silica contents. This clay has a silica-alumina ratio of 0.97, and it would therefore appear as if some other hydrous aluminum silicate than kaolinite were present (see Pholerite, p. 50). Were it not for nearly 4 per cent of fluxes, its refractoriness would be quite high. These few samples, will, however, serve to show the practica application of the facts mentioned above." Effect of titanium. It will be noticed that the percentage of titanium oxide has been determined separately in several of the above analyses, and from the quantity present it is believed to exert some influence. As KINDS OF CLAYS 177 has been mentioned under Titanium (p. 84), the presence of 2 per cent of titanium seems to lower the refractoriness a whole cone number, while 0.5 per cent lowered it half a cone when it was mixed with kaolin alone. Physical properties. As mentioned above, the term fire-clay does not signify the presence of any other character than refractoriness, and fire-clays may therefore vary widely in their plasticity, shrinkage, texture, color, tensile strength, and other physical properties, all of which affect the behavior of the clay during the process of manufacture, but none of which can be used as a sure guide in determining its probable refractori- ness. Color may be an aid under certain conditions, since pure white clays and light yellowish clays are often at least semi-refractory and sometimes highly refractory. Some fire-clays are tinged a deep yellow or yellowish red, as though they contained considerable iron oxide, and yet they have excellent heat-resisting power. If the clay is black or bluish black, there is no means of telling from mere inspection what its heat-resisting qualities are, for under these conditions both a clay with very little iron oxide and one with much might outwardly appear the same. Plasticity has little or no direct relation to refractoriness, although Seger has pointed out that of two clays of unequal refractoriness the one of lower fire-resisting qualities may withstand the action of molten materials better if it is of high plasticity, as this makes it burn to a dense body at a comparatively low temperature. The result of this is that the pores are closed and the clay resists the corrosive action of a fused mass better than the more refractory clay, which does not burn dense at as low a temperature as the first one, and which, therefore, permits a molten mass to enter the pore-spaces between its grains. Fire-clays are of variable tensile strength. Some of the highest grades show low tensile strength and often require a more plastic material to raise it, such an addition being sometimes necessarily done at a slight sacrifice of refractoriness. Analyses of fire-clays. The analyses shown on page 178 give the composition of a number of fire-clays from various localities in the United States, and for additional ones reference should be made to the State descriptions. Occurrence and distribution. Fire-clays may be of either residual or sedimentary origin, and of the two the latter are by far the most important commercially. This class is further subdivisible into plastic fire-clays and flint-clays. The former are plastic when wet, the latter are hard and flint-like, with a smooth, shell-like fracture and dense texture. They develop but little plasticity, even when ground fine, 178 CLAYS ANALYSES OF FIRE-CLAYS I. II. III. IV. V. VI. Silica (SiO 2 ) 74.25 17.25 1.19 63.00 23.57 .46 1 87 52.52 31.84 .67 59.92 27.56 1.03 62.89 21.49 51 . 92 31.64 Alumina (A1 2 O 3 ) Ferric oxide (Fe 2 O 3 ) Ferrous oxide (FeO) 1.81 .38 .56 2.52 1.13 .03 .44 .40 Lime (CaO) .40 tr. .52 .44 .89 (2.401 I -29J .50 .19 .59 tr. tr. .67 Potash (K O) \ Soda (Na 2 O) J Sulphur trioxide (SO 3 ) Titanic acid (TiO ) . 1.10 6.45 1.68 11.68 "9". 70' 1.82 7.58 1 16 1.16 13.49 Water (H O) 6.30 Moisture Total 99.91 100.47 99.67 98.88 100.21 100.21 VII. VIII. IX. X. XI. XII. Silica (SiO 2 ) 51.56 33.13 .78 46.56 37.47 tr. 59.36 23.26 3.06 61.44 26.18 .30 36 73.00 15.79 .63 50 . 35 33.64 .75 Alumina (A1 2 O 3 ) Ferric oxide (Fe O 3 ) Ferrous oxide (FeO) Lime (CaO) tr. tr. tr. tr. .112 tr. .281 .28] .65 .42 .63 .35 .12 1.29 1.53 .10 .16 tr. .49 .09 .80 11.75 2.13 Magnesia (MsrO) Potash (K O) / Soda (Na O) 1 .02 Sulphur trioxide (SO 3 ) Titanic acid (TiO 2 ) 1.91 1.01 / 10. 20 I 2.74 1.39 9.07 .77 .43 5.76 Water (H 2 O). \ 12.50 13.03 Moisture / Total 99.88 97.732 101.68 99.65 98.69 100.00 I. Bibbville, Ala. Ala. Geol. Surv., Bull. 6, p. 152, 1900. II. Mecca, Parke County, Ind. Ind. Dept. Geol. and Nat. Res., 29th Ann. Kept., p. 507, 1905. III. Mineral Point, O. (Flint-clay). Mo. Geol. Surv., XI, p. 591, 1896. IV. Saline ville, O. (Flint-clay). Ohio Geol. Surv., VII, p. 221, 1893. V. Lower Kittanning clay, New Brighton, Pa., 2d Pa. Geol. Surv., MM, p. 262. VI. Bolivar flint fire-clay, Salina, Pa. Ibid., p. 259. VII. Woodbridge, N. J. No. 1 fire-clay, N. J. Geol. Surv., VI, p. 441, 1904. VIII. Boone Furnace, Ky. Coal measures, U. S. Geol. Surv., Prof. Pap. 11, p. 119. IX. St. Louis, Mo. Mo. Geol. Surv., XI, p. 571, 1896. X. Piedmont, W. Va. Mount Savage clay, W. Va. Geol. Surv., III. XI. Athens, Tex. O. H. Palm, analyst. XII. Golden, Colo. U. S. Geol. Surv.. Mon. XXVII, p. 390 but are usually highly refractory. Flint-clays are found at a number of points in the Carboniferous of Pennsylvania, Ohio, Maryland, Kentucky,, and West Virginia, where they occur often underlying coal-seams and in the same bed with the plastic clay, the two showing no regularity of arrangement, and often differing but little if at all in chemical composi- tion. Their peculiar character has been a puzzling problem to geologists,, but it seems probable that they may have been formed by a solution and reprecipitation of the clay by percolating water subsequent to its forma- KINDS OF CLAYS 179 tion. A second type of flint-clay is that found occupying basins in. Palaeozoic limestones in Missouri (which see). In many States 1 fire-clays are often found underlying coal-beds, and on this account it has been suggested that their alkalies and other fluxing; impurities have been abstracted by the roots of plants which grew in. the swamps in which these clays were deposited, while the decay of these plants later gave rise to the coal-bed overlying the clay. This theory seems rather improbable, as in some States, such as Michigan and Alabama, the clays and shales underlying the coals always contain sufficient impurities to render them non-refractory. Furthermore, tha extensive beds of refractory clay, found in the Tertiary-Cretaceous: formations of the Atlantic and Gulf coastal plains, are very rarely- associated with coal-beds. We must, therefore, assume that these clays were either derived from rocks running low in fusible impurities, or else that these were removed by solution during the transportation and deposition of the clay particles.. In the United States fire-clays are widely distributed, both geologically and geographically. The most important occurrences are in the Car- boniferous of Ohio, Pennsylvania, Kentucky, Indiana, Illinois, Maryland, West Virginia, and Missouri. Many other deposits are, however, found in the Cretaceous of New Jersey, Maryland, Georgia, South Carolina, Ala- bama, Texas, Iowa, Colorado, South Dakota, etc., and in the Tertiary of New Jersey, Georgia, South Carolina, Alabama, Texas, Arkansas, and California. In Pennsylvania, Maryland, Alabama, and North Carolina some pre- Devonian ones occur, but they are of limited extent. Uses. The main use of fire-clays is for the manufacture of the various- shapes of fire-brick, but in addition they are used wholly or in part in the manufacture of gas- and zinc-retorts, locomotive and furnace linings, crucibles, floor-tiles, terra-cotta, conduits, pressed and paving bricks, etc. Glass-pot clays form a special grade used in the manufacture of glass pots and blocks for glass-tank furnaces. These require a clay which is not only refractory but burns dense at a moderately low temperature, so that it will resist the fluxing action of the molten glass. It must possess good bonding power and burn without warping. Great care is necessary in the selection of the clay and the manufacture of the pot. 2 1 Ohio, Pennsylvania, Kentucky, Indiana, and West Virginia. 2 Ries, U. S. Geol. Surv., Min. Res., 1901. 180 CLAYS In testing a glass-pot clay physical tests are of more value than chemical analyses. Glass-pot clay is obtained from both Pennsyl- vania and Missouri, but much is still imported from the Gross-Almerode district of Germany. Stoneware-clays Physical properties. Stoneware is usually made from a refractory or semi-refractory clay, but at some small potteries a much lower grade of material is used. The proper physical qualities are of paramount importance. Stoneware-clay should have sufficient plasticity and toughness to permit its being turned on a potter's wheel, this depending partly on the amount of clay substance present and on the fineness of the sand. A size of grain of from 0.002 to 0.01 of an inch for the non- plastic grains in stoneware clays has proved to be most suitable. Coarse sand renders the clay so absorbent that it will not hold its shape in .turning. 1 A tensile strength of 125 Ibs. per square inch or over is desirable, and the clay should also show low fire-shrinkage, good vitrifying qualities, ;and yet sufficient refractoriness to make the ware hold its shape in burning. Concretionary minerals, such as iron or lime, which are liable to cause blisters, should be avoided. Most stoneware is now made from a mixture of clays, so as to produce a body of the proper qualities, both before and after burning. Chemical composition. Orton 2 gives the following average of ten separate analyses of stoneware-clays in use in Ohio potteries: Clay base 56.65 Sandy matter - 37 . 45 Fluxing matter 4 . 44 Moisture 1 . 57 100.14 Total silica 65 .09 A high silica content was formerly considered essential in order to produce a successful salt-glaze, but this feature is of little importance now as other kinds of glazes are almost exclusively used. The following analyses give the composition of stoneware clays from a number of different localities. 1 la. Geol. Surv., XIV, p. 233, 1904. 2 Ohio Geol. Surv., VII, p. 95, 1893. KINDS OF CLAYS 181 ANALYSES OF STONEWARE CLAYS I. II. III. IV. V. VI. VII. VIII. Silica (SiO ) 67 10 71 94 67 84 57 20 64 26 68 3 60 34 69 2& Alumina (A1 2 O 3 ). . 19 37 17 60 21 83 24 82 22 95 20 1 20 55 18 97 Ferric oxide (Fe 2 O 3 ). . . Ferrous oxide (FeO). 2.88 2.35 1.57 3.25 1 42 1.28 1.0 tr 3.53 49 1.57 55 Lime (CaO) . . tr. 62 28 73 45 tr 38 12 Magnesia (MgO) .725 .56 24 .13 37 2 4 1 12 36 Potash (K 2 0) Soda (Na 2 O) .672 1.50 2.24 .93 1.96 tr. .6 2.89 .73 2.27 33 Titanic acid (TiO 2 ). . . . 1.2 .92 1 5 Water (H 2 O) 6.08 5.27 5.9 8.25 6.74 6.6 6.42 5 46 Moisture 1.71 1.01 .8 2.10 2.05 2.35 Phosphorous acid (P<>Oe) 55 Total 98.537 100.85 100.70 97.41 100.06 100 . 20 100.27 100.37 I. Thirteen miles from Fayette C. H., Fayette County, Ala. Ala. Geol. Surv., Bull. 6, p. 176, 1900. II. Calhoun, Henry County, Mo. Mo. Geol. Surv., XI, p. 564, 1896. III. Woodbridge, Sussex County, N. J. N. J. Clay Kept., 1878, p. 99. IV. Lincolntoii, N. C. N. C. Geol. Surv., Bull. 13, p. 78, 1897. V. Akron, Summit County., O. Ohio Geol. Surv., VII, p. 94, 1893. VI. Elmendorf, Bexar County, Tex. O. H. Palm, anal. VII. Bridgeport, Harrison County, W. Va. W. Va. Geol. Surv., Ill, p. 162, 1906. VIII. Huntingburg, Ind. Ind. Dept. Geol. and Nat. Res., 29th Ann. Kept., p. 508, 1904. Physical tests. The following data will serve to illustrate the physical characters of some stoneware clays: Calhoun, Henry County, Mo. A very plastic, buff-burning clay re- quiring 16.5 per cent water; average tensile strength, 150 Ibs. per sq., in.; air-shrinkage, 5.5 per cent; fire-shrinkage, 2.2 per cent; incipient fusion, 2100 F.; vitrification, 2300 F.; viscosity, 2500 F. 1 Northport, Long Island, N. Y. A yellow sandy clay requiring 25 per cent water, and having fair plasticity; average tensile strength, 25 pounds per square inch; air-shrinkage, 5.5 per cent.; fire-shrinkage, 6.5 per cent; nearly vitrified at 2300 F; viscous at cone 27. This is mixed with a more plastic clay for use. 2 South Amboy, N. J. No. 2 stoneware clay. Water required, 37 per cent; average tensile strength, 109 Ibs. per sq. in.; air-shrinkage,. 7 per cent; fire-shrinkage at cone 10, 9 per cent and absorption .24 per cent; viscous at cone 30. 3 Athens, Henderson County, Tex. Water required, 26.4 per cent; average tensile strength, 143 Ibs. per sq. in.; air-shrinkage, 6.9 per cent- At cone 9, fire-shrinkage, 6 per cent; color, buff; absorption, 7.45 per cent; viscous at cone 30. 4 1 Mo. Geol. Surv., XI, p. 575, 1896. J N. Y. State Museum, Bull. 35, p. 821, 1900. 1 N. J. Geol. Surv., Fin. Kept., VI, p. 459, 1904. 4 Unpublished notes. 182 CLAYS It will be noticed that no examples are given from Ohio or Indiana, 'both important producers of stoneware clays, the reason for this being that no tests have been published. Stoneware clays are used not only for the manufacture of all grades of stoneware, but also for yellow ware, art ware, earthenware, and more recently even for terra-cotta. Terra-cotta Clays Terra-cotta is made from many different kinds of clay, but most manufacturers of this material are now using semi-fire clays, or a mixture of these with a more impure clay or shale, since these give the best results at the temperatures (cone 6-8) usually attained in their kilns. Some are used because of their dense-burning character and bonding power, others because of a low shrinkage and freedom from warping, while absence of soluble salts is an important as well as desirable property In all. Buff-burning clays are commonly chosen, partly because they burn to a hard body at the desired temperature, and there is little danger of overburning. The color of the body is of no great importance, since the final color is applied superficially. Very few terra-cotta manu- facturers at the present day employ a low-grade clay. The soluble salts are undesirable, because in drying they may come out through the color-slip, but they can be rendered insoluble, if necessary, by treating the clay with barium chloride or carbonate. To give a tabulated statement of the properties of clays used for terra-cotta manufacture would involve listing a very large number. It may be of interest, however, to give the properties of a terra-cotta mixture used at a large Eastern factory, the tests being made on a soft green body, as tempered at the works. Its physical properties were as follows: l Air-shrinkage, 4J per cent; tensile strength, 97.5 Ibs. per sq. in. Its .behavior in burning was as follows: Cone 01. Cone 5. Cone 10. Fire-shrinkage 1.5% 4.8% 5% Hardness not steel-hard nearly steel-hard Absorption very absorbent slightly absorbent nearly impervious Color pale buff gray buff gray buff In making terra-cotta the clay is not carried to the temperature last given, as there would be danger of its warping, but it is usually 1 N. J. Geol. Surv., Final Kept., VI, p. 270, 1904. KINDS OF CLAYS 183 fired between cones 6 and 8, at which point this danger is greatly, if not entirely, diminished. The table on page 184 giving the physical character of some of the New Jersey clays used for terra-cotta manufacture shows what a variety of materials are employed. 1 Clays suitable for terra-cotta manufacture are widely distributed, but those mostly used in this country are the Cretaceous clays of New Jersey and the Carboniferous clays of Pennsylvania, Indiana, and Missouri. Sewer-pipe Clays Since sewer-pipes have to be vitrified in burning/they require a clay high in fluxes, and the clays employed are similar to those needed for paving-brick manufacture, so that the two products are sometimes made at the same factory from the same clay. Ordinarily, some fire- clay is mixed in with the verifiable material, to hold its shape better in burning. A high iron percentage is said to aid the formation of the salt-glaze with which the pipes are covered, but a high percentage of soluble salts is objectionable. The following are analyses of sewer-pipe clays from various localities: ANALYSES OF SEWER-PIPE CLAYS I. II. III. IV. V. Silica (SiO ) 57.10 55.60 63.00 59.96 57 52 21.29 24.34 23.57 15.76 21 76 Kprrif* oxidf* (Fe O ^ 7.31 6.11 1.87 7 72 3 41 Ferrous oxide (FeO) .46 3 70 JLime (CaO) .29 .43 .44 .60 .60 1.53 .77 .89 .93 .88 Potash (K 2 O) 3.44 3.00 2.40 3.66 3 57 Soda (Na 2 O) .61 .09 .29 .03 Titanium oxide (TiO ) 1.10 83 Water (H 2 O) 6.00 6.75 6.45 7.70 7.27 1.30 2.65 .86 Sulphur trioxide (SO 3 ) 73 Phosphorus pentoxide (P 2 O 5 ) 14 Total 98.87 99.74 99 88 98 06 99.57 I. Shale, Canton, O- Ohio Geol. Surv., VII, p. 133, 1893. II. Shale and fire-clay mixture. Ibid. III. Underclay, Mecca, Parker County, Ind. Ind. Dept. Geol. and Nat. Res., 29th Ann. Kept., p. 114, 1904. IV. Laclede mine, St. Louis, Mo. Mo. Geol. Surv., XI, p. 570, 1896. V. Kittanning clay. JStna mine, New Cumberland, W. Va. W. Va. Geol. Surv.. Ill, p. 219, 1906. 1 N. J. Geol. Surv., Final Kept., VI, p. 270, 1904. 184 CLAYS 1- T3T3 G ^ P n 1 2 ^T ^V ^J 1 EC ^1 S M c' 51 -^ ^ III 1 1 a3 _o a fli i -O G G "2 T3 'cj'cS ^ ^ X rn O 1 o *J Nearly ste< Nearly imj Imperviouf Viscous. Vitrifies th CD o3 CD R J2 ^3 73 o fill 11 ^CD 'o c3 CD ? g : : : : ! ! ! g . >TJ 3 : : : . . : w . . ^ * i 3 S ' H b ' a ^^ |J^ ' **-H I-* F-H .. * s s HI . || :5 |ss i . ^"J ^&b id ^-^sd pS'S,'^ * d d d l?l?fe -s ^ 3Q> PQ ;ffflc '3&a- ^M . SQO 1 ^ ^ CO cot-t^t- CO CO t^t- 52; }uao jad *a3B5|uiJUs-aji j -* O5CQ fs O CO t^ Ci l-H -M T^ O 1-1 I-H CM C^l C^ w T-H 5 1 g^ 10 ^; 00 CO r^^HCOOb- O I-H CM 10 CO lO 00 g 1000 ^ lO 00 O 8 8 nun jo anoQ O ^5 O O d c a c CD CD G G G G G G G G G G G G G G G G G G 8 3533 55 33333 3553 5555 553 1 CJ ui 'bs jad -sqi 6 (M g 2 S CO H j^> G r^ "B OH G O OQ 8 O "fl 03 & g 3 - 3 2 s * G a 5 O 1 (j) OQ 1 1 G M 3 s | I g (H i 3'" ^ H 1 1 O ja 3'" | M a P- CH *2 "^ ^ 1 ^J* ^* fl5 G OQ S ^ _ t>a "j i 2J fr ^ s e- 01 o3 JB O CD O o PH "fl 03 M w | o x| ^ | P S d H^ fi 5 KINDS OF CLAYS 185 The sewer-pipe clays in the Eastern and Central States are obtained chiefly from the Carboniferous formations, and to a small extent from the Devonian ones. The Cretaceous and Tertiary beds of the coastal plain States are not as a rule adapted to sewer-pipe manufacture, but in the Rocky Mountain region and Black Hills area some of the Creta- ceous shales have good vitrifying qualities. Pleistocene clays are used only to mix in with the other materials. Brick-clays Common brick. The clays or shales used for common brick are usually of a low grade, and in most cases red-burning. The main requis- ites are that they shall mold easily and burn hard at as low a temperature as possible, with a minimum loss from cracking and warping. Since many common clays or shales when used alone show a higher air- and fire-shrinkage than is desirable, it is customary to decrease this by mixing some sand with the clay or by mixing a loamy or sandy clay with a more plastic one. Common-brick clays vary widely in their composition, but most of them contain a rather high percentage of fluxing impurities. While the chemical composition is of importance in affecting the color-burning qualities and fusibility of the mass, the physical characters are even more important, since they affect not only the color in burning but often exert an influence on the process of molding to be chosen. The following analyses will serve to represent their range in com- position : ANALYSES OF BRICK-CLAYS I.* II. III. IV. V. VI. VII. VIII. IX. Silica (SiO 2 ). . . . Alumina (A1 2 O 3 ). Ferric oxide (Fe,O,) 66.67 18.27 3.11 1.18 1.09 2.92 1.30 .85 4.03 71.50 13.86 4.78 .56 .11 2.29 .81 1.44 4.61 42.28 8.26 3.84 13.05 6.01 2.51 .49 .05 122.07 68.62 14.92 4.16 1.48 1.09 1.50 1.86 52.30 18.85 6.55 3.36 4.49 4.65 1.35 56.50 19.31 5.89 l.OOo 1.85a 5.98 88.71 4.88 2.00 .30 .97 tr. tr. 18.62 3.23 1.26 41. 3C .42 56.81 20.62 6.13 .65 .58 4.47 Lime (CaO) Magnesia (MgO). Potash (K 2 O) . . . Soda (Na 2 O) Titanic acid (TiO 2 ) .90 2.28 tr. 2.42 32.50 8.60 Water (H 2 O).... Carbon dioxide (CO 2 ) 3.55 .64 5.30 3.04 9.47& Marsanese dioxide(MnO 2 ) Moisture 2.78 1.64 Total 99.42 99.96 98.56 100.60 99.89 100.0C 100.04 99.75 99.50 a. Determined as carbonate. 6. Includes organic matter. *For references see foot of table, page 186. 186 CLAYS PHYSICAL PROPERTIES OF SOME or THE PRECEDING I. II. III. VI. VII. Per ce Plasti Air-sh Avera nt water required 22 Good 6 108 20.9 Good 6.4 89.6 17.40 1.6 15.08 5 7.1 Red 19.8 High 6.5 316 .4 23.23 slightly swelled 22.63 2.7 16.35 Cream 32 Good 6 105 3 c .2 ' ' Jj g : sl 111 flj Red 20.9 Low 6.6 117 city .... rinkage . ge tensile strength, Ibs. per sq. in . . Cone 010 Fire-shrinkage Absorption 4.3 7.88 8.6 .1 Red 11.77 13.27 Red Cone 05 Fire-shrinkage Absorption. Cone 1 Fire-shrinkage Absorption. . . . Color when burned. ... . . I. Pleistocene clay, Little Ferry, N. J. N. J. Geol. Surv., VI, 220, 1904. II. Pleistocene clay, Richmond, Va. Va. Geol. Surv., Bull. II, p. 130, 1906. III. Calcareous Pleistocene clay, Whitewater, Wis. Wis. Geol. and Nat. Hist. Surv., Bull., 1906. IV. Loess, Gut one Centre, la. la. Geol. Surv., XIV, p. 541, 1904. V. Salina shale, Warners, N. Y. N. Y. State Mus., Bull. 35, p. 830, 1900. VI. Carboniferous shale, Grand Rapids, Mich. Mich. Geol. Sun-., VIII, Pt. I, p. 41, 1899. VII. Pleistocene brick-loam, Texarkana, Tex. O. H. Palm, anal. VIII. Seguin, Guadalupe County, Tex. O. H. Palm, anal. IX. Residual clay, Greensboro, N. C. N. C. Geol. Surv., Bull. 13, p. 114, 1897. Some pretty poor clays are at times used for common-brick manu- facture, but this is due to the fact that common brick will not always bear the cost of transportation, and it is sometimes necessary to use the best material that can be obtained locally, even though it be not thoroughly satisfactory. Common-brick clays are widely distributed, both geologically and geographically. Two varieties of brick-clay, of common occurrence west of the Missis- sippi River, may be mentioned here. Adobe. This is a calcareous silty clay, common throughout the Southwestern States and much used for making sun-dried or adobe brick. Analyses of some adobe soils, showing their calcareous character, are given on page 187. Loess. This name has been applied to extensive Pleistocene deposits, which are not unlike adobe, but regarding whose origin there has been much dispute, some claiming them to be of subaqueous origin, while others consider them to be seolian formations. The loess is a very common deposit throughout the Mississippi Valley, and much used for brickmaking. Analyses by Russell l are given in the second table on page 187. 1 Geol. Mag., VI, pp. 289 and 342, 1889- KINDS OF CLAYS ANALYSES OF ADOBE SOILS 187 I. 11. III. Silica (SiO 8 ) 58 19 19 24 66 69 Alumina (A1 2 O 3 ) 11 19 3 26 14 16 Ferric oxide (Fe 2 O 3 ). . 2 77 1 OQ 4 ^8 Lime (CaO). . 12 16 38 94 2 4Q Magnesia (MgO). .. . 80 2 75 i 28 Potash (K 2 O) tr tr 1 21 Soda (Na 2 O) 18 tr 67 Titanium oxide (TiO 2 ) 1.05 Water (H 2 O) 2 00 1 67 4 84 Carbon dioxide (CO 2 ). . ... 8 00 29 57 77 Phosphorus pentoxide (P 2 O 6 ) 23 29 Sulphur trioxide (SO 3 ) 53 41 Chlorine (Cl) 11 34 Organic matter 2 96 2 00 Total 96.34 100 35 99 53 I. Laredo, Tex. O. H. Palm, anal. II. Salt Lake City, Utah. L. G. Elkins, anal. U. S. Geol. Surv., Bull. 228, p. 367, 1904. III. Santa Fd, N. Mex. Ibid., p. 368. ANALYSES OF LOESS I. II. III. IV. Silica (SiO ) 72 68 64 61 74 46 60 69 Alumina (Al 2 Oo). 12 03 10 64 12 26 7 95 Ferric oxide (Fe 2 O 3 ) 3 53 2 61 3 25 2 61 Ferrous oxide (FeO) .96 51 12 67 Lime (CaO) v 1 59 5 41 1 69 8 96 Magnesia (MgO) 1 11 3 69 1 12 4 56 Potash (K O) 2 13 2 06 1 83 1 08 Soda (Na O) 1 68 1 35 1 43 1 17 Titanic oxide (TiO 2 ) .... 72 40 14 52 Phosphorus pentoxide (P 2 O 5 ) 23 06 09 13 Manganese oxide (MnO) . 06 05 02 12 Carbon dioxide (CO 2 ) 39 6 31 49 9 63 Sulphur trioxide (SO 3 ) 51 11 06 12 Carbon (C) . 09 13 12 19 Water (HO) 2 50o 2 05 2 70a 1 14 a Total 100.21 99.99 99.78 99 54 a. Contains H of organic matter dried at 100 C. Pressed brick. Pressed brick call for a higher grade of clay. The kinds now in use fall mostly into one of three groups, namely, 1, red -burn- ing clays; 2, white-burning clays; 3, buff-burning clays, usually semi- refractory. The composition of a sample of these three types is given in the table at top of page 188. The physical requirements of a pressed-brick clay are (1) uniformity 188 CLAYS ANALYSES OF PRESSED-BRICK CLAYS I. II. III. Silica (SiO 2 ) 68 28 63 11 65 78 Alumina (A1 2 O 3 ). 18 83 93 30 14 79 Ferric oxide (Fe O 3 ) 2 60 2 23 8 03 Lime (CaO) 70 73 54 Magnesia (MgO) 13 97 1 42 Potash (K 2 O) \ / 93 2 82 Soda (\a O) / 2.29 1 4Q 97 Titanium oxide (TiO 2 ) 07 i ^^ 1 00- Water (H O) G 47 7 81 4 98 Moisture Silp'iur trioxida (3O 3 ) . , I. A cliy used for white brick, Grover, N. C. N. C. Geol. Surv., Bull. 13, p. 81, 1897. II. Hocking Valley, O., clay. L. E. Barringer, anal. Supplied by A. V. Bleininger. III. Shale from Cayuga, Vermillion County, Ind. Ind. Dept. Geol. and Nat. Res., 29th Ann. Kept., p. 503, 1904. of color in burning, (2) freedom from warping or splitting, (3) absence of soluble salts, and (4) sufficient hardness and low absorption when burned at a moderate temperature. The air-shrinkage and fire-shrinkage, as well as tensile strength, vary within the same limits as common bricks. Red-burning clays were formerly much used, but in recent years other colors have found greater favor, and the demand for the former has greatly fallen off. Buff-burning, semi-refractory or refractory clays are, therefore, much employed now, partly on account of their color and partly because coloring materials can be effectively added to them, for since the range of natural colors that can be produced in burning is limited, artificial coloring agents are sometimes used. Manganese is the one most employed. The clays must necessarily burn hard at a moderate temperature, and in the case of red-burning clays the temperature reached may range PHYSICAL PROPERTIES OF SOME NEW JERSEY CLAYS USED FOR FRONT BRICK. 1 Formation. Water required, per cent. Air- shrinkage, per cent. Average tensile strength, Ibs. per sq. in. Cone of firing. Fire- shrink- age, percent. Absorption, per cent. Color. Raritan 32 00 5 65 fCone 1 \ Cone 5 5 11 68 } Buff Cohansey Cohansey 23.17 37.50 7.5 5.5 282 196 [Cone 8 [Cone 1 \ Cone 5 [Cone 8 Cone 8 6.6 2.8 4.5 6.5 9.1 11.34J 8.09] 3.08 J- 0.84J 4.01 Buff Buff 1 N. J. Geol. Surv., Fin. Kept., VI, p. 222, 1904. KINDS OF CLAYS 189 from the fusing-point of cone 06 to 2, while for buff-burning clays it is commonly necessary to go to cone 7 or 8 to get a steel-hard brick, unless calcareous materials are employed, and these are not burned above cone 3, or even cone 1. In the table at bottom of page 188 are given the physical characters of some New Jersey pressed-brick clays. The properties of a shale quar- ried at North Bluff, Kansas City, Mo., 1 are: water required, 22.3; plas- ticity, high; air-shrinkage, 6.9 per cent; fire-shrinkage, 4.8 per cent; average tensile strength, 198 Ibs. per sq. in.; incipient fusion, 1600 F.; vitrification, 1750 F.; viscosity, 1900 F.; color when burned, red. Flashing. 2 Many bricks used for fronts are often darkened on the dges by special treatment in firing, caused chiefly by setting them so that the surfaces to be flashed are exposed to reducing conditions, -either at the end of the firing or during the entire period of burning. This color is superficial and may range from a light gold to a rich, reddish brown. The principle of the operation depends on the formation of ferrous silicate and ferrous oxide and their subsequent partial oxidation to the red or ferric form. This oxidation probably takes place during cooling, for if the kiln be closed so as to shut off the supply of oxygen, the bricks are found to be a light grayish tint. The degree of flashing is affected (1) by the composition and physical condition of the clay, (2) the temperature of burning, (3) the degree of reduction, and (4) the rate of cooling and the amount of air then admitted to the kiln. 1. The percentage of iron oxide should not be large enough to make the brick burn red, but to produce buff coloration, and the clay should have sufficient fluxes to reduce the point of vitrification to within reason- able limits, thus facilitating the flashing. Clays high in silica are appar- ently better adapted to flashing than those low in silica and high in alumina. The condition in which the iron is present in the clay probably exerts some influence, that is, whether it is there as ferric oxide, ferrous silicate, concretionary iron, ferrous sulphide, or perhaps ferrous carbonate. Bleininger's experiments showed that of three clays which were used for flashing, all contained considerable quantities of iron soluble in acid. Some Eastern manufacturers are obliged to add magnetite ores to their clays, which are low in combined iron, and No. 2 fire-clays, which contain more iron than the finer grades, seem to give the best results. As to the effect of the physical condition of the clay, finer grinding seems to give more uniform flashing effects, and the reason that stiff-mud bricks 1 Mo. Geol. Surv., XI. 2 A. V. Bleininger, Notes on Flashing. Trans. Amer. Ceramic Soc., II, p. 74. 190 CLAYS flash better than dry-press ones is claimed by some to be due to vitrifica- tion taking place more easily in the former. The following analysis gives the composition of a No. 2 fire-clay from Ohio used for flashed brick: ANALYSIS OF AN OHIO No. 2 FIRE-CLAY Silica (SiO 2 ) 67 . 14 Alumina (A1 2 O 3 ) 19 . 74 Ferric oxide (Fe 2 O 3 ) 2.46 Lime (CaO) . 53 Magnesia (MgO) 0.71 Potash (K 2 O) 2 . SO Soda (Na 2 O) 0.43 Water (H 2 O) 7 . 01 Total.. 100.82 In one case the green clay showed a total of 2.15 per cent of ferric oxide, of which 0.88 per cent was soluble in acid. The flashed surface of a brick made from this clay gave, on analysis, a total of 2.31 per cent of ferric oxide, of which 0.14 per cent was soluble in nitro-hydrochloric acid, thus indicating that during the burning most of the iron oxide had combined with silica, forming a ferrous silicate. 2. The temperature reached must be sufficient to cause a combination of the iron and silica, and, therefore, it varies with different clays, the combination being aided by the presence of fluxes. If the kiln atmosphere is oxidizing during nearly the entire burning,, with only a small period of reduction at the end, the temperature reached must be comparatively high in order to insure union of the iron, and silica by fusion. If, however, a reducing fire is maintained during most of the burning, then the temperature need not be as high, because the clay will vitrify sooner. (See Fusibility, Chapter III.) At one factory it had formerly been the practice to burn with an oxidizing fire to a high temperature, namely, from cone 11-12, and then to cause reducing conditions to take place in the kiln during the last five or six hours of the burn. This practice, however, was changed, it being found that by maintaining a reducing fire during the entire period following water smoking a lower temperature was sufficient. 3. The oxidation which causes the flashing probably takes place in the first twelve hours after closing the kiln, and can be regulated by a proper handling of the dampers. In the experiments of Bleininger, already referred to, it was found that a reduction of air, equal to 20 per cent below that required for ideal oxidation and considered as 100, is usually sufficient to produce flashing. KINDS OF CLAYS 191 By this is meant that "100 per cent of air represents theoretically ideal conditions, in which just enough air is present to consume all the combustible gases forming CO 2 ; less than 100 per cent of air corresponds to reducing conditions. For instance, if an analysis on calculation represents 90 per cent of air, it tells us that the gases are reducing to the extent of 10 per cent of air; similarly, 110 per cent shows an excess of air to the amount of 10 per cent." While 100 per cent represents theoretically the amount of air required for perfect combustion, still in actual practice with coal-fuel the mixture of gases is not perfect, and it may be necessary to have more than 100 per cent of air present to bring about thorough oxidation. .4. As regards the rate of cooling, it was found that the longer the period of cooling from the maximum temperature down to approximately 700 C. the darker the flash under given conditions. Enameled brick. The clays used for these are similar to those em- ployed in the manufacture of buff pressed brick. The enamel is, of course, an artificial mixture, but must conform to the clay body to avoid cracking or scaling off of the coat. Paving-brick Clays A considerable variety of materials is used for paving-brick manu- facture, ranging from common surface-clays to semi-refractory ones, but those most frequently employed are impure shales, these being often found to give the desired vitrified body at not too high a tempera- ture. Shales of this character have a wide geographical and geological distribution, but those most extensively worked are in the Carboniferous of Ohio, Pennsylvania, Indiana, and Illinois. In New York and Mary- land Devonian shales have yielded excellent results, and in the Western States, such as Colorado, the Cretaceous shales are of importance in this connection. Wheeler l gives the following range of composition of paving-brick clays: RANGE OF COMPOSITION OF PAVING-BRICK CLAYS Mini- mum. Maxi- mum. Average. Silica (SiO ) . . 49.00 75.00 56.00 Alumina (A1 2 O 3 ). 11.00 25.00 22.50 Ferric oxide (Fe 2 O 3 ) 2.00 9.00 6.70 Lime (CaO) .20 3.50 1 20 Magnesia (MsrO) .10 3 00 1 40 Alkalies (Na O K O) 1.00 5.50 3 70 Ignition loss 3.00 13.00 7.00 1 Mo. Geol. Surv., XI, p. 456, 1896. 192 CLAYS Williams l gives the following limits between which the different ingredients of Iowa paving-brick clays range: RANGE OF COMPOSITION OF IOWA PAVING-BRICK CLAYS Maxirmim, Minimum, per cent. per cent. Silica (SiO 2 ) 74 . 58 58 . 56 Alumina (A1 2 O 3 ) 22.33 8.28 Ferric oxide (Fe 2 O 3 ) 5.75 2.88 Lime (CaO) 3.42 1.55 Magnesia (MgO) 3.47 1.22 Potash (K 2 O) 1.15 .29 Soda (Na 2 O) 1 .79 1 .08 Water (H 2 O) 5.33 1.07 Carbon dioxide (CO 2 ) 2.23 1 .73 Sulphur trioxide (SO 3 ) 1 . 85 1 . 28 Moisture 1.13 .28 The analyses show a rather high percentage of total fluxes. Clays for paving brick should possess fair plasticity, since they are commonly molded by the stiff-mud process; they should have good tensile strength, and a range of not less than 250 F. between the points of incipient vitrification and viscosity. Fireproofing and Hollow-brick Clays The clay used for making hollow bricks and fireproofing vary with the locality. At not a few yards where red bricks are manufactured the red-burning surface-clays of Pleistocene age are employed. In New Jersey, where many thousand tons are annually produced to supply the New York and other large Eastern markets, a mixture of red-burning sandy clay and a small amount of low r -grade fire-clay are chosen, while in the States of the Eastern and Central coal-measure areas, as in Pennsyl- vania, Ohio, Indiana, and Illinois, Carboniferous shales are widely used. It is therefore difficult to lay down any fixed set of requirements for the raw materials of this class. This much can be said: They should have sufficient plasticity to flow smoothly through the peculiar shape of die used in making them; they should also possess fair tensile strength; burn to a good hard but not vitrified body at a comparatively low cone. Concretionary masses, if present, should be either removed or crushed. The following analyses show well the composition of clays or shales used for this kind of ware: 1 la. Geol. Surv., XIV, p. 229, 1904. KINDS OF CLAYS 193 ANALYSES OF CLAYS USED FOR HOLLOW BRICK AND FIREPROOFING I. 11. III. Silica (SiO 2 ) . 52.22 29.43 2.78 57.57 21.70 2.26 4.11 51.95 18.34 7.56 Alumina (A1 2 O 3 ). . Ferric oxide (Fe 2 O 3 ) Ferrous oxide (FeO) Lime (CaO) .88 .72 2.10 .75 .32 1.12 2.16 .33 1.10 4.14 3.36 1.43 2.69 Magnesia (MsrO) Pot'ash (K 2 O) Soda (Na O) Titanium "oxide (TiO.) Water (H 2 O) 1 11.10 / 6.78 1 7.39 .42 Moisture / Carbon dioxide (CO 2 ). . . . Sulphur trioxide (SO 3 ). . 2.76 Final Report, VI, p. 282, 1904. eol. and Nat. Res., 29th Ann. II. Underclay beneath Coal II, Cannelton, Ind. Ind. Dept. G Rept., p. 338, 1904. III. Representative shale-clay from Iowa. la. Geol. Surv., XIV, p. 232, 1904. The physical tests of fireproofing clays shown on page 194 are given in the New Jersey Geological Survey report. 1 The tabulation is not without interest, and shows a considerable variation in certain directions. The air-shrinkage shows little variation, but the tensile strength shows a great range. Of these different samples, Nos. 1, 2, and 6 are practically from the same bed. No. 5 is from the base of the Raritan series, and is one of the most dense-burning clays to be found in that section or even New Jersey. Most of these clays have to be burned to cone 01 before becoming steel-hard, the one exception being No. 5, which burns very hard at cone 05. They all burn red. The pyrite and limonite nodules are abundant in some of the layers, and in burning often fuse, swell, and spall off pieces of the ware. Slip-clays A slip-clay is one containing such a high percentage of fluxing im- purities, and of such texture that at a low cone it melts to a greenish or brown glass, thus forming a natural glaze. It must be fine grained, free from lumps or concretions, show a low air-shrinkage, and mature in burning at as little above cone 5 as possible. While easily fusible clays are not uncommon, all do not melt to a good glaze. "A good slip-clay makes a glaze which is free from defects common to artificial glazes. It will fit a wide range of clays, and since it is a 1 N. J. Geol. Surv., Final Kept., VI, p. 280, 104. 194 CLAYS t 1 | j C 8 i ^H (fl w J c "S '^ (H cfi OS . 1 5 "H 2 a'. . 3 llll 1 1^ ! "O J 8 * - Hard. Vitrified. l^asily scr Scratched Scratched . . . bO . fc " ' !* | ijjj s : : ; ; ;3 | ^j O : 1'S- : j II 11;; * ^ * ^ ^, ^-6 a 1; 111 '-i -S CD O5 10 CD OiOrf ^'"c Ja . s o "1 a3 '".SP s >> ^ ^ * *8 -% cr g 1 >> I* -4-i g 1 ^ i i If ^ h Amboy dis receding . . . 1 EC 'C ' 02 "i ! 1 |l 1 d 1 o " & | a^ o W 15 PH PH M 02 Pi GO 02 3 ^i CO 4 iO CD ^ KINDS OF CLAYS 195 natural clay it will undergo the same changes in burning as the body on which it is placed. Artificial mixtures of exactly similar composition to the natural clays have failed to give the excellent results as to gloss or color that are attained by the natural clay." 1 While several fair slip-clays have been found in different parts of the country, none have given thorough satisfaction except the Albany, N. Y., material, which is shipped to all parts of the United States for potters' use. In applying the glaze to the ware the clay is mixed with water to a creamy consistency and applied to the ware either by dipping or spraying. Attempts have sometimes been made to lower the fusing-point of the slip by the addition of fluxing oxides. The following are analyses of slip-clays: ANALYSES OF SLIP-CLAYS I. II. III. IV. V. Silica (SiO 2 ) . 55 . 60 43.94 63.63 38.08 57.01 . Alumina (A1 2 O 3 ) 14.80 11.17 13.57 11.36 11.85 Ferric oxide (Fe 2 O 3 ) 5.80 3.81 7.77 2.60 3.02 Lime (CaO) 5.70 11.64 2.55 23.70 9.56 2.48 4.17 1.47 tr. 1.20 Potash (K 2 O) 3.23 2.90 2.63 .58 .75 Soda (Na 2 O) 1.07 .71 .88 1.60 2.01 .14 Titanium oxide (TiO 2 ) . . . .70 1.13 Phosphorus pentoxide (P O ) 15 Water (H 2 O). . 5.18 3.90 4.75 3.06 4.00 Carbon dioxide (CO 2 ) and moisture. . . . 4.94 15.66 2.90 18.80 8.00 Total . . 98.09 98.00 100.15 100.48 98.53 I. Albany, N. Y. Ohio Geol. Surv., VII, p. 105, 1893. II. Rowley, Mich. Ibid., p. 105. III. Brimfield, O. Ibid., p. 105. IV. Leon Creek near San Antonio, Tex. O. H. Palm, anal. V- Alazan Creek near San Antonio, Tex. O. H. Palm, anal. The use of slip-clays for glazing stoneware is decreasing each year, because an artificial white glaze is now usually preferred. MISCELLANEOUS KINDS OF CLAYS Clays Used when Burned Gumbo-clay. Under this name there are included certain fine- grained, highly plastic, tenacious clays of surface character, which are found at many points in the Western Central States. Their high shrinkage 1 la. Geol. Surv., XIV, p. 224, 1904. 196 CLAYS and dense character prohibits their use for brickmaking, but they are found excellently adapted to the manufacture of railroad ballast. Wheeler, in describing the Missouri occurrences, 1 states that they do not differ chemically from common brick, paving brick, sewer-pipe or other burnt clays, and " their peculiar value for burnt ballast is entirely a physical one." He gives the following variation in composition: Silica (SiO 2 ) 55 -65 Alumina (A1 2 O 3 ). 15 -20 Ferric oxide (Fe 2 O 3 ) 5 -7 Lime (CaO) 1 -3 Magnesia (MgO) 5-2 Alkalies (Na 2 O, K 2 O) 2.5-4 Water (H 2 O) 6 -10 Fluxes 10 -15 Their physical properties range as below : Water required 22-25 per cent. Average tensile strength 270-410 Ibs. per sq. in. Air-shrinkage 8-10 per cent. Fire-shrinkage 1-6 per cent. Incipient vitrification 1600-1700 F. Complete vitrification 1750-1850 F. Viscosity 1900-2000 F. Retort-clay. A dense-burning, plastic, semi-refractory clay used chiefly in the manufacture of gas-retorts and zinc-retorts. In New Jersey the term is often applied to stoneware-clays. Pot-clay. A clay used for the manufacture of glass pots, and conse- quently representing a very dense-burning fire-clay. In refractoriness it ranges from a highly refractory to a refractory clay. Ware-clay. A term sometimes used for ball-clays, especially in the Woodbridge, N. J., district. Pipe-clay. This is a term applied to almost any fine-grained plastic clay. Strictly speaking, it would refer to a clay used for making sewer- pipe. Sagger-clay. This is a term applied to clays which are used in a mixture for making the saggers in which the white ware and other high grades of pottery are burned. They are commonly rather siliceous in their character, although some may be used on account of their bonding power and freedom from grit to hold the more porous grades together. As far as the physical properties go the sagger-clays are not, therefore, represented by any one type. Their refractoriness varies from that of a_ refractory to a semi-refractory clay. 1 Mo. Geol. Surv., XI, p. 542, 1896. See also la. Geol. Surv., XIV, p. 534, 1904. KINDS OF CLAYS 197 Wad-clay. This is a low grade of fire-clay, which is used for grouting the joints between the saggers when they are set up in bungs in the kilns. Portland-cement clay. The use of clay or shale for Portland cement is the most important of what may be termed the minor uses of clay. Portland cement is essentially an artificial mixture of lime, silica, and alumina. The first of these is usually supplied by some form of calcareous material, such as limestone, marl, or chalk, while the other two are obtained by the selection of clay or shale, the mixture con- sisting approximately of 75 per cent lime carbonate and 25 per cent clay or shale. Clays or shales to be used for Portland-cement manufacture should be as free as possible from coarse particles or lumps of sand, gravel, or concretions. These conditions are best met by the transported clays, since residual clays are frequently sandy or stony, and many glacial clays notably so. An examination of the analyses of clays used at different works in this country shows that the silica percentage ranges from 50 to 70 per cent; when calcareous clays are used it may fall below 50 per cent. The analyses shown on page 198 give the composition of clays em- ployed at a number of different localities. It is not to be understood from what has been said above that the clays whose analyses are given can be used only for Portland-cement manufacture; indeed nearly all of them could be utilized for some kind of clay product. Clays Used in Unburned Condition Paper-clays. These form a type of clay much used by paper manu- facturers, and which are mixed in with the pulp fiber, so that the latter can enmesh a certain amount of the clay particles. The degree of plasticity of the clay seems to play an important role, since it is found that a given paper will often retain a much greater proportion of some clays than others, those of which the greatest quantity is retained being the most plastic. Sand is an undesirable constituent of paper-clay, for the reason that the sand-grains wear the wires of the screens through which the materials have to pass. It can often be eliminated from the clay by washing. Whiteness of color is a third essential, and must be a primary character of the clay. The best grades of paper-clay are some imported washed kaolins, but large quantities of good paper-clay are also obtained from the Potomac formations of Georgia, and the Cretaceous and Tertiary ones of South 198 CLAYS ANALYSES OF PORTLAND-CEMENT CLAYS I. II. III. IV. V. VI. Silica (SiOs) Alumina (A1 2 O 3 ) 53.30 23.29 9.52 .36 1.49 1.36 2.76 63.73 22.12 9.01 2.83 }> 74.29 12.06 4.92 .41 .68 f .76 1 1.80 64.85 17.98 5.92 2.24 1.40 55.27 10.20 3.40 9.12 5.73 40.56 8.52 2.84 20.94 1.32 } 1.97 Ferric oxide (Fe 2 O 3 ) Lime (CaO) . .... Magnesia (MgO) Potash (K 2 O) Soda (Na 2 O) . . . Sulphur trioxide (SO 3 ) . . Caibon dioxide (CO 2 ). . . } 4.98 {: 17. 5.95 Water (H 2 O) 5.16 VII. VIII. IX. X. XI. Silica (SiO 2 ) 57.98 18.26 4.57 1.75 1.83 61.09 19.19 6.78 2.51 .65 1.8 54.30 19.33 5.57 3.29 2.57 61.92 16.58 7.84 2.01 1.58 1 3.64 tr. 55.27 } 28.15 5.84 2.25 .12 Alumina (Al 2 Oo) .... Ferric oxide (Ft^O^ . ... Lime (CaO) Magnesia (MgO) Potash (K 2 O) Soda (Na O) 1.36 Sulphur trioxide (SOg) Carbon dioxide (CO 2 ) 1.28 | 12.08 1.42 5.13 2.36 Water (H 2 O) I. Little Rock, Ark. Amer. Inst. Min. Eng., Trans., XXVII, 62. II Santa Cruz, Cal. Min. Indus., I, p. 52. III. Bedford, Ind. Ind. Dept. Geol. and Nat. Res., 25th Ann. Rept., p. 328. IV. Millbury, O. Mich. Geol. Surv., VIII, Pt. Ill, p. 229. V. Syracuse, Ind. Ind. Dept. Geol. and Nat. Res., 25th Ann. Rept., p. 28. VI. Bristol, Ind. U. S. Geol. Surv., 21st Ann. Rept., Pt. 6 (ctd.), p. 400. VII. Yankton, S. Dak. Min. Indus., VI, p. 97. VIII. Alpena, Mich. Mich. Geol. Surv., VIII, Pt. Ill, p. 227. IX. La Salle, 111. U. S. Geol. Surv., 20th Ann. Rept., Pt. 6 (ctd.), p. 544. X. Catskill, N. Y. Supplied by company. XI. Glens Falls, N. Y. Min. Indus., VI, p. 97. Carolina. The Algonkian kaolins of Maryland, Delaware, and Connecticut, as well as the white residual Cambro-Silurian ones of southeastern Pennsylvania, have also been used for this purpose. Many of these clays are, however, also utilized for the manufacture of clay-products, such as white earthenware, wall-tile, etc. Mineral paint. Certain clays and shales, when ground and mixed with oil, make a good grade of mineral paint. Their color in most cases is due to some form of iron oxide, or more rarely manganese. Ocher is often nothing more than a fine-grained ferruginous clay colored by limonite, and the same may be true of sienna. Mineral paints made from clays and shales form a cheap and satisfac- tory form of pigment for application to wooden surfaces. The value cf the material depends to a large extent on the shade of color, its texture, KINDS OF CLAYS 199 and the amount of oil that has to be mixed with it in order to get the proper degree of fluidity. Ultramarine manufacture. Washed kaolin or even very fine-grained white sedimentary clays are used in the manufacture of ultramarine to serve as a nucleus for gathering the coloring material. For this work the clay should be as low in iron or lime as possible, and an excess of silica is undesirable. Polishing and abrasive materials. Many clays exert a combined polishing and abrasive action, on account of the very finely divided grains of sand which they contain. The well-known Bath brick which has such an extensive domestic use for scouring steel utensils is simply a fine-grained siliceous clay, which is deposited during high tide along the banks of the Parrot River in England. Some clay is used for bonding purposes in the manufacture of corundum-wheels. These are burned before use, so that the clay vit- rifies and holds the corundum-grains together. METHODS OF MINING AND MANUFACTURE METHODS OF MINING Prospecting for Clays A knowledge of the facts given in Chapter I will, if borne in mind, be of much aid to the clay-worker in prospecting for clays, but several additional points may be mentioned by which beds of clay may be located. Outcrops. The presence of a clay-bed is usually detected by means of an outcrop. These exposures are commonly to be found on inclined surfaces, such as hilltops, or where natural or artificial cuts have been made. The washing out of gullies by heavy rains, the cutting of a stream valley, railroad or wagon-road cuts, all form good places in which to look for outcropping clay-beds. The newer the cut the better the exposure, for the sides of such excavations wash down rapidly, and a muddy-red surface-clay or loam will often run down over a bed of lighter colored clay beneath so as to completely hide it from view. If the cut is deep and freshly made the depth of weathering can frequently be determined. Springs. In many cases the presence of clay is shown by the occur- rence of one or more springs issuing from the same level along some hill-slope. These are caused by waters seeping down from the surface (Fig. 38) until they reach the top of some impervious clay stratum, 200 CLAYS which they then follow to the face of the bank where they issue. The presence of springs, however, cannot be used as a positive indication of _ __ _ - _ \ Spring _ \ FIG. 38. Formation of spring due to ground-water following a clay-layer. clay, for a bed of cemented iron sand, or even dense silt, may produce the same effect (Fig. 39). FIG. 39. Formation of spring due to a layer of cemented sand. Ponds. In many regions covered by glacial drift, pools of water are often retained in depressions, because of the presence below of a water- tight bed of clay (Fig. 40). It does not necessarily indicate a thick *~-^l^riviwi : "~-"-- -^^^ FIG. 40. Formation of a pond due to a clay-bed beneath a depression. deposit, for a very thin layer often holds up a considerable body of water. Such ponds may likewise in rarer instances be caused by ground-water seeping down from higher levels, even in the absence of clay. Vegetation. Clay-deposits in some areas produce a different type of plant growth from other soils, but the character of the vegetation can only be used as a subordinate aid in the search of clay. PLATE VIII Showing method of working clay in a rectangular pit. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 34, 1904.) 201 KINDS OF CLAYS 203 EXPLOITATION OF CLAY-DEPOSITS The location of a clay-deposit is followed by a determination of its thickness, extent, character, and uses. The first two points and some facts bearing on the third are determined in the field; the behavior of the clay when mixed up and burned is found out by tests made in the laboratory or at some factory, and the information thus obtained indicates the commercial value of the material. To determine the thickness and extent of the deposit a careful examination should be made of all clay outcrops in neighboring gullies, or other cuts on the property having the clay. Since, however, most clay-slopes wash down easily, it may be necessary to dig ditches from the top to the bottom of the cut or hillside in order to uncover the undis- turbed clay-beds. In most cases, however, the cuts are not sufficiently close together and additional means have to be taken to determine the thickness of the deposit at intermediate points. Such data are sometimes obtainable from wells or excavations made for deep cellars, but the information thus obtained has to be taken on hearsay. Borings made with an auger furnish a more satisfactory and rapid means of determining the thickness of the clay-deposit away from the outcrop: A post-hole auger, cutting a hole of three to four inches diameter, can easily be used to a depth of 30 or 40 feet, while one of two inches diameter can be sunk to 100 feet without much difficulty. From comparison of the data obtained from the bore-holes and outcrops, any vertical or horizontal variations in the deposit can usually be traced. Limonite concretions or crusts, if present in any abundance, are almost sure to be discovered, and even the dryness of the beds can be ascertained. Variations in the thickness of the bed and amount of stripping are also determinable. If small samples are desired for labora- tory testing these can be taken from the outcrops and bore-holes, but if large samples are wanted from the intermediate points it is best to sink test-pits where the borings were made. In some regions the clay-miners make use of an auger to guide them in their digging operations, this being often necessary on account of the rapid variations that may occur in any one deposit. Adaptability of Clay for Working Having determined the thickness, extent, and character of the clay there still remain several important points which have to be considered. One of these is the amount of stripping, for if the clay is not of high 204 CLAYS grade it will not pay to remove much overburden unless the latter can be used. It is sometimes utilized for filling, where the factory is to be erected next to the bank, or for admixture with the clay, especially if the latter is too plastic or fat. In such event, ho\vever, the overburden should be free from pebbles, or if not it should be screened. Frequent neglect of this often injures the bricks. If the overburden is clean sand it can often be disposed of for foundry use, building or other puiposes. Drainage facilities must be looked out for, since dryness is essential for successful and economic working of the clay-bed. In some districts the clay is underlain by a stratum of wet sand, which should not be pene- trated. In rare cases an underlying sand-bed is dry and may even serve for drainage purposes. If the clay-deposit lies below the level of the surrounding country, drainage will be more difficult than where the bed outcrops on a hillside, although in the latter case trouble may be and often is caused by springs. Some banks contain several different grades of clay, and it then remains to see whether they are all of marketable character, or, if not, whether the expense of separating the worthless clay will overbalance the profit derived from the salable earth. Transportation facilities are not to be overlooked, either for the raw clay or for the product, where the factory is located at the pit or bank. Long haulages with teams are costly, and steam haulage is far more economical when the output warrants it; but, even with the establish- ment of favorable conditions in every case, the successful marketing of the product is sometimes a long and tedious task, for many manufacturers hesitate to experiment with new clays. Methods of Winning the Clay Clays and shales are commonly worked either as open pits or quarry workings or by underground methods. The open-pit method is practised at most localities where the deposit lies at or near the surface and there is little or no overburden to be removed. If the clay is soft and the quan- tity to be dug small picks and shovels are commonly used, but for more extensive operations plows and scrapers are cheaper and of greater capacity. In extensive works steam-shovels (PL XXVI, Fig. 1) are the best and most economical means, and capable of excavating even soft shales. They can be used with a face of 15 or 20 feet height, but have the disadvantage of mixing the clay from the top to the bottom of the bank. In deposits of very tough clay or hard shale blasting is frequently OF THf UNIVERSITY KINDS OF CLAYS . 205 , . X^'jro_R necessary in order to loosen up the material. Since surface-waters often trickle through the soil until they reach a clay-surface and follow it, there is not infrequently a series of small springs emerging along the top of a clay-bank, and the water from these is usually diverted by means of properly constructed ditches. In addition to these ditches, however, it is commonly necessary to have additional ones on the ground at the base of the bank. If the bank is high, that is seventy-five feet or more and of soft clay, it is safer to work it in several benches or steps (PL XXXIII, Fig. 2) and not as a vertical face, for the latter will be apt to slide if the clay gets water-soaked. Neither should the factory be located close to the base of such a bank, where there is danger of slides, and the writer has seen several instances in which yards have been buried in this manner. The ease with which large masses of clay will sometimes cave or slide when softened with water was well illustrated recently at Haverstraw, N. Y., when a portion of a large cliff overlooking the clay- pits sank down, carrying many houses and people with it. Where the clay is not of uniform quality from top to bottom, or when a number of layers of different kinds, as terra-cotta, fire-, and stone- ware-clay are present, it is then necessary to strip off each one separately and place it in a storage pile by itself. This is notably the custom in the Woodbridge and Perth Amboy districts of New Jersey, and the practice followed there may be described in some detail, as the same method might be adopted in other parts of the coastal plain area. In the area referred to the better grades of clay are generally dug by small pits. These are commonly square, and about ten to fifteen feet or more on a side (Fig. 41), and the depth is usually that of the thickness of the good clay in the bed. Around Woodbridge the miners commonly penetrate the No. 1 fire-clay or sometimes the extra sandy clay below, but the depth is oftentimes determined by the character of the ground "and presence or absence of water underneath. Where there is danger of the pit caving in, the sides are sometimes protected in the weak parts by planking, held in place by cross-timbers. The clay is dug by a gouge-spade, which differs from an ordinary spade in having a curved or semi-cylindrical blade, as well as a tread on its upper edge, to aid the digger in forcing it into the tough clay. A lump of clay dug by the pitman is termed a spit, and in taking out the material it is customary to dig over the area of the bottom of the pit to the depth of a spade and then begin a new spit. The thickness of any bed of clay, therefore, is always judged in spits. Where a pit is dug so deep that it is not possible for the workman to throw or lift the lumps to the surface of the ground, a platform may 206 CLAYS be built in the pit half-way up its side, or else the clay is loaded into buckets (PL V1I1) and hoisted to the surface by means of a derrick operated by steam- or horse-power. As soon as a pit is worked out a new one is begun next to it, but a wall of clay, 1 to 2 feet thick, is com- monly left between the two. When the second pit is done as much as possible of this wall is removed. A platform of planking is laid on one side of the pit on the ground, and the clay thrown upon this, the different grades being kept separate. When the clay lies above the ground- or road-level there is less trouble with water, and it is not necessary to work the clay in pits, although the general system of working forward in a succession of pit-like excavations Sandy clay Stoneware clay Pipe clay FIG. 41. Section of pit working in Middlesex district. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 33, 1904.) or recesses is followed. In such banks the cart or car is backed against the face of the excavation and the clay thrown into it. Unless a number of pits are being dug at the same time, the output of any one deposit or of any one grade is necessarily small, since five or six different kinds are sometimes obtained from one pit. It would also seem that by this method any one grade of clay might show greater variation than if the excavations were more extended, for the reason that since clay-beds are liable to horizontal variation, the material extracted from one pit might be different from that taken from another farther on. Against this we may of course argue that the clays from different pits get mixed up on the storage pile. As these pits are small and the time required for sinking one, namely, two or three days, is not very great, but little water runs in them, although in some much water comes from sand or other layers it at are sometimes inter-stratified with the clay. The surface drainage is commonly diverted by means of ditches dug around the top of the pit. In some districts PLATE IX FIG. 1. Digging clay by means of open pits. At the top of the bank, in the back- ground, a workman is driving a wedge into the clay in order to break it off. The clay is hauled to the yards in carts. (After Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 35, 1904.) FIG. 2. Removing the overburden from a shale-bed by hydraulicking. Photo loaned by Illinois Geological Survey.) 207 KINDS OF CLAYS 209 there is a bed of water-bearing sand underlying the lowest clay dug, and, as this is approached, hand-pumps have to be used to keep down the water until the last spit of clay is all taken out. In digging a pit of clay, it is well to avoid discarding a clay of lower grade or mixing it with the dirt stripping, because it has no market value at the time. Careless handling of the medium-grade clays in the Woodbridge and Perth Amboy districts in the early days of their develop- ment has been the means of spoiling much clay that would now be salable. Haulage. If the distance from the bank to works or shipping-point is short, wheelbarrows or one-horse carts are used, but, if a longer haulage is necessary, it is more economical to lay light tracks and haul the clay In cars drawn by horses or small engines. Steam haulage is economical for a distance of perhaps not less than 1000 feet, and provided the locomotive is kept constantly employed. When a pit is to be opened, the top dirt, stripping or bearing, as it Is variously called, is first removed to some place where it will not have to be disturbed, in order to avoid the cost of a second moving, but, after one pit has been started, it is often customary to use the stripping from a new pit for filling the old one. The cost of removing the stripping will depend on its character, whether hard or soft, the distance to be moved, and the possibility of its being used for any purpose, such as filling or grading. The methods of removal employed will also affect the expense. If the thickness of the overburden is considerable and a large quantity has to be removed, it is cheaper to dig it with a steam-shovel than by hand. Wheel-scrapers are also employed at times, and if the distance to the dump-heap is short the material can be carried there in the scraper. If the stripping can be used to mix with the clay it is sometimes dug with shovels and screened to free it from pebbles. A method tried at some localities is to remove the sandy or gravelly overburden by washing (PI. IX, Fig. 2). This Is done by directing a powerful stream of water from a hose against the face or surface of the gravel and washing it down into some ditch along which it runs off. In selecting the site for a dump-heap, care should be taken not to locate it over any clay -deposit which is to be worked out later, but the presence or absence of such clay under the proposed dump can commonly be determined by a few bore-holes made with an auger. Kaolin-mining. Since most of the kaolin-deposits worked in the United States are long and narrow, a method often adopted consists in sinking a circular pit in the kaolin about 25 feet in diameter. As the 210 CLAYS pit proceeds in depth it is lined with a cribwork of wood (PI. XXXIV, Fig. 1). This lining is extended to the full depth of the pit, which varies from 50 to 100 or even 120 feet. When the bottom of the kaolin has been reached the filling-in of the pit is begun, the cribwork being removed from the bottom upwards as the filling proceeds. If there is any overburden it is used for filling up the old pits. The kaolin is removed from the pit with a bucket-hoist, and as soon as one pit is filled a new one may be sunk in the same manner right next to it. In this way the whole vein is worked out, and, if the deposit is large, several pits may be sunk at the same time. A somewhat unique method of mining is that practiced in the Corn- wall, Eng., district where the material to be mined is a sandy kaolin of great depth. The method of working is described by J. H. Collins 1 as follows: "The depth of the overburden and the extent of the workable clay-ground having been sufficiently ascertained by pitting or boring (often by a combination of both methods), a shaft is sunk in the firm rock, near the clay which is to be worked, and to a depth of 15 or 20 fathoms. A cross-cut is put out from the bottom of the shaft into the clay-ground. This must be securely timbered where it approaches the clay-ground. The overburden having been removed arid deposited at a con- venient spot, a raise is put up vertically through the clay to the surface. In this is placed (vertically) a wooden launder, which reaches within a fathom or two of the surface, and is provided with lateral openings a foot or two apart, each of which is closed by a temporary wooden cover. This is called a 'buttonhole' launder. The shaft having been equipped with a suitable pump, work may be begun at once. The clay-ground, to a depth of a fathom or so around the buttonhole launder, is removed and a stream of water, pumped from the shaft or brought along from some other source, is made to flow over the broken ground, which is at the same time stirred up as may be necessary. The fine clay particles, held in suspension in the milky stream, pass down the launder and along the cross-cut to the shaft, whence they are pumped up for further treatment. The quartz-grains ('sand') and the coarser particles of mica, schorl (tourmaline), etc., are shoveled up from around the launder and trammed away to the waste-dump. As the depth of the workings increases, other 'buttonholes' are opened, the inclination of the clay 'stopes' being at the same time maintained by removing more overburden and by cutting away the margin of the pit. "The clay raised in suspension from the shaft by the pump is made to flcvr through a long series of shallow troughs called ' micas '; these are set nearly level, and the stream is divided again and again so as to lessen the rate of flow and to allow the fine sandy and micaceous particles to settle. Finally, the refined-clay stream is led into circular stone-lined pits, preferably from 12 to 18 ft. deep, where the clay settles to a creamy consistency, while the overflow of nearly clear water is conducted back to the clay-stop 3s, where it again serves for the washing pro- cess. The deposit in the 'micas' is swept out from time to time, an operation which 1 Min. Indus., XIII, p. 472, 1905. KINDS OF CLAYS 211 occupies only a few minutes, after which they are again ready to receive the clay stream. The thickened clay from the pits passes to large stone-built or stone- lined tanks, which are from 5 to 8 ft. deep. In many cases they consist merely of two dry-built rubble walls placed as far rpart as the depth of the tank and puddled between with waste sand, containing a little clay from some previous working. From the tanks, after further settlement, it is trammed into the kiln or 'dry.' The deposit in the micas is sometimes re-washed, so as to yield an inferior product, which is commercially sold as 'mica' or 'mica-clay.' "Carclazite 1 varies much in productiveness; in obtaining one ton of fine clay the following by-products have to be dealt with : From 3 to 7 tons of sand, average 4 tons; 2 to 5 cwt. of coarse mica, average 3 cwt.; 1 to 3 cwt. of fine mica (mica clay), average 2 cwt.; to 1 cwt. of stones, mostly quartz, with, generally, much 'schorl' from the stony veins or branches. A cubic fathom of carclazite of good quality will yield about three tons of fine clay; on an average nearly half a cubic fathom of overburden must be removed in order to get it." A somewhat similar method has recently been adopted to work the kaolin-deposits 2 at West Cornwall, Conn., and the following description of it is given by A. R. Ledoux : 2 "The kaolin-deposit of West Cornwall is an alteration in situ that is, it is not sedimentary. A series of clay-veins, dipping about 50 from the vertical, lie between a foot-wall of limonite and a hanging-wall of gneiss and hornblende schist. The clay-veins alternate with veins or seams of more or less broken quartz and unaltered feldspar. The deposit, which occurs at a point about 600 ft. above the Housatonic River, was opened five years ago, and about 5000 tons of washed kaolin has been extracted from open pits and sold. "Mr. Wanner conceived the scheme to disintegrate the kaolin in situ by means of jets of water under sufficient pressure, and floating the resultant product to the surface. To accomplish this result holes are drilled through the overlying gneiss, a pipe of 4-in. internal diameter is inserted into the bore and driven into the clay- body to within a few feet of the foot-wall. The wells in operation are from 50 to 198 ft. deep. Into this 4-in. pipe or 'casing ' an interior pipe is inserted of 2-in. external diameter, leaving an annular space of 1 in. for the flow of the slip. The lower end of the internal pipe is provided with a mouthpiece with several nozzle- like openings for the exit of the water; the mouthpiece rests on the clay-body, and the interior pipe sinks gradually as the clay is removed until it rests on the foot- wall of the vein. For the operation of these 'hydraulics' a head of water equivalent to a pressure of from 40 to 60 Ibs. per sq. in. is required, according to the nature of the vein-matter. "Residual kaolin slacks more or less readily, according to the amount of sand and mica mixed with it. In the case in point, it has been found that a pressure of 40 Ibs. is amply sufficient to cause the disintegration, the vein-matter contains 20 per cent and the slip, discharged by the hydraulics, from 60 to 75 per cent of pure kaolin. The purity of the discharged slip is inversely proportional to the veloc- ity of the overflow. 1 A name applied to the kaolin. 2 Amer. Inst. Min. Eng., Bi-monthly Bull., No. 9, p. 379, 1906. 212 CLAYS "Observations made during the 1905 season's work have shown that the overflow contains from 5 to 10 per cent of solid matter. A discharge of 100 gaL per min. through the annular space of 9.42 sq. in. from a depth of 127 ft. yielded 5 per cent of solid matter, of which 75 per cent was pure kaolin, while a discharge of 200 gal. per min., through the same orifice from the same depth, gave a slip con- taining 10 per cent of solid matter but only 54 per cent of pure kaolin, the rest being finely divided quartz and mica. "In addition to the lessening of the cost of extraction, the method described has effectually solved the transportation of the product to the railroad. Hereto. fore, the kaolin washed and dried at the mines was carted by teams over a difficult mountain road to West Cornwall, 4 miles distant. The fuel for the whole plant had to be hauled up the mountain the same distance. With slip issuing from the hydraulics of only 10 per cent of solid matter and sufficient fineness to pass through 100-mesh screens, the conveyance of the product through a pipe-line to the Housa- tonic Valley offers no difficulty, and the company now contemplates the erection of a new washing-plant adjacent to the river and railroad." Underground workings. This method may be resorted to when the clay-bed is covered by such a great thickness of overburden that its removal would be too costly. If the bed sought outcrops on the side of a hill, a tunnel or drift is driven in along the clay-bed, as shown in PI. VII, Fig. 2, but in case no outcrop is accessible it is necessary to sink a vertical shaft (Fig. 53) until the bed of clay is reached, and from this, levels or tunnels may be driven along the clay-bed. Underground methods are desirable, however, only under certain conditions, which may be enumerated herewith: 1. In the case of high-grade clays. 2. Where there is much overburden as compared with the thickness of the clay-deposit. 3. There should, if possible, be a solid dense layer overlying the clay stratum, otherwise the expense of timbering for supporting the roof may be too great. Timbering is nearly always necessary in underground clay-work. Where the clay is not inter-stratified between dense water- tight beds, it is often necessary to leave the upper and lower foot of clay to form a roof and floor. 4. The workings should be free from water, both on account of the cost of removing the same and because of the tendency of wet ground to slide. 5. The output is usually restricted, unless the workings underlie a. large area, and can be worked by several shafts or drifts. Soft clays are rarely worked by underground methods, but in Mary- land, Indiana, Missouri, Pennsylvania, and a few other localities, the shaly clays associated with the coals are frequently mined by shafts, drifts, or slopes. KINDS OF CLAYS 213 " Some of the mines are lighted by electricity and also equipped with electric hoists, drills, and haulage. Preparation of Clay for Market Unless clay is to be used for higher grades of ware, it rarely requires much preparation to make it marketable, for, since the impurities in clay often run in streaks or beds, they can be avoided in mining. Large concretions, pyrite nodules, and lumps of lignite are often picked out by hand and thrown to one side. Where the impurities are present in a finely divided form and distributed throughout the clay, screening or hand-picking may be ineffective, and washing is necessary. Washing. The method of washing most commonly adopted is the troughing method, in which the clay, after being stirred up and disinte- grated with water, is washed into a long trough along which it passes, dropping its sandy impurities on the way and finally reaching the set- tling-vats, into which the clay and water are discharged, and where the clay finally settles. Details. The disintegration of the clay is generally accomplished in washing-troughs. These consist of cylindrical or rectangular troughs, in which there revolves a shaft, bearing a series of arms or stirrers. The clay may be taken from the bank direct to the washer, or it may first receive a soaking in a pit to slake it. As the clay is put into the washer a stream of water is directed on it, and the revolving blades break up the clay so that it goes more readily into suspension. The water, with suspended clay, then passes out at the opposite end from which the water entered. The troughing (PI. X, Fig. 1) into which the material is discharged is constructed of planking and has a rectangular cross-section. Its slope is very gentle, not more than 1 inch in 20 feet usually, and its total length may be from 500 to 700 feet, or even 1000 feet. In order to economize space it is usually built in short lengths, which are set side by side, and thus the water and clay follow a zigzag course. The pitch, width, and depth of the troughing may be varied to suit the conditions, for at some localities it is necessary to remove more sand than at others. If the clay contains very much fine sand the pitch must be less than if the sand is coarse, since fine sand will not settle in a fast current. In the case of very sandy clays, it is customary to place sand-wheels at the upper end of the troughing. These are wooden wheels bearing a number of iron scoops on their periphery. As the wheel revolves the scoops pick up the coarse sand which has settled in the trough and, as the 214 CLAYS scoop reaches the upper limit of its turn on the wheel, by its inverted position it drops the sand upon a slanting chute, which carries it outside the trough. By the time the water reaches the end of the troughing nearly all the sand has been dropped and the water and clay are discharged into the settling-tanks, passing first, however, through a screen of about 80 or 100 mesh. This catches any particles of dirt or twigs and thus keeps the clay as clean as possible. The settling-tanks (PL X, Fig. 1) are of wood, usually about 4 feet deep, 8 feet wide, and 40 or 50 feet long. As soon as one is filled the water and clay are diverted into another. When the clay has settled, most of the clear water is drawn off, and the cream-like mass of clay and water in the bottom of the vat is drawn off by means of slip-pumps and forced into the presses (PI. X, Fig. 2). These consist of flat iron or wooden frames, between which are flat canvas bags. The latter are either con- nected by nipples with the supply-tubes, or else there may be a central opening in all the press bags and frames, which, being in line, form a central tube when the press is closed up. By means of pressure from the pumps, the slip is then forced into the press, and the water is also driven out of it. When the water has been squeezed out the press is opened, and the sheets of clay are removed from the press cloths and sent to the drying-room or racks. Washing is applied chiefly to kaolins, but is carried out to a less extent on fire-clays, glass-pot clays, and ball-clays. Air separation. This is a method of cleansing clays which has been rarely tried, yet, in some of the cases where it has been used, is said to have met with success. It is especially applicable to those clays from which it is necessary to remove simply coarse or sandy particles. The process consists, in brief, in feeding the dry clay into a pulverizer, which reduces it to the condition of a very fine powder. As the material is discharged from the pulverizer into a long box or tunnel, it is seized by a powerful current of air, which at once picks up the fine particles and carries them along to the end of the airway, where they are dropped into a bin. The coarser particles, which are too heavy to be picked up by the current, drop back and are carried through the pulverizer once more. Such a method would be especially applicable to kaolins that are free from iron, but probably would not be found adaptable to many of those containing ferruginous particles. There are several forms of separators on the market. In the Ray- mond pulverizer and separator the material is pulverized in the lower part of the machine and then thrown upward, the finer particles being PLATE X FIG. 1. View showing portion of sand-troughs, settling-tanks, and drying-racks at a kaolin-washing plant. (After Ries, Md. Geol. Surv., IV, p. 270, 1902.) j? IG 2. Filter-press for removing water from washed or blunged clays. The portion at the left end has been emptied and the leaves of clay taken from it are on the car. The workman is just removing a leaf of clay from the press. (After Ries, N. Y. State Mus., Bull. 35, p. 792, 1900.) 215 KINDS OF CLAYS 217 earned off by a fan to the discharge-hopper, the coarser ones falling back into the hopper. THE MANUFACTURE OF CLAY PRODUCTS Uses of Clay Probably few persons have any conception of the many different applications of clay in either its raw or burned condition. These varied uses can be best shown by the following table, compiled originally by R. T. Hill 1 and amplified by the writer: Domestic. Porcelain, white ware, stoneware, yellow ware, and Rockingham ware for table service and for cooking; majolica stoves; polishing-brick, Bath brick, fire-kindlers. Structural. Brick; common, front, pressed, ornamental, hollow, glazed, adobe; terra-cotta; roofing-tile; glazed and encaustic tile; drain- tile; paving-brick; chimney-flues; chimney-pots; door-knobs; fireproofing; terra-cotta lumber; copings; fence-posts. Refractories. Crucibles 'and other assaying apparatus; gas-retorts; fire-bricks; glass pots and blocks, for tank-furnaces; saggers; stove and furnace bricks; blocks for fire-boxes; tuyeres; cupola bricks; mold linings for steel castings. Engineering. Puddle; Portland cement; railroad ballast; water conduits; turbine-wheels; electrical conduits; road metal. Hygienic. Urinals, closet bowls, sinks, washtubs, bathtubs, pitchers, sewer-pipe, ventilating-flues, foundation-blocks, vitrified bricks. Decorative. Ornamental pottery, terra-cotta, majolica, garden- stands, tombstones. Minor uses. Food adulterant; paint fillers; paper filling; electric insulators; pumps; fulling cloth; scouring-soap ; packing for horses' feet; chemical apparatus; condensing-worms; ink-bottles; ultramarine manufacture; emery-wheels; play ing-marbles; battery-cups; pins, stilts and spurs for potters' use; shuttle-eyes and thread -guides; smoking-pipes; umbrella-stands; pedestals; filter-tubes; caster-wheels; pump-wheels; electrical porcelain; foot-rules; plaster; alum. METHODS OF MANUFACTURE In the following pages it is intended to give a brief account of the methods of manufacture employed, so as to enable one to see what requirements a clay has to meet. The more important products are 1 Mineral Resources, U. S., 1891, p. 475, Washington. 218 CLAYS taken up in the following order: Building- and paving-brick; sewer- pipe; drain-tile; hollow ware; conduits; fire-brick; roofing- tile; terra- cotta; floor- and wall-tile; pottery. Building-brick and Paving-brick Building-brick include common brick, face and pressed brick, enamel brick, and glazed brick, while paving-brick form a class by themselves. Common brick include all those used for ordinary structural work, and are employed usually for side and rear walls of buildings, or, indeed, for any portion of the structure where appearance is of minor importance, although for the sake of economy they are sometimes used for front walls. They are often made without much regard to color, smoothness of surface, or sharpness of edges. Face, front, or pressed brick include those made with greater care, and usually from a better grade of clay, much consideration being given to their uniformity of color, even surface, and straightness of outline. Red ones were formerly in great demand, but at the present time buff, white, and buff with manganese speckles are the most sought. Enamel brick are those which have a coating of enamel on one or sometimes two sides. The body is usually a fire-clay. Glazed brick differ from enamel brick in being coated with a trans- parent glaze instead of an opaque enamel. They are used more in Europe than in the United States. The clays used for brickmaking have already been described (p. 185). Manufacture of Brick The methods employed in the manufacture of common and pressed brick are usually very similar, the differences lying chiefly in the selection of material, the degree of preparation, and the amount of care taken in burning. The manufacture of bricks may be separated into the following steps: preparation, molding, drying, and burning. Preparation In brickmaking some preparation of the clay is commonly necessary, since few clays can be sent direct from the bank to the molding-machine, although some common-brick manufacturers reduce the preparation process to a minimum. Many clays are prepared by weathering, especially if they are to be KINDS OF CLAYS 219 used in the manufacture of pressed brick. This is done by distributing the clay over some flat surface in a thin layer not more than 2 or 3 feet in thickness and allowing it to lie there exposed to frost, rain, wind, and sun, which results in a slow but thorough disintegration or slacking. Iron nodules, if present, tend to rust, and are thus more easily seen and rejected, while pyrite, if present, may also decompose and give rise to soluble compounds, which form a white crust on the surface of the clay. Although some clays are prepared by weathering, yet in great part their disintegration is done by artificial means. Crushers. When the clay or shale is to be disintegrated or crushed,, it is commonly done dry, and the machine employed varies with the character of the material. Hard shale is often disintegrated in a jaw- crusher, which consists of two movable jaws that interact and are set closer together at their lower than at their upper ends. Dry pans. Where a soft shale or a hard, tough, dry clay is to be used,, dry pans (PI. XI, Fig. 1) are frequently employed. These consist of a. circular pan in which there revolve two iron wheels on a horizontal axis. The wheels turn because of the friction against the bottom of the pan, the latter being rotated by steam-power, and in turning they grind by reason of their weight, which ranges from 2000 to 5000 pounds. The bottom of the pan is made of removable perforated plates, so that the material falls through as soon as it is ground fine enough. Two scrapers are placed in front of the rollers to throw the material in their path. Disintegrators, which are sometimes used for breaking up clay or shale, consist of several drums, or knives on axles, revolving rapidly within a case and in opposite directions. As the lumps of clay are dropped into the machine they are thrown violently about between the drums and also strike against each other, thus pulverizing the material' completely and rapidly. Their capacity is large, but much power is also required to drive them. Rolls. These are often employed for breaking up clay and pebbles,, and where dry material is used they are quite effective; but if damp clay is put through them, as is done at some yards, the lumps are simply- flattened out. The surface of the rolls is smooth, corrugated or toothed,, or tapering, and the two rolls revolve in opposite directions and with differential velocities of from 500 to 700 revolutions per minute. In some the stones in the clay are crushed, in others they are thrown out, by reason of the construction of the machine. All the machines mentioned above are used on dry or nearly dry clay, but there are several other types which are employed for wet clays 220 CLAYS only, and these in addition to breaking up the clay may also be used to mix it. The process is sometimes termed tempering. Soak-pits. Soak-pits, used at many small yards for preparing the clay, are simply pits in which the clay, with water added, is allowed to soak overnight. Ring-pits. Ring-pits (PL XI, Fig. 2), employed at many common- brick yards, are circular pits from 20 to 25 feet in diameter, about 3 feet deep, and lined with boards or brick. Revolving in this pit is an iron wheel, 6 feet in diameter, so geared as to travel around the pit in a spiral path, thus thoroughly mixing the mass. The tempering is accomplished usually in 5 or 6 hours, and one pit commonly holds enough clay for from 25,000 to 30,000 brick. Ring-pits are cheaper than pug-mills, but have a lower capacity and require more room. They are operated by either steam- or horse-power. Pug-mills (Fig. 42) are semi-cylindrical troughs, varying in length from 3 to 14 feet, with 6 feet as a fair average. In. this trough there revolves a horizontal shaft, bearing knives set spirally around it and having a variable pitch. The clay and water are charged at one end, and the blades on the shaft not only cut up the clay lumps, but mix the mass, at the same time pushing it towards the discharge end. Pug-mills are thorough and continuous in their action, take up less space than ring-pits, and do not require much power to operate. They are used in connection with both stiff-mud and soft-mud machines. Wet pans (PL XII, Fig. 1). These are similar to dry pans, but differ from them in having a solid bottom. The material and water are put into the pan, and the clay is crushed and tempered at the same time. Where the clay contains hard lumps of limonite or pyrite nodules, a wet pan is superior to a pug-mill or disintegrator, for the charge is crushed and tempered in a few minutes, and can then be replaced by another one. Molding Bricks are molded by one of four methods, namely, soft-mud, stiff- mud, dry-press, and semi-dry-press, although in reality there is not much difference between the last two. Soft-mud process. In this method the clay, or clay and sand, are mixed with water to the consistency of a soft mud or paste and pressed into wooden molds. Since, however, the wet clay is sticky and likely to adhere to a wooden surface, the molds are sanded each time before being filled. Soft-mud bricks, therefore, show five sanded surfaces, PLATE XI FIG. 1. Dry pan used for grinding hard clays, shale, and brick. (After H. Ries, N. Y. State Museum, Bull. 35, p. 765, 1600.) FIG. 2. Ring-pit for mixing clays. (After H. Ries, N. Y. State Museum, Bull. 35, p. 659, 1900.) 221 OF THf UNIVERSITY OF PLATE Xli FIG. 1. Wet pan for grinding and mixing clays or shales. (After H. Ries, Md. Geol., IV, p. 356, 1902.) FIG. 2. Cutting-table of stiff-mud brick-machine. (After H. Ries, N. Y. State Mus., Bull. 35, p. 662, 1900.) 225 or THF f UNIVERSITY ] OF KINDS OF CLAYS 227 and the sixth surface will be somewhat rough, due to the excess of clay being wiped off even with the top of the mold. Soft-mud bricks are molded either by hand or in machines. The soft-mud machine (Fig. 43) consists usually of an upright box of wood or iron, in which there revolves a vertical shaft bearing several blades or arms. Attached to the bottom of the shaft is a curved arm which forces the clay into the press-box. The molds, after being sanded, are shoved underneath the press-box from the rear side of the machine. Each mold has six divisions, and as it comes under the press-box the FIG. 43. A soft-mud brick-machine. plunger descends and forces the soft clay into it. The filled mold is then pushed forward automatically upon the delivery-table, while an empty one moves into its place. As soon as the mold is delivered its upper surface is " struck" off by means of an iron scraper. Under favorable conditions soft-mud machines have a capacity of about 40,000 brick per day of ten hours, although they rarely attain this. The soft-mud process was the first method of molding employed, and is still largely used at many localities. It is adaptable to a wider range of clays than any of the others, and possesses the advantage of producing not only a brick of very homogeneous structure, but one that is rarely affected by frost action. 228 CLAYS Stiff-mud process. With this method (PL XII, Fig. 2, and Fig. 44.), the clay is tempered with less water and consequently is much stiffer. The principle of the process consists in taking the clay thus prepared and forcing it through a die in the form of a rectangular bar, which is then cut up into bricks. The most general form of the stiff-mud machine, known as the auger machine, is that of a cylinder closed at one end, but at the other end tapering off into a rectangular die whose cross- section is the same as either the end or the largest side of a brick. Within this cylinder, which is set in a horizontal position, there is a shaft, carrying blades similar to those of a pug-mill, but at the end of the shaft nearest the die there is a tapering screw. The die is heated by steam or lubricated by oil on its inner side, in order to facilitate the flow of the clay through it. The tempered clay is charged into the cylinder at the end farthest from the die, is mixed up by the revolving blades, and at the same time it is moved forward until seized by the screw and pushed through the die. Since this involves considerable power, it results in a marked compression of the clay, and there is also some friction between the sides of the bar and the interior of the die, causing the center of the stream of clay to move faster than the outer portion. Excessive friction between die surface and clay is likely to cause the latter to tear on the edges, producing serrations like the teeth of a saw. The effect of the screw at the end of the shaft, together with the differential velocities within the stream of clay, also produces a laminated structure in the brick, which is often greatest in highly plastic clays, but is sometimes marked in clays of only moderate plasticity when machines of a particular structure are used. The brick made in auger machines are either end-cut or side-cut, depending on whether the area of the cross-sections of the bar of clay corresponds to the end or side of a brick, and consequently the mouth of the die varies in size and shape. The auger machine is probably used more extensively at the present day than either the soft-mud or dry- press machine, especially for making paving-brick. It has a large capacity and can produce 45,000 or even 60,000 brick in ten hours, the output of the machine being sometimes increased by the use of double or even triple dies, though this is not a desirable practice. As the bar of clay issues from the machine it is received on the cutting- table, where it is cut up into bricks. The stiff-mud process is adapted mainly to clays of moderate plas- ticity. The stiff-mud brick, like the soft-mud ones, can be re-pressed, and many face brick are now made by this process. KINDS OF CLAYS 231 Dry-press (PL XIII) and semi-dry-press process. This process is commonly used for the production of front brick, but in some States is extensively employed even for common-brick manufacture. The clay is powdered and then pressed into steel molds in a dry or nearly dry condi- tion. In order to prepare the clay for disintegration, it is usually stored in sheds for some time before being used, and is then broken up either in a disintegrator or a dry pan before passing to the screen, which is com- monly from 12 to 16 mesh. The molding-machine consists of a steel frame of varying height and heaviness, with a delivery-table about 3 feet above the ground, and a press-box sunk into the rear of it. The charger is connected with the clay-hopper by means of a canvas tube, and forms a framework which slides back and forth over the molds. It is filled on the backward stroke, and on its forward stroke lets the clay fall into the mold-box. As the charger recedes to be refilled, a plunger descends, pressing the clay into the mold; but at the same time the bottom of the mold, which is movable, rises slightly, and the clay is subjected to great pressure, which may be repeated after a moment's interval. The plunger, then rises, while the bottom of the mold also ascends, with the freshly molded bricks, to a level with the delivery- table. These are then pushed forward by the charger as it advances to refill the molds. The faces of the mold are of hard steel and heated by steam to prevent adherence of the clay. Air-holes are also made in the dies to permit the air, which becomes imprisoned between the clay particles, to escape. If this were not done, the air in the clay would be com- pressed, and when the pressure was released, its expansion would tend to split the brick. At several localities in the United States an hydraulic dry-press machine is used, in which the gradually applied pressure is produced by a pair of hydraulic rams acting from above and below. The advantages claimed for the dry-press process are that in one operation it produces a brick with sharp edges and smooth faces. There is practically no water to be driven off, as the clay has been pressed in a nearly dry condition, hence drying is done more rapidly. When hard- burned, dry-pressed bricks are as strong as others, but on account of the method of molding they often show a granular structure. The capacity of a dry-press machine is about the same as that of a soft-mud one, provided six bricks are molded at a time. Two- and four-mold machines are, however, also made. The initial cost of the machinery is considerable, although this may be more than offset by the saving in drying. 232 CLAYS Re-pressing. Many soft-mud and stiff-mud brick that are to be used for fronts are improved in appearance and often in density by re- pressing, an operation which smoothens the surface and straightens and sharpens the edges of the product, as well as sometimes increasing the strength. A re-pressing machine is shown in PI. XIV, Fig. 1. The change in volume that occurs in a brick in re-pressing can be seen from the following measurements of a paving-brick : Before re-pressing, 8f by 4| by 3^ inches, = H9f cubic inches. After re-pressing, 8H by 4| by 3 inches, = 109^ cubic inches. Drying Bricks made by either the stiff-mud or soft-mud process have to be freed from most of their water of tempering before they can be burned. Open yards. These are used at most soft-mud brick-plants, and are simply smooth flat floors of earth or brick, on which the bricks are dumped as soon as molded, and allowed to dry in the sun. At some yards the drying-floor is partly covered. Pallet driers. These are covered frames for holding the boards or " pallets " on which the bricks are dumped from the mold at the machine. They are used at many soft-mud yards and even some stiff-mud plants, and possess the advantage of cheapness, large capacity, economy of space, and protection against rain. One disadvantage of the above method is that the driers can not be used in cold weather. Dampness in summer may also interfere with them, and therefore sunlight and wind are usually the most favorable weather conditions. Some clays are quite susceptible to air-currents, however, and crack easily when exposed to them. Drying-tunnels. Many brickmakers dry their product by this method, especially if they continue in operation throughout the year. With this system the bricks, after molding, are piled on cars, which are run into an artificially heated tunnel (Fig. 45). Several of these tunnels are generally constructed side by side, and the green bricks are run in at the cooler end, and pushed along slowly to the warmer end, where they are removed, this passage through the tunnel requiring commonly from 24 to 48 hours. The tunnel driers used at different localities differ chiefly in the manner in which they are heated, the following methods being employed: 1. Parallel flues underneath and heated by fireplaces at one end. 2. By steam heat, the pipes being laid on the floor or sides of the tunnel or both. 3. By hot air, the latter being supplied from cooling-kilns, PLATE XIII Dry-press brick-machine. (After H. Ries, N. Y. State Mus., Bull. 35, p. 665, 1900.) 233 KINDS OF CLAYS 235 o I" 236 CLAYS or by passing the outer air over steam-coils before it is drawn through the tunnel by natural draft or fan. If the air is too hot, cooler air is mixed with it before it enters the drier. The temperature to which tunnels are heated varies, and in most cases is not over 120 C. (250 F.). Floor driers. Floor driers are used at some brick-works, although their application is more extended at fire-brick works. They are made of brick, and have flues passing underneath their entire length, from the fireplace at one end to the chimney at the other. Such floors are cheap to construct, but the distribution of the heat under them is rather unequal, and a large amount of labor is required to handle the material dried on them. In some cases drying-racks are set up on the top of the kiln. Burning Kilns. Bricks are burned in a variety of kilns, ranging from tempo- rary structures, which are torn down after each lot of brick is burned (PL XIV, Fig. 2), to patented or other permanent forms of complicated design. They are built on one of two principles, either up-draft or down- draft. In the former the heat from the fire-boxes at the bottom passes directly into the body of the kiln and up through the wares, escaping from suitable chimneys or openings at the top. In the latter the heat from the fire-boxes is conducted first to the top of the kiln chamber, by means of suitable flues on the interior wall, and then down through the wares ; being carried off through flues in the bottom of the kiln to the stack (PL XV, Fig. 2). The down-draft system is growing in favor, as the burning can be regulated better. Furthermore, since the bricks at the top receive the greatest heat, and these at the bottom the least, there is less danger of the bricks in the lower courses being crushed out of shape if heated too high. The amount of heat required for burning brick will vary with the clay and the color, density or degree of hardness desired, the same clay giving different results when burned at different temperatures. Common bricks are rarely burned any higher than cone 05, and usually not above cone 010, while pressed brick are frequently fired to cone 7 or 8, because the clays generally used have to be burned to that point to render them hard. Up-draft kilns. The simplest type of kiln with rising draft is known as the "scove-kiln" (PL XIV, Fig. 2, and PL XV, Fig. 1), which is in use at many yards making common brick, and is of a temporary character. The bricks are set in large rectangular blocks from 38 to 54 courses PLATE XIV FIG. 1. A steam-power re-press. The bricks on the belt are being brought from the stiff-mud machine. (Photo by H. Ries.) FIG. 2. Setting brick for a scove-kiln. (After H. Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 240, 1900.) 237 -- -e " O THE ERSITY ) OF KINDS OF CLAYS 239 high, depending on the kind of clay. In building up the mass a series of parallel arches is left running through the mass from side to side, and with their centers about two feet apart. After the bricks are set up they are surrounded by a wall two courses deep of " double-coal" brick, and the whole outside of the mass daubed with wet clay to prevent the entrance of cold air during burning. The top of the kiln is then closed by a layer of bricks laid close together and termed the platting. Kilns of this type involve little cost except the labor of building. They are, however, adapted only to common brick, and are not capable of being heated to a high temperature. The so-called Dutch kilns are a slight improvement over the scove- kilns, since they have permanent side walls, and so yield somewhat better results, for they heat up better and admit less cold air. Many common brick and nearly all front brick, however, are burned in kilns that are walled and roofed, with a door at each end for filling and emptying. They are, therefore, far more reliable, capable of better regulation, attain higher temperatures, and are both up-draft and down- draft. The fuel used is sometimes wood, but mostly coal, not a few manufacturers employing anthracite in part. With coal, the fuel is sometimes placed on grate-bars or on the floor of the hearth. In plan they are either rectangular or circular. The bricks are set in much the same way as in the others. Down-draft kilns. In these the heat from the fires is conducted first to the top of the kiln-chamber by means of suitable flues on the inner wall of the kiln, and then down through the ware, being carried off through flues in the bottom of the kiln to the stack. With this system the burning can be regulated better, and there is less loss from cracked and overburned brick. Furthermore, since the bricks at the top receive the greatest heat, and those at the bottom the least, there is less danger of the bricks in the lower courses being crushed out of shape. Down-draft kilns are either circular or rectangular in form. The latter, which have greater capacity and are more economical of space, are employed commonly for burning brick, while the former are preferred for drain-tile, sewer-pipe, or stoneware. There are a number of different types of down-draft kilns, which differ in the arrangement and structure of the flues, arrangement of the fire- place, etc. Continuous kilns (PI. XVI, Fig. 2). These were originally designed to utilize the waste heat from burning. Many types have appeared, some of which are patented, but the principle of all is the same. It consists essentially in having a series of chambers arranged in a line, 240 CLAYS circle, or oval, and connected with each other and also with a central stack by means of flues. Each chamber holds about 22,000 bricks. In starting the kiln, a chamber full of bricks is first fired by means of exterior fire-boxes, and while the water-smoke or steam is passing off the vapors are conducted to the stack, but as soon as this ceases the heat from the chamber first fired is conducted through several other chambers ahead of it, before it finally passes to the stack. In this manner the waste heat from any chamber is used to heat the others. When any one compartment becomes red hot, fuel in the form of coal-slack is added through small openings in the roof, which are kept covered by iron caps. As soon as one chamber has reached its maximum temperature, the next two or three ahead of it are being heated up, while those behind it are cooling down. A wave of maximum temperature is therefore con- tinually passing around the kiln. It is thus possible to be burning brick in certain chambers, filling others, and emptying still others, all at the same time, making the process a continuous one. Continuous kilns are employed in many states for burning common brick with considerable success. Sewer-pipe Manufacture While some works use a soft clay for sewer-pipe, the largest factories in the United States, namely, those located in Ohio, run chiefly on shale, to which a certain amount of refractory clay is sometimes added. The material therefore requires crushing before tempering. Dry pans (p. 219) are used for this purpose. The ground-clay is then screened and mixed in pug-mills (p. 220), wet pans (p. 220), or chaser-mills (p. 265). Sewer-pipes are made in a special form of press (Figs. 46 and 47, and PI. XVII, Fig. 1) consisting of two cylinders, connected with a continuous piston and placed one above the other. The upper is the steam and the lower the clay cylinder. The size ratio of these tw r o cylinders varies from 1 : 2 to 1 : 3. 1 "The piston is propelled by the admission of steam to the upper cylinder, giving it a downward movement which presses the clay through a die at the bottom of the lower cylinder. The action is then intermittent, the piston receding when it has reached its length of stroke and a supply of clay is needed. "The clay previously prepared and in plastic condition is brought to the press on a moving belt. Each time the piston recedes, the cylinder 1 Beyer and Williams, hi. (Jeol. Surv., XIV, p. 214, 1904. PLATE XV FIG. 1. Side view of a scove-kiln for burning common brick, exterior daubed over with wet clay. The firing-holes are shown at bottom of one side. (After H. Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 240, 1904.) FIG. 2. Down-draft kilns. (Photo loaned by Robinson Clay-product Co.) 241 PLATE XVI FIG. 1. Interior view of circular down-draft kiln. (Photo loaned by Robinson Clay-product Manufacturing Co.) FIG. 2. Haight continuous kiln. (After H. Ries, N. Y. State Mus., Bull. 35, p. 679, 1900.) 243 KINDS OF CLAYS 245 is filled with clay by throwing this belt into motion. The die which forms the pipe consists of a central cone and an outer die or bell, the space between the cone and bell determining the thickness of the wall of the pipe. By changing these the various sizes of sewer-pipe are FIG. 46. Side elevation of a sewer-pipe press. made. It has been found of advantage to have the issue, or the dis- tance through which the clay must travel between the dies, compressed to its maximum thickness, quite long. J. E. Minter l recommends an issue of not less than three inches for dies smaller than eight inches 1 Brick, XV11I, No. 1, p. 48. 246 CLAYS and not below four inches for dies over eight inches in diameter. The basis for this recommendation is that where the issue is short, blebs of air imprisoned in the clay will remain and are apt to form blisters on the pipes, while with a long issue the air will back upwards through FIG. 47. Front elevation of a sewer-pipe press. the loose clay and escape in the direction of least resistance rather than remain in the clay." Beneath the die is the pipe-table which receives the pipe as it issues from the cylinder. The table is supported by a vertical rod which is kept in perfect alignment with the center of the cylinder. The table KINDS OF CLAYS 247 is raised and lowered by weights which may be so adjusted as to counter- balance. After the pipe is forced out the desired length it is cut by hand, by wire, or automatically by means of a power cutter, the last consisting of a knife edge in the lower part of the cylinder, which is thrust out and given a circular motion that severs the pipe when the cutting mechanism is thrown into gear. The length of stroke of the piston and therefore the maximum length of the pipe is about four feet. The diameter of the pipes ranges from three or four inches to three feet. Special shapes, such as traps, sockets, elbows, and trees, are usually made by hand in plaster molds, and require careful drying. At times Y shapes can be made by cutting two straight pieces on the slant and joining them together with wet clay. Sewer-pipes are dried on floors, heated by steam-pipes, and burned in down-draft kilns. For burning they are stood on end and salt-glazed. All defects, such as iron spots, blisters, imperfect glazing, or warp- ing, cause the product to be placed among seconds. Drain-tile Drain-tile are made in several styles as follows: Horseshoe- tile, of horseshoe-shaped cross -section. Sole-tile, cylindrical with a flat base. Pipe-tile, with cylindrical cross-section. For the making of drain-tile the clay should be thoroughly tempered before molding, this being commonly done in a pug-mill (p. 220). Mold- ing is usually done in some form of stiff-mud machine, the cylinder of clay as it issues from the die being cut up into the desired lengths. Drying is commonly done on pallet-racks (p. 232), such as are used for common bricks, or it may also be done in tunnels. The burning, which is usually done at a low temperature, presents no special difficulties, and is done in a variety of kilns, the tile being often burned with com- mon brick. Hollow Ware for Structural Work Under this heading are included fireproofing, terra-cotta lumber, hollow blocks and hollow bricks. These are all hollow (PL XVII, Fig. 2), being molded through a stiff-mud die and may contain one or more cross webs or partitions to give them strength. Fireproofing 248 CLAYS is the term applied to those forms used in the construction of floor- arches, partitions, and wall-furring for columns, girders, and other purposes in fireproof buildings. Terra-cotta lumber is a form of fire- proofing that is soft and porous, owing to the addition of a large per- centage of sawdust to the clay. The former burns off in the kiln, thus leaving the material so soft and porous that nails can be driven into it. It is used chiefly for partitions. Hollow blocks are used for exterior walls, in both fireproof and non-fireproof buildings. They are of rec- tangular outline. Hollow brick are like hollow blocks in form, but no larger than ordinary building-bricks. A number of different shapes and sizes of fireproofing are made, and while the majority of them agree in being 12 inches long the other two dimensions may vary. Thus of the blocks which are 12 inches long, the other dimensions may be 6 by 3 in., 6 by 4 in., 6 by 5 in., 6 by 6 in., 6 by 7 in., etc., or perhaps 3 by 8 in., or 3 by 12 in., etc. A large number of the fireproof shapes made are for floor-arches, and in such cases the architect commonly specifies the depth of the arch, while the width of the blocks is governed by the width of the span. The weight of the arch will depend on its depth. Thus, 6-inch floor-arches weigh about 25 pounds per square foot. 7 " it tt tt tt 2g tt tt c 10 " tt tt tt tt 35 tt 12 " tt tt tt tt 42 tt it it 3 " book-tile ' ' tt 15 tt tt 1 1 3 " partition-tile ' ' tt 15 tt tt it 6 " tt it it tt 21 " " tt ti 8 " tt .< tt 28 " it tt 2 " wall furring ' ' 8.5 " K it 3 " tt tt " 10.5 " it n 2 " column covering " " 13 " it tt 3 " it t t it 15 " tt it The cost of fireproofing is commonly figured by the ton. Hollow blocks are usually made in 8-inch lengths, but vary in their other dimensions, being 4 by 16 in., 6 by 16 in., 8 by 16 in., 10 by 16 in., 12 by 16 in., etc. They are used quite extensively in the Central States, but not so much in the Eastern ones. Hollow blocks are made with either smooth, corrugated, or ornamental surfaces. Sizes 8 by 4 by 16 in. are sold for about $0.07 each, and 8 by 8 by 16 in. at $0.10 each. Hollow bricks are often used for the interior course of exterior walls, and the plaster can be laid directly on them with- out the use of lathing. PLATE XVII FIG. 1. Molding 30-inch sewer-pipe in pipe-press. (Photo loaned by Robinson Clay-product Co.) FIG. 2. Some forms of fireproofing made by stiff-mud machine. (Photo by C. M. Doyle in N. Y. State Museum, Bull. 35, p. 775, 1900.) 249 KINDS OF CLAYS 251 In some States shales are used for making hollow ware, while in others plastic clays are employed. Calcareous clays are undesirable as being unsuited to the production of a vitrified ware. The clays used for making fireproofing have been referred to on p. 192. Manufacture. The method of preparation used for making hol- low blocks or fireproofing is essentially the same as that employed in the manufacture of stiff-mud bricks. Shales are sometimes first ground in a dry pan (p. 219) or disintegrator (p. 219) and then screened, followed by mixing in a pug-mill (p. 220) ; or a wet pan (p. 220) may do the combined work of crushing and tempering. Molding is done in a stiff-mud machine (p. 228), care being necessary to have the clay suffi- ciently plastic to permit its flowing freely from the die and prevent tearing on the corners or edges. The die is of a special type, which emits a hollow tube with cross- partitions, and the cutting-table is likewise sometimes of a specialized type, so designed that as the brick reaches the end of the table it is turned to an upright position to facilitate handling. Hollow blocks and fireproofing are dried on racks (p. 232) in tunnel- driers (p. 232), or even on heated floors, the last being the method most commonly used. When hot floors are used they are heated by steam-pipes passing under them or around the walls of the drying-room. In burning any of these shapes they are stood on end, and the smaller ones are sometimes burned in the same kilns with brick. Williams 1 gives the following advantages for hollow blocks: Lightness. Sufficient strength, to insure a large factor of safety in any common building construction Amount of clay required from one third to one half that necessary for solid brick. Smaller expense of transportation due to decreased weight of product. Full protection against dampness and temperature. Possibility of terra-cotta decora- tion on exterior of block. 2 Conduits Manufacture. Conduits form a line of clay-products, the use of which has greatly increased in the last few years. These are hollow blocks of varying length, having sometimes several cross-partitions and rounded edges, and are used as pipes for electrical cables and wires 1 la. Geol. Surv., XIV, p. 213. 2 See E. G. Durant. Hollow Building-blocks. Published by American Clay- working Machinery Co., Bucyrus, O. (No date.) 252 CLAYS below ground. On this account they have to be hard-burned with dense body, and are salt-glazed. The clays used are similar to those employed for making fireproofing, although they are somewhat more carefully selected with regard to plasticity and freedom from pyrite and limonite lumps. They must also burn dense at a moderate temperature. The clays are prepared in essentially the same manner as for hol- low blocks, and are molded in auger stiff-mud machines. They are then removed from the cutting-table on a pallet and placed on a stand, where the ends are trimmed smooth before the pieces are taken to the drying-floor or drying-tunnel. In drying, the conduits are stood on end. The burning is commonly done in down-draft kilns, between cones 8 and 9, although some manufacturers burn lower than this. The average shrinkage that takes place in a long conduit is about as follows: 1 Length, freshly molded, 39 inches; length, air-dried, 37 inches; length, burned, 35 inches. There has been a great demand for conduits in many cities during the last few years, many being used in New York City especially, in the construction of the rapid-transit subway, and some large plants are run almost exclusively on this line of work. Conduits are also occasionally made at the fireproofing factories. Fire-brick Most fire-brick makers employ a mixture of several grades of clay, to which there is added a certain percentage of ground fire-brick or even coarse quartz. These ingredients are sometimes ground in a dry pan (p. 219) or disintegrator (p. 219), then screened, and tempered in a pug-mill (p. 220). At some plants a wet pan (p. 220) combines the crushing and tempering operation. Where soft clays exclusively are used, the tempering is occasionally done in a ring-pit (p. 220). Fire-bricks were originally molded entirely by hand, and some manufacturers still cling to this method, but many now employ the soft-mud (p. 220) or stiff-mud machine (p. 228). In all these methods the brick requires re-pressing after it has been drying for a few hours. A few works manufacture dry-press (p. 231) brick, and for some pur- poses these may be desirable, but they are not regarded as altogether satisfactory. Drying is generally done on brick floors, heated by flues passing underneath them, but some manufacturers prefer dry ing- tun- nels (p. 232). 1 N. J. Geol. Surv., Final Kept., VI, p. 284, 1904. KINDS OF CLAYS 253 Most fire-brick makers burn their brick in down-draft kilns, but there is a remarkable difference in the temperature reached, this in the United States ranging from cones 5 to 18. Fire-bricks are made in many different shapes, and vary greatly in their density, hardness, and texture, according to the conditions under which they are to be used. For abrasive resistance they must be hard, to resist corrosion they must be dense, while, for resistance to high heats and changes of temperature, porosity and coarseness are of importance. ' 1 23456789 10 12 14 16 IE 20 22 24 2ft 28 30 32 ?l- 36 38 40 42 44 s 1 2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 If umber of Analysis FIG. 48. Graphic representation of composition and fusibility of some domestic fire-brick. (After Weber.) The influence of texture and composition on refractoriness has been well set forth by the experiments by Weber, 1 which are graphically illustrated in Fig. 48. From these tests he concluded that the refractoriness of a fire-brick depends on the total quantity of fluxes present, the silica percentage, and the coarseness of grain. 1 Trans. Amer. Inst. Min. Eng., Sept., 1904. 254 CLAYS Roofing-tile Although used for many years abroad, the manufacture of roofing- tile has not been very extensively developed in the United States, but its growth in the last decade is nevertheless gratifying. Roofing-tile are made in the following shapes: Shingle-tile, which are perfectly flat, and laid on the roof in the same manner as slate. Roman tile, of semi-circular cross- sect ion, and laid with the con- vex and concave side up alternately, so that one straddles two others- Interlocking-tile, with grooves and ridges which fit into each other, thus locking the tiles together. The first are usually vitrified, the others may or may not be, and if porous are often salt-glazed. The crushing and preparation of the clay is done by the same methods as are used for making stiff-mud brick. Shinge-tile and Roman tile can be molded by forcing a ribbon of clay from an auger-machine die, but interlocking-tile are made by repressing slabs of the tempered clay in a special form of machine. (PL XVIII, Fig. 1.) The tiles are dried in tun- nels and burned in up- or down-draft kilns to the proper temperature. Terra-cotta The term terra-cotta is applied to those clay-products used for struc- tural decorative work, and which cannot be formed by machinery. They are therefore to be molded by hand. The requisite qualities of terra-cotta clays have been referred to on p. 182. Most factories use not only a mixture of several clays, but add in a variable quantity of grog, i.e., ground fire-brick, terra-cotta, or sewer-pipe. The object of using such a mixture is to produce a body of the proper plasticity, shrinkage, and density after burning, and the color of the body is of no great importance, since the color is applied superficially. Manufacture. The manufacture of terra-cotta stands on a much higher plane in ceramic technology than it did a few years ago, so that the number of colors now made is much greater; and attention has also been directed towards producing effects which closely imitate differ- ent kinds of building stones, as well as increasing the complexity in the designs which can be executed. Indeed, the use of terra-cotta for exterior decoration has met with such success that but few modem buildings of large size are erected at the present day without the use of a large quantity of this product. Architectural fayence, of high artistic merit, and consisting of a terra-cotta body covered with matt- PLATE XVIII FIG. 1. Roofing-tile press for molding interlocking tile. (After H. Ries, N. Y. State Mus., Bull. 35, p. 765, 1900.) FIG. 2. Modeling terra-cotta objects. (Photo by H. Ries.) 255 KINDS OF CLAYS 257 glaze or bright enamel, is a form of terra-cotta now made by several art potteries as well as terra-cotta works. In the manufacture of terra-cotta the clay is usually ground first in a dry pan (p. 219), having sometimes been previously exposed to the weather, partly for the purpose of disintegrating the clay. The ground-clays are often tempered in a wet pan (p. 220), and may then be subjected to still further mixing in a pug-mill of either vertical or hori- zontal type. The clay issues from this as a square bar, and is cut up into Lumps which are piled up and kept covered until ready for use. Terra-cotta is always formed by hand, either in plaster molds or by modeling. The former method is employed for all simple forms, but for intricate undercut designs it is necessary to model the pieces free-hand (PI. XVIII, Fig. 2), and every terra-cotta factory has its corps of skilled modelers for this purpose. In making a mold it is first neces- sary to make a plaster model around which the mold can be cast. Small and simple designs can be molded in one piece, but larger objects or special shapes have to be formed in several pieces which are joined together when set in the building. In filling a plaster mold the tem- pered clay is pushed into all the corners and crevices and spread over the entire inner surface of the mold to a depth of about an inch and a half, after which the sides are connected by clay walls or partitions to strengthen the piece. The mold is then set aside for several hours in order to permit the clay to shrink sufficiently to allow of its being removed from the plaster form. Any rough or uneven edges are then usually trimmed off with a knife. Terra-cotta is usually dried on steam-heated floors, and this process must be carried on slowly and carefully with large pieces. For large complex pieces, the drying may even be retarded. After thorough air-drying the green ware is taken to the spraying-room, where the slip which is to form the surface coating is sprayed on it, thus form- ing a thin layer over all the surface, and also being somewhat absorbed by the body. The slip, which is commonly a mixture of kaolin, ball- clay, quartz, and feldspar (or other fluxes) to which the proper color- ing ingredients are added, forms an impervious layer on the surface of the terra-cotta, and also produces the color effect on the ware. It is sometimes of such composition as to burn to a dull enamel. Full- glazed terra-cotta is but little made in the United States, but the demand for matt-glazed or semi-dull glazed terra-cotta has greatly increased in the last two years. This effect was first produced by sand- blasting a full-glazed surface, but proved unsatisfactory, and at present the best plants are covering such ware with a regular matt-glaze. 258 CLAYS Terra-cotta is commonly burned in circular down-draft kilns, whose diameter ranges from 15 to 25 feet, the kilns being of the muffle type. That is to say, they have a double wall through which the gases of com- bustion pass, and do not come in contact with the ware, which becomes heated by radiation from the walls of the muffle. The different pieces are set in the kiln surrounded by a framework of tiles and pipes of fire- clay (PL XIX, Fig. 1), so that during the burning no object has to bear any weight other than its own. The total shrinkage in drying and burning is commonly about 8 per cent, and the ware is never burned to vitrification. Some terra-cotta manufacturers burn at as low a cone as 02, but the majority probably reach cones 6 or 8. Floor-tile Under this heading are included tile of a variety of shapes and colors which are used for flooring. On account of the conditions under which they are used they should possess sufficient hardness to resist abrasive action, sufficient transverse strength to resist knocks, and sufficient density to prevent excessive absorption of water. White tiles show little or no absorption, but some of the other colors soak up from 1 to 5 per cent of moisture, or perhaps even more. 1 Great care is necessary in the selection of raw materials for floor- tile as the clays used must be such that they will not form surface cracks after being air-pressed. The clay should also be free from any ten- dency to warp or split in burning and furthermore the manufacturer must aim to adjust his mixtures for facing and backing in case they are different. Clays used for floor-tile should also be as free from soluble salts as those used for the manufacture of pressed brick or terra-cotta, although, as pointed out by Langenbeck, 2 soluble lime salts may come from the coloring materials used. Thus the manganese and umber used for chocolates, brown and black, are seldom free from gypsum. Purdy 3 has suggested the following classification of floor-tiles: [ Vitreous j White Colored . i r \ Prepared facing body on a Face-tile. . . . { , . . j Porous j Clay Colors f Vitreous j White Colored SM bodieg formed 1 esserse -j . . , I Encaustic j Clay Colors geometric shapes. 1 N. J. Geol. Surv., Fin. Kept,, VI, p. 287, 1904. 2 Chemistry of Pottery, p. 155. 3 Trans. Amer. Cer. Soc., VII, p. 95, 1905. 8 I $3 o|g ^ o ^r 10 C hC r-5 KINDS OF CLAYS 261 Floor-tile when white are commonly made of a mixture of white- burning clays, flint, and feldspar. Buff-colored tiles and artificial ones are usually made from fire-clays, while red tiles are often made from a red-burning clay or shale. A certain amount of flint and feldspar is generally added to the clay to regulate the shrinkage or degree of vitri- fication in burning. Floor-tiles are always molded by the dry-press process in hand- potoer machines, the raw material being first carefully ground and mixed. In burning tiles they are placed in saggers and burned in down-draft kilns. The face-tiles include the plain or Alhambra 6X6 tile strips of various sizes, such as 6X3 and 6X1J used as body tile, and are most generally made with a prepared facing body backed by a common body, the latter being ground in a dry pan to a 16-mesh powder. In the manufacture of these plain tiles the face of the die is covered to the required thickness with the required facing body and the rest of the die filled up with backing clay, after which the pressure is applied. For making inlaid tile a brass cell frame of the same depth as the facing body is used, and consists of a framework of brass strips arranged so as to form the outline of the colors making the pattern. The frame* work is placed in the mold and the colored clays sifted into their proper divisions. This is done by using a sieve so perforated as to expose only certain cells, and the exposed cells being filled with the facing mixture of the desired color. This means, of course, that it is necessary to use as many sieves as there are colors in the design. The cell frame is then lifted out and the die is filled with a clay backing. In making tessera the body is solid, namely, made entirely from one body mixture. The vitreous tesserae 1 are porcelains, so com- pounded as to develop the greatest toughness or resistance to wear under feet that is consistent with the texture of the body and the brilliancy of the colors demanded by the trade. Encaustic tesserae tiles have for their base buff- and red-burning clays. Since the iron in these is mainly present as free oxide, it is im- possible to burn such tiles to vitrification without destroying the color. Wall-tile These are quite different from floor-tile in the character of body and style and decoration. The body is made of white-burning clay and is 'Purdy, op. cit., p. 101. 282 CLAYS not burned to vitrification, but on the contrary is usually just hard enough to resist scratching with a knife. It is therefore very porous. Wall-tile are molded in dry-press machines and burned first in saggers in a biscuit-kiln. They are then glazed and fired in a muffle- kiln at a much lower temperature. Many different shades, colors, and styles of decoration are now produced. In some cases the decoration is applied by a relief design impressed on the surface of the clay during molding, in others different colored glazes are used, or a considerable variation can be obtained in the shades of one color by varying the thickness of the glaze over different parts of the tile. Print-work and hand-painting also are employed at times to ornament the ware. Pottery Classification. Under the term of pottery there is included a great series of products for ornamental or domestic use, ranging from the common red earthenware flower-pot to the highly artistic and deli- cate porcelain vase. The different kinds may be defined as follows: Common earthenware, made from the lower grades of plastic clays, and having a porous body, usually of red but sometimes cream color, and as a rule not glazed. Decoration is given to it by relief designs, produced during the molding process, or more rarely by painting or glazing. Yellow or Rockingham ware, covering wares made of semi-fire clays or fire-clays, and having a porous buff-colored body, which is covered with a glaze. Majolica and Fayence. Both these terms are rather loosely used, but a definition recently suggested by S. G. Burt l gives fayence as pottery in which the colored clay body is covered with a clear glaze, and majolica as pottery in which the colored clay body is concealed with an opaque enamel. Stoneware, made of vitrifiable clays, often of semi-refractory char- acter, and having a vitrified body, often of bluish color but never white. The surface is glazed. White ware, including those products having a white or nearly white porous body, usually covered with a glaze. There are several trade varieties of this known as C. C. ware, white granite ware or ironstone china, semi-vitreous ware, semi-porcelain, and china. Some of these differ at times in name only. Theoretically they differ in the white- ness and degree of vitrification of the body. 1 Trans. Amer. Cer. Soc., VI, p. 109, 1904. KINDS OF CLAYS 263 The technology of the lower grades of pottery is comparatively simple, but for the manufacture of white ware or porcelain the success- ful completion of the product calls for skill, intelligence, and good mate- rials. There was a time when whiteware mixtures and glazes of the proper quality could be obtained only after long and tedious experimenting and the expenditure of much time and money, and while many potters are still groping in the dark, the day of this cut-and-try method can be said to have passed. Modern ceramic technology has worked wonders and a knowledge of it proves invaluable to the progressive potter in aiding him to work out the proper combinations of body and glaze. It enables him to adjust them if they do not agree, or to find out often in a comparatively short time where the trouble lies when failures occur. To take advantage of the facts and principles of ceramic technology does not so much require a very profound knowledge of chemistry as a good technical training, and the potter who seeks and grasps these ceramic principles will advance rapidly, while, on the other hand, he who rejects them and carefully guards some elementary facts as imagin- ary secrets of great value does himself a positive injury. Freedom of discussion has proven an invaluable aid in other technical branches, and there is no apparent reason why it should not do the same for the pottery industry. The subject of ceramic technology in America has been behind that of Europe for many years, although it is now coming forward with rapid strides. The annual meetings of the American Ceramic Society form a center where clay-workers can gather, and both give and receive information without the necessity of disclosing any business secrets. Indeed, so successful have these meetings become that the printed transaction of the society form a most valuable series of works dealing in a technical and scientific way with clays and clay- products. In addition to this ceramic schools have been established in several States, and provision thereby made for instruction in modern ceramic technology and the investigation of allied subjects. Manufacture of Pottery In making pottery there are certain steps that are common to all grades of ware, but the care of preparation and the number of steps are increased in the manufacture of the higher grades. The different steps may be grouped as follows: 264 CLAYS Preparation Tempering Molding Weathering Grinding Washing by sedimentation Blunging and filter-pressing ( Ball-mills f Chaser-mills J Pug-mills Hand-wedging Wedging-tables Turning Jollying or jiggering Pressing Casting Drying Biscuit-burning Dipping Glost-burning Decorating Preparation Weathering and grinding. For the commoner grades of pottery, such as red earthenware and often even for stoneware, the clay or shale are used as they come from the bank or mine. Weathering is sometimes resorted to in order to soften the clay and disintegrate it, so that it can be more readily washed, or to facili- tate mixing it when washing is omitted. Shales are sometimes crushed without being weathered. Washing. For the higher grades, such as white ware and porce- lains, the raw clay is washed in order to free it from sand or other heavy and coarse impurities. Blunging and filter-pressing. The Hunger consists of a circular vat in which there revolves two arms with stirring-rods attached. In this the clay mixture and water become thoroughly stirred and mixed, after which the contents of the blunger are run through a fine screen of 100 or 150 meshes to the inch into a cistern, from which it is pumped to the filter-press (p. 214 and PL X, Fig. 2). The pressed clay then goes to a pug-mill after which it is further wedged before use. This process of preparation is now used by nearly all potteries of any size, except those manufacturing common earthenware. For glazed earthen- ware bodies it means simply washing, blunging, screening, and filter- KINDS OF CLAYS 265 pressing the clay body, but for white-ware bodies a somewhat more elaborate system of treatment is necessary, since these carry kaolin, ball-clay, quartz, and feldspar, which must be intimately mixed. Ball-mills. Ball-mills are employed in the preparation of clay in the manufacture of some of the finer grades of wares, where fine grinding and intimate mixture of ingredients is especially important. They con- sist of a hollow cylinder that rotates on a horizontal axle and into which the "clay to be ground is admitted through an opening at one side or end. The machine is charged with the clay and balls (which fill about one third of the volume of the cylinder), the latter being of porcelain or water-worn Iceland-flint pebbles. The material is pulverized by abrasion or rubbing friction between these balls as they are caused to move upon each other by the rotation of the cylinder. There are two principal types of ball-mills which may be designated as the inter- mittent and the continuous. The former are those which are run with a given charge until the requisite degree of fineness is attained, when this is removed and another charge put in. This class of apparatus may be used to grind either in the dry or wet state. The latter or con- tinuous class includes the more improved types of ball-mills for turning out a large product of very finely dry-ground materials. They are so arranged that the raw ingredients are fed in at one end of the rotating cylinder and gradually work their way towards the other end, becoming finer and finer until they are discharged in the desired state of com> minution, when the opposite end of the drum is reached. The continu- ous ball-mill is in use very little, if at all, in this country, but is rapidly coming into use in Germany. The periodic mill is used to some extent by potteries in this country. Tempering Chaser-mills, which may be regarded as a form of wet pan, are some- times used at the stoneware factories. They consist of a circular iron pan in which there revolves a frame bearing two narrow iron wheels* 30 to 36 inches in diameter. As this frame revolves the wheels, by means of a gearing, travel around the pan in a spiral path. The clay and water are placed in the pan and the action of the wheels grinds a.id cuts it up, the tempering taking from one to two hours. The action of such a machine is quite thorough, but considerable power is required to operate it. Their use has been largely discontinued since the intro- duction of the blunger and filter-press. Pug-mills and hand- wedging. The washed clays or mixtures of clays as they come from the filter-press are tempered in a vertical or 266 CLAYS horizontal pug-mill, which is similar in its action to that described under Brick (p. 220). This is then followed by hand-wedging in order to render the clay perfectly homogeneous and free from air-bubbles. This latter operation consists in taking a large lump of the pugged clay, cutting it in two, bringing the two parts together with force, and then kneading the reunited lumps, this treatment being repeated a num- ber of times. Wedging-tables. Kneading-tables are used at some factories for working the clay by machine instead of wedging it by hand. Although much used abroad, then- introduction into this country has been rather restricted. The machine consists of a circular table about 6 feet in diameter, the upper surface of which slopes outward. On this are two conical rolls, 20 to 30 inches in diameter and about 8 inches wide. These rolls have corrugated rims, and are attached to opposite ends of a hori- zontal axis, having a slight vertical play. The clay is laid on the table, and as the rolls travel around on it the clay is spread out into a broad band. A second axle carries two other pah's of rolls of the same shape but smaller size, which travel around in a horizontal plane. These rolls press the band of clay together again. In this way the clay is subjected to alternating vertical and lateral pressure and all air-spaces are thus closed. The rolls make 10 to 12 revolutions per minute, and the machine kneads 2 to 3 charges of 700 pounds per hour. Molding After the clay has been properly tempered, the next step in the process of manufacture is molding. As indicated above, this is done in four different ways, the clay having first been thoroughly kneaded, usually by hand, in order to insure its complete homogeneity and free- dom from all air-bubbles. Turning is done by the potter taking a lump of clay and placing it on a rapidly revolving horizontal disk and gradually working it up into the desired form (PI. XXI). After being turned the object is then detached from the wheel by running a thin wire underneath it. Only articles with a circular cross-section and thick walls can be formed in this manner, since they have to hold their shape under their own weight. Turning represents the earliest methods of the potter, and is much used still at small factories, but in the larger ones it has been mostly superseded by the next process. Jollying or jiggering is a more rapid method than turning, and the clay for this purpose is tempered to a softer consistency. The jolly PLATE XX Bergstrom & Bass Tile-press. 267 KINDS OF CLAYS 269 is a wheel fitted with a hollow head to receive the plaster mold, the interior of which is the same shape as the outside of the object to be molded. A lump of clay is placed in the revolving mold and shaped into the proper form, first by means of the fingers and lastly by means of a template or so-called "shoe" attached to a pull-down arm, which is brought down into the mold. Cups, jars, jugs, and the larger flower-pots are molded in this manner. A modification of this method termed " pressing " is used for the smaller sizes of flower-pots. This consists of a revolving steel mold, with a steel plunger of the shape and size of the interior of the pot. The tempered clay is first put through a plunger-machine, from which it issues in the form of columns, which are cut up by wires into a number of pieces, each containing just enough clay for making a pot of the desired size. These lumps of clay are then placed one at a time in the mold, and the latter raised by means of a lever, until the plungers fit into it, thus pressing the clay into the mold. The bottom of the mold is movable, so that as the mold is lowered the bottom rises and pushes out the pot. Such machines have a large capacity, and are now used at most flower-pot factories. 1 A modification of jollying, used for making plates and saucers, con- sists in having a plaster mold, the surface of which has the same shape as the interior or upper surface of the plate to be formed. The potter's assistant takes a piece of clay of the desired size, and pounds it to a flat cake, called a "bat," which is laid on the mold; he then shapes the other side or bottom of the plate by pressing a wooden template of the proper profile against it as it revolves. Pressing. Ewers and vessels of oval or elliptical section are usu- ally made by means of sectional molds, consisting of two or three pieces, the inner surface of which conforms to the outer surface of the object to be molded. A slab of clay is laid in each section and carefully pressed in, the mold put together, and all seams smoothed with a wet sponge. After drying for a few hours the parts of the mold are lifted off. Clocks, lamps, water-pitchers, and similar articles are made in this manner. Casting. This consists in pouring a clay-slip into a plaster mold which absorbs some of the water, and causes a thin layer of the clay to adhere to the interior surface of the mold. In order to produce a slip with less water some alkaline salt is added to the mixture. When the layer on the inner surface of the mold is sufficiently thick, the mold is inverted and the remaining slip is poured out, the mold being removed 1 Fire-clay crucibles are sometimes molded by this method. 270 CLAYS in a few hours. This method is extensively used in making thin por- celain ornaments, as well as many white-ware objects. It is also employed for making belleek. The forming of pottery by casting is much more extensively done in Europe than in the United States. Drying This, of necessity, often has to proceed rather slowly, especially if the ware is of complicated shape. The ware is usually dried first in an open room, and then removed to the heated green- ware dry-room. Subsequent steps Up to this point, the method of treatment has been much the same except for the blunging of white ware or porcelain mixtures. From the drying stage on, the methods of treatment of the different kinds of ware diverge somewhat. Common red earthenware, such as flower-pots, is usually burned at a low heat, often not above the melting-point of cone 010, and the kilns used are generally rectangular or circular up-draft ones. The ware after burning is quite porous and not steel-hard. If to be decorated this can be done by incised designs, the appli- cation of relief decoration, or by covering it with a glaze of easy fusi- bility. Yellow and Rockingham ware. In making this the clay is first burned to develop the body, after which it is glazed and then fired a second time to develop the glaze, the process in this respect being similar to that employed for white ware, and the ware being placed in saggers to protect it from the flames and dirt. The glazes are artificial mixtures which melt to a glass at a lower temperature than that re- quired to burn the body. Stoneware. In this class of product the body and glaze are de- veloped together, so that after drying the objects are ready to have the glaze applied. A type sometimes used is some form of natural glaze or slip-clay (see p. 193), which melts to a brown glass at a temperature at which the body of the ware is nearly vitrified. For application the slip-clay is mixed with water to a creamy con- sistency and the ware dipped in it. Although slip-clays have been found at a number of localities in the United States, that obtained from Albany, N. Y., continues to be the most satisfactory and is shipped all over the country. The amount of slip-clay required even by a KINDS OF CLAYS 271 factory of moderate size is not very large, so that the annual domestic consumption of this kind of clay is limited. Salt-glazing represents the simplest form of glazing a ware, and is applied more often to sewer-pipe than stoneware. When the wares are to be salt-glazed they are placed in the kiln, unprotected from the flames. As soon as the kiln has reached its highest temperature, the salt is put in the fireplaces, one or two shovelsfull at a time, at regular intervals, so that the addition of the salt may extend over several hours. When the salt is placed in the fires the heat volatilizes it, and the vapors in passing up through the kiln unite with the clay, forming a glaze on the surface of the ware. Many clays are capable of taking a good salt- glaze, but some take a poor one, and others do not glaze at all. From experiments made by L. E. Barringer l it seems that a clay may be either too aluminous or too siliceous to be successfully salt- glazed, but that, if the process of salt-glazing is properly carried out, clays in which the proportion of silica to alumina is more than 4.6 to 1 and less than 12.5 to 1 are capable of receiving a glaze. The degree of fineness of the free silica in the clay makes little difference. The finer the sand the lighter the color of the glaze. Barringer also found that, contrary to what was usually supposed, a considerable quantity of soluble salts, as much as 3 per cent, can be present in a clay without seriously interfering with the salt-glazing when conducted at cone 8. Bristol glazes, representing a third type, are an artificial mixture of fluxes, kaolin, ball-clays, and flint. They can be produced in a variety of colors, and white, due to zinc or tin, is a common one. This is the type of glazing generally used on stoneware. The burning of stoneware is carried out in up-draft or down-draft kilns, and the cone reached varies in different localities, but where fire-clays or semi-fire clays are employed it ranges probably from 6 to 8. White ware and porcelain. Both of these are made from artificial mixtures, consisting of kaolin, ba,ll-clay, quartz, and feldspar, and the materials used are selected with a view to their white-burning qualities. The kaolin supplies white color and refractoriness but is low in plas- ticity, and to supply this deficiency ball-clay is added. Quartz serves to diminish the shrinkage, and feldspar or calcined bones as a flux. Porcelain in which spar is the flux is termed hard, feldspar or true 1 Trans. Amer. Cer. Soc., IV, p. 223. 272 CLAYS porcelain, and shows a bluish-white color by transmitted lights, while that which is fluxed in part by calcined bones or lime phosphate is termed bone china and shows a yellowish color by transmitted light. The proportions in which these several substances are used are commonly kept secret by the potter, but enough has been published to show the general mixtures. In the molding of white and porcelain wares jiggering and pressing are extensively employed, and the burning is done in much the same manner as in yellow w r are. Saggers, which are oval or cylindrical receptacles made of fire-clay with a flat bottom, about 20 inches in diameter and a height usually of about 8 inches, are used for protecting the ware in the kilns. The saggers are filled with unburned ware and set one on top of the other (PI. XIX, Fig. 2), so that the bottom of one forms a cover for the one below it, the joint between the two being closed by a strip of " wad "-clay. The use of these saggers is to protect the ware from the smoke, gases, and ashes of the kiln-fire. The chief requisite of a sagger-clay is that it shall stand more heat than the ware placed in it, and repeated firing and cooling, as well as handling without breaking. Saggers are generally made from a plastic, refractory clay, with the maximum admixture of grog, i.e., ground old saggers, broken fire-brick, etc. The kilns are usually of the circular up-draft type having a diam- eter of from 10 to 18 feet. Down-draft kilns are but little used for burning white ware in the United States, although in Europe the down- draft method of burning has superseded the up-draft. The temperature reached in burning varies. White ware is commonly burned at from cones 8 to 9, while the porcelain may be fired as high as cones 12 to 16. Since the color of ferrous iron is less noticeable than ferric iron the fires should be reducing during at least the last part of the firing, and the kiln is then cooled down as rapidly as possible to prevent the oxi- dation of whatever iron may be in the clay. For all pottery ware, except hard or feldspar porcelains, the body is first burned in the biscuit-kiln, then glazed and burned a second time in the glost-kiln. For white ware the biscuit-burn is done at perhaps cones 8 to 9, while the glost-burn at about 2 to 6. For yellow and Rock- ingham ware, fayence and majolica, the biscuit-burn ranges between cones 2 to 8, while the glost is from cones 07 to 03. For porcelain the biscuit-burn is about cone 2, while the glost-burn is at a higher heat, and in this country ranges probably from cones 11 to 13. The glazes for white ware and porcelain are complex compounds PLATE XXI Views illustrating the process of turning jars. (Photo by H. H. Hindshaw Md. Geol. Surv., IV, p. 358, 1902.) 273 KINDS OF CLAYS 275 of an artificial character. They consist of a mixture of acids and bases combined according to a definite formula, in such proportions that they will melt to a glass at the temperature reached in burning. A glaze thus produced must furthermore agree with the body in its shrinkage and coefficient of expansion, in order to prevent various defects, such as crazing, shivering, peeling, etc. A discussion of the composition and methods of calculating glaze formulas hardly lies within the province of this work, and those wishing to become acquainted with this sub- ject are referred to a most excellent little manual of Ceramic Calcula- tions issued by the American Ceramic Society. 1 The glazes used on white ware are usually fritted first. That is, the ingredients of the glaze after mixing are melted either in a frit- kiln or a sagger, broken up and ground wet, together with certain added materials. This glaze mixture is then of a cream-like consistency and the biscuit ware is dipped into it (PL XXIIj. In the glost-kiln this thin coating of glaze melts to a glassy layer and covers the body en- tirely. White-ware glazes commonly owe their easy fusibility to borax and lead, while those used on porcelain contain no lead, and require a higher heat for maturing. White ware and porcelain are often elaborately decorated, either under or over the glaze, but the form of decoration most often seen is print-work. This is done by printing a copper-plate design on special paper, and applying this to the surface of the ware. After being allowed to stand for a few hours the paper is washed off, but the ink cf the design is retained on the surface of the ware. The colors are then fixed by firing in a muffle-kiln at a dull-red heat. The print-work is some- times " filled in" and elaborated by brush-work, or, on better grades of ware, the entire design may be hand-painted. The more delicate colors as well as gold have to be applied over the glaze as they are de- stroyed by hard-firing. With chromolithography a soft and orna- mental multicolored design can be produced at one operation, but it is but little used in this country, although productive of beautiful effects. Electrical porcelain. This forms a separate branch of the clay- working industry. These insulating materials are made of a mixture of white-burning clays, feldspar, and flint, and molded by the dry- press process. It is necessary to burn them to vitrification, and none are probably burned below cone 10 and some at cone 12. They are usually glazed in one burning. 1 Purchasable for $1.00 from Ed. Orton, Jr., Sec'y, Columbus, Ohio. 276 CLAYS Sanitary ware is made sometimes from the same clay bodies as white ware, but the body is usually vitrified or nearly so, and is glazed. The ware is formed by hand in plaster molds, and great care has to be exer- cised in drying and burning. Bathtubs and washtubs. These are commonly made from buff- burning clays, such as are used in terra-cotta manufacture, and covered with both a white slip and a glaze. The lining is usually vitrified, but not the body, and they are termed porcelain lined. The pressing, drying, and burning of such a large object as a bathtub requires much care and time. The pressing is done by hand in large plaster molds, and the wares are burned commonly at from cones 9 to 10, or perhaps slightly higher. A finished bathtub may weigh as much as 1100 pounds. \ CHAPTER VI DISTRIBUTION OF CLAY IN THE UNITED STATES ALABAMA LOUISIANA Introduction. In this chapter and the two following ones it is proposed to describe briefly the occurrence, properties, and uses 1 of the clays found in the different States. While it is thought that the more important facts are grouped here, still there may be some who wish to obtain additional details, which they can do by looking up the refer- ences given at the end of the discussion of each State. A grouping of the clays according to geologic formations has been adopted partly because the subject is treated mainly from the stand- point of the- economic geologist, and partly because it admits of greater uniformity in mode of presentation. For the benefit of those who would prefer a grouping by kinds, the index has been made as complete as possible, in order to enable them to find .he data for which they are searching. Statistics of Production. Doubtless few people realize the im- portance of the clay-working industry in the United States, and yet this is not so surprising, since clay has less popular attraction than many other mineral products, such as gold, silver, etc. A casual glance, however, at the annual figures of production will probably speedily convince one that clay is to be classed among the fore- most mineral products of the country, being outranked only by coal and iron. The statistics of production for 1904, as published by the United States Geological Survey, are given on p. 278. 1 This refers to their use for the manufacture of clay-products. 277 278 CLAYS VALUE OF CLAY-PRODUCTS OF THE UNITED STATES IN 1904 P-duct. Value. Common brick $51,768,558 39 . 51 Vitrified paving-brick 7,557,425 5.77 Front brick 5,560,131 4 . 24 Fancy or ornamental brick. . . 845,630 .65 Drain-tile 5,348,555 4.08 Sewer-pipe 9,187,423 7.01 Architectural terra-cotta 4,107,473 3 . 14 Fireproofing 2,502,603 1 . 91 Hollow blocks 1,126,498 .86 Tile, not drain 3,023,428 2.31 Fire-brick 11,167,972 8.52 Miscellaneous 3,669,282 2 . 80 Red earthenware 756,625 . 58 Stoneware 3,41 1 ,025 2 . 60 Yellow and Rockingham ware 290,819 .22 C. C. ware 854,389 . 65 White granite and semi-porcelain 10,836,117 8.27 China 1,583,513 1 . 21 Bone china, delft, and belleek 162,500 . 12 Sanitary ware 3,585,375 2.74 Porcelain electrical supplies 1,431,452 1 .09 Miscellaneous pottery. 2,246,455 1.72 Total $131,023,248 100.00 CLAY MIXED AND SOLD IN THE UNITED STATES IN 1904 Kind. Value. Kaolin. . $304,582 Paper 276,381 Slip 11,942 Ball 142,028 Fire 1,306 053 Stoneware 83,904 Miscellaneous. . 195,272 Total $2.320 162 Alabama The clay-deposits of this State are distributed over a wide range of geologic formations, whose characters are briefly referred to below. Archaean and Algonkian The rocks of this age, which underlie a roughly triangular area of the eastern part of the State, consist of granites, gneisses, and schists, PLATE XXII Dipping biscuit ware into the glazing-tubs. (Photo by H. Ries.) 279 DISTRIBUTION OF CLAY IN THE UNITED STATES 281 all of which have, by surface decay, furnished a residual clay, usually of ferruginous character. In the schist areas, however, there are not a few pegmatite veins, whose decomposition has resulted in the forma- tion of kaolin. Such occurrences are found near Milner, Pinetucky, and Micaville, Randolph County, and Stone Hill in Cleburne County, but they are all undeveloped, owing to lack of railroad facilities. The Alabama kaolins in their crude condition are rather siliceous, highly refractory, and burn to a very white color. Cambrian and Silurian The clays obtained from these formations are either residual deposits or are concentrates from these, which have been carried by surface- waters down into sinks and other depressions. While the Silurian rocks contain some shaly members they are not, so far as known, used for brickmaking, but the residual clays which are usually impure are ex- tensively employed for this purpose. At certain localities, such as at Gadsden, Kymulga, Peaceburgh, and Oaxanna, white clays occur sur- rounded by the impure ones, and those found in Cherokee County have been used for fire-brick manufacture. Lower Carboniferous Although occupying a number of small areas in the northern portion of the State no clays of economic value have been noted from these. In Will's Valley, however, it carries an important bed of white clay, which is also found farther north near the State line. The white clay, which is known locally as chalk, and has an aggregate thickness of about 40 feet, is worked near the State line about Eureka station, and thence southward for two miles. Coal-measures These occupy a large triangular area in the northern part of the State, but since a great portion of the region is remote from the railways, whatever shales or clays it may contain have been but little developed. The most important deposits are the under-clays found in some of the coal-fields, which have been employed for making pottery, as at Jugtown, Fort Payne, Rodentown, etc. The shales are also used in some parts of the State for making vitrified brick, especially at Coaldale and North Birmingham. No fire-clays have thus far been found in the coal- measures. 282 CLAYS Cretaceous This contains the most important clay-deposits in the State, but most of the beds have thus far been found in one member, namely, the Tuscaloosa. This consists usually of yellow and grayish sands, with smaller beds of pink and light-purple sands thinly laminated, dark- gray clays holding many leaf impressions, and gray lenses of massive clay which vary in color. The formation occupies a belt of country extending from the northwest corner of the State around the edges of the Paleozoic formations to the Georgia State line at Columbus, attain- ing its greatest width at the northwestern boundary of the State. The purer clays have as yet been found only in the northern part of this area, in Fayette, Marion, Franklin, and Colbert counties, and the ad- joining parts of Mississippi, but the following section from 12 miles east of Tuscaloosa affords a good idea of the character of the deposits. SECTION 12 MILES EAST OF TUSCALOOSA, ALA. Feet. In. 1. Purple massive clays 5 2. Ferruginous sandstone crusts 6-8 3. Variegated clayey sands 10 4. Purple clays with sand partings 10 5. Ferruginous crusts 1 6. Laminated, gray and yellow sandy clay 6-8 7. Lignite with pyrite nodules 2 6 8. Dark-gray massive clays 6 8 9. Covered 1 8 10. Purple clay This section shows great vertical variation and a similar one may occur horizontally. Nevertheless, the formation contains not a few deposits of workable size, which are employed for stoneware and common earthenware, as at Sulligent, Tuscaloosa, etc. In Colbert County the Tuscaloosa formation carries fire-clays, and other deposits are known near Woodstock and Bibbville, A curious white siliceous clay occurs near Chalk Bluff and Pearce's Mill, Marion County, but it has not been utilized. DISTRIBUTION OF CLAY IN THE UNITED STATES 283 Tertiary The Tertiary formations underlie the southern third of Alabama, and while it is known that they contain extensive deposits of clay, these have been but little investigated. The most promising occurrences of clay in this section are in the Grand Gulf formation (Pliocene) which, according to Dr. E. A. Smith, overlies unconformably most of the older Tertiary beds. A siliceous clay, resembling flint-clay in appearance, is found in abundance in Choctaw, Clarke, Conecuh, and other counties. Its analysis is given in the appended table. Pleistocene Over much of the coastal plain in the second bottoms of the rivers there is a great extent of yellow loam suitable for brickmaking, which corresponds to the Columbia loams of the Northern States. Division of Clays by Kinds China-clays. The only kaolins are those occurring chiefly in Ran- dolph County. Fire-clays. The fire-clays of Alabama come from four geologic horizons, namely: (1) The Cambrian and Silurian limestone forma- tions of the Coosa Valley region, seen at Peaceburgh, Calhoun County, Oaxanna County, and Rock Run, Cherokee County; (2) the cherty limestone of the Lower Carboniferous formations of Will's Valley, seen at Will's Valley and Valley Head, Dekalb County; (3) the Tuscaloosa formation of the Lower Cretaceous, occurrences being known at Bibb ville and Woodstock in Bibb County, Hull station and Tuscaloosa in Tuscaloosa County, Potter's Mills in Marion County, and Pegram in Colbert County; (4) the Lower Tertiary formation, Choctaw County. Pottery-clays. These are found at a number of localities, including Blount County; Rock Run, Cherokee County; Fort Payne, Dekalb County; Coosada, Elmore County; Bedford and Fernbank, Lamar County; Tuscaloosa, Shirley's Mill, Fayette County; Pegram, Colbert County. Brick-clays. Many deposits are found in all parts of the State. In the following table there are given a number of physical tests and chemical analyses of Alabama clays. Additional ones will be found in Reference 4, on page 285. 284 CLAYS - X' S^Hj! 1 a O CO O O *O QJ 00 00 Tf O Tf id o^ O ^ ^ O^ CO o o u "^t 1 O^ I-H o o o J O iO OS O a) (M O CM -H O 2 O CO r- I-H -^ O : | >-c S DISTRIBUTION OF CLAY IN THE UNITED STATES LOCALITIES OF CLAYS IN PRECEDING TABLE 285 No. Locality. Geological Age. Uses. I. II. III. IV. V. VI. VII. VIII. IX. X. Gadsden Car L(H Coa Lo\ i f abro-Silurian 1 1 (i N t t ot wor t ( ked Peaceburg Eureka ver Carboniferous 1-measures. . Birmingham Bibbville ver Cretaceous 1 1 Bedford Shirley's Mills it Bexar ti Pegram ( f Tuscaloosa ( e Nos. I-X from Bull. 6, Ala. Geol. Survey. References on Alabama Clays 1. McCalley, H., Report on the Valley Regions of Alabama (PalsR- ozoic strata): Clays. In two parts. I. The Tennessee Valley Region, Ala. Geol. Surv., p. 68, 1896. 2. Ibid., II. The Coosa Valley Region, p. 84, 1897. 3. Mell, P. H., Jr., The Southern soapstones, kaolin, and fire-clays and their uses, Amer. Inst. Min. Eng., Trans., X, p. 318, 1882. 4. Ries, H., The Clays of Alabama, Ala. Geol. Surv., Bull. 6, p. 220, 1900. 5. Smith, E. A., The Clay Resources of Alabama and the industries dependent on them, Eng. and Min. Jour., LXVI, p. 369, 1898. 6. Smith, E. A., Geological relations of the clays of Alabama, Ala. Geol. Surv., Bull. 6, pp. 69-113, 1900. Arkansas In the Mesozoic regions of Arkansas there are found a great variety cf clays. Those occurring within the Tertiary region are said to have been used for the manufacture of pottery, while kaolin is said to occur in Pike, Pulaski, Saline, and Ouachita counties, but the beds are rarely over 2 feet in thickness. The Pulaski deposits are the only true kaolins of those mentioned. Brick-clays are abundant in the Pleistocene formations. The shales associated with the Carboniferous coals should also prove of value for the manufacture of clay-products. According to Branner they occur in great abundance between Little Rock and Fort Smith. 1 The following analyses are given by Branner in the paper referred to above : 1 Branner, Amer. Inst. Min. Eng., Trans., XXVIII, p. 42, 1897. 286 CLAYS ANALYSES OF ARKANSAS CLAYS I II. 111. IV. V. VI. VII. VIII. IX. Silica (SiO 2 ).. . 53.30 62.36 58.43 51.3 63.07 48.34 76.33 75 . 99 45.28 Alumina 23.29 25.52 22.50 24.69 23.92 34.58 16.04 16.12 37.39 (A1 2 3 ), Ferric oxide 9.52 2.16 8.36 10.57 1.94 1.65 1.24 1.35 1.71 (FeAO Lime (CaO). . . .36 .51 .32 .32 .23 .81 1 By f 1.83 Magnesia diff. (MgO) 1.49 .29 1.14 .63 trace trace .99 1.45 1.10 \4.28 4.40 3.43 3.06 3.16 Water (H 2 O) 12 48 1.12 1.42 1 37 99 1.24 JVloisture 4.91 5.24 5.06 5 36 6 28 day substance 99.00 Ouartz 1.00 "Clay base 34.15 47.36 34.04 28.75 27.82 Non-fluxing impurities 46.86 36.69 48.18 53.55 53.99 Tluxes. . 18.87 15.65 18.15 17.86 18.93 I. We*t Cornwall, kaolin, H Ries. anal. II. S. Windsor, Conn., East Windsor Hill Brick Co. III. NewfieM, Tuttle Bros. IV Berlin, Berlin Brick Co. V North Haven. I. L. Stiles & Sons. References on Connecticut Clays 1. Loughlin, G. F., The Clays and Clay Industries of Connecticut, Conn. Geol. and Nat. Hist. Surv., Bull. 4, 1905. 2. Sheldon, J. M. A., Concretions from the Champlain Clays of the Connecticut Valley, 45 pp., 1900, Boston, Mass.; Abstracted in Amer. Jour. Sci., 4th ser., Vol. 11, p. 397, 1901. Delaware The clay resources of this State are of comparatively little import- ance, nor has much been published regarding them. In the north- western part, along the Pennsylvania boundary, there are deposits of kaolin similar to those found in southeastern Pennsylvania. The prod- uct is washed before shipment. The Potomac beds of the coastal plain area are said to contain stone- ware and fire-clays, which have been dug at two localities not far from Wilmington. District of Columbia According to Darton 1 there is an abundance of brick-clay around Washington and much of it is used, in fact large areas have been dug over in the immediate vicinity of the city. The materials employed 1 U. S. Geol. Atlas, Folio No. 70, Washington, D. C. DISTRIBUTION OF CLAY IN THE UNITED STATES 297 are chiefly loams belonging to the Columbian formation, but the sandy clays of the Potomac beds are also used. Florida The clays of Florida are mostly surface deposits of Tertiary and Pleistocene age, and occur chiefly in the northern part of the State, the majority of them being more or less sandy in their character, and adapted to little else than common brick. They have been worked to some ex- tent around Jacksonville, and also at a few other localities. While most of these are ferruginous, calcareous ones are also known, and have been, noted from several localities as 18 miles southwest of Tallahassee, and one half mile southeast of Jackson Blutf. Their composition is given below. The ball-clays are the most important ones found in the State. These are white-burning, plastic, sedimentary clays, of high refractoriness, which are much used by the white-ware potteries. The clay occurs at several points in northcentral Florida (Fig. 36), and the different areas may represent portions of a formerly continuous bed. It consists of a mixture of white clay and quartz pebbles, the latter forming 65 to 75 per cent of the entire mass. A section measured in the pit at Edgar l gave: Top-soil 8 ft. Impure upper clay 8-10 " White clay 25 " Green clay The thickness of the green clay is not exactly known, but at some localities it appears to rest on limestone. An extensive belt of ball- clay also occurs along the Palatlakaha River south of Leesburg, and at Bartow Junction. On page 298 are given analyses of both the calcareous clays and the ball-clays. References on Florida Clays 1. Memminger, C. G., Florida kaolin-deposits, Eng. and Min. Jour., LVII,p. 436, 1894. 2. Ries, H., The Clays of Florida, U. S. Geol. Surv., 17th Ann. Kept., Pt. Ill, p. 871, 1898. 3. Ries, H., See Florida, U.S. Geol. Surv., Prof. Pap. 11, p. 81, 1903 1 See Reference 2 below. 298 CLAYS ANALYSES OF FLORIDA CLAYS I. 11. III. IV. Silica (SiO 2 ) 35 95 30 83 46 11 45 39 Alumina (A^Oa) 13 23 15 40 39 5 39 19 Ferric oxide (F^Os) 1 27 1 40 35 4^ Lime (CaO) 15 00 13.78 51 Magnesia (MgO) 5.40 7 50 13 29 AJkalies (Na 2 O,K2O) undet. 83 Water (H 2 O) 10.55 7.16 13 78 14 01 Carbon dioxide (COa) 18 50 20 14 Sulphur trioxide (SOs) 07 Total 99.90 96.21 99.94 100 67 I. Calcareous clay, Leon County, H. Hies. anal. II. Calcareous clay, near Jackson Bluff on Ocklocknee River, H. Ries, anal. III. Washed clay from Palatlakaha River. IV. Washed clay from Edgar, C. Langenbeck, anal. I-IV from U. S. Geol. Surv., Prof. Pap. 11, p. 83. Georgia This State is divisible geologically into three areas, namely: (1) A northwestern area, underlain by shales, limestones, and sandstones of Palaeozoic age; (2) a broad central belt of pre-Cambrian rocks, such as granites and gneisses; (3) a southeastern belt, in the coastal plain region composed of unconsolidated sedimentary rocks of Cretaceous, Tertiary, and Pleistocene age. Palaeozoic Area This belt includes the counties of Polk, Floyd, Bartow, Gordon, Mur- Tay, Whitfield, Catoosa, Chattooga, Walker, and Dade, and while the rocks in this area range from Cambrian to Carboniferous inclusive, the residual clays derived from them are all somewhat similar. The shales are often calcareous, with the exception of the Carboniferous ones. The residual clay-deposits, which are chiefly adapted to common-brick man- ufacture, are often of considerable extent, and generally ferruginous character, but here and there contain pockets of white clay which may be suitable for fire-brick; those derived from the limestones often con- tain cherty nodules. Pre-Cambrian Belt This covers an area of about 12,000 square miles, and consists of -granites, gneisses, schists, marbles, and in places pegmatite veins, of which the last should afford kaolin. Residual clays are abundant throughout the region, and the wash from them may form secondary -.deposits in the valleys. PLATE XXV FIG. 1. Kaolin-pit at West Corn wall, Conn. (Photo loaned by The Kaolin Company.) FIG. 2. White clay and sands of Cretaceous age, overlain by Tertiary beds, Rich Hill near Knoxville, Ga. (After G. E. Ladd, Ga. Geol. Surv., Bull. 6A, p. 32, 1898.) 299 DISTRIBUTION OF CLAY IN THE UNITED STATES 301 Coastal Plain Region This region includes that portion of the State lying to the southeast of a line drawn through Augusta, Macon, and Columbus, and coinciding approximately with the fall line (Fig. 50). Within this area the formations range from Cretaceous to Pleistocene and carry many clay-deposits of variable character, ranging from easily fusible ferruginous clays to snowy white ones (PL XXV, Fig. 2) of high refractoriness. The form of most of these is rather irregular (a characteristic of most coastal plain clays), the majority being lens .shaped, and surrounded by sand or sandy clay. Of the several formations, the Cretaceous has the smallest surface area, forming a triangle, the base of which is on the Chattahoochee River, the apex at Macon, and the northwest side agreeing with the fall line. Nevertheless, this area includes, so far as known, the most important clays found in Georgia. The Cretaceous shows a section of .about 1640 feet of southeasterly dipping beds, which are well exposed along the Chattahoochee River below Columbus, and other good expo- sures occur along the Georgia Central Railroad, between Columbus and Macon, but the best clays are found in the region around Griswoldville, about 10 miles east of Macon. In this last area, which includes the southern half of Jones and Baldwin counties and the northern half of Twiggs and Wilkinson, the clays are 6 to 10 feet thick, often white in .color, free from grit, and with a soapy feel, due to the presence of many muscovite scales of microscopic size. Other exposures occur in the vicinity of Lewiston, Gordon, Mclntyre, Augusta, Butler, etc. The following section given by Ladd from Lewiston is fairly typical of their occurrence : Feet. 1. Red and yellow clayey sand, with seams of laminated clay; also thin seams of limonite with coarse pebbles 6 2. Irregular siliceous beds resembling quartzite, and containing drusy quartz cavities and many fragments of shells 4 3. White sand, free from iron stain, at times cross-bedded, and contain- ing mica and white clay 7 4. White clay, free from grit 7 5. White sand at bottom 2 The following analyses and tests, taken from the reports of Ladd and Spencer, 1 represent the character of some of the Georgia materials. 1 See references at end of Georgia. 302 CLAYS DISTRIBUTION OF CLAY IN THE UNITED STATES 303 ANALYSES AND PHYSICAL TESTS OF GEORGIA CLAYS I. II. ill. IV. V. VI. Silica (SiOo) 41 20 52 82 46 17 56 28 46 62 77 AH Alumina (A^Os). 38 60 26 17 39 13 14 64 38 28 10 QO Ferric oxide (Fe 2 O 3 ) Lime (CaO). . 1.45 9.46 trace 0.45 18 0.28 7 08 1.02 18 2.25 Magnesia (MgO). ... 30 1 08 11 1 71 fi^ Potash (ICO) 09 2 71 51 1 05 1 83 Soda (Na 2 O) 02 20 63 j 4. 23 08 32 Water (H 2 O) 16 35 7 00 Ism If?n Isrn Moisture 35 23 13.08 57 11.24 8 7 13.64 72 4.70 2ft Titanic oxide (TiO 2 ) 1.95 with 1 98 Tensile strength A1 2 3 25 213 24 Air-shrinkage . . . 8 25 8 Fire-shrinkage 6 2 Cone of fusion 36 35 Specific gravity 1 76 9-1 2 1 69 to Color when burned buff 1.75 yellow No. Locality. Geological Ages. Uses. I. Flowery Branch Silurian. . . . Not worked II Near Cartersville. . Oostanaula series III. Griswoldville Potomac clay . IV Fitzpatrick. Tertiary Not worked v Steven's pottery. . Potomac Fire-brick pottery VI. Rome Columbia . . and sewer-pipe. References on Georgia Clays 1. Ladd, G. E., Preliminary Report on Clays of Georgia, Ga. Geol. Surv., Bull. 6A, 204 pp., 1898. 2. Ladd, G. E. , Notes on the Cretaceous and Associated Clays of Middle Georgia, Amer. Geol., XXIII, p. 240, 1899. 3. Spencer, J. W., The Palaeozoic Group, Ga. Geol. Surv., 1893, p. 276. 4. See also U. S. Geol. Surv., Geol. Atlas Folios relating to Georgia. Illinois The clay materials of this State are obtainable from the Ordovician, the coal-measures, and the drift. 304 CLAYS Ordovician So far as known this is of little importance, but the Cincinnati shales, outcropping in Daviess and Boone counties, may prove of value for the manufacture of brick, hollow brick, and perhaps earthenware, since the same material has been successfully used in Iowa, and tested with good results in Wisconsin. Coal-measures These underlie a large area in central, eastern, and southern Illinois, within a line passing from Hampton in Rock Island County, to the junction of the Kankakee and Iroquois rivers, thence southward to near Chatsworth in Livingston County and eastward to tne Indiana boundary. The coal-measures consist of a series of coal-beds, shales, sandstones, and clays, those underlying the coal being sometimes of a refractory character. Owing to the nearly horizontal position of the beds, mining is usually carried on by shaft, although at several localities , as Galesburg, etc., great outcrops of shale occur. Unfortunately, the published information regarding these Carbonifer- ous clays and shales is not of recent character, although they form the basis of an active clay- working industry, and are much used for paving- brick around Galesburg, 111. A number of localities are mentioned by Worthen in the old report of the Geological Survey of Illinois (see below) Tertiary Clays In Pulaski and Alexander counties the Tertiary contains beds of pottery-clay, as at Mound City on the Ohio River and near Santa Fe. Drift-clays These form a most abundant source of brick- and tile-clays in many parts of the State. Around Chicago these clays are lake-deposits of considerable extent, but they are highly calcareous and often pebbly. They form the basis of a large local brick industry, and the smoother ones have been used for drain-tile and even roofing-tiles. In other parts of the State the clays are found either in the glacial drift or under- lying terraces along the broader rivers, especially the Illinois. The sandy loess-clay is much used at many points. PLATE XXVT. FIG. 1. Carboniferous shale used for paving-brick. Galesburg. 111. The excavat- ing is done with a steam-shovel. (Photo loaned by 111. Geol. Surv.) p IG 2. View in Knobstone shale-pit, Crawfordsville, Ind. (After Blatchley, Ind. Dept. Geol. and Nat, Res., 29th Ann. Kept., 1895.) 305 DISTRIBUTION OF CLAY IN THE UNITED STATES 307 References on Illinois Clays 1. Leverett, F., The Illinois Glacial Lobe, U. S. Geol. Surv., Mon. XXXVII. Describes distribution of drift, but is not a paper of eco- nomic character. 2. Worthen, A. H., Reports on Economic Geology of Illinois, 111. Geol. Surv., I, II, III. Indiana The Ordovician, Silurian, Devonian, and Carboniferous contain ex- tensive shale-deposits, but only the last have thus far proven of com- mercial value. Ordovician The Ordovician rocks outcrop only in the southeast corner of the S ate, and there are often covered by a thin drift layer. The only shales are the Hudson River, but these are too calcareous to use, and of no value even when weathered. Silurian The beds of this age underlie a large area in eastern and northcen- tral Indiana, but carry few shales, and these are of no value. Devonian The Devonian beds underlie a great area, extending northwest and southeast through central part of State, but offer little promise to the clay-worker, as they are usually too bituminous. Mississippian or Lower Carboniferous The rocks of this age afford residual clays and shales. Residual clays. Since a large part of the Mississippian area occurs in the driftless region, the residual clays derived from underlying lime- stone and sandstones are available, and occur at many points in Monroe, Lawrence, Orange, Harrison, and Floyd counties, as well as parts of the adjoining ones, so that they form the most important source of the brick- and tile-clays worked in these counties. Shales. Those of the Knobstone formation (Fig. 51) are important and destined to become prominent in the future, although they have been neglected in the past. Indeed they are next to the coal-measure shales, the most important in the State. According to Blatchley (Ref. 3) the Knobstone shale forms the surface-rock of a strip of territory 3 308 CLAYS B.I g a O *4^j d ~j If Longitude DISTRIBUTION OF CLAY IN THE UNITED STATES. 309 to 38 miles wide on the eastern side of the Lower Carboniferous area, extending from the Ohio River southwest of New Albany in a west of north direction to a point a few miles south of Rensselaer, Jasper County. While the formation is often covered by a heavy mantle of drift, many excellent exposures have been formed by the cutting of the larger streams, as along the West White River near Martinsville; along Sugar Creek, above and below Crawfordville, and along Shawnee Creek south of Attica. Many additional outcrops have been found in other counties within the belt occupied by these shales. The Knobstone formation consists of blue-gray shales, shaly sand- stones, and sandstones, with rarely a little limestone. Nodules of sider- ite are not uncommon. These shales are utilized at New Albany for stiff-mud and dry-press brick; it is also possible that they could be used for sewer-pipe when admixed with some of the Carboniferous under-clays. Carboniferous The rocks of this period carry the most valuable clay-deposits of the State, and cover an area of about 7500 square miles in 14 counties of western and southwestern Indiana (Fig. 51). They form part of a large basin, underlying western and southwestern Indiana and southern Illinois, so that those in Indiana are on the eastern edge, and therefore dip southwestward and westward. This being so, the lowest rocks of the section outcrop on the eastern and northeastern edge of the area, while the higher lying ones outcrop farther westward. The Carboniferous rocks consist of a lower member, the Mansfield sandstone, and an upper member, the coal-measures. Kaolin or indianaite. At the base of the Mansfield sandstone there is a thin seam of coal, which is replaced at a number of localities in Lawrence, Martin, and Owen counties by a bed of kaolin called indiana- ite. Professor Blatchley states that " Wherever this kaolin is found it is always at the horizon of coal I. The coal and kaolin are never found at the same place, though often they occur but short distances apart. At Huron, Lawrence County, where the best-known deposit is located, the kaolin lies in a horizontal stratum 4 to 1 1 feet in thickness, which is overlain by a sandstone, and in places contains a light-green mineral known as allophane. The upper half of the kaolin stratum is chiefly composed of massive sno\v-white clay associated with which, near its MPP2F part, are occasional concretionary masses, some of them a foot 310 CLAYS or more in diameter. These disintegrate on exposure to air, but the kaolin is non-plastic. "An analysis of the kaolin showed: Silica (SiO 2 ) 44.75 Alumina (A1 2 O 3 ) 38.69 Water (H 2 O) 15. 17 Ferric oxide (Fe 2 O 3 ) 95 Lime (CaO) 37 Magnesia (MgO) 30 Potash (K 2 O) 12 Soda (Na 2 O) 23 100.58 " While of high purity, this clay is not now used, although at one time it was made into alum sulphate for sizing-paper." There has been much discussion regarding the origin of this kaolin, and while two theories have been advanced to explain its formation, both acknowledge its residual character, and that of the inclosing rocks, as sedimentary. E. T. Cox 1 argued that the kaolin occupied the position of a lime- stone bed, and that carbonated waters, acting on the latter, replaced the limestone with kaolinite. Thompson 2 seconded this theory , but added the belief that the surface-water had leached the alumina and silica from the overlying sandstones. Lesquereaux, on the other hand , believed that the kaolin was formed by the burning-out of coal-beds, a view in which Ashley concurred. Although the author is not personally acquainted with the region, it seems to him that there are certain marked objections to the latter theory. The burning-out of the coal would probably produce sufficient heat to cause some dehydration of the kaolin, whereas there is no evidence of this. In just what \vay the kaolin resembles baked fire-clay is not mentioned. It is not necessary to suppose any complex chemical reactions in order to derive kaolin from limestone. A calcareous rock, containing aluminous matter very low in impurities, might easily yield a mass of kaolin by simple leaching, and residual limestone clays of rather high purity are known in Missouri and also Virginia. 1 Sixth Ann. Rep. Geol. Surv. of Ind., 1874, p. 15. 2 Ind. Dept. Geol. and Nat. Hist., loth Ann. Rep., p. 37, 1886. DISTRIBUTION OF CLAY IN THE UNITED STATES 311 Coal-measure clays and shales. The Coal-measures include a series of coals, clays, shales, and sandstones (Fig. 52), and are found in a number of counties in the southwestern part of the State (Fig. 51). Ashley 1 has divided them vertically into eight divisions designated by Roman numerals, these divisions being based on the position of some principal coal-beds or horizons, the type section occurring in Clay and Vigo counties. The Mansfield sandstone found in general along the east- ern edge of the coal-field forms division I, and the main-worked coals,, clays, and shales occur above it stratigraphically. - Under Section Near Glen Mine, East of Coal Bluff 1. Soil and surface clay. __ 10 2. Potters.' clay ___________ 1 3. CoalVb ______________ 1 4. Under-clay ___________ 8 5. Surface soil and clay. ____ 6. Gravel and hard pan.. ..20 7. Under-clay. ____________ 6 8. Gray sandy shale ______ 10 9. Gray sandstone _______ 20 10. Coal Va _____________ l 11. Under-clay ___________ 8 12. Drab clayey shale _____ 14 13. Coal V. _______________ 2 14. Under-clay. ___________ n 15. Coal IV. _____________ 4 16. Under-clay. ___________ 5+ FIG. 52. Section near Glen Mine, Coal Bluff, Ind., showing association of coals , under-clays, etc. (After Blatchley, Ind. Dept. Geol. and Nat. Res., 29th Ann. Kept., p. 183, 1905.) A part of a typical vertical section showing the arrangement of the different strata of the coal-measures and their relation to each other is given by Blatchley (Ref. 3) as follows: Feet. Inches. 1. Soil- and surface-clay 5 2 2. Sandstone, massive or shelly 2 8 3. Blue compact shale 27 4. Coal VII 4 10 5. Fire-clay 6 2 Ind. Dept. Geol. and Nat. Res., 23d. Ann. Rept., 1899. 312 CLAYS Feet. Inches. 6. Drab siliceous shale * 18 7. Limestone 3 8 8. Black bituminous shale 2 4 9. CoalVIfc 8 10. Fire-clay 5 6 11. Sandstone 13 12. Dark-gray shale 11 2 13. Coal VI 6 3 14. Hard impure bluish fire-clay 11 15. Sandstone 21 16. Blue limestone 11 17. Black slaty bituminous shale 5 4 18. CoalV 5 2 19. Fire-clay 4 8 The fire-clays (Nos. 5, 10, 14, and 19) are almost universal accompani- ments of the overlying coal-seams. They are usually one to six feet thick, and are a soft homogeneous clay, whitish or gray in color, highly plastic, and often of excellent refractoriness. At times, however, these under-clays are composed of a hard, bluish, siliceous clay with more or less pyrite and other impurities. No. 14 is of this character, and similar clays usually occur beneath coals III and V, but those below coals II, IV, VI, and VIII are often of excellent quality. The blue, gray, and drab shales (Nos. 3, 6, and 12) make up the greater part of the Coal-measure rocks of Indiana, and include the most valuable clay-deposits found in the State. When freshly exposed they are usually hard, but weather down easily to a plastic clay. The relations of the shales, clays, and coal are such that the three <;an often be mined by one shaft. The coal-measure clays and shales are worked for a variety of purposes, including pressed and paving brick, fireproofing, sewer-pipe, stoneware and fire-brick. At Brazil, Clay County, which is a most important clay-working center, the following section is instructive. Feet. Inches. 1. Soil and yellow clay 12 2. Bowlder clay, blue 7 3. Gray clayey shale 33 4. CoalV 2 3 5. Under-clay (potters' clay) 3 2 6. Blue clayey shale 19 7. Bituminous fossil shale 1 6 8. Coal IV 3 6 9. Under-cla-.. 5 4 DISTRIBUTION OF CLAY IN THE UNITED STATES 313 No. 9 and an overlying shale are used for sewer-pipe, flue-linings, wall-coping, etc. No. 3 is also used for a variety of purposes. The best deposits of unworked shales and clays for making vitrified bricks lie just east of Mecca, Parke County; west of Montezuma, Parke County; west of Terra Haute, and near Riley, Vigo County. Pleistocene Clays These are soft, plastic clays, found at the surface or at no great distance below it, and, while occurring over a large part of the State, they are especially important in the northwestern part of Indiana, and on this account have been made the subject of a special report. (Ref. 1.) In this region three classes are distinguishable, namely, drift-clays or "hard-pans," alluvial clays, and silty or marly clays. The drift-clays are the most common type, forming a large percentage of the unstratih'ed morainic material, but they are usually too impure and calcareous for making anything but common brick and tile. The alluvial clays form larger deposits along the lowlands and second bottoms of the large streams of northwestern Indiana, having been formed during periods of overflow, and in some places showing a thickness of 30 to 90 feet. The silty or marly clays resemble those of the preceding class very closely, but differ in having been deposited in bays, lakes, or harbors in quiet water. These clays are usually finer grained than the alluvial ones, thinly laminated, and often highly calcareous, so that they produce a buff product. They are an important source of brick and tile material in Benton, Newton, Jasper, Starke, Lake, Porter, Laporte,and St. Joseph counties. In other parts of the State there are many scattered deposits of surface-clays used for brick and tile, while south of the terminal moraine in southwestern Indiana there are many deposits of loess which are available for the same purpose. The analyses on page 314 are given by Blatchley (Ref. 3) as repre- sentative of the different types of Indiana clays and shales. References on Indiana Clays 1. Blatchley, W. S., Clays and Clay Industries of Northwestern Indiana, Rept. of Indiana State Geologist for 1897, p. 106. 2. Blatchley, W. S., Preliminary Report on the Clays and Clay In- 314 CLAYS dustries of the Coal-bearing Counties of Indiana, Ind. Dept. of Geol. and Nat. Res., 20th Ann. Kept., p. 23, 1896. 3. Blatchley, W. S., The Clays and Clay Industries of Indiana, Ind. Dept, Geol. and Nat. Res., 29th Ann. Rept,, pp. 13-658, 1904. 4. See also scattered references in the other annual reports of this survey. ANALYSES OF IXDIAXA CLAYS I. II, III, IV. V VI. Silica (SiO,) 59 77 58 83 65 78 67 65 55 09 83 44 Alumina (AlAO Ferric oxide (Fe 2 O 3 ) Ferrous oxide (FeO) Lime (CaO) Magnesia (MgO) Potash (KsjQ). Soda (Na,O) Titanic acid (TiO L> ) Carbon dioxide (CO,-), etc 20.60 2.22 3.70 0.64 1.98 3.10 85 0.80 0.90 22 . 84 5.13 1.44 0.49 1.56 4.18 0.63 0.70 14.79 8.03 0.54 1.42 2.82 0.97 1.00 0.26 19.97 0.72 '6^48 0.59 1.75 2.29 1.01 3 04 20.76 3.00 4.01 1.51 1.18 2.36 0.34 1.20 10.36 0.27 0.28 0.36 0.14 03 0.71 1.29 Water (HoO) 4 . 53 5 . 22 4.98 5.96 7 01 3 15 VII. VIII. IX. X. XI. XII. Silica (SiO->) 69 23 65 25 59 64 63 88 70 eo 6 11 Alumina (Al..O 3 ) Ferric oxide (Fe-O^). . . . 18.97 1 57 17.30 2.30 19.14 3.39 17.85 5 38 13.89 2 83 13.78 5 35 Ferrous oxide (FeO). 55 4 20 3 56 Lime (CaO) 12 0.50 0.26 38 CO 1 67 Magnesia (MgO) 36 0.20 2.31 1 47 1 78 Potash (K,O) Soda (Xa 2 6) Titanic acid (TiO.,) Carbon dioxide (CO.), etc Water (H,O) 2.27 0.33 1.50 5.46 1.56 0.98 e'so 5.40 3.53 0.80 1.05 0.35 4.36 3.98 1.29 0.91 4*99 2.76 1.60 0.43 0.51 3.19 2.11 1.15 6^34 XIII. XIV. XV. XVI. XVII. Silica (SiO.) 71 20 72 56 50 56 50 47 44 75 Alumina (AI.OO- 18.56 10 44 13.11 12 77 38 69 Ferric oxide (Fe-O ). . . . 1 .34 7.45 2.98 2 44 95 Ferrous oxide (FeO) Lime (CaO) Magnesia (MgO) Potash (KoO). 0.15 0.14 0.52 0.32 43 0.82 1.09 2.05 2.32 7.87 5.06 3.74 2.52 8.17 5.22 3.70 0'37' 0.30 0.12 Soda (Xa 2 O) Titanic acid ( TiO->) 1.26 88 0.73 31 0.70 1 00 0.73 1 45 0.23 Carbon dioxide (CO,) etc 9 62 9 , V Water (H-O) 6 30 4 54 2 76 3 14 15.17 DISTRIBUTION OF CLAY IN THE UNITED STATES RATIONAL ANALYSES OF THE PRECEDING 315 i. II. III. IV. V. Quartz 26 . 04 22.81 34.34 28.29 20.90 Feldspathic detritus. 8.37 8 30 12 58 34.77 2.03 Ferrous carbonate 2.37 6.46 Magnesium carbonate 50 1 13 Clay substance 63.22 68.89 52.58 36 . 94 69.48 VI. VII. IX. X. XL 46 33 39 36 25 57 17 93 56 65 Feldspathic detritus 39 28 1 67 6 86 42 03 16 63 Ferrous carbonate 1 07 Magnesium carbonate. . . 67 08 Clay substance 14 39 58 37 66 90 40 04 25 57 LOCALITIES OF THE PRECEDING No. Location. Geological Age. I. II. III. IV. V. VI. VII. VIII IX. X. XI. XII. XIII. XIV XV. XVI. XVII. Mecca, Mecca Coal and Mining Company Cayuga, Cayuga Brick and Coal Company. . . . Mecca, Mecca Coal and Mining Company Cayuga, Cayuga Brick and Coal Company. . . . W Montezuma Burns & Hancock Carboniferous shale < t < < Coal-measures under-clay n 1 1 ( 1 1 ( t fC ( 11 It (( < t ( < e t < i 1 1 Knobstone shale ( ( < C (I (I Alluvial Surface Loess Residual Pleistocene Pleistocene Residual Huntingburg, Bockting Bros Huntingburg C Fuchs. . Blue Lick New Albany Martinsville Branch & Sons . Terre Haute. Princeton Four miles south of Bloomington . . Hobart . . . Michigan . Indianaite Huron Dr Gardner. . Indian Territory 1 The greater part of the Cherokee and Creek nations and the northern part of the Choctaw nation contains extensive deposits of clays of Penn- sylvanian age, which are very similar to the brick- and tile-clays of south- eastern Kansas, and the presence of gas in that region will warrant the development of extensive industries. In the western part of the Chicka- saw nation the country is underlain with red clay of the Permian red From note supplied by Professor C. N. Gould. 316 CLAYS beds, the same as that found in Oklahoma, while in the southern part of the Choctaw and Chickasaw nations the clay is of Lower Cretaceous age, similar to that in central Texas. Probably the best clay in Indian Territory so far discovered is from the formation known as Sylvan Shale of Silurian age, which outcrops in various places in the Arbuckle Mountains in the eastern part of the Chickasaw nation. A company is now engaged in developing the clay- products at Oolite, where plants are being erected for the manufacture of brick, tile, sewer-pipe, fireproofing, and cement. Iowa Every great rock formation of Iowa, except one, the Sioux quartzite contains more or less important clay- or shale-deposits, but the different ones represent a wide range of structural characters and physical or chemical properties, these variations occurring sometimes within the same formation. Cambrian Saint Croix sandstone. This carries a few shale-beds which outcrop in portions of Allamakee and Clayton counties, but nothing is known regarding their economic value. Ordovician Galena-Trenton. Although essentially a limestone formation, this nevertheless contains a few beds of shale, which may be adaptable to pottery manufacture. The best exposure is on Silver Creek, Makee township, Allamakee County. Concretions and fossils are apt to render this shale worthless. Maquoketa shale. This, the oldest shale formation of importance in the State, forms a narrow, sinuous band from Jackson County on the south to Winneshiek and Howard counties. The shale is divisible into two groups, the upper consisting of a plastic clay, with occasional limestone layers, while the lower is of lean fissile shales, with some earthy, fossiliferous beds. They are mostly red-burning, but may at times be quite calcareous, and though their chief use is for common brick, they have also given excellent results for earthenware manufacture and hollow brick. Silurian The beds of this system are practically devoid of shale-deposits. DISTRIBUTION OF CLAY IN THE UNITED STATES 317 318 CLAYS Devonian The lower argillaceous beds, known as the Independenc outcrop in limited measure in Cedar, Linn, and Buchanan counties, but are of no economic importance. The upper shales, which are typically developed along Lime Creek in Cerro Gordo and Floyd counties, and at Rockford and Mason City are of much greater value. Owing to a variable lime-content the clays burn either light red or cream, but in either case have yielded good results in the manufacture of common and hollow brick and drain-tile. The shales are too fusible to take a salt-glaze. Carboniferous Practically all of the great formations of the Carboniferous contain clays of importance, but those of the Kinderhook and Coal-measures are especially important. According to Beyer and Williams, "Rocks referable to the Carboniferous comprise the indurated rocks over nearly one half of the surface of the State. The system may be divided into two parts: (1) the Lower Carboniferous beds, which are prevailingly calcareous in character, and (2) the Upper Carboniferous, in which arenaceous and argillaceous deposits predominate, with important limestone bands in the upper portion. The latter division contains all of the workable coal in the State. On account of the abundance of raw material suitable for the manufacture of clay wares and cheap fuel, the Upper Carbon- iferous or Coal-measures constitute the most important formation to the clay-worker in the State. "The Lower Carboniferous comprises a belt averaging from thirty to forty miles in width, and extending diagonally across the State from Kossuth and Winnebago counties on the north to Des Moines and Lee counties on the south. Narrow strips have been laid bare by the lower courses of the Skunk and Des Moines rivers, and unimportant detached areas appear in Story and Webster counties. Three stages represent the Lower Carboniferous in Iowa, namely, the Kinderhook, Augusta, and Saint Louis." Kinderhook. The shales of this formation are specially prominent in Des Moines and Lee counties; they are red- or brown-burning and used for common brick. Augusta. These shales are of little importance except in Lee County, and even there are rather calcareous. PLATE XXVII FIG. 1. Carboniferous shale for paving-blocks near Veedersburg, Ind. (After Blatchley. 29th Ann. Rep., Ind. Dept. Geol. and Nat. Res., p. 80.) FIG. 2. Cretaceous shale, Sioux City, la. (After Williams, la. Geol. Surv., XIV, p. 518, 1904 ) 319 DISTRIBUTION OF CLAY IN THE UNITED STATES 321 Coal-measures The rocks of this age cover nearly one third of the State and carry a great range of argillaceous beds grouped as (1) argillaceous, (2) arena- ceous, (3) carbonaceous or bituminous, and (4) calcareous varieties. These grade into each other both vertically and horizontally. Although the coal-measures are present in ninety-nine counties of the State, the clay-shales are utilized for making clay-products in but sixteen. The argillaceous shales are often found underlying the coal-seams, and are not uncommonly of refractory character, but the calcareous ones contain too much limey matter to be of great value. Those beds of the Coal-measures prominent along the Des Moines River 'contain argillaceous, bituminous, and arenaceous shales, while in the beds most prominent along the Missouri River the calcareous members are more prominent. It is difficult to generalize regarding the clays of this series, but at any one point it is not uncommon to find several grades of clay ranging from common brick-clay to fire-clay in the same section. The shales are worked at a number of points, among which Van Meter, Dallas County; Des Moines, Polk County; Ottumwa, Wapello County; and Fort Dodge, Wapello County may be mentioned. The clays are worked either as open pits or undergound mining and the products include common and pressed brick, paving-brick, hollow blocks, drain-tile, stoneware, and fire-bricks. Analyses of these are given on a later page. Cretaceous The Cretaceous of Iowa consists of a lower sandstone and shale series, the Dakota, and an upper series of interbedded sandstones, shales, and marly limestones. These rocks cover approximately the north- western third of the State, shale-beds of this age being known in Sioux (PL XXVII, Fig. 2), Plymouth, Woodbury, Sac, Calhoun, and Montgomery counties. The shales show about the same textural and chemical range as the Carboniferous ones, but on the whole are more siliceous. At Red Oak, Montgomery County, both white stoneware and fire-brick are made, and it has been suggested that washing might render the clay available for glass-pot manufacture. Other products from these shales are paving and common brick. 322 CLAYS Pleistocene Covering all of the State, with the exception of a small area in the northeastern corner, is a thick mantle of glacial deposits which range in thickness from zero up to three or four hundred feet. The glacial drift is composed of a heterogeneous mass of bowlder beds, gravel, and sand-deposits, and more rarely beds of clay, which, owing to a natural washing process which they have undergone, are sufficiently plastic to be molded into clay wares. They often suffer, however, from the presence of lime pebbles or stones, and even if free from these are still unsatisfac- tory because of their high shrinkage, which causes a loss due to checking in drying and burning. A few of the drift-sheets, however, contain clays of satisfactory character for brick manufacture. Loess. Associated with the drift-sheets and of far greater economic importance are the massive structureless deposits of loess. (PI. XXVIII, Fig. 1.) These consist of clays or clayey silts, which form a mantle over about two thirds of the area of the State, affording an inexhaustible supply of brick material. This occurs beyond the borders of the drift-sheets and even over- lapping them. It covers more than one half the surface of the State and shows great irregularity in thickness, being over one hundred feet thick along the Missouri River. It affords an exhaustless supply of material suitable for the manufacture of brick by the soft-mud, stiff- mud, or dry-press process, and moreover is a very cheap clay to work. Of the several types of loess recognized in the State, the "gumbo" is noteworthy. This is a thoroughly oxidized and leached red clay which on drying breaks up into a number of angular fragments. In the southern part of the State the gumbo is gray or drab in color. Its peculiarity is its excessive shrinkage which precludes its use for the manufacture of brick, but makes it admirably adapted to the manufacture of burned-clay ballast. The chemical composition of a number of representative Iowa clays and shales is given in the table on page 325. References on Iowa Clays 1. Beyer, S. W., Origin and Classification of Iowa Clays, Clay Record, XX, No. 3. 2. Beyer, Weems and Williams, The Clays of Iowa, la. Geol. Surv., XIV, 1904. PLATE XXVIII FJG. 1. Loess-bank, Muscatine, la. (After Williams, la. Geol. Surv., XIV, 1904.) FIG. 2. Bank of (Devonian) shale used for paving-brick, Cumberland, Md. H. Ries, Md. Geol. Surv., IV, p. 454, 1902.) 323 (After DISTRIBUTION OF CLAY IN THE UNITED STATES 325 3. Youtz, L. A., Clays of the Indianola Brick, Tile, .and Pottery Works, la. Acad. Sci. Proc., Ill, p. 40, 1896. ANALYSES OF IOWA CLAYS ULTIMATE ANALYSES I. II. III. IV. V. VI. VII. VIII. Silica (SiO 2 ) 67.50 61.59 73.43 63.78 58.56 75.85 58 05 77 39 Alumina (A1 2 O 3 ) Ferric oxide (Fe 2 O 3 ). . .. Lime (CaO) ;.. Magnesia (MgO) 15.75 4.80 2.57 1.57 21.01 4.72 3.58 2 16 11.94 3.83 1.00 86 19.78 l!55 1.22 22.33 2.87 3.60 1.44 10.73 1.43 1.00 49 23.05 3.83 0.30 2 04 5.16 2.40 3.65 3 13 Potash (K 2 O) Soda (Na 2 O) . ... 0.95 1.56 0.52 1 13 0.05 0.95 0.54 1.20 i!os 0.24 0.70 0.90 2 04 1.44 2 79 Comb, water (H 2 O). . . . Carbon dioxide (CO 2 ). . Sulphur trioxide (SO 3 ). . Moisture 3.22 with noist. with moist. 2.88 4.51 0.95 0.4? 4.33 0.90 1.65 0.63 2.92 with moist, with moist. 3.88 7.11 with moist, with moist. 2.98 6.38 with moist, with moist. 3 18 8.1G 0.86 96 1.46 1.44 13 IX. X. XI XII. XIII. XIV. XV. XVI. Silica_(SiO 2 ) Alumina (A1 2 O 3 ) Ferric oxide (Fe 2 O 3 ). . . Lime (CaO) 58.33 15.54 3.84 9.42 47.40 22.20 12.40 0.70 28.82 10.37 3.76 19.14 66.44 12.64 4.00 4.02 51.95 18.34 7.56 4.14 44.39 13.72 7.80 7 88 68.22 10.21 2.87 3 90 67.92 11.76 6.72 1 63 Magnesia (MgO) Potash (K 2 O). 3.03 1.19 1.10 3.10 5.40 5.38 1.80 1.14 3.26 1.43 6.05 1.56 3.16 58 1.18 1 87 Soda (Na 2 O) 1.76 0.50 7.41 1.90 2.69 5.29 1 68 1 92 Comb, water (H 2 O).. . . Carbon dioxide (CO 2 ) 3.47 2 02 7.90 16.24 5.83 7.3C 12.18 1.52 5 86 5.36 Sulphur trioxide (SO 3 ).. 1.10 2.40 3.01 2.76 1.45 Moisture 42 2 10 43 2 33 42 89 62 1 49 RATIONAL ANALYSES I. II. III. IV. V. VI. VII. VIII. Clay 52.85 56.79 41.47 61.57 57.40 38.20 68.20 24 92 Quartz 25.99 19.63 55.29 20.53 31.17 51.10 25.81 51.39 Feldspar 15 80 21 96 3 24 13 47 4 38 7 62 5 99 19 64 Carbonates and sul- phates of Ca + Mg. 5 36 1.62 4 43 7 05 3 08 4 05 IX. X. XI. XII. XIII. XIV. XV. XVI. Clay. 64.47 74.90 68 . 20 38.80 47.08 40.61 19 72 39 90 Quartz 18 67 12 70 21 75 36 36 41 45 28 00 40 29 40 28 Feldspar 11 13 8 81 4 98 24 84 6 98 4 62 25 74 19 82 Carbonates and sul- phates of Ca + Mg . . 5 73 3 5f 5 12 4 49 26 77 14 25 326 CLAYS LOCALITIES OF THE PRECEDING No. Locality. Geological Age. Uses. I II III IV V VI VII VIII, IX. X. XL XII. XIII. XIV. XV. XVI. Flint Brick Co., Des Moines. , Iowa Brick Co., Des Moines , Flint Brick Co., Des Moines Capital CityBrick Co., Des Moines J. Holman, Sargent's Bluff Corey Pr. Br. Co., Lehigh Granite Br. Co., Cascade Cream City B. & T. Co., Rockford Boone Br. & T. Co., Boone Clermont Storm Lake. . Mason City. . . Edge wood. . . . Council Bluffs. Gladbrook. Coal-measures n it Cretaceous Coal-measures Kinderhook Devonian Coal-measures Maquoketa Drift Devonian Maquoketa Loess (Mo.) Inland Loess Paving- and building-brick Paving-brick, builders, and hollow ware, bottom Ditto, top Paving-brick; green-brick mixture Brick and tile Common, face, paving- brick, sidewalk brick Pressed face brick and or- mentals Common and paving brick Brick and tile Paving, hollow ware, com- mon brick Brick and tile Drain -tile Brick and tile Brick and tile Soft-mud, stiff-mud, and pressed brick Pressed brick These analyses are all from Vol. XIV, la. Geol. Surv., and have been kindly selected as representative by Professor I. A. Williams. Kansas This State probably contains an abundance of clays of low and medium grade, but they have not as yet been systematically investigated. The formations yielding them are of Carboniferous, Permian, Triassic, Cre- taceous, Tertiary, and Pleistocene age. Carboniferous The Coal-measures underlie a rather extensive area in eastern Kansas, and consist of alternating strata of limestones, shales, and sandstones, with occasional coals. These beds dip gently to the westward, so that any one bed passes under the overlying ones if traced in that direction. The shales of this series are mostly red-burning and at different localities have been found adapted to the manufacture of common and pressed brick, drain-tile, vitrified brick, and more recently even for roofing-tile and stoneware. They were first worked at Atchison in 1887, but since then factories have been opened up at Topeka, Pittsburg, Chanute, Coffeeville, etc. Those at Cherryvale are found immediately DISTRIBUTION OF CLAY IN THE UNITED STATES 327 underlying the Independence limestone, while the beds worked at lola overlie the lola limestone. At Lawrence the beds utilized occupy, a position near the middle of the Lawrence shales and right under the Oread limestone. The coal-measure shales of southeastern Kansas are ideally located, because of the supply of natural-gas fuel. The Permian outcrops to the west of the coal-measures being found particularly in the Flint Hills area, and Haworth states that the shales are purer than those of the coal-measures. Triassic These occur in abundance, as at near Kingman, and Prosser states that they have been used for paint. Cretaceous The Dakota shales are well exposed near Salina, Dickinson County, but so far as known have not been utilized to any extent. Pleistocene The surface-clays are widely distributed over Kansas, but are chiefly important in the eastern portion. The gumbo clay, dug in many of the river valleys has been burned in large quantities for railroad ballast. References on Kansas Clays 1. Grimsley, G. P., Kansas Mineral Products, Eleventh Bien. Rept., Kas. Board of Agric., 1897-98, p. 507, 1898. 2. Haworth, E., Annual Bulletins on Mineral Resources of Kansas, issued by Univ. Geol. Survey, as follows: 1899, p. 57; 1900 and 1901, p. 60; 1902, p. 40; 1897, p. 81; 1898, p. 61. 3. Hay, R., Geology and Mineral Resources of Kansas, Eight Bien. Rept., State Agric. Board, 1891-92, p. 54, 1893. 4. Prosser, C. S., Clay-deposits of Kansas, U. S. Geol. Surv., Min. Res. for 1892, p. 731, 1394. 5. Schrader, F. C., and Haworth, E., Clay Industries of the Indepen- dence District, U. S. Geol. Surv., Bull. 260, p. 546, 1905. 328 CLAYS Kentucky The clays of this State, like those of many others, have never been systematically investigated, although the former Kentucky Geological Survey published a large number of analyses. 1 A great many scattered notes and short articles are also found in the various reports, from which the following are largely taken. Within the State there are found a series of geologic formations ranging from the Ordovician to the Pleistocene. Some of these con- tain deposits of soft, plastic clays or shales, while others yield clays only as a result of surface-weathering. A section across the State from east to west shows that the formations are not highly tilted as they are farther eastward, but that they are rather flat, having a comparatively gentle dip, so that in any one area where two formations are exposed the older of the two may have been laid bare as the result of erosion. Ordovician-Devonian The Ordovician, Silurian, and Devonian formations occupy a some- what circular area in central and north-central Kentucky. They con- tain a series of shales, limestones, and sandstones, the first of which are usually calcareous, and probably of little value except for common- brick manufacture; but nearly all of these formations yield residual clays which are mostly of low lime-content and generally high in iron. They are used for common-brick manufacture, and those at Waco are stated to be of value for pottery. 2 Carboniferous Lower Carboniferous. The beds of this age are found in both the eastern and western parts of the State and include several deposits of shales and clays, which to judge from the published analyses are of low fusibility and of red-burning character. 1 Ky. Geol. Surv., Chem. Analyses, A, Pts. I, II, and 111. 2 For Ordovician, see Ky. Geol. Surv., reports on Oldham County, p. 19; Kenton County, p. 133; Jefferson County, p. 50; and Chem. Analyses, Pt. I, 1884, pp. 34 and 76. For Silurian, consult Ky. Geol. Surv., new series, III, p. 156; Chem. Analyses, Pt. I, pp. 83, 130, and 288; Fleming County, p. 70; Clark County p. 28. DISTRIBUTION OF CLAY IN THE UNITED STATES 329 Coal-measures. The coal-measure beds will undoubtedly be found to contain the most valuable clays of the State, arid all of the high- grade fire-clays thus far dug in Kentucky have been obtained from them. They occur in both the eastern arid western portions of the State, in the coal-fields, but the beds have not been systematically traced or tested. In the eastern field a fire-clay is said to occur near the base of the subconglomerate, but is lacking in persistence. This is said to correspond to the fire-clay worked at Sciotoville, Ohio, and is found in Greenup, Boyd, Carter, and Lawrence counties; indeed, it is reported to have been shipped in large quantities from Indian Run in Greenup County. Clay of high refractoriness is obtained near Olive Hill and molded for fire-brick. Fire-clay is also stated to accompany many of the coal-seams in parts of Jackson, Pulaski, and Rockcastle counties. 1 The upper Ferriferous Limestone contains a bed of ore, usually overlain by a fire-clay, in Greenup, Carter, and Boyd counties, it has been worked for fire-brick at Bellefonte, and also for pottery near Cincinnati. 2 In the western coal-field fire-clays are known to occur, but there is little available information regarding them. Vitrified brick-clay is worked at Cloverport in Grayson County. Tertiary Tertiary clays of sandy to highly plastic character, and often of good refractoriness, occur at a number of points in the extreme western part of the State, while ball-clay has been dug in large quantities from the area around Mayfield. 3 Recent Clays Alluvial deposits suitable for making common brick are to be looked for along many of the river valleys. The analyses shown on page 330 are selected from the published reports of the Kentucky Geological Survey. See Ky. Geol. Surv., Eastern Coal-field, 1884, pp. 30, 32, 33, 43, 201; also U. S. Geol. Surv., Geol. Atlas, Folio 47, London sheet. 2 Ky. Geol. Surv., Eastern Coal-field, pp. 140 and 141. 3 U. S. Geol. Surv., Prof. Pap. 11, p. 39, 1903. 330 CLAYS References on Kentucky Clays 1. Crump, H. M., The Clays and Building Stones of Kentucky, Eng. and Min. Jour., LXVI, p. 190, 1898. 2. Many reports of Ky. Geol. Surv., for summary of which see U. S. GeoL Surv., Prof. Pap. No. 11, 1903. 3. Reports of Ky. Geol. Surv., Chemical Analyses, A, Pts. 1, 11, and III, contain many analyses. 4. Ky. Geol. Surv., Kept, on Jackson-Purchase Region, deals chiefly with the Tertiary clays. ANALYSES OF KENTUCKY CLAYS i. II. III. IV. V. VI. Silica (SiO 2 ) . . 56 40 59 97 63 12 61 10 46 56 43 58 Alumina (Al.Os) 1 18.20 37.47 40 86 Ferric oxide (Fe 2 O 3 ) . . J 29.97* 27 . 64* 8.56 6 00 trace 76 Lime (CaO) . 6 26 4 90 112 29 Magnesia (MgO). . 1 51 60 2 03 1 54 trace 14 Potash (K 2 O). 3 53 3 93 1 36 4 10 28 19 Soda (Na 2 O). . ... 55 54 82 28 05 Phosphoric acid (P2O-) 0.16 with 14 25 Loss on ignition 7.10 Al,0 3 7.02 12 00 3 33 13 03 14 43 Lime carbonate (CaCO 3 ) 0.76 0.28 VII. VIII. IX. X. XI. XII Silica (SiO 2 "> 62 92 47 56 84 76 40 14 A 44 or: 10 Alumina (A1 2 O 3 ), Ferric oxide (Fe 2 O 3 ) 20 '73 3 82 40.66 trace } 11.40 43.72 1 98 128.00 10.26 1 12 Lime (CaO) . 21 28 trace ) trace Magnesia (MgO) . 13 49 65 \ 1 60 1.30 06 Potash (K 2 O). . 19 30 1 58 95 Soda (Na 2 O). . 21 40 05 14 Phosphoric acid (P 2 O 5 ) Sulphur trioxide (SO 3 ) 0.62 undet 0.24 trace 12.56 14.30 Loss on ignition 13 66 10 03 1 56 J 2 27 XIII. XIV. XV. XVI. XVII. XVIII. Silica (SiO 2 ) 74 10 61 68 56 98 62 68 75 55 59 50 Alumina (A1 2 O 3 ) 16 46 28 50 32 16 25 88 16 75 24 96 Ferric oxide (Fe 2 O 3 ) 2 70 1 68 2 16 2 90 1 19 72 Lime (CaO) . 35 10 32 Magnesia (MgO). . 18 13 20 31 14 39 Potash (K 2 O). 55 1 15 83 1 14 1 09 1 93 Soda (Na 2 O) . . 13 82 11 92 21 28 Loss on ignition 5 50 5 92 7 54 6 14 5 04 11 87 Includes MnO. DISTRIBUTION OF CLAY IN THE UNITED STATES 331 LOCALITIES OF THE PRECEDING No. 1. II. 111. IV. V. VI. VII. via. IX. X. XI. XII. XIII. XIV. XV. XVI. XVII. XVIII. Location Two miles south of Covington Waco. . Nelson County Boone Furnace Perry's branch, Tygart Creek, near E. L. &B. S. R. R Two miles from Ken ton Furnace Wing's branch, Shultz Creek Whitley County Ashland (used) Columbus Hickman's Bluff Three miles east of New Providence. Bell City Six miles east of Mayfield Wickliffe Four miles south of Paducah . . Geological Age. Cincinnati group Lower Silurian Upper Silurian ''Ohio" Devonian shale Keokuk, Lower Carboniferous Coal-measures Tert ary Louisiana The workable clays of Louisiana (Ref . 1) are all of transported char- acter and post-Tertiary age. Three distinct types of clay are worked in Louisiana, and each of these is characteristic of that portion of the State in which it occurs. The first, and oldest, is the Columbian mottled-gray clay of south- eastern and southwestern Louisiana. It constitutes the "pine flats" of the coast, and the so-called "second bottoms" of the coastal plain These clays have been worked at a number of points, especially along the Pearl, Chefuncte, and Sabine rivers. "The second group includes clays of later Columbian age, skirting, though lying 30 to 50 feet above, the alluvial valley of the modern Missis- sippi River. Upon the eastern bank they form a continuous bluff from the Mississippi State line to Baton Rouge, thence bear southwestward to near Lake Mauripas as an escarpment bordering the modern Mississippi alluvium. Upon the immediate front, and extending some two or three miles back from the river, these yellow and somewhat loamy clays are covered by the brown loam or loess, and in such position have not been worked." But at Baton Rouge, where the loam has been largely removed, they are extensively dug for common brick. Clays of similar character and geologic age form a somewhat inter- rupted escarpment on the western side of the present Mississippi Valley. These clays have been worked at Markville, Washington, and New Iberia, 332 CLAYS and utilized for tile, common brick, and dry-pressed brick. The heaviest and perhaps best of these deposits are found in West Carroll, Richland, and Franklin parishes. The third group includes a series of pocket-like deposits in the modern alluvium of the Red River. Near Shreveport, and further north in the bluffs of Caddo and Bossier parishes, are outcrops of lignite shales which may be of value. References on Louisiana Clays N 1. Clendenin, W. W., Clays of Louisiana, Eng. and Min. Jour., LXVI, p. 456, 1898. 2. Ries, H., Report on some Louisiana Clay Samples, La. Exp. Stat., Ft. V, p. 263, 1899. CHAPTER VI MAINE NORTH CAROLINA Maine, New Hampshire, and Vermont THE larger portion of these three States is underlain by either pre- Cambrian crystalline rocks or metamorphosed Palaeozoic formations, consequently little clay is to be looked for in these. Covering the entire surface of these States, however, is a mantle of Pleistocene deposits, mostly glacial drift, which is employed at many places for the manufac- ture of bricks, as it often contains clayey members. None of the deposits are refractory, and indeed they may often be quite calcareous. The glacial clays are found in the till or have accumulated in hollows, but in addition to these are to be found in a series of estuarine deposits, represented by the clay-beds that have been formed in the larger valleys during a depression of the land in Pleistocene time. The subsequent uplift of the surface, and their erosion by streams, has left the clays as terrace deposits along the valleys. Deposits of this character are com- monly more persistent and thicker than the preceding type of drift-clay. An extensive series underlies the terraces along the eastern shore of Lake Champlain, where they reach a height of several hundred feet above sea-level. These Pleistocene clays are mostly of value only for making common brick and drain-tile, although the smoother ones could be employed for red earthenware. A rather important series of residual clays is found in Vermont in connection with limonite and manganese deposits. They have been recorded from Brandon, Monkton, and Bennington, as well as in Shafts- bury, Wallingford, Plymouth, and Chittenden. Some of these are of white color, and although now used chiefly for paper manufacture, have also been tried for the manufacture of porcelain, stoneware, and fire- brick. The following analyses show the composition of one from Forest- dale, Vt. 333 334 CLAYS ANALYSES OF VERMONT KAOLINS 1. II. Silica (SiO 2 ) 53.70 48 91 Alumina (A1,O<) 35. 12 39.99 Ferric oxide (Fe,O.,) 06 33 Lime (CaO), . , trace 0.34 Magnesia (MgO), trace Loss on ignition 10 . 55 8 . 92 Alkalies, by difference. 0. 57 1 . 51 Total 100.00 100.00 I. J N Nevius anal. II. H Carmichael anal. A decomposed talcose schist known as "fire-clay" is worked near Rutland, and used for patent wall-plaster, stove-lining, etc. References on Vermont Clays 1. Nevius, J. N., Kaolin in Vermont, Eng, and Min. Jour., LXIV. p. 189, 1897. 2. Perkins, G. H., Kept. Vt. State Geologist, 1903-1904, p. 52, 1904. Maryland The Maryland clay-deposits (Ref . 5) occur in formations ranging from Algonkian to Pleistocene, and the several formations of each system are each more or less limited to one of the three topographic provinces into which the State is divisible, as follows: Coastal Plain area, containing Pleistocene, Tertiary, Jura-Trias, and some of the Algonkian formations; bounded approximately on north- west by a line passing through Wilmington, Baltimore, and Washington. Piedmont Plateau region, containing Palaeozoic, Mesozoic, and pre- Cambrian formations. The first two yield shales, while the third gives a series of residual clays which may at times be of value. This region extends from the western boundary of the coastal plain to the Appala- chian Mountains. Appalachian region, consisting of parallel mountain ridges com- posed of upturned Palaeozoic strata. These are largely Devonian and Carboniferous shales which are abundant in Allegany and Garret t counties. Algonkian Clays These are exclusively of residual character and usually highly ferrugi- nous; there are, however, in Cecil County a number of scattered kaolin- deposits derived from feldspathic gneiss, and one near Northeast has MAINE NORTH CAROLINA 335 been worked to some extent for use in paper manufacture. A second pit has been worked near Dorsey station in Howard County and used in fire-brick making. The impure, ferruginous residuals, which have been derived from a variety of rocks and are all red-burning, vary in thickness, and except in the case of limestone residuals invariably pass by slow gradation into the parent rock below. They are widely distributed in the Pied- mont area. A broad belt of limestone clay is prominent in Washington County. Silurian Shales Most of these occurrences have no value for brick manufacture, unless they have at least partly weathered to residual clays. One good deposit occurs near the cement-works at Pinto, Allegany County. Devonian Shales These are represented in Allegany and Garrett counties by a great series of shales, sandy shales and shaly limestones. In some cases the shales have been so altered by folding that they develop little or no plasticity when ground and mixed with water, while at other times they are of excellent value for the manufacture of clay-products. The most important member is the Jennings shale, which is well exposed east of Cumberland and has been used for the manufacture of a red vitrified brick. Carboniferous Shales These are found in the western part of the State in Garrett County and western Allegany County. The important clay-bearing formations, together with their characteristics, are as follows: Mauch Chunk. A red shale with interbedded reddish sandstones, which at times weathers down to a plastic clay. The outcrops flank the ridges of western Allegany and eastern Garrett counties, but the beds are not worked. Pottsville. This, the only one of the Carboniferous formations which has been commercially exploited in Maryland, contains a valuable deposit of fire-clay. The bed, which is known as the Mount Savage fire-clay, underlies the Mount Savage coal, and has already been opened up at several points on Savage Mountain, west of Frostburg, Mount Savage, and Ellerslie respectively. Outcrops have also been found near Elaine and at Swallows Falls. The bed sometimes contains flint-clay and sometimes plastic shale, the two occurring irregularly. 336 CLAYS Allegany. This outcrops on the eastern side of the George's Creek coal-basin high up on the western slope of Dans and Little Allegheny mountains. It contains many beds of shale, but none are worked, and it is doubtful if many could be used for clay-product manufacture. Conemaugh. The shales of this member are usually argillaceous, and sometimes associated with coal. There are other shaly formations, but none except those mentioned seem promising. 1 Cretaceous and Jura-Trias Clays The clay-deposits of these two ages underlie large areas in eastern Maryland and are perhaps the most important clay series in the State. They are divisible into the following groups in Upper Cretaceous.. f Rancocas IMonmouth Matawan Lower Cretaceous J Raritan ] | Patapsco Potomac. Jura Trias. . . | Arundel j Group. 1 Patuxent The Upper Cretaceous deposits of Maryland are a continuation of similar beds in Delaware and New Jersey and cross the State from north- east to southwest, being especially developed in Cecil, Kent, Anne Arundel, and Prince George counties. In Maryland, however, these deposits carry but little clay. Those of the Potomac Group or Lower Cretaceous are of much importance, and consist of a series of sand, sandy clays, and gravels which have been deposited at different periods and under vari- ous conditions, the result being that the most unlike materials pass into each other horizontally. The characters of the several subdivisions of the Potomac together with their uses are as follows: Patuxent. This is best developed in the upper valleys of the Big Patuxent and Little Patuxent rivers and is sometimes found resting on the crystalline rocks of the Piedmont Plateau. It is traceable as a narrow, irregular, and sometimes broken belt from Cecil County on the northeast across Harford, Baltimore, Anne Arundel, and Prince George counties to the border of the District of Columbia. The Patuxent at times contains beds of refractory clay, the best occurrences having been ' For distribution, see Reports on Allegany and Garrett counties issued by Maryland Geological Survey. MAINE NORTH CAROLINA 337 noted around Baltimore and near Sewell in Harford County. The clays, which commonly show low tensile strength and low air- and fire-shrink- age, have been used with much success for admixture with the more plastic Arundel clays in the manufacture of terra-cotta. Arundel formation. Although highly developed in Anne Arundel County, the deposits of this horizon can be traced as a broken belt from Cecil County to the District of Columbia. The deposits form a series of large and small lenses of clays bearing carbonate iron ore (PL IV, Fig. 1) which have commonly been deposited in old depressions in the surface of the Patuxent formation. They vary considerably in size, ranging from a few feet up to 125 feet, and are usually made up of a blue, often siliceous clay of good plasticity but not high tensile strength. Cecil, Harford, Anne Arundel, Howard, Prince George, and Baltimore counties all contain many beds of Arundel clay. They are mostly red-burning and so their chief use has been for the manufacture of common and pressed brick, but some has been dug near Baltimore for making sewer- pipe and common pottery, in fact refractory clay is at times found and used for terra-cotta. Patapsco formation. The type exposures of this are on the shores of the Patapsco River, although the formation extends across the State. The clays are chiefly bright colored, mottled materials, which are often surrounded by sand-deposits. At the base of the formation there is often a bed of bluish stoneware clay, which is worked in Cecil County. Raritan formation. The beds in this formation are predominatingly sandy, and alt-hough at times they contain lenses of clay they are of far less importance than those in New Jersey. Tertiary Clays An important bed of red clay of Tertiary age extends from the South River southwestward, showing many outcrops, especially along the Western and Charles branches of the Patuxent, at Upper Marlboro in the Potomac Valley, in Prince George County, etc. It is a somewhat fine-grained plastic clay, at least 20 feet thick, and burns to a good hard red body, but is not worked, although it could be used for pressed brick. Pleistocene This overlies the earlier formations of the coastal plain, and in some cases extends up on the rocks of the Piedmont Plateau, forming a mantle of sandy clay, loam, and gravel of varying thickness. The loams, which belong to the Columbia formation, are very extensive and form an abun- 338 CLAYS dant source of brick material, being much used for this purpose around Baltimore. Occasionally the Pleistocene carries stoneware clays, as along Chesa- peake Bay south of Bodkin Point. The physical propeities and chemical composition of clays from the different formations are given below, all of them being taken from Volume IV of the Maryland Geological Survey. ANALYSES OF MARYLAND CLAYS I 11. 111, IV V. VI Silica (SiO 2 ) 70 25 56.15 75 40 69.40 59 70 68 30 Alumina (Al 2 Oa) 17 71 33 295 16 73 19.70 27.00 21 27 Ferric oxide (Fe 2 O 3 ) Lime (CaO). 4.10 70 0.59 17 1.27 0.35 2.00 0.20 2.10 0.60 1.43 52 Magnesia (MgO). . 40 0.115 0.90 0.60 0.52 80 Alkalies (Na 2 O,K 2 O). Ignition 1.76 4 80 9.68 0.50 5.30 0.62 7.85 1.96 8.20 0.20 7 55 Total 99.72 100.00 100.45 100.37 100.08 100 07 VII VIII. IX. X. XL XII. Silica (SiO 2 ) 72 50 55 65 61 00 46 10 58 60 67 50 Alumina (Al 2 Os) 17 00 30 53 26 36 38 05 28 71 17 20 Ferric oxide (Fe^Os) 1 50 97 83 1 05 3 22 6 70 Lime (CaO) 35 0.75 0.21 39 40 45 Magnesia (MgO) 60 60 0.10 0.60 35 Alkalies (Na 2 O,K 2 O) 1.10 0.20 trace 0.63 1.76 Ignition 6.50 12.30 11.60 12.95 8.90 5 90 Total 99 45 100 35 100 04 99 14 100 81 99 51 LOCALITIES OF THE ABOVE No. Locality. Geological Age. Uses. J. Bottom shale, brick works, Cumberland, Allegany County. Devonian Paving-brick II. 111. Flint-clay, Mount Savage, Allegany County. . Baldwin's sand-pit, Raritan River, Anne Arundel County Carboniferous Raritan Fire-brick Not worked IV Bodkin Point, Anne Arundel County Pleistocene V Baltimore, Baltimore County Arundel Brick VI. Link's pit, south of Baltimore, Baltimore County Arundel Terra-cotta VII Carpenter Point Cecil County Patapsco Stoneware VIII Northeast Cecil County Algonkian Kaolin IX. x Flint-clay, Swallows Falls, Garrett County. . Shale Swallows Falls Garrett County Carboniferous < t Not worked IX. XII. Upper Marlboro, Prince George County Residual limestone clay, Williamsport, Wash- ington County Eocene Pleistocene it ii Bricks MAINE NORTH CAROLINA 339 PHYSICAL TESTS OF MARYLAND CLAYS I. II. III. IV, V. VI. Per cent water required 19 30 40 . 19 22 5 23 Air-shrinkage per cent. 4 6 11 4 6 6 .Fire-shrinkage 5 4 9 6 g 10 Aver. tens, strength, Ibs. per sq. in. . . f incipient fusion. . . . 55 01 40 8 223 05 65 3 77 1 110 01 Cone of \ vitrification 4 27 + 2 8 + 6 8 [ viscosity 7 7 10 12 Plasticity. . lean good high fair good hiffh VII. VIII. IX. X. XI. XII. Per cent water required 20 30 18 20 25 35 Air-shrinkage per cent 2 6 1 5 5 4 9 Fire-shrinkage 4 4 12 5 3 5 5 11 Aver. tens, strength, Ibs. per sq. in. ... f incipient fusion. . . 10 27 40 8 20 10 100 3 15 27 + 132 05 Cone of \ vitrification 27 + 27 8 Q [ viscosity 10 + 10 Plasticity lean fair lean fair lean fair LOCALITIES OF THE ABOVE No. Locality, Geological Age. Uses. I, II. III. Savage Mountain, Allegany County. . . . Bodkin Point, Anne Arundel County. . Two miles south of Bodkin Point, Anne Arundel County . . Mauch Chunk Pleistocene tt Not worked i< tt tt IV. One-half mile south of Harman, Anne Arundel County Raritan Dry-pressed brick V. Link-pit, Baltimore, Anne Arundel County Arundel Terra-cotta VI Near Elkton, Cecil County Patapsco Stoneware VII Leslie, Cecil County Residual Stove-lining VIII. Patapsco Not worked IX Northeast Cecil County . . Residual Paper-clay x Shannon Hill Cecil County Patapsco Not worked XI Dorsey Howard County . . . Residual Fire-brick XII. Upper Marlboro, Prince George County . Eocene Not worked References on Maryland Clays 1. Bibbins, A., Md. Geol. Surv., Report on Cecil County. 2. Cook, R. A., The Manufacture of Fire-brick at Mount Savage, Maryland, Amer. Inst. Min. Eng., Trans., XIV, p. 698, 1886. 3. Martin, G. C., Md. Geol. Surv., Rept. on Garrett County, p. 212, 1902. 4. Prosser, C. S., Palaeozoic Formations of Allegany County, Jour. Geol., IX, No. 5, p. 409, 1901. 340 CLAYS 5. Ries, H. ; Report on the Clays of Maryland, Vol. IV, Md. GeoL Surv., Pt. Ill, pp. 205-505, 1902. 6. Ries, H., Md. Geol. Surv., Rept. on Allegany County, p. 180, 1900. Massachusetts Most of the clays dug in the State are obtained from the Pleistocene formations, while comparatively small amounts are taken from the Cretaceous and Tertiary strata, and residual clays are rare. Residual Clays Two deposits of white residual clay or kaolin have been recorded from Massachusetts. One of these is at Blandford, Hampden County; the other is 4 miles south of Clayton, Berkshire County. The first has originated by the decomposition of a pegmatite vein in mica-schist, and has a width of nearly 100 feet. 1 It has been used for the manu- facture of white brick and terra-cotta. The second has been derived from feldspathic quartzite or gneiss, and in its crude state is lean and sandy. The following analyses represent the composition of washed samples of the Blandford (I) and Clayton (II) materials. ANALYSES OF MASSACHUSETTS KAOLINS I. II. Silica (SiO 2 ) 52.03 50.00 Alumina (A1 2 O 3 ) 31 .76 44.00 Ferric oxide (Fe 2 O 3 ) trace Ferrous oxide (FeO) 1 .00 Lime (CaO) : trace .024 Magnesia (MgO) 54 Alkalies (Na 2 O,K 2 O) trace 1 . 24 Water (H 2 O) 15.55 Total 99.88 96.264 Residual clays are known in Essex County, but are of no com- mercial value. One bed of fine white kaolin derived from felsite occurs on the west side of Kent's Island, Newbury. Another mass is found in South Lawrence, but neither have been worked, as they are too small. Crosby, Technol. Quart., Ill, 1890. MAINE NORTH CAROLINA 341 Cretaceous and Tertiary Clays The Cretaceous and Tertiary beds form a thick series of clays and sands, well exposed in the Gay Head clifts. The clay-deposits are pockety, owing partly to the frequent changes of conditions during deposition, and partly to their subsequent disturbance by the ice of the continental glacier as it advanced southward. These clays have been used to a slight extent for bricks, and somewhat for souvenir pottery. Pleistocene Clays These form the most important clay resource of the State, but con- tain no high-grade materials. They are extensively developed on the islands of Martha's Vineyard, Nan tucket, and in southeastern Massa- chusetts on Cape Cod, but most of these are not well adapted to brick manufacture, as they vary too much in burning. The true glacial clays are found and worked at many points. (Ref . 6.) Some of these were formed in estuaries, others in pools under or in front of the ice, while still others occur in the morainal drift and represent ground-up rock-flour. In the region south and east of a line from the mouth of the Merrimac River to Stonington, Conn., they are not found above an elevation of 100 feet. Around Boston these glacial clays are well developed in the estuaries of the Charles, Mystic, and Saugus rivers north and west of Boston. The clays are bluish, plastic, and very fine, but may at times contain bowlders or scattered pebbles. Similar clays are extensively worked along the Mystic River at Medford; at Cambridge and Belmont on the Charles River; at Holyoke and South Hadley on the Connecticut; and at Taunton on the Taunton River. They are used chiefly for common-brick manufacture. There are but few published analyses of Massachusetts clays. Of the two given below, No. I is a glacial clay from West Cambridge, J. Card, analyst, ANALYSES OF MASSACHUSETTS CLAYS I. II. Silica (SiO 2 ) 48.99 57.50 Alumina (A1 8 O.) 28.90 31.21 Ferric oxide (Fe 2 O 3 ) 3 . 89 Lime (CaO) 7.1 0.19 Magnesia (MgO) 3.66 0.20 Alkalies (Na 2 O,K 2 O) 4.73 0.40 Water (H 2 O) 3.31 9.83 Total ., .100.58 99.33 342 CLAYS and No. II a red clay from south end of Gay Head section. (7th Ann, Kept., U. S. Geol. Surv., p. 359.) In Essex County, in which brickmaking began over 200 years ago, Pleistocene surface-clays are much used for bricks and pottery. They are of variable thickness, some exceeding thirty feet in depth, and are worked at Danversport, Haverhill, Beverly, and Salem. Some of the deposits are excavated below sea-level. It is interesting to note the variety of products made from these com- mon surface-clays, for they include common and pressed brick, fire- proofing, and earthenware. A fine pottery is made at New bury port from a mixture of local clay and Ohio clays. References on Massachusetts Clays 1. Brown, R. M., Clays of the Boston Basin, Amer. Jour. Sci., IV, XIV, p. 445, 1902. 2. Crosby, W. O., Kaolin at Blandford, Mass., Technol. Quart., Ill, 1890. 3. Sears, J. H., The Physical Geography, Geology, Mineralogy, and Palaeontology of Essex County, Mass., Clays, p. 357, 1905. 5. Shaler, N. S., Report on the Geology of Martha's Vineyard, U. S. Geol. Surv., 7th Ann. Rept., p. 297, 1888. 5. Shaler, N. S., Wood worth, J. B., and Marbut, C. F., The Glacial Brick-clays of Rhode Island and Southeastern Massachusetts, U. S. Geol. Surv., 17th Ann. Rept., Pt. I, p. 957, 1896. 6. Whittle, C. L., The Clays and Clay Industries of Massachusetts, Eng. and Min. Jour., LXVI, p. 245, 1898. Michigan The clays of Michigan are derived from two types of deposits, namely, (1) Paleozoic shales and (2) Pleistocene clays. The former belong to the Silurian, Devonian, and Carboniferous. Silurian Hudson River. This formation carries a number of beds of shale, but most of these are either too gritty or too calcareous to be used for the manufacture of clay-products. THF UNIVERSITY OF MAINE NORTH CAROLINA 343 Devonian Hamilton shales. These outcrop around Alpena, but have not been used in the manufacture of clay-products, although their chemical com- position seems to show that they may be promising. Marshall series. The shales of this formation are very extensive and are well developed around East Jordan, where the mellowed out- crops form a very tough plastic clay and are used in the manufacture of brick. They form a promising clay resource, but one objection to them is the occasional high content of soluble salts. Carboniferous The Carboniferous shales found in Michigan belong in the coal- measures, and are found interbedded with the coal-seams and sandstones. Three types were noted, namely, (1) a light-gray shale often underlying the coal and erroneously called fire-clay. (2) A black fine-grained, brittle shale, and (3) a dark grayish-black shale. The last two usually overlie the coal-seam. The shales are found associated with the coals in the different mines around Saginaw, Owosso, Corunna, St, Charles, Verne, Bay City, and Sebewaing. When ground up. and mixed with water most of these shales give a plastic mass, but one whose tensile strength is usually low. They have been found in several places sufficiently plastic to be molded in a stiff-mud brick-machine, and used to make paving-brick or sewer-pipe. They usually vitrify around cones 3 and 4 and become viscous anywhere from cones 5 to 11. The coal and the shales form a basin northeast of Saginaw, which has a diameter of about 50 miles. The outcrops are found chiefly around the edge of the basin, and in the center the shales are not only at a considerable depth below the surface but there is usually a heavy covering of glacial drift or lake- deposits at many points. Michigan shales. The rocks of this series form a belt from 10 to 20 miles wide surrounding the coal-measure rocks in the lower peninsula. They are best exposed at Grand Rapids, where they form a bed from 6 to 10 feet thick overlying a gypsum deposit, but additional exposures occur in Huron and Arenac counties, as well as along the Cass River in Tuscola County. From laboratory tests it is found that the Michigan shales are usually more fusible than those of the coal-measures and that they burn to a good red color, although they may in some cases contain an abundance of soluble salts. Samples of them taken from the weathered 344 CLAYS outcrops show considerable plasticity. These shales have been worked for the manufacture of brick at Grand Rapids. Coldwater shales. The deposits of this series are very extensive, and have been opened up in quarries at Bronson, Union City, and Cold- water and on the northeast side of the coal-measure area, they are well exposed near Forestville (PI. XXIX, Fig. 1) on Lake Huron. Many beds of this shale series will no doubt be found to be well suited for the manufacture of clay-products, for samples tested show that they vitrify at about cone 2 and become viscous at cone 5. Pleistocene The clays of this age are divisible into three groups, namely, lake- deposits, river-deposits, and moraine-deposits. All of these are very cal- careous, except the river-clays which are less so, but show a high amount of grit. In many cases the lake-clays have been leached in their upper portions and, being freed from lime, these beds nearer the surface tend to burn red. The lake-clays are extensively developed at Detroit, Port Huron, South Haven, Marquette, Saginaw, and Escanaba, and are often found as much as 50 or 60 feet above the present lake-level. These Pleistocene clays are usually fine-grained, nearly always calcareous, and fuse at a low temperature. Their tensile strength commonly ranges from 150 to 170 pounds per square inch. The morainal clays form irregular masses in the terminal moraine and are worked at Ionia (PL XXX, Fig. 1) and Lansing. Their physical properties are similar to these of the lake-deposits. The river-clays are less extensive. No clays of a refractory nature have thus far been found in the State. At Rowley in Ontonagon County there is found a very fine-grained calcareous clay which has been used as a slip. ANALYSES OF MICHIGAN CLAYS AND SHALES I. II. III. IV. V. Silica (SiO 2 ). 55 30 44 30 56 50 53 44 55 95 Alumina (A^Os) . . 14 20 23 72 19 31 24 80 17 43 Ferric oxide (Fe 2 O 3 ) Lime (CaO) 3.62 30* 7.68 1 11 5.89 1 00* 0.76 25 7.67 2 14* Magnesia (MgO) 2 61t 1 50 1 85f 1 55t Potash (K 2 O) ] Soda (Na 2 O) } 2.15 2.00 5.98 2.86 2 36 j>20 75 Water (H 2 O) \ ^21.82 17.64 9.47 | 12.40 CaCO a = MgC0 3 . PLATE XXIX FIG. 1. Coldwater (Carboniferous) shales at White Rock, near Forestville, Mich. (After H. Ries, Mich. Geol. Surv., VIII, Pt. I, p. 44, 1900.) FIG. 2. Carboniferous shale used for paving-brick. Flushing, Mich. (After H. Ries, Mich. Geol. Surv., VIII, Pt. I, p. 29, 1900 ) 345 MAINE NORTH CAROLINA ANALYSES OF MICHIGAN CLAYS AND SHALES Continued 347 VI. VII. VIII. IX. X. Silica (SiO 2 ). . . . 61 09 54 62 44 15 41 86 52 92 Alumina (AlgOa) 19 19 12 82 10 00 10 70 12 25 Ferric oxide (FeaOa). ... 6 78 2 00 4 08 5 02 6 45 Lime (CaO) 2 51 13 68 24 64* 14 33* 13 84* Magnesia (MgO) 65 4 25 1 50f 2 81f 3 55f Potash (K 2 O) . ... Soda (Na 2 O) . . } 3 - 16 j J 1.55 2.80 3.35 Carbon dioxide (CO2). . 12.01 14 50 Water (H 2 O) 5 13 J 12 13 8 00 7 14 Organic -f* SO 3 1 . 42 1 95 * = CaCO 3 . t = MgCO 3 . PHYSICAL TESTS OF MICHIGAN CLAYS AND SHALES I. III. IV. V. VIII. Per cent H 2 O required for mixing . . . 20 32 21 18 Tensile strength ... . ... 55-65 105 125-139 80-95 Plasticity. . fair coed good hiffh Air-shrinkage per cent 4 6 7 7 g Fire-shrinkage per cent 6 10 9 6 Incipient fusion cone. 1 05 03 05 05 Vitrification cone. . 4 01 2 01 2 Viscosity, cone 9 3 5 2 3-4 Color when burned red red red deep red buff LOCALITIES OF THE ABOVE No. Locality. Geological Age. Uses. I. II. Saginaw Grand Ledge. . Coal-measures Carboniferous Not worked Sewer-pipe Ill Grand Rapids Michigan series . . Common brick IV Coldwater. . Coldwater series . (i it v East Jordan . Devonian Brick Portland cement VI Alpena. . . Hamilton shale. Portland cement VII. VIII Marquette. . . . Ionia. . . . Quaternary (lake). . . . ' ' (glacial) Not worked Brick IX. X. Lansing Rockland " '* (lake). .'. .' Red and white brick, white tile Slip-glazing All of the above are taken from Vol. VIII, Pt. I, of the Michigan Geological Survey. References on Michigan Clays 1. Fall, D., Marls and Clays in Michigan, Mich. Miner, III, No. 11, p. 11, 1901, and Mich. Geol. Surv., VIII, Pt. Ill, p. 343, 1903. 2. Ries, H., Clays and Shales of Michigan, Mich. Geol. Surv., VIII, Pt. I, 1900. 348 CLAYS 3. Russell, I. C., The Portland Cement Industry of Michigan, U. S. Geol. Surv., 22d Ann. Kept,, Pt. Ill, p. 629, 1902. Minnesota The clays of this State can be divided into two groups, namely, (1) residual clays and (2) transported clays. Residual Clays These have been derived from either crystalline rocks or limestones. Crystalline rocks are abundant in certain parts of the State, but what- ever clays may have been formed from them have been largely removed by glacial erosion. Deeply decayed granitic gneisses are, however, ex- posed at a few places in the Minnesota Valley, as, for example, at Redwood Falls, but the deposits appear to be of little value. Limestone residuals occur in the "driftless area" of southeastern Minnesota, but they are overlain by the loess, and the two are worked together for brick manu- facture. Transported Clays Pre-Cambrian Argillaceous slates of Kewaatin age have been worked for making dry-press brick at Thompson, thirty miles southwest of Duluth; but the enterprise has not been highly successful, although the plant was in operation in 1904. Ordovician Shales of this age are found only in the southeastern quarter of the State, and are well exposed in the Minnesota river bluffs near St. Paul. The shales are usually interstratified with limestones, and may themselves be calcareous, so that only certain beds can be used. These, however, have been successfully worked at St. Paul for pressed-brick manufacture. Cretaceous The Cretaceous beds are probably the most valuable clay resource of the State, but unfortunately the only important occurrence occupies but a very limited area near Red Wing (PL XXX, Fig. 2), where it has been worked for some years to make an excellent grade of stoneware. Other deposits are known in the western half of the State, but are deeply covered by drift as well as being of poor quality. PLATE XXX FIG. 1. Deposit of calcareous glacial clay, Ionia, Mich. (After H. Ries, Mich. Geol. Surv., VIII, Ft. I, p. 52, 1900.) FIG. 2. Cretaceous stoneware-clay, Red Wing, Minn. (Photo loaned by Red Wing Stoneware Co.) 349 MAINE NORTH CAROLINA 351 Pleistocene Glacial clays, represented by t ill-deposits, lake-deposits, or stream- deposits, are of importance in Minnesota, for common-brick manufacture at least. They are either red- or cream-burning, depending on the pre- dominance of iron or lime. Representative of the first of these three subtypes are the deposits near Princeton, Mille Lacs County. Those of the second, which were probably of interglacial age, occur near the eastern border of the State, a specially important one being worked at Wrenshall, Carlton County. The third subtype, which includes river silts deposited during the with- drawal of the ice, is prominent in two areas, namely, along the present Minnesota River from Shakopee to New Ulm and along the Mississippi River from Minneapolis to Little Falls. In both cases the worked clays underlie terraces bordering the present river channels. They are exten- sively worked at Chester and Minneapolis. .Loess-deposits. Most of the clays worked on a small scale belong to this type, but all are not true loess accumulations. In this class belong the Red River Valley clays, worked at Moorhead and East Grand Forks. ANALYSES OF MINNESOTA CLAYS I. II. III. IV. Silica (SiOo) 69 84 60-31 59 72 73 34 Alumina (AljOs) 23 07 23 77 30 00 14 75 Ferric oxide (Fe-iOs) 48 7 96 5 45 Lime (CaO) 0.11 2 5 82 28 .Magnesia (MgO). 0.14 1.75 51 05 Potash (KoO) \ Soda (Na 2 O) > trace 2.42 trace Water (H-.O) 6 35 10 34 4 71 Total , 90.99 98.71 101.39 98.58 I. Red Wing, Good hue County J H. Rich sewer-pipe works. II. Minneapolis, McLeod County M. C. Madsden, anal, III. Ottawa, Lesueur County Ottawa Brick Co. IV. Mankato, Blue Earth County. Minn, Geol. Surv., 1872. References on Minnesota Clays 1. Berkey, C. P., Origin and Distribution of Minnesota Clays, Amer. Geol., XXIX, p. 171, 1902. 2. Winchell, A., County descriptions in the series of Final Reports, Vols. I, II, and IV of the Minn. Geol. and Nat. Hist. Surv. 3. Winchell, N. H., Brick Clays, Minn. Geol. and Nat. Hist. Surv,, Miscel. Pub., No. 8, 1881. 352 CLAYS Mississippi The clay -bearing formations of Mississippi include the Devonian, Carboniferous, Cretaceous, Tertiary, and Pleistocene, but little informa- tion has been published regarding them. The clays of the Potomac formation of the Cretaceous, and the Lignitic formation of the Eocene, are probably of considerable value. The Potomac formation, which occupies a narrow zone extending from Tishomingo County on the north to Monroe County on the south, consists of gravels, sands, clays, and some lignite beds, and is overlain unconformably by the Lafayette and Columbia formations. The clays are of various colors, some being white, but the percentages of iron oxide indicated by the analyses show that they are not white- burning. They have been used at Miston, Itawamba County, for common stoneware. The Lignitic clay belt "extends from northern Marshall County to the Alabama line along the eastern border of Lauderdale County, but the better grades of clay occur along a line passing through the central part of the outcrop of the formation. The clay-deposits are known to occur at a number of points, but Holly Springs, where the materials are worked for making common stone- ware, appears to be the most important locality. Most of the published analyses indicate too high a contents of iron oxide to be white-burning. Not a few are apparently fire-clays, but few would be classed as highly refractory from the analyses. References on Mississippi Clays 1. Eckel, E. C., Stoneware Clays of Western Tennessee and North- western Mississippi, U. S. Geol. Surv., Bull. 213, p. 382. 2. Hilgard, E. W., Report on the Geology of Mississippi, p. 244, 1844. 3. Logan, W. N., and Hand, W. F., Preliminary Report on the Clays of Mississippi, Geol. Surv. Miss., Bull. 3, 1905. Missouri In the variety of its clays Missouri (Ref. 6) stands well up towards the head of the clay-producing States. As can be seen from a glance at the map (Fig. 54) , the clay-bearing formations range from Cambrian to Pleistocene, exclusive of Cretaceous, and Jura-Trias. A discussion of the clays by formations is not perhaps wholly satis- factory, but is better in order to maintain uniformity of treatment as far as possible. MAINE NORTH CAROLINA 353 i o -* a. _^ o " O 354 ICLAYS Palaeozoic Limestone Clays These consist of four kinds, namely, kaolins, flint-clays, ball-clays, and stoneware-clays. Kaolins. The Missouri kaolins occur south of the Missouri River (Fig. 55) and are separable into three districts. These, together with the formations in which the kaolin occurs, are: FIG. 55. Map showing distribution of Missouri kaolins. (After Wheeler, Mo. Geol. Surv., XI, p. 200, 1896.) Southeastern district of Cape Girardeau, Bollinger, and Howell counties, in Ordovician and Cambrian limestones. Central district of Morgan and Cooper counties, in Ordovician lime- stone. Southwestern district of Aurora and Lawrence counties, in Mississip- pian limestone. According to Wheeler, the kaolins appear to be the insoluble fine residual matter left by the removal by solution of heavy beds of limestone. Only those of the southeastern district have been worked, and these to but a limited extent. The output has been sold for use in the manu- facture of white ware, paper, or kalsomine, and Glen Allen is the most important locality. Flint-clays. These are compact, dense, flinty clays with a con- choidal fracture, which are found filling pockets or basins in limestone. The deposits range from 50 to 200 feet in diameter and 15 to 50 feet in depth, while between the limestone wall and the clay there is usually a sheet of sandstone several feet thick (Fig. 56). The pockets are thought by Wheeler to be old sink-holes in limestones that have be- come filled by aluminous matter being washed into them, but he further MAINE NORTH CAROLINA 355 suggests that since this they have been slightly altered chemically by leaching with a recrystallization of the kaolinite; indeed, their remark- able freedom from impurities and high alumina content are puzzling features. The flint-clays occur in the eastern-central portion of the State (Fig. 54), at a distance of 40 to 140 miles west of St. Louis, along the FIG. 56. Section of a Missouri flint-clay deposit. (After Wheeler, Mo. Geol. Surv., XI, p, 202, 1896.) Wabash, Rock Island, Missouri Pacific, and Frisco railroads; but although the clays occur in sub-Carboniferous and Ordovician limestones, they were possibly formed in Cretaceous times. The flint-clays show the following properties: hardness, 2.5 to 3.5; specific gravity, 2.33 to 2.45; slaking qualities, none; plasticity, very low; tensile strength, 10 to 38 Ibs. per sq. in.; air-shrinkage, 2.5 to 3.5 per cent; fire-shrinkage, 9 to 14 per cent; incipient fusion, about 2300 F., but unaffected at 2700 F. and able to withstand 3000 F. Average composition: Si(>2, 45.8 per cent; Al2O 3 ,40 per cent; H20, 14.2 per cent. Their silica-alumina ratio has led Wheeler to suggest that they contain pholerite rather than kaolinite, or at least a mixture of the two. Flint-clay bricks have high powers of heat resistance, but low abrasive resistance. They work well in the arch of an open-hearth furnace or in the checkerwork of a regenerator. Ball-clays. These appear to have been derived by the weathering of flint-clays. Stoneware-clays. These have a similar origin to the flint-clays, but are less pure and have not been consolidated by secondary chemical changes. They are of local extent, and are found in rocks ranging from the Lower Carboniferous down to the Cambrian, but the Burlington and Trenton limestones appear to be the most favorable situations. 356 CLAYS Coal-measures The Coal-measures of Missouri contain two important series of deposits, namely, plastic fire-clays and impure shales. Plastic fire-clays. All of the Missouri plastic fire-clays occur in the Carboniferous, at the base of the Coal-measures, and are found in the eastern part of the State in two different basins known respect- ively as the St. Louis and Mexico areas. The former is on the western edge of the eastern interior coal-field, and the latter on the eastern edge of the western interior field. In the St. Louis basin there are several beds of clay and shale, but only the St. Louis fire-clay seam is refractory. This has an average thickness of 6 to 8 feet, with a sandstone floor, a thin bituminous coal- roof, and is worked by shafts (PI. XXXI, Fig. 1) or adits. It is hard when fresh, but disintegrates on exposure. A special grade known as pot-clay comes from a purer and more uniform seam near the middle or top of the bed. The St. Louis clay is coarse-grained, often carries pyrite, and although high in iron, still the latter is uniformly distributed and finely divided. The range of physical properties of this clay is given by Wheeler as follows: average tensile strength, 80 to 150 Ibs. per sq. in.; air-shiink- age, 6 to 9 per cent; fire-shrinkage, 4 to 8.5 per cent; vitrification at 2300 to 2450 F.; viscosity, 2500 to 2700 F. This clay is much used for glass pots, zinc-retorts, and gas-retorts. It also makes a durable fire-brick if not exposed to excessive heat, as its fusion-point does not exceed cone 30 or 31. The average composition of seven clays was as follows: AVERAGE COMPOSITION OF ST. Louis FIRE-CLAY Mi ne- run. Washed. Combined silica (SiO,)- 32 32 Free silica (SiOo) 30 25 Alumina (A1,O C <) 24 24 Ferric oxide (Fe,O 3 ) 1.9 1 .85 Ferrous exide (FeO) 1.2 1 .00 Lime (CaO) 7 .7 Magnesia (MgO). . , 3 .2 Potash (K,O) 5 .55 Soda 2. Pit of Raritan (Cretaceous) clays, Woodbridge, N. J. (After H. Ries, N. J. Geol. Surv., Fin. Rept., VI, p. 340, 1904.) 357 MAINE NORTH CAROLINA 359 lower 6 to 12 feet are worked, and this through shafts. The range of physical properties is given by Wheeler as follows: Average tensile strength, 40 to 80 Ibs. per square inch; air-shrinkage, 4 to 5 per cent; fire-shrinkage, 6 to 7 per cent; vitrification, 2400 to 2500 F.; viscosity, 2600 to 270U F. The average composition is also given by Wheeler as follows: Silica (Si0 2 ) 52.00 Alumina (A1 2 O 3 ) 33.00 Ferric oxide (Fe 2 O 3 ) 1.5 Lime (CaO) 5 Magnesia (MgO) ' 7 Alkalies (Na 2 O, K 2 O) 12.00 Total fluxes 3.4 Stoneware-clays. Those found in the coal-measures are the most important known in the State, including many clay- and shale-beds, the most extensive of which are found in Henry County. They have been much used by potteries in Kansas as well as other portions of the West and Southwest. The so-called fire-clays of the barren coal-measures are usually impure, and consequently fusible and likely to blister or give a dark body after burning. The true fire-clays have also been used to some extent for stoneware. Impure shales. Many excellent beds of these are found in the coal- measures. They are all impure, but are eminently useful for making paving-brick, sewer-pipe, drain-tile, roofing-tile, terra-cotta, brick, and hollow ware, but they are not usually pure enough for refractory goods,, stoneware, or white ware, and their main use has been for paving-bricks. Nearly all of them make a fair grade of brick by any process of molding, but the majority have to be finely ground or weathered. In their physical properties the range is: average tensile strength, 50 to 250 Ibs. per sq. in., usually between 125 and 175 Ibs.; water re- quired for tempering, 16 to 25 per cent; air-shrinkage, 4 to 8 per cent; fire-shrinkage, 1 to 10.6 per cent, but usually 4 to 6 per cent; incipient fusion, 1500 to 1700 F.; vitrification, 1700 to 1900 F. The range of chemical composition is given by Wheeler as: Silica (SiO 2 ) 50-75 Alumina (A1 2 O 3 ) 10-27 Ferric oxide (Fe 2 O 3 ) 3-10 Lime (CaO) 5-2 Magnesia (MgO) 5-2 Alkalies (Na 2 O, K 2 O) 3-4 Water (H 2 O) 5-12 Total fluxes. . 10-15 360 CLAYS Tertiary The Tertiary beds occupy a small area in the southeastern corner of the State. They contain much clay admirably adapted to stone- ware manufacture and which is dug to supply local potteries. An important deposit is known at Commerce. Pleistocene Pleistocene clays are widely scattered over the State, and form the main supply of material for common brick, although a few are suffi- ciently pure and plastic for stoneware manufacture. Three types are recognizable: 1. Loess-clays, confined mostly to the neighborhood of the larger streams, especially the Missouri and Mississippi. They are yellow to brown in color, unstratified, and often of columnar structure. Their thickness is considerable, 75 to 100 feet being common along the lower Missouri, while at the Iowa line they have a thickness of 200 feet. The loess extends from 3 to 10 miles back from the streams, and appears to get stronger as the distance from the rivers increases, this change interfering with its being worked by the mud process. It is, however, the most valuable of the surface-clays. 2. Glacial clays, of varying character, confined to the counties north of the Missouri River and rarely over 50 feet thick. The material is usually very strong, red-burning, and often contains bowlders of con- cretions, but occasionally shows beds of better clay suitable for stone- ware or drain-tile. 3. Alluvial clays, found along the present streams, and of little im- portance. The tables on pp. 361, 362 give the analyses and phyical tests of a number of Missouri clays which may be regarded as representative. 1 References on Missouri Clays 1. Keyes, C. R., The Geological Occurrence of Clay, Mo. Geol. Surv., XI, "p. 35, 1896. 2. Keyes, C. R,. Distribution and Character of Mis- souri Clays, Min. Indus., VI, p. 127, 1897. 3. Ladd, G. E., Notes on Cer- tain Undescribed Clay Occurrences in Missouri, Science, n. s., Ill, p. 691, 1896. 4. Ladd, G. E., Mo. Geol. Surv., Bulls. Nos. 3 and 5. 5. Sea- man, W. H., Zinciferous Clays of Southwestern Missouri, Amer. Jour. ScL, iii, XXXIX, p. 38. 6. Wheeler, H. A., Clay-deposits, Mo. Geol. 1 These were selected for the writer by Professor H. A. Wheeler. MAINE NORTH CAROLINA 361 Surv., Xi, 1896. 7. Wheeler, H. A., Clays and Shales (Bevier sheet), Mo. Geol. Surv., IX, sheet rept. No. 2, p. 57, 1896. 8. Wheeler, H. A., Fire-clays of Missouri, Amer. Inst. Min. Eng., Bimonthly Bull., Jan., 1905. ANALYSES OF MISSOURI CLAYS ULTIMATE ANALYSES I. II. III. IV. V. VI. VIL VIII. Silica (SiO 2 ). 55.12 72.30 54.90 74.39 43 82 71 94 54 80 72 00- Alumina (Al 2 Os) 30.71 18.94 18.03 12.03 38.24 17 60 23 73 11 97 Ferric oxide (Fe 2 O 3 ). .. . Lime (CaO) 1.51 0.54 0.40 0.68 6.03 2.88 4.06 1.50 0.23 1.93 2.35 62 8.67 64 3.51 1 80 Magnesia (MgO) trace 0.39 1.10 1.52 56 2 23 1 35 Potash (K 2 O) Soda (Na 2 O) i 1.37 0.42 3.40 3.01 0.73 1.51 3.80 3.25 Moisture 6.72 1 01 Comb water 10.56 7.04 6.90 3.17 14.94 5 27 6 00 6 42 IX. X. XI. XII. XIII. XIV. XV. Silica (SiO 2 ) 49.04 65.01 61.19 59.36 60 70 73 92 43 5& Alumina (Al 2 Oa) . . . 34 85 19 30 15 48 23 26 18 22 11 65 41 48 Ferric oxide (Fe 2 Oa). . . . 71 4 91 5 49 3 06 7 58 4 74 35 Lime (CaO) 1 33 1 40 1 95 65 2 68 1 45 45 Magnesia (MgO) . ... 1 04 40 1 56 42 trace 60 Potash (K 2 O) Soda (Na 2 O) JO. 85 2.60 2.82 0.63 3.67 3.13 0.20 Titanic oxide (TiO 2 ). . . , 1 01 Sulphur trioxide (SOa). . 0.35 1.03 3.11 2.74 2 18 Comb water 12.33 5.51 9.02 10.20 7.77 3 08 14 05 PHYSICAL TESTS OF MISSOURI CLAYS I. II. III. IV. V. VI. VII. VIII. Size of grain Aver, tensile strength, Ibs per sq in. C.* 62 V.F. 12 V.F. 380 C. 131 V.F. 8 V.F. 150 V.F. 115 F. 151 % H 2 O for plasticity. . . Plasticity 14.8 lean 23.2 lean 22.3 very 17.2 lean 15.1 very 16.5 plastic 21.5 plastic 18.4 lean Air-shrinkage, per cent . Fire-shrinkage, per cent. Speed 4.4 6.4 R. 4.0 8.4 S. plastic 9.6 1.4 S. 5.7 4.3 R. i lean 3.1 11.6 S. 5.5 2.2 S. 5.9 2.8 V.S. 5.1 5.7 R. Incipient fusion, degs. F. Complete fusion.degs. F. Viscosity, degrees F. . . . Specific gravity 2200 2400 2600 2.46 2200 2500 'i!89' 1600 1750 1900 2.01 2000 2000 2300 2.09 2350 2700 2700 2.85 2100 2300 2500 2.34 1500 1700 1900 2.37 2000 2200 2200 2.17 *C. = coarse; V.F, = very fine; F. = fine; S.=slow; R=rapid; V.S. = very slow. 362 CLAYS PHYSICAL TESTS OF MISSOURI CLAYS Continued IX. X. XI. XII. XIII. XIV. XV. Size of grain V F c V F c c p F Aver, tensile strength, Ibs per sq. in. . 198 92 273 78 177 173 13 % H 2 O for plasticity . . . Plasticity 23.4 plastic 18.4 slightly 23.1 verv 15.0 lean 20 plastic 17.1 plastic 15.2 Air -shrinkage, per cent . Fire-shrinkage, percent. Speed . 7.7 9.8 s lean 5.2 3.5 R VC1J plastic 8.0 1.5 V S 6.3 5.4 R 5.3 8.3 R 5.3 5.5 R 2.4 8.9 S Incipient fusion, degs.F. Complete fusion, degs. F. Viscosity, degrees F. . . . Specific gravity. . . 1800 2100 2400 1 69 1850 2050 2250 2 41 1650 1800 1950 2 05 2250 2450 2650 2 41 1700 1900 2100 1800 1950 2050 1 98 2400 2700 2750 2 39 LOCALITIES OF THE PRECEDING No. Locality. Geological Age. Uses. I Mexico Coal-measures Fire-brick II Glen Allen Residual White ware III Norborne Pleistocene . Railway ballast IV Jefferson City Coal-measures Red brick v Leasburg Fire-brick VI Calhoun . Coal-measures Stoneware VII Kansas City . . i i Paving-brick VIII (i it 1 1 Red brick IX De Soto Residual. . . . White ware x Moberlv ... Coal-measures Paving-brick XI St Peter's Pleistocene . . . Railway ballast XII St Louis (Evens and Howard) Coa 1-m easu res Fire-brick XIII Prospect Hill St Louis ( C Roofing-tile XIV. xv St. Louis (Hyd. Pr. Co.) Truesdale (Kelley's pit) . f I 1 1 Red brick Fire-brick Nebraska According to E. H. Barbour (Ref. 1), this State contains an abun- dance of clays, the most important being found in the Carboniferous and Dakota Cretaceous formations, while others occur in the Tertiary and Quaternary. Carboniferous The rocks of this formation (Ref. 2) occupy a V-shaped area in southeastern Nebraska, with the apex in the vicinity of Blair, and the base along the Kansas-Nebraska line from a point near Wymore to the MAINE NORTH CAROLINA 363 Missouri River. The Carboniferous, including the Permian, consists of massive grayish-yellow limestones, interstratified with clays, shales, and an occasional layer of coal. " The clays are usually of a dull-blue color interbedded with streaks of red and buff-colored sands, but there are also thin layers of disintegrated limestone, calcite concretions, and sand. ... " Frequently these thick deposits of clay form prominent bluffs along either side of the valley for some distance, especially where the clay is protected from erosion by some overlying layer of a somewhat harder material, such as limestone. . . . There are also many other available clay-banks along the Platte and Missouri rivers, notably at Nebraska City, where extensive brick-works are in operation, utilizing the clays of the Carboniferous for vitrified paving-brick. Terra-cotta ware has also been made here. Other localities where the clays are well exposed, and in some cases worked, are Minorsville, Peru, and Table Rock." Nearly all of the best deposits along the Missouri River in southeastern Nebraska are located along the Nebraska City branch of the Burlington and Missouri Railroad, Cretaceous The Dakota formation rests stratigraphically on top of the Carbonifer- ous, with an unconformity between. The surface underlain by it is on the west and northwestern sides of the Carboniferous area, forming a strip about 30 miles wide and 200 miles long. It also forms a belt along the Missouri River north of the Carboniferous area. The formation consists of a series of shales and sandstones, but the latter, owing to their higher resistance to erosion, stand out more promi- nently, so that the mellowed outcrops of the shales are less noticeable. These shales vary from a sandy material of yellowish-brown color to highly plastic clays, the different beds showing a great variety of colors. Lens-shaped layers of sandstone are, however, not uncommon in the shale. These Dakota clays are available at many localities, and are said to have given excellent results for both pottery and brick manu- facture. Loess and Alluvium The great bulk of brick made in Nebraska are manufactured from loess and alluvium (Ref. 3). The loess, or "bluff-deposit" as it is commonly called, consists of a light buff-colored loam, of generally uni- form texture, but containing some shells. It is found over about half the area of the State. 364 CLAYS The alluvium or valley-wash is a dark-colored soil of very fine tex- ture, with interbedded layers of fine sand and gravel, and is being deported at the present time in narrow 7 strips along nearly all the large streams in the State. References on Nebraska Clays 1. Barbour, Nebr. Geol. Surv., I, p. 202, 1903. 2. Gould, C. N., and Fisher, C. A., Ann. Kept. Neb. State Board of Agric. for 1900, pp. 185. 3. Fisher, C.' A., Ann. Kept, Neb. State Board of Agric. for 1900, p. 181. New Jersey Nearly all of the larger geological formations in the State contain deposits of clay, but the important ones belong to the following: Ordo- vician, Triassic, Lower Cretaceous, Upper Cretaceous, Miocene and Pliocene of Tertiary and Pleistocene. Cambrian and Ordovician The Cambrian and Ordovician rocks include beds of limestones and shales w r ith some beds of sandstone and quart zite, and occur chiefly in Warren and Sussex counties in the great Kittatinny Valley, but are found also at a few^ other localities. Southwest of the terminal moraine (Fig. 57) the limestone yields a sticky yellow residual clay with flints, and that worked near Beattystown is of this character. The shale, also, where found south of the moraine is often deeply weathered, and at Port Murray is utilized for the manufacture of fireproofing. There it is found to be red-burning, of low plasticity, and fusing about cone 1. . Triassic The Triassic or Newark series consists chiefly of red shales and sand- stones wdth masses of trap-rock, and forms a belt extending across the State between the Highlands on the northwest and Cretaceous on the southeast. In places the shale has disintegrated to a sandy clay- soil, w r hich has been used locally for common brick, but the fresh shale has in most cases been found too sandy to make into clay-products, although at one point, Kingsland, the shales have been used with appar- ent success. They burn to a hard red brick, but fuse at a low cone, and are not highly plastic. MAINE NORTH CAROLINA 365 FIG. 57. Map of New Jersey showing distribution of important clay-bearing formations. (Adapted from map by Kiimmel and Knapp, N. J. Geol. Surv. Fin. Rept., VI, 1904.) 366 CLAYS Cretaceous The New Jersey Cretaceous is divisible into three parts, which, begin- ning at the bottom, are: 1. Clay series of Lower Cretaceous; 2. Clay- marl series of Upper Cretaceous; and 3. Glaucoriitic marl series (see Fig. 57). Of these three, the first contains many important clay- deposits, the second some clays of economic value, but the third is of no interest in the present discussion. Lower Cretaceous clay series. This was termed the Raritan or Plastic Clay series by Dr. Cook (1878) and consists of a number of beds of clay, sand, and even gravel. The clays show great variety, ranging from nearly white or steel-blue fire-clay of high quality to black sandy clays containing varying amounts of pyrite, and useful only for common- brick manufacture. A similar variation is found in the sand-beds. A peculiar feature of the Raritan series is trie rapid alternation of strata, so that the clays often change suddenly, both vertically and horizontally, much as shown in Fig. 3. This fact often makes it uncertain whether two pits sunk within a short distance of each other will yield the same kinds of clay. Notwithstanding these frequent changes in character and the impossibility of establishing divisions in the Raritan series, which can be accurately identified at widely separated intervals, it is possible, nevertheless, to recognize certain divisions, whose general features are sufficiently persistent to permit their being traced throughout the region of Middlesex County in which the beds have been so extensively worked. In other areas these subdivisions do not seem to hold. The boundary between the upper part of the Raritan clays and the overlying clay marls is easily recognized, the upper bed of the former being a loose sand or sandy clay, while the lower bed of the latter is a glauconitic clay, black when fresh, but rusty brown when weathered, and often fossiliferous. Underlying the Raritan beds is the Triassic shale. The Raritan series occupies a broad belt (Fig. 57) extending from Raritan Bay across the State to Trenton and Bordentown, and a much narrower strip along the Delaware River to Salem County. Over most of its outcrop across the State it is covered by later formations: In the Middlesex County area the Raritan is divisible into nine members, which, beginning at the bottom together with their characters, are as follows: 1. Raritan clays. This member carries both a fire-clay and potter's PLATE XXXII FIG. 1. Clay-loam deposit of shallow character, west of Mount Holly, N. J. (After H. Ries, N. J. Geol. Surv., Fin. Kept., VI, p. 122, 1904.) FIG. 2. Pleistocene brick-clay, Little Ferry, X. J. (After H. Ries, X. J. Geol. Surv., Fin. Rept., VI, p. 374, 1904.) 367 MAINE NORTH CAROLINA 369 clay. The former is usually drab, but sometimes mottled or black, and generally quite sandy. It is dug around Sand Hills, and sparingly at \Voodbridge and Mill Brook. Its main use is for fire-brick, and its refractoriness is usually about cone 27. The potter's clay is a white or Mulsh-white clay of variable color and composition. It is worked east of Martin's Dock and south of Metuchen. 2. No. 1 fire-sand, a bed of quartz-sand. 3. Wooibridge clays. This, the most important member of the Raritan series, consists of an upper bed of black, laminated sandy clay, and a lower bed of fire-clay. The laminated clay is red-burning, plastic, and contains more or less lignite and pyrite; it is extensively worked for the manufacture of fireproofing, common brick, conduits, etc., and large pits have been opened in it around South River, Sayreville, and other points. The fire-clay ranges from a fine-grained clay of high plasticity and high refractoriness (cone 35) to sandy clays of lower grade fusing at cone 27. It can be stated in general that the bed is less refractory at the southwest end. This clay is used in the manufacture of fire-brick, pressed brick, retorts, stoneware, and as an ingredient in fireproofing and conduits. A small amount dug near Woodbridge is sufficiently white-burning and refractory for white-ware manufacture. 4. No. 2 sand. Included in this sand formation are two important he: Is whose names are somewhat misleading, namely, the feldspar and kaolin beds. The feldspar is a coarse feldspathic sand or gravel with more or less decomposed feldspar and pellets of white clay, while the kaolin is not in any sense such, but is a micaceous quartz-sand. 5. South Amboy fire-clay. This outcrops chiefly south of the Raritan River between Sayreville and South Amboy, but is also found at several points north of it. It is generally a white, light blue, or red- mottled clay, ranging from 15 to 30 feet in thickness, and varying greatly in its quality. Its refractoriness is moderate. 6. No. 3 sand. 7. Amboy stoneware-clay. An important bed of stoneware-clay, best exposed southeast of South Amboy. Like the other members it is of variable character, but the better grades are used for stoneware. s. Laminated sands of little value. 9. Cliffwood lignitic sands and clays. These form a series of beds of massive black clay and gray-black laminated sands and clays, which often carry lignite and pyrite. They are extensively exposed in the brick-pits around Cliffwood and along Cheesequake Creek, and are all red-burning. 370 CLAYS The other Raritan areas, around Trenton, Burlington, Bordentown, Bridgeboro, etc., afford clays of refractory character, but it is not pos- sible to correlate the sections with those of Middlesex County. The Raritan formation is by far the most important clay-bearing formation in New Jersey containing as it does such a wide range of materials. Even a hasty consideration of the uses to which they are put indicates in a measure what a wide range of materials must be contained within the limits at the Raritan strata, for among the products made from these clays are common brick, fireproofing, drain-tile, conduits, terra-cotta, front brick, fire-brick, stoneware, earthenware, tubs, and sinks, foundry materials, paper filling, etc. The physical tests and chemical analyses on pp. 372 and 374 will serve to give a good idea of their character. Clay-marl series. The outcrops of this series extend from the shores of Raritan Bay across the State in a southwest direction to the Delaware River north of Salem, forming a belt varying in width from 2J to 8 miles. Its base is marked by a glauconitic sandy clay which weathers to a characteristic cinnamon-brown, indurated earth. The top is emphasized by the passage of a bed of loose reddish sand with quartz grains of pea size into a compact greenish marl. At many points a fossil bed 1 to 4 feet thick is present. Five members are recognizable as follows: 1. Black, sandy, often glauconitic clay, weathering cinnamon-brown. 2. Black, non-glauconitic clay, weathering to chocolate. 3. Varicolored sands. 4. Black laminated sand and clay, strongly glauconitic to the south- west. 5. Red quartz-sand. Top. Both Nos. 1 and 2 are important sources of brick- and sometimes tile-clay, the former being worked near Camden, Keyport, High ts town, etc., and the latter near Matawan, Kinkora, Maple Shade, Camden, etc. Indeed, the two are sometimes worked in the same or adjoining banks. Tertiary The Tertiary clay-deposits occur in scattered areas lying to the south- east of the Lower Cretaceous belt. They are beds of irregular form, with a tendency towards basin-shaped structure. Owing to the almost universal mantle of sand over this region and the flatness of the surface, prospecting for the deposits is rendered more or less difficult. The clay-deposits recognized in the recent work of the New Jersey Geological Survey are the Cohansey, Alloway, and Asbury clays. The MAINE NORTH CAROLINA 371 Cohansey is really a sand formation, but carries many lenses of clay which average 8 to 10 feet in thickness. They occur in the southern portion of the State, in Ocean and Atlantic counties, in southern Burling- ton, Camden, and Gloucester counties, and in Central Cumberland coun- ties. Deposits have been worked at Rosenhayn, Millville, May's Land- ing, Woodmansie, Whitney's, etc. The clays are white, yellow, choco- late, and black, and sometimes even lignitic. Many are buff-burning and semi-refractory, on which account they are much sought after for the manufacture of buff bricks and terra-cotta. The Alloway clay, which extends from near Swans Mills, Gloucester County, to a point 2 miles south of Alloway in Salem County, is a light- brown clay, of great toughness and high plasticity. Where weathered it contains many joints often filled with iron crusts, which greatly diminish its value. The Alloway clay is a red- and dense-burning material, of rather high air- and fire-shrinkage, but excellently adapted to the manu- facture of stiff-mud brick and drain-tile. The Asbury clay is well exposed west of Asbury Park, and is usually a dark sandy clay with laminae of sand, adapted only to common-brick manufacture. Pleistocene Clays Pleistocene clays are widely scattered over the State. To the north of the terminal moraine (Fig. 57) they consist of first, basin-shaped beds occurring in the valleys; second, stony clays or till found in the glacial drift (PI. Ill, Fig. 1); and, third, estuarine clays, occurring in great abundance in the vicinity of Hackensack (PL XXXII, Fig. 2). They are all impure materials adapted in most cases only to the manu- facture of common brick or drain-tile. In the region south of the terminal moraine the most important clays are those of the Cape May formation. These clays occur in a sand and gravel formation, found underlying terraces along the rivers from the coast inland to an altitude of from 40 to 60 feet. Along the Dela- ware River they are specially prominent, but other points are Cohansey Creek near Bridgeton, the Maurice River south of Millville, etc. The beds of clay are usually of limited extent and grade into sand. The Cape May clays are of value chiefly for the manufacture of red brick and drain-tile, but occasionally small lenses of buff-burning clays are found. Up to the present time no fire-clays have been found in the Cape May formation. 372 CLAYS In the following tables will be found the analyses and physical tests of a number of representative samples of New Jersey clays: ANALYSES OF NEW JERSEY CLAYS I. II. III. IV. V. VI. Sand } r 1 Combined silica (biOo). . . J 66.67 66.66 77 .72 72.37 66.12J 42 80 Alumina (Al 2 Os) 18 27 14 15 15 74 14 40 22 07 38 34 Ferric oxide (te 2 O 3 ) 3 11 3 43 49 3 43 1 31 86 Lime (CaO) 1 18 2,15 trace 75 50 Magnesia (MgO) 1 09 38 81 49 9 5 Potash (K 2 O). . ... 2 92 2 32 trace f 26 Soda (Na 2 O) 1 30 1 38 trace 1 1.60 1.S1 1 18 Titanium oxide (TiO 2 ) 85 1 20 Ignition 4.03 8 40 5 62 6 70 7.94 13.50 Moisture 1.10 VII. VIII. IX. X. XI. XII. Sand 5.20 1 [8.10 > Combined silica (SiO 2 ) Alumina (A1 2 O3) . 40.40 38 40 > 64 . 00 29 08 \ 39 . 8C 36 34 \ 60. 1 23 23 51 . 56 33 13 68.38 20 11 Ferric oxide (Fe 2 Oa). . 1 20 1 12 1 01 3 27 78 1 71 Lime (CaO). 22 1 00 trace Magnesia (MgO). . 25 04 67 trace 73 Potash (K 2 O). . . . 59 2 64 15 2 58 trace 2 58 Soda (Na 2 O). 80 trace Titanium oxide (TiO 2 ). . . . * * * 1 91 1 01 Ignition . 12 50 6 80 12 90 8 54 12 50 5 . 55 Moisture . . 1 30 1 20 XIII. XIV. XV. XVI. XVII. Sand c 28 81 51 80 48 40 1 Combined silica (SiO 2 ) 45.76< 31 12 9Q 00 19 44 J 68.96 Alumina (Al 2 Os) 39 05 26 95 18 9? 21 83 17 87 Ferric oxide (Fe 2 OO. . . trace 1 24 88 1 57 3 27 Lime (CaO) . 95 9 8 0.25 Magnesia (MgO). . 04 07 24 0.25 Potash (K 2 O). trace trace 48 2 ?4 1 2.10 Soda (NaoO) trace trace Titanium oxide (TiO 2 ) 1 90 Ignition 14 46 9 63 6 70 5 -90 6.95 Moisture 57 50 80 * With A 2 10 3 MAINE NORTH CAROLINA 373 LOCALITIES OF THE PRECEDING No. Locality. Geological Age. Uses. Ref. I Little Ferry Pleistocene. . . Bricks. . B 373 II Budd Bros. Camden. . . Clay Marl I. Bricks. . B 396 III. H Hylton Palmyra. . . . Raritan Fire-bricks B 392 IV. A. E. Burchem, Buckshutem. Cape May Bricks .... B 415 V. Clayville Min. & Brick Co., Clayville Cohansey Conduits B409 VI. Geo. Such, Burt Creek South Amboy, VII. VIII. IX. E. Roberts, Florida Grove Grossman Clay Co., Sand Hills . R. N. and H. Valentine, Sand Hills . .* Raritan do. Woodbridge. . . . Woodbridge Ball-clay No. 1 fire-clay Top-white clay Fire-bricks A 198 A 135 A 145 A 154 X. XI. Sayre and Fisher, Sayreville. . . . No. 1 fire-clay, Anness and Pot- ter Woodbridge. . . . . Woodbridge .... 1 1 Common brick Fire-brick. . . B467 B 441 XII. XIII. W. H. Berry, Woodbridge \V. H. Cutter, Woodbridge . . . n n Sewer-pipe. . . . Ball-clay. . . . A 82 B443 XIV. W. B. Dixon, Woodbridge Raritan Fire-clay. . A 79 XV. XVL Extra sandy clay, Lough ridge and Powers, Woodbridge. . . . S. A. Meeker, Woodbridge Woodbridge . . ft Fire-clay Stoneware-clay A 93 A 99 XVII D Haines & Son Yorktown Alloway Brick and tile B 496 A, Report on Clays of New Jersey, 1878. B, N. J. Geol. Surv., Fin. Rept., VI, 1904. References on New Jersey Clays 1. Cook, G. H., Report on the Clay Deposits of Woodbridge, South Amboy, and other Places in New Jersey, N. J. Geol. Surv., 1877. 2. Hollick, A., Minerals from Fire-clay Beds at Green Ridge, Staten Island, Amer Nat., XXV, p. 403, 1891. 3. Hunt, T. S., On the Origin of Clays on the Atlantic Seaboard, Amer. Inst. Min. Eng., Trans., VI, p. 188, 1879. 4. Newberry, J. S., On the Raritan Clays of New Jersey, Amer. Assoc. Adv. ScL, 1869. 5. Ries, H., Kummel, H. B., and Knapp, G. N., The Clays and Clay Industry of New Jersey, N. J. Geol. Surv., Fin. Rept., Vol. VI. 1904. 6. Smock, J. C., Mining Clay, Amer. Inst. Min. Eng., Trans., Ill, p. 211. 7. Smock, J. C., Plastic Clays of New Jersey, Amer. Inst. Min. Eng., Trans., VI, p. 177. 374 CL^YS PHYSICAL TESTS OF NEW JERSEY CLAYS I. 11. III. IV. V. Per cent Air-shrin Plasticity Average Cone 05 - Cone 1 Cone 5 Cone 8 Cone of A Color wh water required 18.5 2 low 51 1.6 16.14 4.6 8.82 7 3.2G red 21 2 fair 150 2 6.56 1 red 20 5.3 fair 65 1.3 1.3 14.52 2 12.82 27 buff 32 7 fair 52 3 19.69 5 16.75 27 + buff 33 3.4 fair 33 6.2 14.6 7.14 4 + white kage per cent. . . T . . . . tensile strength, Ibs. per sq. in. ' Fire-shrinkage, per cent Absorption, per cent Fire-shrinkage, per cent Absorption, per cent Fire-shrinkage, per cent Absorption, per cent Fire-shrinkage, per cent Absorption per cent isoosity en burned VI. VII. VIII. IX. X. Per cent Air-shrin Plasticity Average Cone 05 < Cone 1 < Cone 5 Cone 8 Cone of i Color wh water required 33 4.4 fair 48 13.6 7.07 13.8* 6.47 32 buff 33 5 fair 41 7.1 13.74 11 9.10 34 + buff 30.5 7 g 2 0d 6.6 10.17 7 9.30 8 12 red 25.5 6.5 good 88 1.5 17.93 3 13.61 3.7 9.98 6 10.70 12? red 20 6 good U6 1.3 16.54 2.6 12.68- 2.3 10.17 8 red kage, per cent ' ;ensile strength, Ibs. per sq. in. Fire-shrinkage, per cent [ Absorption, per cent Fire- shrinkage per cent [ Absorption, per cent ' Fire- shrinkage, per cent Absorption, per cent Fire-shrinkage, per cent Absorption, per cent viscosity. en burned XI. XII. XIII. XIV. XV. Per cent Air-shrin Plasticity Average Cone 05 Cone 1 Cone 5 Cone 8 < Cone of i Color wh water required 34.9 10 high 286 3.3 11.12 3.3 9.92 10 red 27 7.6 high 229 1 13.42 2.7 8.9 5.7 1.21 12+ red 23.4 8 high 293 .3 11.65 3.3 6.2 4 4.36 5 buff 27.2 li h 3.3 12.46 6 5.5 3.51 red 22 6 good 108 4.3 7.88 8.6 .10 3 + red kage per cent. . . T . . tensile strength, Ibs. per sq. in. \ Fire-shrinkage, per cent. . . . [ Absorption per cent .... ' Fire-shrinkage, per cent , Absorption, per cent ' Fire-shrinkage, per cent Absorption! per cent {Fire-shrinkage per cent Absorption, per cent viscosity . en burned * Cone 10. MAINE NORTH CAROLINA LOCALITIES OF THE PRECEDING 375 No. Locality. Geological Age- Uses. Ref. i Port Murray. . . Hudson River Fireproofing A 11 Kingsland. . . . Triassic Brick III. IV. v H. Hylton, Palmyra C. S. Edgar, Bonhamtown W. H. Cutter, Woodbridge Cretaceous Raritan VVood bridge fire Fire-brick .... Saggers C I> VI. R. H. and N. Valentine, Sand Hills, No. 1 blue clay. clay beds do White ware. . . Fire-brick K F* VII. No. 1 clay, An ness and Potter, Woodbridge. . . do < t Q VIII. IX. X. Sayre and Fisher, Sayreville Carman and Avery, Cliffwood. . . . Budd Bros., Camden Woodbridge black laminated clay . . Cliffwood lami- nated sands and clays Clay Marl I Common brick < tt ( t t ( H I j XL XII One mile south of Collingswood. . . Yorktown Clay Marl II. ... Alloway Brick and tile . it < < K T. XIII May's Landing Cohansey M XIV. XV A. E. Burchem, Buckshutem Little Ferry Cape May Pleistocene Common brick N o Ref. 449; E, 394; K, A, N. J. Geol. Surv., Fin. Kept., VI, p. 5 do., p. 442; F., do., p. 447; G, do., p. do., p. 397; L., do., p. 495; M., do, p. 37( 07; B, do., p. 374; C 140; H, do., p. 467; ); N., do, p. 414; O, ( 5, do., p. 392; D, c I, do., p. 474; J, d io., p. 373. o., p. o., p~ New Mexico Adobe brick are made at many points from the calcareous valley clays, and common burned brick are also manufactured at different points. The Cretaceous shales at Las Vegas have yielded good results with the dry-press brick process. Fire-clays have been worked at Socorro and were formerly made into fire-brick. New York The greater portion of New York State is underlain by sedimentary rocks of Palaeozoic age, ranging from the Cambrian to the Carboniferous inclusive. These consist in very large part of shales, but sandstones and limestones are at times prominent. The Cretaceous and Tertiary formations, so abundant in States farther south, are found in New York only, on Staten Island, Long Island, and Fisher's Island. Overlying all of the above are Pleistocene deposits. Residual clays are rare. The clay-deposits of the State may, therefore, be grouped as follows: Residual clays, Palaeozoic shales, Cretaceous, and Tertiary clays, Pleistocene clays. Residual Clays These are of but little importance in New York State, and may be passed over with the statement that some deposits of kaolin have 376 CLAYS been found east or southeast of Sharon, but so far as known none have ever proven of economic value. Palaeozoic Shales Those occurring in New York State and including beds of value to the clay-worker belong to the Medina, Salina, Hamilton, Portage, and Chemung. The Hudson, Clinton, and Niagara formations are of little or no value for the manufacture of clay-products. All of these shale formations, with the exception of the Hudson, form bands of variable width extending across the State in an east-west direction, and their distribution can best be seen by reference to the geologic map of New York, from which it will appear that the oldest formations outcrop towards the north, in belts running parallel to Lake Ontario. Their characters are briefly as follows: Hudson River shale. This formation, although widely distributed in the eastern part of the State, is of no economic value for the manu- facture of clay-products, since it is deficient in plasticity and is very .siliceous. Niagara shale. This also, on account of its calcareous and siliceous character, is of little or no value. Medina shale. Along the Niagara River at Lewiston, and also along the Genesee River, there are outcrops of this rock. It is not utilized in New York State, but has given good results for dry-pressed brick in Ontario. Clinton shales. These are about 30 feet thick in places, notably in eastern Wayne County, and 24 feet thick at Rochester and Wolcott Furnace. They have not been used and are probably often calcareous. Salina shales. This series forms a belt extending from Syracuse westward. The shale is soft, weathers easily, and possesses good plas- ticity, but may be quite calcareous, and not infrequently carries lumps of selenite. It is red-burning, and used for common and paving brick, drain-tile, or conduits. Hamilton shale. Though extending from the Hudson River to Lake Erie, this formation shows considerable lithologic variation ranging from a sandstone to a clay-shale. The latter phase is more common in the western part of the State. It is worked for paving-brick at Cairo, Greene County, and beds of good quality are known at Windom, Erie County. Portage shale. This overlies the Hamilton stratigraphically, and hence outcrops to the south of the Hamilton belt. It consists of shales and sandstones, the former being well exposed along Cashaqua Creek, also along Seneca Lake and at Penn Yan, but becomes very gritty east MAINE-NORTH CAROLINA 377 of this point. The shale has been worked at Angola for fireproofing, at Jewettville for pressed brick, and at Hornellsville for paving-bricks. Chemung shale. This somewhat extensive shale formation, the most southern in New York State, has been utilized at several points for making clay-products. At Corning (PL XXXIII, Fig. 1) it is quarried 378 CLAYS for paving-brick, at Alfred Center for roofing-tile, and at Elmira for common brick. Cretaceous and Tertiary Clays These include the Cretaceous clays of the Coastal Plain region of Long Island, Staten Island, and Fisher's Island, as well as some others of possible Tertiary age, but the deposits are of exceedingly variable character, ranging from ferruginous ones to others of good refractori- ness. They, moreover, partake of the character of other Coastal Plain clays in being often of highly siliceous character as well as pockety or lens shaped in form. The more important points at which these clays .are exposed are at Kreischerville, Staten Island; Little Neck near Northport, West Neck, Oyster Bay, Wyandance, and Farmingdale, Long Island. All of these, except the first two, are adapted only to the manufacture of common brick. The deposits at Glencove and North- port have been worked for a number of years, those of the latter locality having been used for fire-brick, stove-linings, and stoneware. Pleistocene Clays These can be divided into four groups, namely, (1) morainal clays; (2) lacustrine clays; (3) pond deposits; (4) estuarine deposits. The morainal clays are usually too stony to be of any value, although at Newfield, Tompkins County, one lens in the moraine has been worked for fifteen years. The lacustrine clays were laid down during post-Glacial time, when the waters of Lakes Erie and Ontario were dammed up to the north by the retreating continental glacier, and spread over the land in the western .and northwestern part of the State, much clay being deposited during this time. These clays underlie the flats around Buffalo, Lancaster, Tonawanda, and other places in western New York, and are used for making brick and drain-tile. They often contain lime pebbles. The pond deposits are widely distributed throughout the State, being found in many of the flat-bottomed valleys. They are prevailingly impure, often contain sandy streaks, and are rarely deep. Most of them burn red and are worked for common brick or tile, but hollow t>rick are also manufactured. The estuarine clays are confined to the Hudson River and Champlain Valleys, and were deposited during post-Glacial times. They form an extensive and often thick deposit, which underlies the terraces border- ing these valleys (PI. XXXIII, Fig. 2). The section usually involves .an upper sand-bed, a yellow weathered clay, and a blue clay. The clays PLATE XXXIII FIG. 1. Bank of Chemung shale used for brick, Corning, N. Y. (After H. Ries> N. Y. State Mus., Bull. 35, p. 838, 1900.) FIG. 2. Bank of Pleistocene clay overlain by sand, Roseton, N. Y. (After H. Ries, N. Y. State Mus., Bull. 35, p. 698, 1900.) 379 MAINE NORTH CAROLINA 381 are laminated materials, plastic, red-burning, and easily fusible. Those in the Hudson Valley especially are extensively dug for the manufacture of common brick, but are probably useless for much else, although certain beds near Albany make an admirable slip-clay which is shipped to all parts of the United States. In the following tables there are given a number of selected analyses and physical tests of New York clays: ANALYSES OF NEW YORK CLAYS* i. II. III. IV. V. Silica (SiO 2 ) 59 50 52 30 65 15 53 20 68 34 \liuniiiii (AloOs) 20 60 18 35 15 29 23 25 19 89 Kerrrc oxide (FegOs) . . 8 00 6 55 6 16 10 90 90 Lime (CaO) 80 3 36 3 50 1 35 Magnesia (MsO) . 35 4 49 1 57 62 trace Potash (K..O) 1 o , f 4 65 1 e T-I f 3 55 Soda (NaoO) [3.60 j 1 35 5.71 2.69 { 0.84 Combined water (H 2 O) Miscellaneous 5 . 50 | + organic 5.30 ]' C0 2 I i \ 6.39 MnO 2 0.52 TiO 2 0.91 6.03 } 1 3. 04 / SO 3 0.41 } VI VII. VIII. XI. X. Silica (SiO 2 ) Alumina (A1 2 O 3 ) 47.40 39.01 55.00 51.61 19.20 57.36 16.20 51.30 12.21 Ferric oxide (Fe 2 O^) 0.15 1 34 . 54 j 8.19 4.55 3.32 Lime (CaO) Magnesia (MgO) trace trace 5.33 3 43 7.60 1 25 5.34 3 90 11.63 4 73 Potash (K.O) trace Soda (Nfa 2 O) trace > . 48 5.32 6.98 4.33 Combined water (H 2 O) Moisture . 14.10 1.22 / + C0 2 1 1 7.25) Miscellaneous ..( organic 1 KA 1 1 .50 * From N. Y. State Mus,, Bull. 35. PHYSICAL TESTS OF THE ABOVE I. III. IV. VI. Per cent H 2 O to form plastic mass Plasticity . . . 16 lean 15 3 6 cone .04 1 4 21.4 fair 92 4 10 06 01 4 20 moderate 61 4 9 06 01 3 38 fair 11-14 10 8.7 35+ 35+ Average tensile strength, Ibs. per sq. in Air-shrinkage Incipient fusion Vitrification Viscosity . 382 CLAYS LOCALITIES OF THE PRECEDING No. Locality. Geological Age Uses. I Lewiston Medina Not worked II. Ill IV. V. VI. VII Warners Angola Alfred Center. . Near North pori Kreischerville . . Roseton Salina Portage Chemung Cretaceous Pleistocene Paving, common, and hollow brick Flue-linings Roofing-tile Stoneware Fire-brick Common brick VIII Croton Point < < t IX. Buffalo 14 it tt x New field " (drift) Common and paving brick References on New York Clays 1. Dwight, W. B., A Peculiar Feature of the Clay -beds on the Western Bank of the Hudson, three miles north of Newburg, Trans., Vassar Bros. Inst., Poughkeepsie, 1884-1885. > 2. Jones, C. C., A Geologic and Economic Survey of the Clay-deposits of the Lower Hudson River Valley, Amer. Inst. Min. Eng., Trans., XXIX, p. 40, 1900. 3. Martin, D. S., A Note on the Colored Clays Recently Exposed at Morrisania, N. Y. Acad. Sci., Trans., IX, p. 46. 4. Merrill, F. J. H., Origin of the White and Variegated Clays of the North Shore of Long Island, N. Y. Acad. Sci., Annals, XII, p. 113, 1900. 5. Merrill, F. J. H., Note on Colored Clays at Morrisania, N. Y., N. Y. Acad. Sci., Trans., IX., p. 45. 6. Prosser, C. S., Distribution of Hamilton and Chemung Series of Central New York, N. Y. State Geologist, 15th Ann. Kept., p. 87, 1899. 7. Ries, H., Clays of New York, their Properties and Uses, N. Y. State Museum, Bull. 35, 1900. 8. Ries, H., Physical Tests of Devonian Shales of New York State, 15th Ann. Kept., N. Y. State Geologist, Vol. I, p. 673, 1897. 9. Ries, H., On the Occurrence of Cretaceous Clays at Northport, Long Island, School of Mines Quart., XV, p. 354, 1894, North Carolina The clay-deposits found in North Carolina are of two types, namely, residual clays and sedimentary clays, these subdivisions corresponding more or less closely also to geological ones, that is to say, the residual clays are derived from rocks of pre-Cambrian and Palaeozoic age, while the sedimentary clays are of Mesozoic age or younger. PLATE XXXIV FIG. 1. Kaolin-mine near Webster, N. C., showing kaolin mining by circular pits. (After Ries, N. C. Geol. Survt, Bull. 13, p. 56, 1897.) FIG. 2. Bank of Carboniferous shale near Akron, O. (Photo loaned by Robinson Clay-product Co.) 3-3 MAINE NORTH CAROLINA 385 Residual Clays These may occur in any portion of the State west of the coastal plain region. The eastern border of this area passes through Halifax, Frank- lin, Wait, Chatham, Moore, and Anson. The clays are usually impure and gritty, and suited for little else than the manufacture of common brick, although in a few instances, as at Pomona and Grover, they may be of semi-refractory character. A noteworthy exception to the above occurrences are the deposits of kaolin which are found in the western part of the State in the Smoky Mountain region. Here many veins of pegmatite, carrying coarsely crystalline quartz, feldspar, and mica (generally muscovite), with some garnet, have been weathered to kaolin to a depth of from 60 to 100 feet. The veins vary in width from a few inches to several hundred feet and may be many hundred feet long. They also branch or curve and pinch or swell. The most im- portant of these deposits is near Webster, but others have been noted at Syiva, Jackson County; Bostick's Mills, Richmond County; Troy, Montgomery County; West's Mills, Macon County; two miles west of north of Bryson City, Swayne County; two miles south of Hall Station, Jackson County; and two and a half miles southwest of Canton, Hay wood County. All of these kaolins need washing before they can be shipped to the market, and have been extensively used for the manufacture of white ware. Sedimentary Clays Beds of these are found widely distributed throughout both the coastal plain area and the broader upland valleys of the State. In the former area there are many extensive beds of laminated clay which are often well exposed in the river-banks traversing that region. Most of the clay-deposits found in the Coastal Plain area are rather lentic- ular in their character and pass horizontally into beds of sand. Among the best deposits of sedimentary clays thus far developed in the State may be mentioned those around Fayetteville, Goldsboro, Weldon, Greens- boro, etc. They are nearly all red-burning, and are used for the manu- facture of a brick or drain-tile. In many valleys of the uplands the rivers are bordered by terraces underlain by clays of Pleistocene age, such clays being abundant along the Catawba River near Morgantown and Mount Holly, on the Clark River at Lincolnton, along the French Broad River at Asheville, and along the Yadkin River at Wilkesboro. The depth of these terrace-clays commonly ranges from 5 to 10 feet, and they are in most instances covered by from 6 inches to a foot or more 386 CLAYS of sandy loam. The majority are adapted only to the manufacture of common brick, but here and there we find beds of very plastic material; sufficiently free from grit to be used for the manufacture of common stoneware. The Triassic shales form a narrow belt in Grandville, Durham, Chatham, Moore, Southeast, Montgomery, and Anson coun- ties, but their value for making clay-products is said to have been but little tested. At Pomona a weathered-shale outcrop has been used in the manufacture of sewer-pipe. ANALYSES OF NORTH CAROLINA CLAYS ULTIMATE ANALYSES I. II. III. IV, V. Silica (SiO 2 ^ 53.07 45.70 56 81 50 17 64 93 Alumina (Al 2 Oa) 29.54 40.61 20 . 62 28 77 17 08 1.27 1.39 6 13 2 88 5 57 Lime (CaO) 0.15 0.45 65 05 43 \Iasrnesia (MsjO) 14 09 58 " 59 Potash (K 2 O) 1.28 | Soda (Na 2 O) 0.87 / 2.82 4.47 1.04 3.85 Combined water, ignition. . . 9.93 1.29 8.98 0.35 8.60 1.64 14.03 J 2.08 I 6.58 2.48 FeO l.OC VI. VII. VIII. IX. X. .Silica (SiO 2 ) 58.17 59.27 70.45 69.58 53.75 Alumina (A^Os) , . . . . 20.10 22.31 17 34 14 03 24 91 Ferric oxide (Fe 2 Os). . . . . . 7.43 6.69 3 16 6 41 7 99 Lime (CaO) 0.60 25 25 40 70 jVlagnesia (MffO) 0.77 0.13 22 27 1 12 Potash (KoO) Soda (Na 2 6) } 2.60 0.90 0.70 1.65 2.94 Combined water, ignition . . Moisture 7.34 3.23 9.00 1.90 6.63 0.98 5.73 1.68 7.60 1 03 FeO 0.33 RATIONAL ANALYSES I. II. III. IV. V. Clay substance 61.99 96.81 58.85 73.19 53.13 Free sand 36.55 25.40 40.65 26.05 45.90 VI. VII. VIII. IX. X. Clay substance 48 09 67 20 48 26 45 47 34 04 Free sand 52 15 33 25 51 50 51 28 46"00 Nos. I-Xfrom N. C. Geol. Surv.. Bull. 13, 1897. MAINE NORTH CAROLINA 387 PHYSICAL TESTS OF NORTH CAROLINA CLAYS I. II. IV. V. Per cent water for working 28 good 8 5 39 slow fine 2100 2300 2500 whitish 2.24 42 lean 6 4 20 slow very fine 2300 2500 2700 + white 2.43 30 very good 7 148 slow fine 1950 2100 2250 / gray \ brown 2.35 28 good 8.5 5 144 fast medium 1900 2050 2200 red 2.55 Plasticity Air-shrinkage, per cent. Fire-shrinkage, per cent. Average tensile strength, Ibs. per sq. in. Rate of slaking. . Texture Incipient fusion degrees F. Vitrification, degrees F Viscosity degrees F Spcific gravity. . . . VI. VII. VIII. IX. X. Per cent water for working. . Plasticity 28.5 fair 9.8 7 84 slow fine 1850 2050 2250 red 2.45 28 lean 10 6 66 fast coarse 2100 2400 2500 red 2.46 26 lean 10 2 47 slow coarse 2150 2350 2550 buff 2.55 36 slight 9.6 4.5 60 fast fine 1950 2100 2250 red 2.59 25 lean 5 10 74 fast fine 1900 2100 2300 deep red 2.63 Air-shrinkage, per cent Fire-shrinkage, per cent. . . . Average tensile strength, Ibs. per sq. in Rate of slaking Texture Incipient fusion, degrees F. . Vitrification, degrees F Viscosity, degrees F 'Color when burned. . . Sp3cific gravity .... LOCALITIES OP THE PRECEDING. No. Locality. Geological Age. Uses. I Grover Residual \Vhite pressed brick II. Webster < < \Vhite ware Ill Greensboro 4 Brick IV. N.W. of Blackburn. . . Stoneware V. Fayetteville (average). . Bricks VI. Fayetteville Not worked VII Green sboro Pleistocene. . . Brick VIII Pomona Brick IX \Iorgantown Columbia. . . Not worked x Wilkesboro C ( Nos. I-X from N. C. Geol. Surv., Bull. 13, 1897. 388 CLAYS References on North Carolina Clays 1. Holmes, J. A., Notes on the Kaolin and Clay-deposits of North Carolina, Amer. Inst. Min. Eng., Trans., XXV, p. 929, 1896. 2. Kerr, W. C., and Genth, F. A., Report on Minerals and Mineral Localities of North Carolina, 1885. 3. Pratt, J. H., The Mining Industry of North Carolina, N. Ca. Geol. Survey; separate bulletins issued for 1901, 1902, 1903, and 1904. 4. Ries, H., Clay-deposits and Clay Industry in North Carolina, N. Ca. Geol. Surv., Bull. 13, 1897. CHAPTER VII NORTH DAKOTA TO WYOMING North Dakota THE North Dakota clays (Ref. 1) are found in the Cretaceous, Ter- tiary, and Pleistocene formations, the first being probably the most important. Cretaceous Most of the divisions of this system of rocks carry extensive deposits- of clay, whose character is briefly as follows: Benton and Niobrara. These two formations, composed chiefly of blue clays and shales, are closely associated and similar. They are well developed in the central and northern parts of the State, but rarely appear along the eastern border. The clays of the Niobrara and ad- joining portions of the Benton often carry carbonate of lime and small amounts of iron pyrites, alum, gypsum, and lignite. Pierre. This includes a great accumulation of clays and shales found throughout a large area in the central portion of the State. The beds are uniform in character, of a bluish-gray color, and almost free from sand, but at times thin seams of gypsum occur. The formation is prominent in the Pembina and Turtle Mountain region. Fox Hills. The Fox Hills group appears to carry few clays of value. Laramie and Tertiary These two formations, which are not differentiated by Babcock, extend over a large portion of the State west of the Missouri River, and consist principally of clays, shales, and lignites, with occasional layers of sand and sandstone. Some of the clays appear to be of re- fractory character, and a number of beds, adapted to a variety of pur- poses, have been noted around Dickinson, where they have been worked 380 390 CLAYS to some extent. Red-burning shales occur with the coal at Minot and in Mercer County. Pleistocene Pleistocene clays of blue or yellow color, and often of gravelly or stony character, are found over a large portion of the State. They are frequently calcareous, and around Grand Forks are worked for cream- colored brick. Red-burning brick-clays occur along the Missouri River near Bismarck, and are much used. Grayson, Walhalla, and Fargo are also promising localities. The following analyses are taken from Babcock's report: ANALYSES OF NORTH DAKOTA CLAYS I II. III. IV. V. VI VII. VIII. Silica (SiO 2 ) Alumina (AljOs). ... Ferric oxide (Fe 2 O 3 ). . Lime (CaO) 72.66 17.33 1.05 0.13 "6'.36 0.38 9.35 60.79 16.23 4.49 0.65 1.02 0.19 0.28 16.35* 56.86 25.03 6.11 0.71 0.76 0.50 0.016 10.014* 53.72 17.78 3.85 0.81 0.50 0.28 1.72 21.82 58.73 14.98 5.63 2.10 0.74 0.16 0.988 16.67? 55.77 12.15 4.27 5.92 1.90 0.256 0.992 18.742* 71. 2f. 21.94 3.67 0.74 o.sr 51.27 9.33 3.52 11.15 2.31 0.50 J2.08 Magnesia (MgO) Potash (K 2 O) !Soda (Na 2 O). Loss on ignition * By difference. I. Grand Forks, brick-clay. II. Clay with coal. Mercer County. III. Clay over coal, Minot. IV. Clay under coal, Minot. V. Alluvial clay, Missouri River, Bismarck. VI Lehigh coal-mine, east of Dickinson. VII. Under-clay, same locality, after ignition. VIII. Brick-clay, Grand Forks. References on North Dakota Clays 1. Babcock, E. J., First Biennial Report, N. Dak. Geol. Surv., p. 29, 1901. Ohio The geologic scale of Ohio includes strata ranging from the Ordo- vician to the Permian, while overlying these are beds of Quaternary age. Ordovician and Silurian 1 The rocks of these two ages underlie a larger area in the western half of the State, those of the former age being found chiefly in the 1 Profs. E. Orton, Jr., and C. S. Prosser have kindly given the author much information regarding the shale formations of the State. NORTH DAKOTA TO WYOMING 391 southwestern part. They include several shale formations, among them the Eden, Lorraine, Richmond, Saluda, and Osgood; but most of these are highly calcareous and of little value for the manufacture of clay- products. The Saluda has been used for drain-tile. 1 1 Ohio Geol. Surv., Vol. VII, Pt. I, p. 56. 392 CLAYS Devonian The Devonian rocks underlie a large area in the northwestern corner of the State, and also extend across the west-central part from Lake Erie to the Ohio River. The shale formations are the Oletangy and the Ohio. The former is 20 to 35 feet thick in central Ohio with numerous outcrops and shows even greater thickness in the northern part of the State. It is actively worked at Delaware for making drain-tile and fireproofing, but has also been used at Columbus for the manufacture of sewer-pipe and common brick. The Ohio shale is divisible, in the northern part of the State at least, into three parts, known as the Huron, Chagrin, and Cleveland shales. Professor C. S. Prosser states that the Chagrin shale is gray to greenish, and extends from the Black River as surface outcrops along the shore of Lake Erie in a belt several: miles broad to Pennsylvania, and is re_ garded as promising for the manufacture of clay-products. Many red pressed brick are made from it at Cleveland. Lower Carboniferous The Bedford shale, which is an important shale formation extend- ing clear across the State, is in part at least frequently of red color; but its greenish phases resemble the Chagrin shales of similar color. It is worked at Bedford, Akron, Independence, and a number of other localities for pressed-brick manufacture; at Willow Station for paving- brick; and at Summit Station for common and sewer brick. It promises to become one of the most important shale formations of Ohio. The Logan shale, occurring in the lower part of the Logan formation, is now extensively used at a number of points, including Newark, Han- over in central Ohio, and Sciotoville in the Ohio Valley region, but, according to Professor E. Orton, Jr., is of non-refractory character. Professor E. Orton states (Ref. 2) that the Low r er Carboniferous or Maxville limestone holds a valuable clay-deposit at a few places in south- ern Ohio, while in many places in Kentucky a hard flint-clay comes into the section. It has been worked largely at Sciotoville and Portsmouth for fire-brick, and is hence known at the Sciotoville clay. It also occurs .near Logan, Hocking County. Coal-measures These underlie the eastern third of the State. The lower members are found in the western portion of the area, while the upper members NORTH DAKOTA TO WYOMING 393 immediately underlie the surface in the middle and eastern parts towards the Pennsylvania border. They include the best clays in the State, and both shales and clays are numerous throughout the entire series. Pottsville series. The section of the Pottsville formation shows the following according to Orton: 1 Homewood (Tionesta) sandstone Mount Savage (Tionesta) coal Mount Savage (Tionesta) clay and shale Upper Mercer ore Upper Mercer limestone Upper Mercer coal Upper Mercer fire-clay Lower Mercer iron ore Lower Mercer limestone Lower Mercer fire-clay Conoquenessing (Massillon) sandstone (upper) Quakertown coal-beds Quakertown shales Conoquenessing (Massillon) sandstone (lower) Sharon shales Sharon coal Sharon clay Sharon sandstone The important beds are the Mount Savage clay and shale, Upper Mercer clay, Lower Mercer clay, Quakertown clay and shales, Sharon clay and shales. 2 Sharon shales. These overlie the Sharon coal and vary in thickness from 1 to 50 feet. They are usually dark blue, sometimes almost black, with heavy iron-ore nodules at certain levels. The shales proper have become the basis of one of the largest sewer-pipe industries in the United States, at Akron and its immediate neighborhood. The same deposit is also worked for roofing-tile, but the shale is usually high in iron oxide. Quakertown clay and shale. These occupy a space between the. two divisions of the Conoquenessing sandstones, when such a separation occurs. They overlie and underlie the Quakertown coal, although the latter may become extremely thin at times. The shales or clays of this 1 The names in parenthesis are those given in Orton's report, Ohio Geol. Surv. VII, while the names in front of them are the later ones. 2 Orton, Ohio Geol. Surv., VII, Pt. 1, p. 59. 394 CLAYS age have been worked in Summit, Portage, and Stark counties. The Summit deposits have furnished stock for the potteries of Springfield, and the Portage bed supplies the Mogadore potteries. The Massillon Fire-brick Company has developed an important deposit at this horizon. It is a streak of hard fire-clay 4 to 5 feet thick immediately underlying the Conoquenessing, and representing the Quakertown coal. The bottom of the clay is 30 feet above the Sharon coal (Ref. 2). Lower Mercer clay and shale. Overlying the Lower Mercer lime- stone there is often an iron ore, while under it is a coal-seam of little value. Underlying the coal there is a shale or more often clay, which has been extensively worked in Stark, Tuscarawas, Muskingum, and especially Hocking counties. The Columbus Brick and Terra-cotta Company at Union Furnace have used it, and it has also been worked at Millersburg, Holmes County. The clay shows considerable varia- tion and is nowhere of high character. The shale or clay immediately overlying the Lower Mercer limestone is also promising. Upper Mercer clay and shale. The Upper Mercer coal is not of economic importance, but the accompanying under-clay is more im- portant. It is a light-colored plastic clay, of wide-spread occurrence in the State, and at Haydenville, Hocking County, is extensively worked under the name of the Mingo clay. It is one of the most valuable clay- deposits found within the Haydenville coal-field, and runs from 8 to 10 feet thick. Mount Savage clay. This, formerly named the Tionesta, occurs from a few feet to 20 feet above the last-named deposits, and there is found at times another valuable clay-bed. It has been used at Union Furnace. Allegheny or Lower Coal-measures The most important clay-deposits of the Ohio coal-measures are given as follows: Upper Freeport clay and shales Lower Freeport clay and shales Middle Kittanning clay and shales Lower Kittanning clay Ferriferous limestone clay Putnam Hill limestone clay and shales Putnam Hill limestone horizon Putnam Hill or Brookville clay. This underlies the Brookville coal and is a valuable clay-deposit in several of the central coal-measure NORTH DAKOTA TO WYOMING 395 counties of Ohio, although of no importance in parts of western Penn- sylvania. It is said to be specially well developed and largely worked in Muskingum County, but is also of importance in the counties of Coshocton, Tuscarawas, and Stark, where it has been much used. Prom- ising beds are also mentioned in Perry, Hocking, and Vinton counties. It has been worked at or near Zanesville for buff- or cream-colored brick, encaustic -tiles, and fire-brick, and at Canton for the manufacture of paving-brick. Other workings are at Greenford, Mahoning County, and New Lexington, Perry County. A red shale said to be of this same age is also worked at the last locality. In the Zanesville area the Brookville clay is stated to vary from 3 to 10 feet in thickness with an average of 6 feet. It is usually divisible into an upper or plastic portion and a lower or more siliceous division. A section six miles above Zanesville on the west side of the river gave: Feet. Putnam Hill limestone Putnam Hill limestone shale 11 White clay 4-5 Dark clay 2 Fire-clay 2 Sandstone and sandy shale 5 Brown clay 14 Ferriferous or Vanport limestone and clays. The clays of this formation are light-colored, plastic, and of fair quality, with a thickness ranging from 2 to 6 feet. Professor E. Orton, Jr., has informed the author that this yields a valuable stoneware-clay in the district running from Zanesville down to New Lexington on the Cincinnati and Muskin- gum Valley Railroad. It is also used in southern Ohio around Scranton, either as a potter's clay or for shipment as a second-grade fire-clay. Lower Kittanning clay and shale. These were pointed out by Professor Orton to constitute the great clay horizon of the State, and lie stratigraphically between the Ferriferous, limestone and Lower Kittanning coal, often filling the interval between them. In the more important occurrences its thickness ranges between 8 and 30 feet, and sometimes is even continuous with the clays above the Lower Kittan- ning, only the coal-seam being between, and thus giving a combined section of not less than 50 feet. The Lower Kittanning clay is best seen where it enters the State from Pennsylvania, and again where it leaves the State in its extension into Kentucky. At both of these localities 396 CLAYS in the Ohio Valley, namely, in Columbiana and Jefferson counties on the one side and in Lawrence County on the other, it shows great quan- tities of clay of good quality. Other counties in which it has been Shales, sandstone, and concealed. Shales, Shales, massive, Morgantown. Limestone, fossiliferous, Ames. Red shales M' Concealed, with shales and flaggy sandstone Coal ...:.;:.:::::. 100 Shale . r ^ Shales drab. { ,_ Shales with coal, Masontown >' Sandstone, Mahoning, and concealed, under river 130 112 FIG. 60. Section of Barren Measures opposite Steubenville, Ohio. (After White, U. S. Geol. Surv., Bull. 65, p. 77, 1891.) developed are Tuscarawas, Stark, and Muskingum; extensive mining has gone on at Haydenville, Hocking County, and Canton, Stark County. The plastic clay from this horizon is used by the eastern Ohio potteries, while a flint-clay is also found at some points, as in Stark, Tuscarawas, and Carroll counties. NORTH DAKOTA TO WYOMING 397 The clay has been used wholly or in part for the manufacture of saggers, Rockingham, yellow and stone ware, sewer-pipe, paving-brick, and fire-brick. Middle Kittanning clay. This is said to furnish a good fire-clay at Oak Hill, Jackson County, and is there used for fire-brick. Nodules of iron are seen in many of its outcrops, and these interfere with its, use. Lower Freeport clay. This is not much developed, but at one locality, namely, in the vicinity of Moxahala, Perry County, the seam is found in the nature of flint-clay, but contains too much iron to permit its use for the highest grades of ware. More often the clay represents the impure type so abundant in the coal-measures. Upper Freeport clay and shale. This bed is more important than the preceding, since it occurs in great quantity and more widely dis- tributed than the coal-seam from which it gets its name. It assumes -a flinty phase at several points. SECTION AT BELLAIRE, OHIO Feet. Inches. Feet Inches. Coal, Waynesburg 2 Shale, sandy 6 Shale 12 Limestone 3 Concealed 5 Coal, blossom, Little Waynesburg Concealed 14 Coal, blossom, Uniontown 1 Shale 4 Sandstone 6 Shale, argillaceous 20 Concealed 32 Shale 2 } 127 6 Sandstone 3 Shale 3 Concealed 33 Calcareous shale, with thin limestones. . . 21 6 Coal 4 Shales, sandy 13 10 Coal, Sewickley Coal 8 J- 27 6 Shales, argillaceous. . . 6 Coal 3 Shale, argillaceous. 2 Limestone, thin clay in center 8 Limestone, magnesia-cement rock 5 Clay 1 Limestone 11 Concealed 11 Coal, Redstone, blossom 2 Concealed 17 1 t Q Shale 1 Coal, Pittsburgh 7 Total. 263 398 CLAYS Conemaugh or Lower Barren Measures. These contain vast deposits of shale, which are extensively used for the manufacture of paving-brick. They are distributed through the entire series, but about the middle portion of this division beds of special prominence occur, as in the Sunday Creek Valley. An excellent shale has been found underlying the coal at Bellaire. Fig. 60 by White (Ref. 6) gives the section of the Barren Measures opposite Steubenville, Ohio. Monongahela or Upper Productive Measures. This series extends from the base of the Pittsburg coal up to the Cassville. The section on page 397, given by I. C. White (Ref. 6), from Bellaire, Belmont County, shows the character of the series. The area of outcrop forms a narrow, sinuous band extending in a. northeasterly direction from Gallipolis to Steubenville, and southward from there to beyond Bellaire. 1 Dunkard or Upper Barren Measures. In Ohio these underlie an area extending through the counties of Belmont, Monroe, Washington, Athens, Meigs, and Gallia. Pleistocene Pleistocene clays are found in all parts of the State, but they are used chiefly for common brick and drain-tile. ANALYSES OF OHIO CLAYS I. II. III. IV. V. VI. VII. Silica (SiO 2 ) 76.24 63.09 52.52 61.86 69.37 69.79 56 44 Alumina (Al 2 Oa) 16.87 20.17 31.84 26.02 19.08 19.31 26 60 Ferric oxide (Fe 2 O3) 16 2 12 67 63 1 26 2 00 Lime (CaO) Magnesia (MgO) . ... 0.50 trace 0.50 19 1.26 19 0.60 0.63 0.47 63 Potash (K->O) 1 -i /O 59 f 2.14 3 20 Soda (Na 2 O) [1.09 2.76 { JO. 31 1 0.02 26 Water (H 2 O) u , f 5.41 11.68 9.73 5.57 5 09 7 57 Moisture > 5.14 \ 6 45 69 94 1 02 2 48 Titanium oxide (TiO 2 ) . . 1 68 29 VIII. IX. X. XL XII. XIII. XIV. Silica (SiO 2 ) 68 13 66 21 57 15 57 10 49 30 58 20 57 28 20 80 21.13 20 26 21 29 24 00 22 47 21 13 Ferric oxide (Fe 2 O3) 1 20 1 28 7 54 7 31 8 40 5 63 8 52 Lime (CaO) . . . 42 51 90 29 56 6 5 79 Magnesia (MgO) 37 18 1 62 1 53 1 60 9 2 13 Potash (K 2 O) 2 28 1 42 3 05 3 44 3 91 3 Of Soda (NaoO) 27 38 58 61 19 4 9 Water (H 2 O) 5 72 6 29 5 50 6 00 9 40 6 15 5 22 Moisture 1 00 1 65 2 70 1 30 1 20 1 6f Titanium oxide (TiO 2 ) See U. S. Geol. Surv., Bull. No. 65, Map II. I. NORTH DAKOTA TO WYOMING ANALYSES OF OHIO CLAYS Continued 399 XV. XVI. XVII. XVIII. XIX. XX. Silica (SiO 2 ). . . . 52 19 53 38 44 60 59 92 57 80 51 72 .Alumina (A^Oa) . . 14 61 19 36 40 05 27 56 25 54 30 10 Ferric oxide (FesOa) 10 00 14 86 80 1 03 2 51 1 94 Lime (CaO) 1 48 27 trace 25 62 Magnesia (MgO) 1 06 trace trace 61 53 Potash (K 2 O) trace 67 2 51 2 74 Soda (NaoO) trace 18 Water (H 2 O) 5.62 14 23 9 70 8 35 9 95 Moisture 12 62 1 12 2 25 1 05 Titanium oxide (TiO2) 1 35 LOCALITIES OF THE ABOVE No. Locality. Geological Age. Uses. I Haydenville Lower Carboniferous Fire-brick II. Ill North Industry Mineral Point Lower Coal-measures Lower Kittanning Paving-brick Refractory wares IV Darlington t( (( Paving-brick v Roseville Stoneware VI Roseville Cooking ware VII Steubenville Stoneware VIII. IX Akron Zanesville Lower Carboniferous Lower Coal-measures. . . . Stoneware Cooking ware x Gloucester Cambridge XI Canton . ... Lower Coal-measures Paving-brick XII. Waynesburg Middle Kittanning f Freeport shale Brick XIII. Zanesville XTV Northern Ohio Bedford shale Paving-brick XV North Industry Lower Carboniferous Pa vin g-brick XVI Canton ( ( tt YVTT Scioto County 1 1 1 1 Fire-brick XVIII Salineville Fire-brick VTV East Palestine Upper Freeport Paving-brick XX. Jefferson County. . . . Sewer-pipe Nos. I-XX from Ohio Geol. Surv., VII. 1893. References on Ohio Clays 1. Leverett, F., On the Significance of the White Clays of the Ohio Region, Amer. Geol., X, p. 18, 1893. 2. Orton, E., The Clays of Ohio, their Origin, Composition, and Varieties, Ohio Geol. Surv., VII, p. 45, 1893. 3. Orton, E., Jr., The Clay-working Industries of Ohio, Ohio Geol. Surv., VII, p. 69, 1893. 4. Prosser, C. S., Geological Scale of Ohio, Ohio Geol. Surv., Bull. 7, 1905. 5. Stevenson, J. J., Carboniferous of the Appalachian Basin, Geol. Soc. Amer., Bull., XV, p. 37, 1904. 400 CLAYS 6. White, I. C., Correlation Papers, Carboniferous, U. S. Geol. Surv.,, Bull. 65, 1891. 7. See also annual reports of inspector of mines. Oklahoma Territory 1 The rocks of the greater part of Oklahoma consist of deposits of red 1 clay-shale. In the eastern part of the Territory these clays are of Penn- sylvanian age, while farther west they belong to Permian formations. In the Osage Nation, and the counties bordering on the Arkansas River, there are beds of gray and drab clay contained between ledges of flinty limestone of Pennsylvanian and Permian age, while in the Wichita Mountains in the southwestern part of the Territory there are beds of kaolin, formed from the disintegration of granite and gabbro rocks. On the uplands in Beaver and Woodward counties there are deposits of Tertiary clay, but much of this contains a considerable amount of lime, and might not therefore be suited to the manufacture of clay-products. Dakota (Cretaceous) clays occur in the extreme northwestern part of Beaver County, and alluvial clays are found in the river valleys in all parts of the Territory. The only use that has been made of the clay-deposits in Oklahoma is for the manufacture of brick. In nearly every small town common brick are made, chiefly of alluvial clay. Pressed-brick plants are in operation at Oklahoma, Chandler, Guthrie, Geary, Mangum, El Reno,, and Anadarko. On account of the utilization of natural gas for fuel at the Kansas brick-yards, and consequent cheaper cost of production, much of the brick used in Oklahoma comes from that State. An analysis of clay from Stucks Canyon, four miles west of Ferguson,. Blaine County, yielded : Silica (SiO 2 ) 64. 17 Alumina (A1 2 3 ) ; . . . 14.80 Ferric oxide (Fe 2 O 3 ) 8. 10 Lime (CaO) 1 .34 Magnesium carbonate (MgC0 3 ) 27 Magnesium sulphate (MgSO 4 ) 5 .57 Water (H 2 O) 6.54 Total 100.79 This shows a curiously high percentage of magnesium sulphate. 1 The notes relating to this Territory have been supplied to the author by Professor C. N. Gould. The general geology of the Territory is described in U. S. Geol. Surv., Water-supply and Irrigation Bull. No. 148, by C. N. Gould. NORTH DAKOTA TO WYOMING 401 Pennsylvania The geologic formations of Pennsylvania range from the pre-Cam- brian crystalline rocks to those of Pleistocene age. In the western part of the State, except the northwestern counties, the rocks are nearly all of Carboniferous age, the beds being bent into a series of gentle folds; but often the exposure of the lower or older beds is due partly to the overlying strata having been worn away. To the eastward the rocks become highly folded in the central coun- ties of the State, so that the strata often have a very steep dip, and not only the Carboniferous, but also the lower-lying Devonian and Silurian formations are exposed, giving rise to bands which extend in a general northeast-southwest direction. On the eastern edge of the State there is a fringe of coastal-plain formations, but, with the exception of the Columbia loams, they have little value in Pennsylvania. North of the terminal moraine the drift- clays are wide-spread. Residual Clays These might occur at almost any point in the area lying south of the terminal moraine, but the deposits of greatest economic value are those found in the Great Valley, along the line of which, as well as in the South Mountain region, there are a number of deposits of white and variegated clays (PL XXXV, Fig. 1). These have been derived from the decomposition of hydromica slates, which are interstratified with Ordovician limestones and quartzites, talcose slates, and lime- stones of Cambrian age. Of recent years these white clays have been much worked for paper manufacture, and to a less extent for tile and fire-brick. The most productive localities have been South Mountain, Cumber- land County; Mertztown, Berks County; Ore Hill, near Roaring Springs in Blair County, etc. A number of localities are mentioned in the reports of the Second Pennsylvania Geo ogical Survey, 1 but many of these are no longer worked. More recently they have been described by T. C. Hopkins. 2 A second type of white residual clay or kaolins are those of Delaware and Chester counties, which have been formed by the weathering of 1 Second Pa. Geol. Surv., Kept. C4, pp. 137, 272, 275, 277, 279, 325, 340, and Kept. CC, p. 203. 2 Kept. Penn. State College for 1898, 1899, and 1900. 402 CLAYS pegmatite veins. These have been worked near Kaolin P. 0., Brandy- wine Summit, etc., but the output is less than formerly, because the deposits, being the product of weathering, have in some cases been exhausted with depth. These kaolins are washed for the market, and in some instances the siliceous material left behind is used for silica brick. Silurian and Devonian Shales The vast beds of shale occurring in these formations in the eastern and south-central portions of Pennsylvania should afford an excellent field for exploitation by the clay-worker. The Devonian is found overlying large areas in northwestern Penn- sylvania and may be of value, but in the northeastern counties the beds are often too siliceous. To the south and southeast the Silurian and Devonian formations appear as a series of bands in Lackawanna, Luzerne, Carbon, Cumber- land, Snyder, Juniata, Perry, and other counties, and the shale-beds found in them are worked at several localities for the manufacture of both building- and paving-brick. The Clinton shales have been dug for brickmaking in Laurel ton and Hartleton townships of Union County; the Mauch Chunk shales at Pine Grove, Williamsport, and Sandy Run ; and the Hudson River shale at Reading. Carboniferous To the clay-worker this is the most important group of formations occurring in Pennsylvania, for it includes a wide range of plastic mate- rials, from saridy shales up to the highest grades of fire-clay. Unfor- tunately, no detailed systematic study of the shales and fire-clays of the entire Carboniferous area of Pennsylvania has ever been undertaken, although many scattered references to them are given in the reports of the Pennsylvania Geological Survey, and Hopkins has treated those of Western Pennsylvania in some detail. The various references are found on p. 414. The occurrences are here taken up in regular order, beginning with the oldest. Pottsville. This member of the Carboniferous is composed chiefly of sandy beds, as sandstones and conglomerates, but there are several beds of shale and coal. The latter is often underlain by shale and in some instances fire-clay. Mercer or Alton fire-clay. The Upper Mercer coal is said to be under- lain by a fire-clay in Elk, Butler, Huntington, McKean, and Cameron PLATE XXXV FIG. 1. Kaolin-deposit at Upper Mill, Mt. Holly Springs, Pa. (After Hopkins, Clays of Pennsylvania, Pt. Ill, p. 18.) FIG. 2. White sedimentary clay, Aiken area, S. C. Surv., Bull. 1, 1904.) (After Sloane, S. C. Geol. 103 NORTH DAKOTA TO WYOMING 405 Bounties, while in Beaver, Lawrence, and Mercer counties shale-beds have been noticed, but no fire-clays. Sharon upper coal fire-clay. In Elk County a bed of fire-clay is said to be often associated with the upper Marshburg coal-bed, and has been worked in Benezette township. Another is also found in Mercer County. Savage Mountain fire-clay. This clay is of importance in Somerset County, and while not of the highest grade is said to have given excel- lent satisfaction for coke-oven brick. Allegheny or Lower Productive Measures. These contain a number of important beds of fire-clay and coal in western and western-central Pennsylvania. The formation rests on the Pottsville sandstone, and extends to the top of the upper Freeport coal. Along the upper Ohio River, where the section is specially impor- tant, the following beds are seen: 1 Oto4 2 to 4 1 to 4 Kr . , ~ A 50 to 70 to 2 to 5 SECTION ALONG THE UPPER OHIO RIVER IN PENNSYLVANIA 1. Upper Freeport coal; " Four-foot" or "Hookstown vein" 2. Fire-clay 3. Limestone 4. Shale and 5. Sandstone 6. Lower Freeport coal (usually absent) 7. Fire-clay 8. Limestone (sometimes present) ........ 9. Sandstone, or sandstone and shale 10. Darlington; "Block vein" at Smith's Ferry 11. Fire-clay 12. Black slate with iron nodules ....... 13. Lower Kittanning coal; " Sulphur vein" 14. Fire-clay 15. Sandstone! 16. Shale ) ; ................ ; 17. Limestone, ferriferous, " Vanport limestone" Black shale f Fire-clay 18. \ Sandy shale [ Fire-clay 19. Clarion coal 20. Fire-clay 21. Sandstone ..... 22. Shale 23. Brookville coal 24. Fire-cla 70 to 90 1 to 2 4 20 to 30 2 to 3 6 to 10J 1 to 20 15 20 1 4 to 6 23 25 6 4 , , nn Brookville clay. The Brookville coal is underlain by a persistent and widely distributed clay. In the upper Ohio and Beaver River region it is irregular and often impure, 2 but in other regions is more 1 U S. Geol. Surv., Bull. 225, p. 467, 1904. 2 R. R. Hice, Trans. Amer. Cer. Soc., Vol. VII, Pt. II, p. 251. 406 CLAYS promising. It is said to have been used for fire-brick manufacture at Sandy Ridge, Blueball, Woodland, and Hope Station, Clearfield County; Benezette, Elk County; Parkville, Jefferson County; Queens Run and Farrandsville, Clinton County. It has also been mined for many years at Blacklick, Indiana County, but has to be handpicked to remove the ferruginous concretions. In Fayette County it is a flint-clay, and has been extensively used for fire-brick manufacture. 1 At Brookville, Jefferson County, the coal is underlain by 15 feet of fire-clay, but only the upper part appears to be- of high purity. 2 Clarion clay. This clay underlies the Clarion coal, and is said to be of good quality at most localities. It has been used at Bolivar for fire-brick, 3 and has also been mined on Brady's Run, Beaver County, but does not appear to have been much developed in that locality, even though purer than the Lower Kittanning clay. This is thought to be- due to the fact that it is less accessible than the Kittanning clays, and because it takes a longer time to weather, and is therefore more difficult to wash for pottery purposes. 4 Other important deposits have been reported from near Kittanning, 5 where they have been worked for buff brick. The clay is also present at Johnstown, and Ben's Run, Cambria County, and Pinkerton Point,. Somerset County. Ferriferous coal under-clay. According to the Pennsylvania Survey reports 6 a deposit of fire-clay occurs between the Ferriferous coal-bed and the Buhrstone iron ore in Armstrong County. It is probably purely local and of doubtful value. Lower Kittanning fire-clay. Underlying the Lower Kittanning coal there is, in many localities, an important bed of fire-clay which is often more vaulable than the coal, and has been extensively used for the? manufacture of clay-products. At times there is an interval of as much as 30 or 50 feet between this clay and the ferriferous limestones, but at others the former rests immediately on top of the latter. White 7 states that "eastward from the Allegheny River this clay 1 Geologic Atlas, U. S., Folio 82 ; U. S. Geol. Surv., p. 20. 2 For other references to this clay, see reports of Pa. Geol. Surv. as follows:: HH, p. 146; H, pp. 120, 124, 134, 225; Q3, pp. 27, 81, 111, 134, etc. 3 Second Penn. Geol. Surv., Kept. K3, p. 43. 4 R. R. Hice, Trans. Amer. Cer. Soc., Vol. VII, Pt. II, p. 253. 6 Pa. Geol. Surv., Kept. H 5, p. 245. H5, pp. 239, 249. 7 U. S. Geol. Surv., Bull. 65, p. 172, 1891. NORTH DAKOTA TO WYOMING 407 does not appear to be very important, but westward from that point it is generally present, and attains its maximum development along the Beaver, and westward from there down the Ohio. It is much used by the pottery and tile works at New Brighton, East Liverpool, etc." Hice l states that in the Upper Ohio and Beaver River region it is persistent, quite constant in quality, and has a good roof, and, on account of the extent to which it has been worked in this area, is sometimes called the "New Brighton Clay." The Lower Kittanning clay appears to vary from 5 to 15 feet in thickness, and often consists of two portions, an upper soft clay and a lower hard clay. White states that the latter is used for fire-brick, 2 but Woolsey claims that this is the more siliceous portion. 3 This clay- bed has been extensively used in Beaver County to supply the factories of pottery, hollow ware, fire-brick, and paving-brick. It is not to be understood, of course, that the same grade is used for all purposes, but that different parts of the deposits are used, either alone or mixed with other clays. The sections given in Fig. 61 represent the position of the Lower Kittanning clay at several localities. The Second Pennsylvania Geo- logical Survey reports refer to it in the counties of Armstrong, 4 Beaver, 5 Fayette, and Westmoreland. 6 Middle Kittanning clay. This bed, known also as the Darlington, is sometimes found under the coal of the same name, and has been noted by the geologists of the Second Pennsylvania Geological Survey in Allegheny, Armstrong, Tioga, Blair, and Beaver counties, but was in- correctly referred by them to the Upper Kittanning. It does not appear to be an important bed. According to Hice 7 it is worked on Brady's Run in Beaver County, and is there partly a flint-clay. The clay is not uniform in thickness, and of more variable quality than the Lower Kittanning. Woolsey 8 states that in the Ohio Valley the bed is a very persistent one, but rarely worked on account of the iron nodules which it contains. Upper Kittanning clay. There seems to be a difference of opinion 'L. c. 2 L. c., p. 172. 3 L. c., p. 470. 4 H5. See also Hopkins, Clays of Western Pennsylvania, Ann. Kept. Pa. State College, 1897, p. 33. 6 Q, pp. 58, 59, 190, 193, 195, 205, and 215. 6 K3, p. 40. 7 L. c. * L. c., p. 472. 408 CLAYS regarding the occurrence of a clay-deposit at this horizon. While it may be present, it is in general of no great value. Lower Freeport clay. Above the Kittanning series come the Free- port series, consisting of two coals and underlying fire-clays, and twoi limestones which underlie the clays. Fire clay Fire clay Lower * Kittanning> tire clay I Ferriferous! limestone [ Fire clay Coal Coal Concealed Coal Fire clay Ferriferous' limestone f FIG. 61. Vertical sections near New Brighton, Pa. (After Hopkins.) The Lower Freeport clay does not appear to have assumed much importance, and little mention has been made of it in print. In the Upper Ohio and Beaver River region it is generally quite thin, but in places reaches a workable thickness, and at one point on Brady's Run 0> tg -" "d 3 I? 5 3 18 NORTH DAKOTA TO \\YOMING 411 22 feet have been mined. It has been used for low-grade fire-brick, but usually carries too many impurities to allow its use for refractory purposes. It is generally thoroughly vitrified at cones 6 and 7. 1 "On Block House Run, Beaver County, it has been worked for sewer-pipe." 2 Upper Freeport limestone clay or Bolivar fire-clay. This limestone is quite generally distributed in western Pennsylvania, but when absent or but slightly represented there is found at its horizon a bed of high- grade fire-clay known as the Bolivar clay, and long mined at the locality of the same name in Westmoreland County. It represents a non-plastic or flint-clay, which has been extensively used in fire-brick manufacture. On the Ohio and Beaver rivers this seems to be replaced by a less refrac- tory shale. At some points the Bolivar clay and upper Freeport clay above, and for which it has sometimes been mistaken, may lie close together, as at Salina, Westmoreland County. It is also known in Fay- ette, Indiana, and other counties of western Pennsylvania. Upper Freeport clay. This underlies the Upper Freeport coal, but is often more persistent than its coal-bed. In the Ohio Valley region it is found at several points, 3 and has been used for fire-brick, being some- times mixed with the Lower Kittanning clay. It has also been worked around Bolivar and Salina. Conemaugh Series or Lower Barren Measures. These consist largely of shales and sandstones with some limestones, the shales pre- dominating in the upper beds of the section and the sandstones in the lower. They extend from the Upper Freeport coal to the base of the Pittsburg coal, and their general character can be well seen from the accompanying section (Fig. 62). They form the surface over a large area in Allegheny, Armstrong, Butler, Beaver, and Westmoreland counties. 4 Although their distribution is referred to in the various county reports of the Second Pennsylvania Geological Survey, their possibility for the manufacture of clay-products was not considered. Their importance was, however, well set forth in a report issued by the Pennsylvania State College. 5 In this Affelder states that at Pittsburg, where 320 feet of strata of the Conemaugh formation are exposed between the level of the Monongahela River and the outcrop of the Pittsburg coal near the hilltop, almost all of the rock is shale, most of which is well adapted to the manufacture of brick. The color is variable, but most of the beds are red-burning. Fire-clays do not appear to be abundant in the Cone- maugh, but some low-grade ones have been found and used to advan- 1 Hice, 1. c. 2 Woolsey, 1. c., p. 472. 3 Ibid. 4 See map, U. S. Geol Surv., Bull. 65. 5 The Clays of Western Pennsylvania, Ann. Kept. Pa. State College, 1897 p. 137. 412 CLAYS Pittsburg coal. Concealed Limestone. . . . lijfj Hvtei^i Shales, variegated. Limestone Red shale fiJl^-Iltf ~ Concealed ~o Sandstone, Morgantown Coal, Elk Lick Shales, variegated EL |^"j^i 50 Limestone J I Shales, variegated |jf 4f|"i Limestone, Ames * ! Coal, crinoidal Red and variegated shale I ^ 30 Sandy shales and shaly sandstone i?S^i-^-_-^-j 50 at Coal, Bakerstown ^^^.-'ff. 3 Shales and sandstone , \ Limestone, Upper Cambridge. Sandstone, massive ..:-.-:..... 50 Limestone, Lower Cambridge. Shales |!4fMlftj 10 ' Coal, Masontown Shales =l^Mrfao' Sandstone, Mahoning ..-.:.-... 100 FIG. 62. Section of Upper Barren Measures in Pittsburg region, Penn. (.After I. C. White, U. S. Geol. Surv., Bull. 65.) NORTH DAKOTA TO WYOMING 413 tage for the manufacture of building- and paving-brick, as at Harmon- ville. Of the 57 yards listed in the report just referred to over two thirds use shale wholly or in part. Monongahela Series or Upper Coal-measures. These show their greatest development in southwestern Pennsylvania, and while the shale-deposits do not appear from published reports to be as abundant as in West Virginia, still occasional thick beds of shale occur. An important clay-parting, 6 to 10 inches thick, is found in the Pitts- burg coal-bed, and is used in the Monongahela Valley. It has to be removed in mining the coal and can hence be made a source of profit. The shale over the coal has been used at Fayette City for making red brick, while at Pittsburg the shale of this group is used for making brick and terra-cotta lumber. Pleistocene Clays These are distributed over most of the State. They are of superficial character and rarely of great extent. Around Philadelphia the Col- umbian loams have for many years been worked for both common and pressed brick. In western Pennsylvania clays are found under many river terraces, notably along the Allegheny, Monongahela, Beaver, Ohio, and Youghio- gheny. 1 Along the Ohio and Beaver rivers there are three well-marked terraces, lying respectively 30-50, 150, and 200-250 feet above the river- level. Clays, which are dug in the highest and lowest of these, are used for brick and earthenware, and excellent results are sometimes also obtained by mixing these with shales. ANALYSES OF PENNSYLVANIA CLAYS I. II. III. IV. V. VI. VII. VIII. Silica (SiO 2 ) 73 30 59 83 46 26 51.72 44 04 55 21 45 65 58 75 Alumina (A^Oa) . . 17 43 26 96 36 25 21 73 39 44 31 18 34 73 25 17 Ferric oxide (Fe 2 O 3 ). . . . Lime (CaO) 0.37 02 1.98 11 1.64 19 f FeO 17.87 06 FeO 0.94 07 J0.07 18 3.54 11 /FeO J2.19 71 Magnesia (MgO) 1 28 50 32 2 37 11 11 61 93 Potash (K a O) 2 99 94 1 69 } A Soda (Na 2 O) 17 24 85 f 4.58 0.72 0.23 5.75 3.53 Water (H 2 O) 4 68 9 56 13 54 J 13 02 8 11 Titanium oxide (TiO2) 87 1 05 Ignition 10.78 14.13 9.65 Sulphur trioxide (SOs) trace Organic and loss 23 Mang dioxide (MnO2) trace * For references see foot of table, p. 414. Hopkins, Ann. Rep. Pa. State College, 1897, p. 144. 414 CLAYS ANALYSES OF PENNSYLVANIA CLAYS. Continued IX. X. XI. XII. XIII. XIV. XV. XVI. Silica (SiO 2 ) Alumina (A^Oa). . .. 50.37 32 89 62.89 21 49 51.92 31 64 55.33 27 84 46.16 26 97 67.78 16 29 61.81 27 18 54.09 10 OK Ferric oxide (Fe 2 O 3 ). . { Lime (CaO) FeO 1.64 31 FeO 1.81 38 FeO 1.13 03 FeO 2.91 58 7.21 2 21 4.57 60 6.96 2 00 9.84 72 Magnesia (MffO) . 35 56 44 75 1 52 72 i 50 1 55 Potash (K 2 O) \ Soda (Na 2 O) } 0.29 2.52 0.40 3.91 3.24 2.00 3.31 Water (H 2 O) 7.58 13.49 7.49 11.22 6 34 2 20 Titanium oxide (TiO 2 ). . 1.03 13.76 1.82 1.16 1.14 JC0 2 0.74 1 0.78 8 98 Moisture 1.16 \ .45 / I. Mount Holly, white mixed clay, residual. II. Conshohqcken, parti-colored clay, residual. III. Brandywine Summit, residual. IV. Wilmarth Station, Mercer fire-clay. V. Fletcher mine, Elk County, Sharon fire-clay. VI. Somerset County, Mt. Savage fire-clay. VII. Sandyridge, Clearfield County, Brookville under-clay. VIII. Kittanning, Clarion coal under-clay. IX. Allegheny Furnace, ferriferous coal under-clay. X. New Brighton, Kittanning lower coal under-clay. XI. Salina, Kier Bros., Bolivar under-clay, flint-clay. XII. plastic clay. XIII. New Brighton, Mendenhall & Chamberlain, terrace-clay. XVI. Elverson & Sherwood, terrace-clay. XV. Allegheny, Allegheny Brick Co., analysis of brick. XVI. Butler, Butler Brick and Tile Co. Nos. I-XVI from U. S. Geol. Surv., Prof. Pap. 11. In other parts of the State many local deposits are employed for common and pressed brick. 1 References on Pennsylvania Clays 1. Ashburner, C. A., Report on the Brandywine Summit Kaolin Bed, Delaware County, Geol. Surv. Pa., Ann. Kept, for 1885, p. 592, 1886 2. Hice, R. R., The Clays of the Upper Ohio and Beaver River Region, Trans. Amer. Ceram. Soc., VII, Pt. II, p. 251, 1905. 3. Hopkins, T. C., Feldspars and Kaolins of Southeastern Pennsyl- vania, Franklin Inst. Jour., CXLVIII, p. 1, 1899. 4. Hopkins, T. C., Fire-clays, Mines and Minerals, XIX, p. 53, 1S9S. 5. Hopkins, T. C., Clays and Clay Industries of Pennsylvania, Pt. Ill; Clays of the Great Valley and South Mountain Areas, Pa. State Coll., Ann. Rept., 1899-1900, Appendix, 45 pp. 6. Hopkins, T. C., Clays and Clay Industries of Pennsylvania, Pt. II; Clays of Southeastern Pennsylvania (in part), Pa. State Coll., Ann. Rept., 1898-99, Appendix, 76 pp., 1900. 1 Many localities are noted in Prof. Paper 11, U. S. Geol. Surv., pp. 235-238. NORTH DAKOTA TO WYOMING 415 7. Hopkins, T. C., A Short Discussion of the Origin of the Coal- measure Fire-clays, Amer. Geol., XXVIII, p. 47, 1901; also Mines and Minerals, XXII, p. 296, 1902. 8. Hopkins, T. C., The White Clays of Southeastern Pennsylvania, Eng. and Min. Jour., LXX, p. 131, 1900. 9. Hopkins, T. C., Clays and Clay Industries of Pennsylvania, Pt. I; Clays of Western Pennsylvania (in part), Pa. State Coll., Ann. Rept. for 1897, Appendix, pp. 1-183, 1898. 10. Platt, F., Tests of Fire-brick, Pa. Geol. Surv., Rept. MM, p. 270. 11. Wright, G. F., The Age of the Philadelphia Brick-clay (Pennsyl- vania), Science, n. s., iii, p. 242, 1896. 12. Many analyses in Penn. Geol. Surv., Rept. MM, p. 257, et. seq. 13. Scattered notes in Reports of Sec. Penn. Geol. Surv., especially H4, H5, C4, C5. Rhode Island This State has very limited clay resources. Glacial clays are known at a few points around Narragansett Bay, but the principal occurrence is found in the town of Barrington, where the deposits of bluish-gray, sometimes sandy clays are worked for the manufacture of common brick. References on Rhode Island Clays 1. Woodworth, J. B., Shaler, N. S., Marbut, C. F., The Glacial Brick- clays of Rhode Island and Southeastern Massachusetts, U. S. Geol. Surv., 17th Ann. Rept., Pt. I, p. 557, 1896. South Carolina The northwestern part of the State is underlain by crystalline rocks, which extend to the edge of the coastal plain, the line of division passing a short distance southeast of Chesterfield and Camden, through Columbia and west of Aiken. Residual Clays These are to be sought for throughout the crystalline belt, and are usually impure. No kaolins are reported, but many of the white-burn- ing sedimentary clays of the coastal plain are incorrectly termed such. Coastal-plain Clays The formations of this area range from Potomac to Columbian in age, 1 and consist of clays, loams, and marls. Of these the Potomac barton. U. S. Geol. Surv.. Bull. 138. 416 CLAYS beds are by far the most important, outcropping in a belt from 4 to 5 miles wide, reaching from Augusta, Ga. ; through Aiken south of Lexing- ton and through Columbia to Camden and Cheraw. 1 This contains lenses of white clay which are worked at Aiken, Columbia, Sievern, and other points. The clay usually has to be washed and is sold chiefly to paper manufacturers. The Eocene deposits to the southeast of the Potomac area also carry clays of value. These deposits have recently been described in some detail by the South Carolina State geologist. 2 The chemical and physical properties of a number of these, taken from this report, are given in the accompanying table. ANALYSES OF SOUTH CAROLINA CLAYS I. II. III. IV. V. Silica (SiO 2 ) 44.23 43.18 44.11 45 69 42 30 Alumina, (AI>Oa) 38 98 37 36 38 19 37 47 36 94 Ferric oxide (Fe 2 O3) . 77 91 1 55 1 01 2 64 Lime (CaO) 03 14 trace 80 Magnesia (MgO) . . 07 50 trace 78 Potash (K 2 O) 26 2 00 50 08 Soda (Na 2 O) 55 53 69 Titanium oxide (TiO 2 ). 85 1 30 1 44 Ignition 13 58 14.32 13 37 13 98 15 43 VI. VII. VIII. IX. X. Silica (SiO 2 ) 79 40 53 19 54 40 52 46 52 41 Alumina (A1 2 O 3 ) Ferric oxide (Fe 2 O 3 ) Lime (CaO) 10.70 2.57 58 33.41 1.67 10 30.14 2.10 46 26.81 1.79 81 21.14 12.02 1 04 Magnesia (MgO) Potash (K 2 O) 1.05 1.21 0.25 66 0.54 87 0.33 0.56 95 Soda (Na->O) 0.23 12 12 1 12 Titanium oxide (TiO 2 ) Ignition 0.55 3.94 0.37 10.63 11.37 14 44 1.47 8.95 I. Immaculate Kaolin Co., Langley. II. Sterling Kaolin Co., near Warren ville. III. J. Brodie, 12 miles north of Aiken. IV. Imperial Kaolin Co., Sievern. V. Carolina Fire-brick Co., east of Killian. VI. A. W. Suder, Clarendon County. VII. Dents' Pond. VIII. A. B. Osborne, Union County. IX. R. Hamilton, Jonesville. X. Dr. Parker, Edgefield. 1 Barton, U. S. Geol. Surv., Bull. 138, p. 208. 2 E. Sloan, S. C. Geol. Surv., Series IV, Bull. I, 1904. PLATE XXXVII FIG. 1. Beds of Cretaceous fire-clay, southwest of Rapid City, S. Dak. (Aftei Todd, S. Dak. Geol. Surv., Brll. 3, p. 113, 1902.) General view of valley at Thurber, Tex., underlain by paving-brick shale. (Photo by H. Ries.) 417 NORTH DAKOTA TO WYOMING 419 South Dakota Very little information has been published regarding the clays and shales of this State, and it is difficult to discuss them by formations, as has been done with most of the other States. Aside from scattered references, the best and most recent informa- tion is that given by J. E. Todd, 1 from which most of the facts below are taken. Clays abound in many parts of the State, the most important deposits being found in the Cretaceous, which is largely composed of clay- or shale-deposits, but clays of the lower grades are not wanting in the Pleistocene formations. None appear to have been noted from the Carboniferous. It seems likely that, owing to the absence of local de- mand, distance from important markets, and in some cases remoteness of the deposits from railroads, the development of the beds, unless of high grade, will be necessarily slow. Kaolin, apparently derived from the weathering of a granite vein, has been reported from the vicinity of Custer, but much of it is said to be white-burning and of comparatively easy fusibility. The possibility of finding it in the Harvey Peak and Nigger Hill regions is also sug- gested. Fire-clays are found at three or four horizons in the Fuson formation of the Cretaceous, and are best developed in the vicinity of Rapid City, where they have been used for fire-brick manufacture. Similar beds occur at Hot Springs. Analyses of the Rapid City clays are given below. It is possible that fire-clays may underlie the lignite beds of the La ramie in the Cave Hills, but no search has been made for them. Potter's clays have not been definitely located, but there are many drab and gray plastic shales in the Fuson, Dakota, Pierre, and Laramie formations of the Cretaceous, which might answer for this purpose. Some of the Tertiary beds may also prove of value. These materials are distributed in all parts of the State, but east of the Missouri River the heavy covering of glacial deposits renders them more or less inaccessible, except where they have been exposed along the larger streams. Brick-clays have not been extensively worked. Professor Todd states that: "Over much of the State, particularly in close proximity to the principal towns, good brick-clay is not very accessible. This results from the fact that the settlements have been mainly made in the glacial region east of the Missouri and in the mountainous region of the Black 1 S. Dak. Geol. Surv., Bull. No. 3, pp. 101-107, 1902. 420 CLAYS Hills, where the clays are generally stony. ... In the regions between, where clay is more abundant, the population has been small and fuel scarce." Alluvium is used for common and pressed brick at Vermilion, Clay County, and the same products are made from similar materials at Rapid City, De Smet, Big Stone City, Lead City, etc. The glacial clays are usually unsatisfactory, because of the pebbles and concretions which they contain. ANALYSES OF SOUTH DAKOTA CLAYS I. II. III. Silica (SiO 2 ) '. 83.30 76.78 81.98 Alumina (A1 2 O 3 ) 12.30 14.43 13.08 Ferric oxide (Fe 2 O 3 ) 0.80 0.18 0.21 Lime (CaO) 1.30 2.18 1.46 Magnesia (MgO) trace 0.95 0.31 Alkalies (Na 2 O, K *) tra ce trace Loss on ignition 4 . 62 4 . 07 97.70 99.14 101.11 I. Rapid City. II East slope of ridge at Rapid City \ From S. Dak. Geol. Surv., Bull 3. III. Rockerville Hill, Rapid City. References on South Dakota Clays 1. Todd, J. E.,The Clay and Stone Resources of South Dakota, Eng. and Min. Jour., LXVI, p. 371, 1898. 2. Todd, J. E., The Mineral Resources of South Dakota, S. Dak. Geol. Surv., Bull. 3. Tenneesse Probably less is known regarding the clays of Tennessee than those of any other Eastern States. The geologic formations occurring in Tenn- essee include pre-Cambrian, Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Eocene, and Pleistocene. The pre-Cambrian rocks occur in small areas along the eastern border, while west of them, and folded into many narrow belts, lie rocks of Cam- bro-Silurian age. The Carboniferous extends from the eastern edge of the Cumberland Plateau westward to beyond the Tennessee River. A large area of Silurian is found in the central part of the State, while another is found along the Tennessee River in the southern half of the State. This is followed by a broad belt of Tertiary, which in turn is separated from the Mississippi River by a band of Pleistocene. NORTH DAKOTA TO WYOMING 421 Pre-Cambrian Clays No kaolin-deposits have been described from the crystalline area, of eastern Tennessee, although it is probable that some at least exist, as the author has seen samples of kaolin from this region. They will be of little commercial value, however, unless located fairly close to lines of transportation. Palaeozoic Residual Clays The rocks of the Palaeozoic formations yield residual clays from both limestones and shales. These are usually impure, although often tough and plastic, and are much used for brick- and tile-making. 1 Some of the highly siliceous clays derived from the Knox dolomite- are refractory, 2 and fire-brick are made from them near Cleveland. At Smith ville a white clay, derived from the slate in the upper part of the Fort Payne division, is used for pottery. Carboniferous There is but little recent reliable information relating to Carbon- iferous clays or shales in Tennessee. J. M. Safford, in his report on the Geology of Tennessee published in 1869, refers to the following occurrences of clay in the Carboniferous: Near the Cumberland Iron Works, in Stewart County, is a bed of fire-clay of Lower Carboniferous age; 3 another occurs 4 miles southwest of Cumberland City, in Stewart County; in the valley of Crow Creek, near Anderson station, the coal-measures at the margin of the table- land show a fire-clay 3 feet thick, 163 feet below the top of the cliff; 4 in Franklin County, near the Grundy County line, and 4 miles northwest of the track of Sewanee road at the old Logan bank, is a bed of clay 115 feet below the conglomerate; 5 near the lower end of the Battle Creek Valley, in Marion County, is a bed of fire-clay 2 feet thick; 5 miles south- east of Tracy City, and 1 J miles from Parmly Bank, a bed of clay under- lies the main Sewanee coal; 6 another occurs at the north end of Lookout 1 Many scattered references, but of very brief character, are to be found in the U. S. Geol. Surv., Geol. Atlas Folios, as follows: No. 21 (Pikeville); 16 (Knoxville); 59 (Bristol); 4 (Kingston); 8 (Sewanee); 2 (Ringgold); 53 (Standingstone); 40 Wartburg; 27 (Morristown); 22 (McMinn ville). 2 U. S. Geol. Surv., Geol. Atlas, Folio No. 2 (Ringgold). 3 Safford, Geology of Tennessee, p. 349. 4 Ibid., p. 372. 5 Ibid., p. 373. 8 Ibid., p. 380. 422 CLAYS Mountain, below the upper conglomerate. 1 Many of the under-clays of the coal-seams, according to Safford, are of refractory character. 2 Fire- clays, mostly undeveloped, are said to be associated with the coals in the areas covered by the following Geologic Atlas Folios: Standingstone, No. 53; Wartburg, No. 40 (used for pottery). 3 In the Kingston region the beds of clay which underlie the coals are no doubt refractory in many cases, but they are wholly undeveloped. 4 Tertiary In western Tennessee the plastic clay immediately underlying the Lafayette formation serves as the basis of a rather active stoneware and fire-brick industry. The section usually seen in the clay-pits involves red Lafayette sands, which seem to overlie unconformably the beds of stoneware-clay and white sands. One pottery, located at Grand Junction, used clay from the various pits of the vicinity. The clay varies in quality. In the pits of the Irwin Clay and Sand Company, 1J miles east of the station, along the railroad, the section is : 5 Feet. Inches. Red Sand White sand 8 White clay 8 Gray lignitic clay 8 10 White clay 20 The clay-deposits are very irregular, sometimes running together to form overlapping lenses in the white and yellow sand. Potteries are in operation at Mackenzie, Jackson, and Pinson, but at the latter locality the clay is also used for fire-brick and tiles. 6 The clay at Hico, 3 miles south of Mackenzie, is shipped to the pot- teries at Akron and East Liverpool, Ohio, and Louisville, Ky., while the clays from Hollow Rock are shipped to Nashville. 1 Safford, Geology of Tennessee, p. 385. 2 Ibid., p. 513. 3 See also Geologic Atlas U. S. Folio 33, Briceville; Folio 21, Pikeville; Folio 4 Kingston. 4 Idem, Folio 4, Kingston. 6 Eckel, U. S. Geol. Surv., Bull. 213, 1903, p. 382. 8 Idem. NORTH DAKOTA TO WYOMING 423 Three miles east of Currier are the pits of I. Mandle, where an area 60 by 50 feet has been opened up. The section is as follows: East Side. West Side. 2 feet clay Reddish sand 4 feet clay 15 feet light-gray clay 1 foot black clay (lignitic) 1 foot black clay 5 feet brown clay (ball-clay) 5 feet ball-clay The bases of the two sections are at the same level, hence the beds are very irregular. The light-gray clay is shipped to East Liverpool, Ohio, for saggers, and the ball-clay is known as Tennesssee ball-clay No. 3. Tests of samples of this clay, made by S. Geijsbeek, show that it leaves 10 per cent residue on a 175-mesh sieve. Its rational com- position is: Per cent. Clay substance 91 . 35 Feldspar 2.70 Quartz 5 . 95 It will carry as much as 72 per cent of non-plastic material. Tha shrinkage at cone 1 is 12.5 per cent; at cone 2, 18 per cent. It burns- white at cone 1 and gray at cone 8, being vitrified at that temperature. This is located 5 miles from Paris, and the clay is shipped from Currier,, which is 3 miles from the mine. Tennessee ball-clay, No. 1, found in Henry County, shows the follow- ing rational analysis: Per cent. Clay substance 86 . 20 Feldspar 2.70 Quartz 11.10 It carries 60 per cent non-plastic material to the mixture. The total fire-shrinkage at cone 8 is 15 per cent, and at this temperature it burns to a cream-white color and dense body. Alluvial Clays Alluvial clays are found in many of the river valleys, and in most cases are the wash from the residual clays of surrounding areas. They often underlie the river terraces. These terrace-clays are used in the Maynardville area. 1 Others are common in the region around Morris- 1 See Geologic Atlas U. S. Folio 75, Maynardville. 424 CLAYS iown, 1 especially in the low grounds of the Lick Creek, Nolichucky, and French Broad valleys. The following analyses of Tennessee clays have been gathered from different sources; ANALYSES OF TENNESSEE CLAYS Locality. Si0 2 . A1 2 3 . Fe 2 3 . CaO. MgO. Alk. H 2 O. Mois- ture. MnO. Remarks. 45 06 30 03 4 50 4 70 4 80 10 1 Crossley, analyses of Powdes Station. 68 35 12.96 6.44 0.23 1 2 14 7 8 0.9 clays J. W. Slocum, anal Chattanooga. . . 68 96 20.42 1.84 0.16 0.33 2.18 6.50 trace Tennessee Paving- brick Co. Hobbins 70.57115.19 7.97 0.78 0.32 2.80 Clay-worker, Dec., 1 1893 References on Tennessee Clays 1. Eckel, E. C., Stoneware and Brick-clays of Western Tennessee and Northwestern Mississippi, U. S. Geol. Surv., Bull. 213, p. 382, 1903. 2. Ries, H., The Clays of the United States East of the Mississippi Hiver, U. S. Geol. Surv., Prof. Pap. 11, 1903. Texas Deposits of clay or shale are scattered over all parts of Texas, but only those in the eastern part of the State have been systematically investigated. Indeed, it is not likely that those occurring in the western part will be developed to any extent for some time, owing to the sparsely settled character of the country and lack of transportation. The annual reports of the First Geological Survey contain scattered references to clay-deposits, but few tests. In 1903 the University Mineral Survey undertook an examination of those deposits lying east of the 99th meridian, and the results of this work have appeared in condensed form. 2 The following remarks, unless otherwise stated, deal with the area mentioned. The map, Fig. 63, shows the location of nearly all the deposits examined, their relation to the geology of the State, and the type of clay found at each locality. From this map it will be seen that the clay-deposits found within the area under discussion range from Carboniferous to Pleistocene in age, the older deposits being found in the northwestern 1 Geologic Atlas U. S., Folio 27, Morristown. 2 Amer. Inst. Min. Eng., Bimon. Bull., 1906. NORTH DAKOTA TO WYOMING 425 part of the area, while those of the Cretaceous and Tertiary lie. to the east, southeast, and south. The Pleistocene clays are found in part in LEGEND ?J LOWER CRETACEOUS EXPLANATION OF CLAY SYMBOLS + SLIP CLAY FIRECLAY STONEWARE COAL MEASURES X O A A RED AND BROWN CALCAREOUS SANDY PAVIN6 BRICK fcj^VSSj APPROXIMATE SCALE PRE-CARBONIFEROuS 30 60 90 120 MILES FTG. 63. Map of eastern Texas, showing distribution of clay-bearing formations. (Compiled from various survey reports.) a belt along the coast, and in part along many of the larger rivers, where they often underlie extensive terraces. 426 CLAYS Carboniferous Clays The Carboniferous rocks of northern Texas outcrop in a broad belt extending from the south side of the Colorado River Valley, between Lampasas and Concho counties, northward as far as the Red River in Montague County. This belt is about 250 miles long and averages about 45 miles in width. The rocks consist of a succession of shales and sandstones, together with occasional beds of limestone and coal, showing a gentle west and northwest dip of a few feet per mile. The entire series is subdivided into five groups (Ref. 2). Scattered through these are a number of beds of shale of excellent quality, some of which are asso- ciated with the coal-seams and could be mined in connection with them, while others outcrop on the surface (PI. XXXVII, Fig. 1), where they are easily accessible for working. These shales have been worked at only three localities, namely, Tlmr- ber, Millsap, and Weatherf ord, and are used for dry-pressed brick, stiff-mud paving-brick, and for pottery. Other good deposits are known to occur at Graham, Bridgeport, and Cisco. None of these, as far as known, are of refractory character. Some, as might be expected from their close association with coal-seams, are quite carbonaceous, and therefore of less value, because of the trouble they would cause in burning. The uniformity of the Carboniferous shale-beds is much greater than that of the Tertiary clays, and they moreover extend over greater areas. Cretaceous Clays Lower Cretaceous. The formations of this age occupy an area to the east and south of the Carboniferous beds. They are not utilized, nor do they appear to contain any deposits of use for anything better than common brick. They can therefore be passed over. Near Leaky, Edwards County, Texas, there occur some most curious deposits of a white clay, which has usually been referred to as kaolin. 1 The material is a whitish clay, with pink and purplish mottlings, which forms vein- like deposits in the Edwards limestone. Scattered through it are crys- talline masses of aragonite(?). Owing to the condition of the workings it is difficult to determine its exact relations to the surrounding limestone. As the deposits are of small extent and 40 miles from the railroad their commercial value is doubtful. Upper Cretaceous. This division of the Cretaceous carries a number of important clay-deposits, some of which are of great extent, but unfortunately are not the most valuable clay-beds in the State. 1 First Geol. Surv. of Texas, 2d Ann. Kept,, p. li, 1891. NORTH DAKOTA TO WYOMING 427 The Upper Cretaceous rocks extend across Texas in a broad belt from the Red River north of Sherman down to Eagle Pass, which lies about the middle of the band. Fort Worth is on the western edge and Austin towards the southeastern border. A second belt extends along the Red River, with narrowing width, until it passes out of the State in the northeastern corner. Since the dip is to the southeast, the older beds are found along the western edge of the belt, and the higher or younger ones on the east where they pass below -the Tertiary strata. Owing to the dissimilarity of the several numbers of this group, it becomes neces- sary to refer to them individually, beginning with the oldest. Woodbine formation. This consists of a series of sandstones, clays, and clayey sands, often containing leaf impressions and lignite. While the clay -beds are usually sandy or even bituminous, they become locally pure enough, as at Denton, to be utilized for clay-products, although even here the beds are rarely of great extent and usually interbedded with sands. The clays, which are worked at both Denton and Lloyd, closely resemble the stoneware-clays of the Tertiary beds to the southeast. They are mostly of very plastic, semi-refractory, buff- burning character and are utilized for both common stoneware and pressed brick. Eagle Ford formation. This includes a series of bituminous clay- shales, which in places contain thin limestone beds. It is one of the most extensive and thickest clay-bearing formations in the entire State of Texas, and occupies a rather long narrow belt, as shown in Fig. 63. While the Eagle Ford clay is of great thickness and well located for working, it contains about all the undesirable elements that a clay might have, namely, concretions, limestone pebbles, gypsum lumps, and even pyrite. Moreover, its bituminous character, as well as extreme tough- ness, causes great trouble in its manipulation, and practically forces the clay-worker to mold it by one method, the dry-press process, other means yielding a brick of too dense character to permit the carbon in the clay to burn off. The clay is red-burning, and extensively used for bricks around Paris, Sherman, Dallas, and Waco. Taylor-Navarro marls, overlying the Eagle Ford stratigraphically but separated from it by the Austin Chalk, form an extensive belt of clay, which parallels that of the Eagle Ford formation. The beds are marly clays, and in their general physical and chemical properties bear a close resemblance to the Eagle Ford beds. The Taylor marls are not clearly distinguishable from the Navarro marls, which outcrop to the southeast of them and resemble them closely, and for this reason the two are included under a single head. 428 CLAYS The Taylor-Navarro marls are all plastic, sometimes glauconitic, red-burning clays, and are worked for dry-press brick at Cooper, Green- ville, Corsicana, Taylor, and Ferris. At Eagle Pass, which lies outside the east and central Texas area studied, the Eagle Pass formation, which occurs at the top of the Upper Cretaceous, contains shales associated with the coals, and while some of these at least are probably adapted to the manufacture of clay-products, no tests of them are available. Tertiary Clays The clays found in the Tertiary formations include the most import- ant ones in eastern Texas, but, owing to the lenticular character of the beds and the enveloping deposits of sand with which they are frequently associated, prospecting for them is often rendered more or less difficult. From the wide distribution of the deposits (Fig. 63) it would appear that in certain belts of the Territory at least, as mentioned below, clays are to be sought for with excellent chances of success. In Webb County, west of Laredo in southern Texas, shales are found associated with the Eocene coals, and some of those obtained from the mines at Cannel are weathered and then shipped to Laredo for making dry-pressed brick. The other Tertiary beds of eastern Texas consist largely of uncon- solidated materials which range from coarse gravels to very fine clay, but containing occasional beds of sandstone, limestone, and lignite. Several members are recognized, namely, Will's Point, Lignitic, Marine, Yegua, Fayette, and Frio. Of these only the Lignitic and Marine are of importance. Lignitic. These beds outcrop in a long but irregular belt (Fig. 63), and contain the following types: 1. Beds of plastic, buff-burning, semi-refractory clay associated with the lignite deposits; they are well adapted to the manufacture of pressed brick. 2. Red-burning, plastic, gritty clays, overlying the lignites, and worked at Rockdale for dry-pressed brick. 3. Red-burning, tough, shaly clay, occurring at New Boston and Sulphur Springs. 4. A widely distributed series of grayish, highly plastic clays of refractory or semi-refractory character, and used for stoneware, fire- brick, etc. The following analyses p. (431) represent groups I, II, III. PLATE XXXVIII F:G. 1. Bank of sewer-pipe clay in Lignitic (Tertiary) formation, Saspamco, Texas. Shows electric system of haulage. (Photo by H. Ries.) FIG. 2. Pit in Beaumont clay, Houston, Tex. The walls of the pit are a very sandy clay underlying the other. (Photo by H. Ries.) 429 NORTH DAKOTA TO WYOMING 431 ANALYSES OF TERTIARY CLAY TYPES I- II. III. Silica (SiO 2 ) 69.33 72.99 70.65 Alumina (A1 2 O 3 ) 19.38 14.70 18.14 Ferric oxide (Fe 2 O 8 ) 1 . 06 4.5 . 82 Lime (CaO) 0.86 0.6 0.339 Magnesia (MgO) 0.86 0.3 0.628 Potash (K 2 O) trace 1.5 0.41 Soda (Na 2 O) 0.08 0.7 0.55 Titanic acid (TiO 2 ) 1.40 1.00 1.14 Water (H 2 O) 5.49 4.20 6.18 Stoneware is made from these clays at Elmendorff, Athens, etc.; fire-bricks at Athens and Sulphur Springs; sewer-pipe at Saspamco, and pressed brick at Elgin, Athens, Malakoff, etc. Marine beds. These are usually of sandy or glauconitic character, but here and there carry clay-deposits of some economic value, and adapted to making buff brick and stoneware. They are worked at Nacogdoches, Henderson, and Rusk. Pleistocene This formation includes clays of several types. They form a rather broad belt along the Gulf Coast (Fig. 63), where they are mostly of sandy character, . the Beaumont clays worked for brick around Beau- mont and Houston being the most notable exception. These are tough, plastic, brown, blue, and yellow clays, carrying irregularly distributed nodules of limestone and underlying a broken belt extending from Cal- houn County to Jefferson County. They are all red-burning, and used chiefly for common brick and to a lesser extent for dry-press brick. A second important type includes the river silts found underlying the terraces along many of the large rivers, such as the Rio Grande, Colorado, Neches, etc. These clays are always silty or sandy and highly calcareous, the lime carbonate being present as concretions, lumps, shells, or in a finely divided condition, and forming at times over 50 per cent of the material without apparently diminishing its plasticity. They are especially well seen and extensively worked at Austin and Laredo. Though chiefly used for common brick, these clays have also been worked for pressed brick, and in a few localities, as near San Antonio, they are of the proper character for employment as a slip for stoneware. For practical purposes the clays found within the area just discussed can be divided into the following groups: I. Fire-clays; II. Stoneware- clays; HI. Brick-clays; (a) Buff-burning, non-calcareous; (6) Red and brown-burning; (c) Calcareous; (d) Sandy; IV. Paving-brick clays; 432 CLAYS V. Slip-clays. Their distribution is shown on the map Fig. 63 and a few representative analyses are given below. ANALYSES OF TEXAS CLAYS I. II. III. IV. V. VI. VII. VIII. Silica (SiO 2 ) 63 07 63.43 45 44 55.10 49.45 73 00 72 9 64 84 Alumina (Al 2 Oa) 19.43 23.42 40.30 23.80 17.11 15.79 14.7 22 44 Ferric oxide (Fe 2 O 3 ). . . . Lime (CaO) Magnesia (MgO) Potash (K 2 O) Soda (Na 2 O) Titanic acid (TiO 2 ). . . . Water (H 2 O) 4.75 1.32 0.50 1.47 6 90 1.15 0.45 1,23 0.07 0.26 1.13 7 00 0.54 trace trace trace 0.38 trace 13 29 3.51 3.28 1.24 0.50 0.21 1.05 6 00 3.45 12.67 1.77 0.13 0.21 0.70 4 84 0.63 1.29 1.53 0.10 0.16 0.43 5 76 4.5 0.6 0.3 1.5 0.7 1.0 4 2 0.80 trace 0.74 0.12 0.71 1.40 6 42 Sulphur trioxide (SO 3 ).. Organic matter 0.15 40 3.37 2.00 Carbon dioxide (CC>2) 1.75 7.10 Total 99 09 100.54 99.95 99.81 99.43 98.69 99.5 99 47 IX. X. XI. XII. XIII. XIV. XV. Silica (SiO 2 ) 74 04 66 01 57 01 77 75 49 40 90 00 53 6 Alumina (Al 2 Os) . 15 15 18 82 11 85 11 04 17 90 4 60 9 Ferric oxide (Fe 2 Os). 50 6 33 3 02 3 K 4 50 1 44 2 6 Lime (CaO) 50 55 9 56 84 9 50 10 17 8 Magnesia (MgO) 27 1 88 1 20 0.38 1.8S 10 1 2 Potash (K 2 O) 42 16 0.75 trace 1 8 Soda (Na 2 O) 1 12 08 2 01 trace trace trace Titanic acid (TiO 2 ) 1.31 95 1 13 1.23 1 05 70 8 Water (H 2 O) 6 00 4 80 4 00 3.24 4.58 3 04 1 Sulphur trioxide (SOs). . 0.51 Organic matter Carbon dioxide (CO 2 ). . . 8.00 9.55 11.6 Total 99.31 99.58 98.53 98.40 97.36 99 98 99 40 PHYSICAL TESTS OF TEXAS CLAYS I. II. III. VI. VIII. IX. Per cent Plasticity Average Air-shrin Cone 05 - Cone 1 Cone 5 Cone 9 Cone of f Color aft water required. . 25.3 good 333 7.7 5.6 3.58 6.3 0.10 23.1 good 202 9.6 5 2.02 44 low 159 6.2 5 32. 7f 10 20.47 13.7 10 7 33 high 487 12.4 4* '4*' 33 high 304 9.3 1 12.9 2.7 7.87 3.5 3.15 30.8 high 257 10.2 1.6 11.44 3.3 6.57 5.7 2.83 9.4 0.82 28 buff r -ensile strength, Ibs.per. sq.in. sage, per cent f Fire-shrinkage, per cent. . . . Absorption per cent ' Fire-shrinkage, per cent. . . . Absorption, per cent Fire-shrinkage per cent. Absorption per cent Fire-shrinkage per cent. . . vit'd 14.7 8 6 Absorption, per cent usion 5 red 14 buff 35 white 5 red 12 red er burning *Dry Pressed. NORTH DAKOTA TO WYOMING 433 PHYSICAL TEST.S OF TEXAS CLAYS Continued X. XI. XII. XIII. XIV. XV. Per cent water reumred 23.1 good 155 8.5 15.68 1.6 13.13 3 14.05 4.3 6.83 30 buff 37.4 high 154 11.6 5.33* 16.49 11.33* 5.77 23.1 good 303 9.4 0.3 10.52 0.3 9.39 0.4 7.29 23 high 316 9.3 0.4 6.63 0.8 4.43 5 red 25.4 low 77 4 -0.3 9.14 9.45 0.7 9.55 1.3 8.39 12 red 25.3 good 253 6.2 -4.7 i 23.49 7 5.95 Plasticity Average tensile strength, Ibs. per sq. in. Air shrinkage per cent fYmP n^ J Fire-shrinkage, per cent. . . * \ Absorption, per cent p 1 | Fire -shrinkage, per cent. . . . \ Absorption, per cent f i r / Fire-shrinkage, per cent. . . . \ Absorption, per cent P Q j Fire-shrinkage, per cent. . . . 1 Absorption, per cent Cone of fusion Color after burning 5 red V red 7 cream * Dry pressed. LOCALITIES OF PRECEDING ANALYSES No. Location. Age. Use. 1 1 hurber Erath County Coal-measures. . Paving-brick II. Top clay over lower coal, Minera, Webb County Cretaceous. . Un worked Ill Laky, Edwards County i ( i ( IV Dallas Dallas County Eagle- Ford-Creta- ceous. . . Brick V. VI. VII. VIII. IX. X. XI. Ferris, Ellis County S. E. of Lena, Fayette County Vogel mine, Rockdale, Milan County. Saspamco, Bexar County Athens, Henderson County New Boston, Bowie County .*. Alazan Creek, San Antonio, Bexar County Taylor marls Tertiary Lignitic-Tertiary n n t ( (( Tertiary '.'. Pleistocene ( t Un worked Brick Sewer-pipe Fire-brick Pressed brick Slip-clay XII Beaumont Jefferson County t < Pressed brick XIII Houston Harris County i * ( t XIV. XV Colmesneil, Tyler County Austin Travis County. . . ( t 1 ' ' ter- Common brick race-clay Common brick Nos. VII and XV, S. H. Wcrrell. analyst; the rest analyzed by O. H. Palm. References on Texas Clays 1. Adams, G. I., Oil- and Gas-fields of the Western Interior and Northern Texas Coal-measures, U. S. Geol. Surv., Bull. 184, pp. 37 to 47, 1901. 2. Drake, N. F., and Thompson, R. A., The Colorado Coal-field of Texas, 4th Ann. Kept., Tex. Geol. Surv., p. 357, 1893. 3. Hayes, C. W., and Kennedy, W., Oil-fields of the Texas Louisiana Gulf Coastal Plain, U. S. Geol. Surv., Bull. 212, pp. 15 to 32, 1903. 434 CLAYS 4. Hill, R. T., Geology and Geography of Black and Grand Prairies, U. S. Geol. Surv., 21st Ann. Kept., Pt. VII, p. 295, 1.901. 5. Kennedy, Wm., Texas Clays and Their Origin, Science, XXII, p. 297, 1893. 6. Penrose, R. A. F., Preliminary Report on the Geology of the Gulf-Tertiary of Texas, Tex. Geol. Surv., 1st Ann. Kept., p. 5, 1890. 7. Ries, H., The Clays of Eastern Texas, Trans. Amer. Inst. Min. Eng., Bimonthly BulL, 1906. 8. Taff, J. A., and Leverett, S., The Cretaceous Area North of the Colorado River, Tex. Geol. Surv., 4th Ann. Kept., p. 241, 1893. 9. Vaughan, T. W., Reconnaissance in the Rio Grande Coal-fields of Texas, U. S. Geol. Surv., BulL 164, 1900. 10. See also scattered references in the first to fourth annual reports of Texas Geological Survey, especially under county descriptions. Utah The writer has not seen any published information of value regard- ing the clay resources of this State. Common brick-clays are to be found at many points, and at the St. Louis Exposition there were exhibited samples of fire-bricks and crucibles made by the Utah Fire-clay Com- pany of Salt Lake City, while kaolin samples were shown from Millard County and Lehi. Virginia Residual Clays The crystalline rocks, consisting of granite, gneisses, and schists with some intrusives extend across ths State from north to south in a belt of increasing width, whose western boundary follows approximately a line running from Harper's Ferry southwestward, passing a few miles east of Front Royal. The eastern edge coincides approximately with the "Fall-line." Residual clays are not uncommon throughout this area, but they are usually impure; and adapted to little else but common brick. Kaolin is found in Henry and Patrick counties and some promising deposits have been developed in the former (PL XXXIX, Figs. 1 and 2). The Cambro-Silurian shales and limestones yield an abundance of impure residual clay, which is well adapted to brick manufacture. These clays, which are likely to be used throughout the Great Valley region, are all red-burning so far as known. PLATE XXXIX FIG. 1. View of kaolin-pit near Oak Level, Va. clearly contrasted to the white kaolin. The ferruginous clay walls are (Photo by H. Ries.) FIG. 2. General view of kaolin washing plant near Oak Level, Va. The crude clay is washed down the trough from the mine. (Photo by H. Ries.) 435 NORTH DAKOTA TO WYOMING 437 Carboniferous Though containing important beds of coal, the clayey members of this formation in southwestern Virginia have received but little notice, but it seems highly probable that they contain shale-deposits of sufficient value for making vitrified wares, and even now they are successfully worked at one locality, namely, Millhall. Triassic The Triassic shales associated with the coals of the Richmond basin have not proven of any value for the manufacture of clay-products. Tertiary The Tertiary and Pleistocene formations of the coastal-plain area have received the most attention by clay-workers in the State. The Tertiary beds consist of a series of clays, sands, marls, sand- stones, and greensands, which dip gently to the southeast, and are over- lain by later formations. The clay-deposits, which are of Miocene age and usually of lenticular character, are most abundant towards the northwestern border of the coastal plain, and have been noted near Richmond, Bermuda Hundred, Curie's Neck, etc. They are red-burning and often yield a vitrified body, but, although to be ranked as among the best clays in the State, they are little used. Some promising Eocene clays are known between Fredericksburg and Stafford Court House. The diatomaceous earths form an extended series of deposits along the Rappahannock River and around Richmond, but they are worked at but one locality, namely, Wilmont (PL XL, Fig. 1), to make boiler- setting brick and fireproofing. Pleistocene Pleistocene clays occur at a number of points, but the deposits are, with few exceptions, of shallow character and the material red-burning. The clays are extensively dug around Richmond for common-brick manu- facture, as well as at Norfolk, Suffolk, Petersburg, and several points along the James River (PL XL, Fig. 2). A semi-refractory Pleistocene clay is found near Wilmont on the Rappahannock. Around Alexandria the Columbian loams are worked on a large scale for the manufacture of common and pressed brick, which supply the Washington market. The following table contains the analyses and physical tests of some of the coastal-plain clays : 438 CLAYS OcO^iOcOt^-OS 00 t>- ro co O O OS frj oo c^^ooupoci^r^co 3 rH COO OO TH O OOO (N rH OS OS Ot^ rH rH ^ X OS ?C t^ rH rH Tf 00 OS ^ OS OS^T^OC I^t-rHCOiC . ^o. <3^ rvj feC rH r _i'~' r 4" ^ os Os) 3.75 0.60 3.41 5.62 37 2 82 Ferrous oxide (FeO) 3.45 3.53 3.7 1.26 1.00 96 Lime (CaO) . 0.46 0.59 0.60 0.61 0.33 39 Magnesia (MgO) 1.44 1.23 0.88 1.55 0.10 1 44 Soda (Na.,O) 1 0.42 0.03 29 08 50 Potash (K 2 O) 3.14 3.79 3.57 3.28 48 3 90 Titanic oxide (TiO->) 0.84 0.82 0.83 0.72 1 11 63 Moisture . 0.38 0.54 0.86 1.27 99 1 39 Phosphoric acid (PoO r ) 11 46 14 21 trace trace Sulphur trioxide (SOs) Ignition 7.25 5.26 7.27 6.18 7.13 5 48 Total 99.91 99.79 100 . 57 100 47 100 11 100 01 * For references see foot of table, p. 450. 450 CLAYS AXALYSES OF WEST VIRGINIA CLAYS Continued XIII. XIV. XV. XVI. XVII. Silica (SiO->) 55.63 58.28 50.80 68.42 63.88 Alumina (Al-iOs) 20.76 21.26 19.47 16.38 17.18 Ferric oxide (Fe-)Oa) 3.94 1.87 8.83 3.05 5.72 Ferrous oxide (FeO) 4 17 3.37 1.9 1.89 50 Lime (CaO) . . 0.86 0.78 1.51 0.94 " 16 Magnesia (MgO) 1.70 1.35 1.74 1.8 1 3 Soda (NaoO) 0.34 0.39 0.89 0.63 0.6 Potash (KoO) 2.97 2.87 2.24 0.93 2.29 Titanic oxide (TiOo) 98 86 68 88 87 1.03 1.30 0.6 1.76 Phosphoric acid (P'-Ot) 0.23 0.39 0.2 08 36 Sulphur trioxide (SOs) trace 6.98 6.84 11.37 4 58 5 60 Total 99.59 99.56 100 . 23 99.58 100 22 PHYSICAL TESTS OF WEST VIRGINIA CLAYS I. II. III. V. VI. VII. VIII. Water required per cent. . . 28 25 2 1 28 24 6 Tensile strength, Ibs. per sq. in. . Air-shrinkage, per cent. . Cone of incipient vitrification . . . 122 4 1 34 3.5 32 3 58 4 40 4 1 46 4 1 Cone of vitrification 5 5 1 26 5 ,5 Cone of viscosity 5 + 30 + 28 Fire-shrinkage per cent. 11 10 2 6 6 Color when burned red red buff buff brown brown IX. X. XI. XII. XIII. XIV. XVII. Water required, per cent Tensile strength, Ibs. per sq. in. . Air-shrinkage, per cent 26 40 3 5 27 36 I 4 20 75 to 90 4 24 89 to 100 4 22 | 109 4 5 25 78 4 5 32 140 Q Cone of incipient vitrification . . . 1 1 1 1 1 Cone of vitrification. 5 5 30 K. 1 K K Cone of viscosity 5 Fire-shrinkage, per cent Color when burned 10 red 8 red buff 6 red 2 red red 12 red II. III. IV. V. VI. VII. VIII. IX. x x !l: XIV. XV. XVI. XVII. Nos Surv. Residual limestone clay, Charlestown, Silurian. Residual shale-clay, Martinsburg, Silurian. Shale, Elkins, Randolph County, Hamilton. Shale, Decker's Creek near Morgantown, Mauch Chunk. Fire-clay, Piedmont, Mount Savage clay. Flint-clay "* Gray shale Blue shale Shale Clifton Mine, New Cumberland, Middle Kittanning. m i n e, New Cumberland, Lower Kittanning. % ay f Thorn t". in Conemaugh series, Mahoning coal horizon. Shale, Morgantown, Pittsburg red shale. Blue shale, Huntington, Conemaugh series. Mixture of Spilman shales, Spilman, Conemaugh series. Parkersburg, Dunkard shale. River-clay, Parkersburg, Pleistocene. I-XVII selected by Dr. Grimsley as representative ones, from Vol. Ill, W. Va. Geol. NORTH DAKOTA TO WYOMING 451 References on West Virginia Clays 1. Grimsley, G. P., The Clays of West Virginia, W. Va. Geol. Surv., Ill, 1906. 2. White, I. C., Correlation Papers, Carboniferous, U. S. Geol. Surv., Bull. 65. LEGEND K\\\\] Lacustrine and glacial clays. | | Estuarin* and glacial cloys. II I I I | MI Loess Residutfl and .stream clays irTtlTTTI mostly red burning. II HI | I || Glacial and stream clays II III I I II mostly red burning. 1 Residual clays red burning. HH Cincinnati Shales mostly cream burning. FIG. 64. Map of Wisconsin, showing distribution of clay-bearing formations. (Adapted from Buckley, Wis. Geol. and Nat. Hist. Surv., Bull. VII, 1901.) Wisconsin In this State the clay-deposits belong to formations representing somewhat the two extremes of the geological column. Those belonging 452 CLAYS to the older formations are nearly all of residual character, while those belonging to the sedimentary deposits are of very recent geologic age. It seems best, therefore, to divide them into two groups, namely, the residual clays and the sedimentary clays. Residual Clays These have been derived from a variety of rocks, including granites and gneisses, greenstones and allied volcanic rocks, limestone and dolomite, sandstone and shale. Pre-Cambrian residuals. These occur at a number of points in the central part of the State, in Eau Claire, Jackson, Wood, Portage, Marathon, and Clark counties. They are usually gritty clays which have been formed by the decomposition of schists or gneisses, and vary in depth from perhaps 2 or 3 feet to as much as 40. Although some- times reaching nearly to the surface, they are at other times covered by a bed of Potsdam sandstone which has apparently protected them from erosion. Deposits of this occur in the vicinity of Grand Rapids, Eau Claire, Black River Falls, Stevens Point, Abbotsford, etc. They are nearly all red-burning, and while refractory ones low in iron are known to occur, the deposits of them so far as found are rather small. Their main use is for the manufacture of common brick, but at Halcyon near Black River Falls the material has been found adapted to the manufacture of dry-press brick and even paving-brick. Potsdam shales. In a few localities there occurs at the base of the Potsdam a tough plastic clay which has been derived by the weathering of a siliceous shale. This material has been exposed near Merrillan, Durand, and other points, but has not been utilized to any extent for the manufacture of clay-products. Ordovician limestone residuals. Within the driftless area of Wis- consin the cherty galena limestone is found weathered in its upper portion to sandy residual clay containing many flint fragments scattered through it. Up to the present time it has not been used for the manu- facture of common brick to which it is chiefly adapted, nor is there any likelihood of its ever becoming of any importance. Sedimentary Clays Hudson River shale. This shale forms a narrow belt in the eastern part of Wisconsin which extends from the southern boundary of the State up to Green Bay. In this State it is not very well adapted to the manufacture of brick, but on weathering breaks down rather easily to a yellow clay which has very fair plasticity and is usually red-burning. PLATE XLIII FIG. 1. Pit of estuarine clay, Fort Atkinson, Wis. The flat area is underlain by clay, while the surrounding low hills are of sand. (Photo by H. Ries.) FIG. 2. Pleistocene brick-clay, Milwaukee, Wis. The mound in middle of pit is sand and is left standing. (Photo by H. Ries.) 453 NORTH DAKOTA TO WYOMING 455 The material has been worked at Stockbridge, Calumet County, and at Oakfield, Fond du Lac County, for the manufacture of brick. At the former locality a mixture of the weathered shale and the partly weathered material is used with excellent results. A second area of these shales is known to occur in Lafayette County, to the east and southeast of Platt- ville, where the material is to be found around the base of the Mound Hills so prominent in that region. It weathers to a yellow clay of high plasticity and one which burns to a very hard body of excellent red color. Pleistocene Clays The Pleistocene clays of Wisconsin have been grouped by Buckley (Ref. 1) as follows: 1. Lacustrine deposits; 2. Stream deposits; 3. Estuarine deposits, and 4. Glacial clays. Lacustrine deposits. These respresent a very extensive type, and were laid down during the former inland extension of the Great Lakes, so that they are now often found some distance from the present lake shore. Thus, around Racine, they occur 18 miles inland. They are also found at Sheboygan, over parts of Door County, and in parts of Manitowoc, Calumet, and Fond du Lac counties; much of Green Lake, Waushara, and Waupaca counties too are underlain by them, while to the north they are found as far as Shawano. These lacustrine deposits, adjoining Lake Michigan on the east and Lake Superior on the north, are an important source of cream-burning brick-clays, and the beds often exceed 100 feet in thickness. Sometimes the upper few feet burn red, owing to the fact that the carbonate of lime has been leached out of them. Around Green Bay, Manitowoc, and Racine these clays are much used for the manufacture of common, pressed brick and drain-tile, but they are of little value for anything else. Estuarine clays. These include all the clays of eastern Wisconsin which are underlain by limestone and have been modified by glacial action. They were formed at the same time and in association with the lake- deposits, but differ from them usually in showing a more variable lime- content and burn hard and dense at a lower temperature. Thus, for example, the lake-clays apparently have to be burned up to cone 3, while the estuarine clays can be burned at cone 05 to 1. These estuarine deposits are found along the Fox, Wolf, Rock, Wisconsin, Eau Claire, Chippewa, Black, Red, Cedar, and many other rivers in the eastern, north- eastern, and southern parts of the State. Glacial clays. These have been deposited over a large part of the northern half of the State and include a series of deposits of uncertain extent and variable character and thickness. In some places they 456 CLAYS consist of bowlder-clay and are therefore of a very stony character, while at others they may represent deposits that have been formed in temporary lakes during the last glacial epoch. Those worked at Athens belong to the former type, and those worked at Menomonie and forming the basis of an extensive local industry belong to the latter type. Under this heading we should perhaps also include the silty loess-clays which cover a large area in the western part of the State and are worked at Platteville, Menomonie, La Crosse, and other places. They represent a good char- acter of clay, which in many instances is used only for common brick, but is also adapted to the manufacture of dry-press brick. ANALYSES OF WISCONSIN CLAYS I. II. III. IV. V. Silica (SiO 2 ) 64.50 62.59 35.93 48.39 44.18 Alumina (Al 2 Oa) 26.20 17.42 11.75 12.50 10.83 Ferric oxide (Fe 2 Os) 0.07 5.88 4.08 5.40 3.30 Lime (CaO) none 12 43 10 88 14 05 Magnesia (MgO). . 1.24 9 92 4 82 5 91 Potash (K 2 O) . . 0.31 8.08 2 46 3 90 3 10 Soda (Na 2 O) 0.52 1.24 68 70 Loss on ignition 8.90 4.15 22.06 13.02 17 34 Titanic acid (TiO 2 ) 0.30 30 0.43 30 Manganese oxide (MnO). . . . SO 3 trace 0.10 trace VI. VII. VIII. IX. X. Silica (SiO 2 ) . . . 40 17 31 90 71 77 65 44 69 86 Alumina (Al 2 Os). . . 9 14 8 74 13 74 13 51 13 55 Ferric oxide (FezOs). . . . 3 00 3 00 3 60 5.40 5.46 Lime (CaO) Magnesia (MgO) 14.49 8 34 17.06 10.63 1.23 1 17 2.95 2.20 0.71 1.43 Potash (K 2 O) 3 06 2 20 2 30 3 44 2 36 Soda (Na 2 O) 34 82 1 20 1 54 1 78 Loss on ignition 21 37 25 19 5 00 4 69 4 40 Titanic acid (TiO 2 ) Manganese oxide (MnO). . . . 0.35 0.09 0.25 0.19 0.45 trace 0.60 trace 0.77 trace LOCALITIES OF THE ABOVE No. Locality. Geological Age. Uses. I. Hersey. . Residual Not worked II. Merrillan Potsdam i ( (i III. Oakfield Hudson Common brick IV. Green Bay. . Pleistocene Br ck V. ( i (i n VI. Milwaukee (i i VII. Watertown 1 1 i VIII. Chippewa Falls Glacial i IX. Menomonie 1 1 Pressed brick X. Whittlesey e i Brick Nos. I-X from Wis. Geol. and Nat. Hist. Surv., Bull. 7, 1901. NORTH DAKOTA TO WYOMING' 457 References on Wisconsin Clays 1. Buckley, E. R., The Clays and Clay Industries of Wisconsin, Wis. Geol. and Nat. Hist. Surv., Bull. 7, Pt. I, 1901. 2. Chamberlain, T. C., Geol. of Wis., I, p. 669. 3. Irving, R. D., On the Kaolins of Wisconsin, Wis. Acad. Arts and Letters, Trans., 1876. 4. Irving, R. D., Geol. Wis., II, p. 630. 5. Irving, R. D., Mineral Resources of Wisconsin, Amer. Inst. Min. Eng., Trans., VIII, p. 478. 6. Ries, H., Clays of Wisconsin, Mining World, Mar. 25, 1905. See also forthcoming bulletin, Wis. Geol. and Nat. Hist. Surv. 7. Sweet, E. T., Milwaukee Clay, Amer. Jour. Sci., iii, XXIV, p. 154. Wyoming Little is known regarding Wyoming clays, owing largely to their lack of development. W. C. Knight says: 1 " So far as is known, the clays of Wyoming that have any commercial importance occur in beds of the sedimentary rocks. These clay-beds are most numerous in the Jurassic and Cretaceous formations, but are found to some extent in the Tertiary." The formations containing these clays are found flanking nearly all of the mountain-ranges in the State, and the clay-beds vary in thickness from 4 to 40 ft. Bowlder-clays, that are so common in the East, are not known and will be found only in small and isolated localities. With the exception of the manufacture of common brick no attention has been paid to any of the clay industries, and all of the fire-clay goods used in Wyoming are manufactured in Colorado, while pressed brick are shipped in from various points. This condition is largely due to the limited popu- lation of the State, and the slight demand for clay-products. The com- mon brick which are, as a rule, manufactured from loess, are very siliceous and fragile, although in a few places there is clay enough in the loess to make a medium-grade brick. Judging from the appearance of the clay- beds and their geological position, they will, when tested, prove equal to the Colorado beds. At Cambria, Weston County, the clays associated with the coals have been found adapted to the manufacture of dry-press brick. Bentonite. A peculiar variety of clay found in Wyoming and known as bentonite was first described by W. C. Knight under the name of 1 Eng. and Min. Jour., LXIV, p. 546, 1898. 458 CLAYS taylorite. 1 Finding that the latter name was preoccupied he proposed the name of bentonite for it 2 from its occurrence in the Benton forma- tion. The deposits in the northeastern part of the State, in the vicinity of Newcastle, were first described in detail by N. H. Darton. 3 Bentonite when fresh has a yellowish-green color, but assumes a light cream tint on exposure. It is fine-grained, soft, and absorbs three times its weight of water, accompanied by swelling. Its specific gravity is 2.18. Professor Knight pointed out its resemblance to the ehren- bergite of Germany, but it differs from it in containing less alkali. The soda reported in the analyses is, as a rule, found in the clay in thin seams as sodium sulphate. The following analyses were made at the Wyoming School of Mines. ANALYSES OF BENTONITE Peach Creek. Crook County. Weston County. Natrona County. Silica (SiO 2 ) 59 78 61 06 63 25 65 24 Alumina (A1 2 O 3 ). 15 10 17 12 17 62 15 88 Ferric oxide (Fe 2 O3) 2.40 3 17 3 70 3 12 Magnesia (MgO) 4 14 1 82 3 70 1 5.34 Lime (CaO) 0.73 2 69 4 12 Soda (Na 2 O) 20 Sulphur trioxide (SO 3 ) 80 1 53 Water (H 2 O) 16 26 9 17 Specific gravity . . . 2 18 2 132 The peculiarity of composition of this clay lies in its high combined water-content as compared with the alumina percentage. The clay, which occurs in the Benton group of the Cretaceous, has been found extensively in Wyoming in Crook, Johnson, Weston, Converse, Natrona, Carbon, Albany, and Laramie counties. More recently addi- tional deposits have been discovered 8 miles east of Frannie, and 5 miles north of Cowley, Wyoming. 4 The distribution of the Benton formation in Wyoming is shown in Fig. 65. Bentonite has been used in the manufacture of soap, as a packing for a special kind of horseshoe, as a diluent for certain powerful drugs sold in the powdered form, and as an adulterant of candy. x Eng. and Min. Jour.. LXI1I, p. 600, 1898. 2 Ibid., LXVI, p. 491. 8 Geologic Atlas, Folio No. 107, 1904. 4 U. S. Geol. Surv., Bull. 260, 562, 1905. NORTH DAKOTA TO WYOMING 459 References on Wyoming Clays 1. Darton, N. H., U. S. Geol. Surv., Geol. Atlas Folio 107, 1904. 2. Fisher, C. A., The Bentonite Deposits of Wyoming, U. S. Geol. Surv., Bull. 260, p. 559, 1905. 3. Knight, W. C., Bentonite, Eng. and Min. Jour., LXIV, p. 491, 1898. 4. Knight, W. C., Wyoming Clays and Building-stones, Eng. and Min. Jour., LXIV, p. 546, 1898. 5. Knight, W. C., Eng. and Min. Jour., LXIII, p. 600. 6. Knight, W. C., Mineral Resources of Wyoming, Wyo. Exper. Sta., Bull. 14, 1893. FIG. 65. Map of Benton formation in Wyoming. (After Fisher, U. S. Geol. Surv., Bull. 260.) CHAPTER VIII FULLERS' EARTH Properties FULLERS' earth is a peculiar type of clay, which has the power of absorbing greasy substances. In its appearance when dry it is often difficult to distinguish from ordinary clay, but when wet is often of lean character. The statement usually seen in print that it lacks plasticity and falls to pieces in water is misleading and of no value- When dried, fullers' earth often adheres strongly to the tongue, but so do some ordinary clays which have no clarifying powers. The color is also variable. The quantitative analysis shows that its common chief difference from ordinary clay lies in its relatively higher percentage of combined water, but a chemical analysis is of little value, and a practical test is necessary in order to determine its worth. An incorrect statement often seen in print is that fullers' earths contain a high magnesia-content. Dana 1 defines fullers' earth as including many kinds of "unctuous clays, gray to dark green in color, and being in part kaolin and in part smectite." It is placed by him with several clay-like minerals (all of them hydrous silicates), namely, smectite and malthacite, of not very definite chemical composition, but all having a high percentage of com- bined water. Smectite proper is defined as a "mountain-green, oil-green, or gray- green clay, from Cilly in Lower Styria." Malthacite is defined as occurring in thin lamina? or scales, and some- times massive, with the color white or yellowish. The original occur- rence is the result of disintegration in a basalt at Steindorfel, in Lausitz. Beraum, in Bohemia, is another locality. It is not quite clear on what evidence Dana proves fullers' earth to be a mixture of "kaolin" 1 System of Mineralogy, 1893, p. 695. 460 FULLERS' EARTH 461 (he probably meant kaolinite) and smectite, for the chemical analysis alone would not warrant this statement, and petrographic examina- tions (see below) afford little aid in this matter. Indeed none of the published analyses of fullers' earth show a composition at all similar to either smectite or malthacite, and what their mineral composition is has not been proven. Merrill 1 states that " the English earth, when examined under the microscope, consists of extremely irregular colored particles of a sili- ceous mineral which in its least altered state is colorless, but which in nearly every case has undergone a chloritic or talcose alteration, whereby the particles are converted into a faintly yellowish-green product. The grains are of all sizes up to .07 mm., but the larger portion of the material is made up of particles fairly uniform in size and about the dimensions mentioned. In addition to these are minute colorless fragments down to sizes .01 mm. and even smaller. The minute size of these colorless particles renders a determination of their mineral nature practically impossible, but the outline of the cleavage flakes is suggestive of a soda-lime feldspar." "The Gadsden County, Fla., earth under the microscope shows the same greenish, faintly doubly refracting particles as does the English, Intermixed with numerous angular particles of quartz." Up to within a few years ago nearly all of the fullers' earth used in the United States was imported from England, where large deposits of this material exist, but since that time deposits have been found in a number of States, including Florida, Georgia, Alabama, Arkansas, Colorado, New York, South Dakota, and California. Distribution in the United States But little has been published regarding the American fullers' earth occurrences. Georgia-Florida. Those of northern Florida and the adjoining parts of Georgia were first described by H. Ries 2 and later by T. W. Vaughan 3 and D. T. Day. 4 According to these writers extensive de- posits of fullers' earth are found in the southern part of Decatur County, Ga., and in Gadsden County, Fla., in the western portion of Leon County, Fla., and a few other points. 1 Guide to Study of Non-metallic Minerals, p. 337, 1901. 2 U. S. Geol. Surv., 17th Ann. Rept., Pt. Ill (ctd.), P- 877. 3 U. S. Geol. Surv., Min. Res., 1901, p. 922, 1903. 4 Jour. Frank. Inst., CL, 1900. 462 CLAYS According to Vaughan's 1 determinations the stratigraphic position of the fullers' earth, excepting that from Alachua County, is Upper Oligocene. The sections seen in the pits vary at the different localities, but the following might serve as representative. Feet. Overburden (Sandy clay) 5 to 20 Fullers' earth 6 to 10 Sandstone with crystals and lumps of calcite or aragonite ... 3 to 4 Fullers' earth 5 to 6 Most of the earth when dry is of whitish color, flaky, brittle, and adheres strongly to the tongue. Analyses are given below, and a view of one of the pits is shown in PL XLIV, Fig. 1. South Carolina, North Carolina, and Virginia. Earth of very fair quality has been obtained from near Sumter, South Carolina, and deposits are also known in North Carolina and Virginia, but the earth from the last two is more or less sandy. 2 New York. In this State deposits of fullers' earth occur at McCon- nellsville, 12 miles north of Rome. The material is a fine-grained, dense, Quaternary clay in layers 2 to 8 inches thick, interbedded with layers of sand of similar thickness. This earth has been used only for cleansing woolen goods. 3 Arkansas. Deposits of earth are worked in Arkansas, and analyses of some fullers' earth from that State are given in the table below. South Dakota. In South Dakota 4 the first deposits were located and opened up five miles southeast of Fairburn, Custer County, the section showing: Feet. Micaceous sandy clay 6 Fullers' earth 9 Micaceous sandstone The earth is a yellowish gritty clay, with a somewhat nudular structure. Other deposits are known near Argyle and Minnekata. The deposits are of Jurassic age. California. Fullers' earth is said to occur in Kern and San Ber- nardino counties, but only that in the former appears to have been 1 L. c., p. 923. 2 Day, 1. c., p. 591. , 3 N. Y. State Mus., Bull. 35, 850, 1900. 4 H. Rig, Amer. Inst. Min. Eng., Trans., XXVII, p. 333, 1898. PLATE XLIV FIG. 1. Fullers'-earth pit, Quincy, Fla. Behind it are the drying-floors. (Photo by H. Ries.) FIG. 2. Outcrop of fullers' earth, northeast of Fairburn, S. Dak. (After Todd, S. Dak. Geol. Surv., Bull. 3, p. 121, 1902.) 463 FULLERS' EARTH 465 worked. 1 It is said to range from 15 to 50 feet in thickness. The deposits are of Cretaceous, Tertiary, and Pleistocene age. The following table gives the composition of fullers' earth from a number of different localities: ANALYSES OF FULLERS' EARTH I. II. III. IV. V. Silica (SiO-0 51.21 12.25 2.07 2.13 4.89 50.17 10.00 9.75 0.50 1.25 47.10 16.27 10.00 2.63 3.15 62.83 10.35 2.45 2.43 3.12 0.74 0.20 7.72 6.41 67.46 10.08 2.49 3.14 4.09 5.61 6.28 Alumina (AlgOs) Ferric oxide (FeoOs) Lime (CaO) Magnesia (MgO). . Potash (K 2 O) Soda (Na 2 O) . . . Water (H a O) 27.89 24.00 15.12 5.73 Moisture ... Loss on ignition Total 100.41 100.06 100.00 96.25 99.15 VI. VII. VIII. IX. X. Silica (SiO v ) 58.72 16.90 4.00 4.06 2.56 } ,n 8.10 2.30 50.36 33.38 3.31 74.90 10.25 1.75 1.30 2.30 1.75 5.80 1.70 54.32 18.88 6.50 1.00 3.22 4.21 | 11.86 63.19 18.76 7.05 0.78 1.68 0.21 1.50 7.57 Alumina (A1 2 O 3 ) Ferric oxide (Fe^Os) Lime (CaO) Magnesia (MgO) Potash (K.O). . . SnHfl (Na O"i Water (H 2 O). 12.05 Moisture Loss on ignition Total ' 1 . 98.45 99.10 99.75 99.99 100.74 I Smectite from Cilly. Pogg. Ann., LXXVII, p. 591, 1849. II. Malthacite from Steindorfel. Dana, Syst. Min., 1893. III. Woburn sands, Eng. (yellow), R. H. Harland, anal. IV. Gadsden County, Fla., P. Fireman, anal. U. S. Geol. Surv., 17th Ann. Kept., Pt. Ill (ctd.), p. 880. V Decatur County, Ga., ibid. VI. Fairburn, S. Dak., E. J. Riederer, anal. U. S. Geol. Surv., 17th Ann. Rept., Pt. Ill (ctd.), p. 880. VII. Glacialite, Enid, Okla, Ter. G. P. Merrill, Non-metallic Minerals. VIII. Sumter, S. Ca., H. Ries, anal. U. S. Geol. Surv., Min. Res., 1901, p. 932, 1902. IX. Bakersfield, Kern County, Calif. Min. Indus., X, p. 273. X. Alexander, Ark., 1 S., 13 W., Sec. 8, S. W. i of S. E. |. Branner, Amer. Inst. Min. Eng., Trans., XXVII, p. 62, 1898. > Calif. State Min. Bur., Bull. 38, p. 274, 1906. 466 CLAYS Mining and Uses According to Ries l "The Florida earth is usually mined with picks and shovels." A good method is to use mattocks, which shave the mate- rial off in thin pieces, and saves subsequent labor in breaking up the fullers' earth after it has been spread upon the drying-floor. After mining the usual method is to spread the material in a thin layer over a drying-floor constructed of planks. It is thus dried in the sun, and in drying it bleaches to a white color. The material is then gathered into sacks for shipment. By this air-drying about 50 per cent of moisture is removed. Drying can be done more rapidly by passing the earth through a hot cylinder. Day 2 states the following regarding the uses of fullers' earth : "The Florida earth, ground to 60 mesh and finer, is used almost exclu- sively as a substitute for bone-black in filtering mineral lubricating-oils, although its use has been somewhat extended for the lightening of the color of cottonseed-oil, but for this latter purpose the employment of. English fullers' earth is still generally practiced. The English earth has not proved any more suitable for the refining of mineral oils than has the American earth for use in vegetable oils. The common practice with these mineral oils is to dry the earth carefully, after it has been ground to 60 mesh, and run it into long cylinders, through which the crude black mineral oils are percolated very slowly. As a resul: the first oil which comes out is perfectly water white in color, and markedly thinner than that which follows. The oil is allowed to continue perco- lating through the fullers' earth until the color reaches a certain maxi- mum shade, when the process is stopped, to be continued with a new portion of earth. The oil is recovered from the spent earth. " With the vegetable oils the process is radically different. The oil is heated to beyond the boiling-point of water in large tanks, and from 5 to 10 per cent of its weight of fullers' earth, ground to 100 or 120 mesh, is then added, and the mixture vigorously stirred for 20 minutes, and then filtered through the bag filters. The coloring-matter remains in the earth, leaving the oil of a very pale straw color, provided the original cottonseed-oil had been sufficiently well refined by the ordinary process to admit of this, and provided the operation had been conducted with sufficient care." 1 L. c., p. 879. 2 U. S. Geol. Surv., 21st Ann. Kept., Pt. 6 (ctd.), P- 592. FULLERS' EARTH 467 Fullers' earth was originally used for fulling cloth, that is, cleansing it of grease, but this is now its least important application. It is also employed in the manufacture of certain soaps. Its use for removing calcium carbonate from water for boiler-supply, thus preventing dele- terious incrustations, is also suggested. 1 Production. The total production of fullers' earth for 1904 is given by the U. S. Geological Survey as 29,480 short tons valued at $168,500, the greater part of the supply coming from Florida, and the balance from Arkansas, Alabama, Massachusetts, Colorado, and New York. The total imports of both prepared and crude earth in 1904 amounted to 9126 long tons valued at $74,006. 1 U. S. Geol. Surv., Min. Res. for 1904, p. 1121, 1905. INDEX A Aarons, cited, 99, 101 Abbotsford, Wis., 452 Acetates, adsorption of, 164 Adobe, analyses of, 187 New Mexico, 373 Adsorption, 163 ^Eolian clays, 23 Agar-agar, effect on plasticity, 102 Affelder, cited, 411 Aiken, S. C., 415, 416 Air-separators, 214 Air shrinkage, 128 cause of, 128 range of, 128 Akron, Ohio, 392, 393 Alabama, clays described, 283 mentioned, 179, 278 Pleistocene clays, 284 Tertiary clays, 283 Albany clay. See Slip-day Albany County, Wyo., 458 Albite, adsorptive power, 164 kaolinization, 3 solubility, 2 Aleksiejew, cited, 98 Alexander County, 111., 304 Alexandria, Va., 437 Alfred Centre, N. Y., 378 Algonkian, 198, 278, 334 Alkalies, determination of, 64 effect on clay, 82 fixed, 82 Allegany County, Md., 335 Allegheny County, 407, 411 series, 336, 394, 405, 445 Allophane, dehydration temperature, 52 mentioned, 309 properties of, 51 Alloway clay, N. J., 370, 371 Alluvial clays, Oklahoma, 400 South Dakota, 420 Tennessee, 423 Texas, 431 Alpena, Mich., 345 Alton clay, Pa., 402 Alum, 389 Alumina, adsorption of, by clay, 163 as coloring agent in clay, 159, 162 determination of, 65 effect on iron coloration, 73 Alumina cream, effect on plasticity, 101. 102 Amboy stone ware- clay, 369 Anadarko, Okla., 400 Analcite, as source of kaolinite, 47 Analyses of, adobe soils, 187 Alabama clays, 284 Arkansas clays, 286 ball-clays, 169 bentonite, 458 brick-clays, common, 185 calcareous clays, 78 clay types, 60 Colorado clays, 293 Connecticut clays, 296 different layers in bank, 60 fire-clays, 178 fire -proofing clay, 193 Florida clays, 298 fullers' earth, 465 Georgia clays, 303 halloysite, 49 Indiana clays, 314 indianaite, 50 Iowa clays, 325 kaolins, 168 Kentucky clays, 330 loess, 187 Maryland clays, 338 Massachusetts clays, 341 kaolins, 340 mechanical separations, 118 Michigan clay, 346, 347 Minnesota clays, 351 Missouri clays, 361 New Jersey clays, 372 fire clays, 175 New York clays, 381 470 INDEX Analyses of North Carolina clays, 386 North Dakota clay, 390 Ohio clays, 398, 399 Pennsylvania clays, 413 Portland -cement clay, 198 pressed brick clays, 188 residual clays, 13 sewer-pipe clays, 183 slip-clays, 195 South Carolina clays, 416 South Dakota clays, 420 stoneware-clays, 181 Tennessee clays, 424 Texas clays, 431 Vermont kaolins, 334 Virginia clays, 438 West Virginia clays, 449, 450 Wisconsin clays, 456 Analysis of albite, 3 altered feldspar, 4, 5 anorthite, 3 clay, Ferguson, Okla., 400 Cornwall stone, 11 glauconite, 57 fire-clay, Mexico, Mo., 359 Ohio, 190 St. Louis, Mo., 356 halloysite, 49, 50 hydrous silica, 70 indianaite, 310 kaolin, 4, 11 kaolinite, 50 artificial, 5 labradorite, 4 non-magnesian clay, 81 orthoclase, 3, 5 shale, Mo., 359 See Rational analysis, Ultimate analy- sis Andalusite, as source of kaolinite, 47 Anderson Station, Tenn., 421 Anglesey, kaolinite crystals, 42 Angola, N. Y., 376 Anne Arundel County, Md., 336, 337 Anorthite, kaolinization of, 3 Anorthoclase, as source of kaolinite, 47 Anticlines, 28 Appalachians, residual clays in, 12 Aragonite, 426 Archaean clays, 278 Arenac County, Mich., 345 Argyle, S. Dak., fullers' earth at, 462 Arizona, clays of, 286 Arkansas, Carboniferous shales, 285 clays described, 285 fullers' earth, 462 kaolin, 285 mentioned, 179 Mesozoic clays, 285 Pleistocene clays, 285 Armstrong County, Pa., 407, 411 Art ware, 182 Arundel formation, 337 Asbury clay, 370 Asbury Park, N. J., 127 Ashley, cited, 311 Atchison, Kan., 326 Athens, Tex., 181, 431 Athens County, Ohio, 398 Atlantic coast plain, dip of clay- beds, 28 Attica, Ind., 309 Auger machine, 228 Augite, 4, 41 Augusta, Ga., 301, 416 Augusta shales, la., 318 Aurora, Mo., 354 halloysite at, 49 Austin, Tex., 431 Austin chalk, Tex., 427 B Bacteria, effect on plasticity, 104 Ball-clay, chemical composition, 169 distribution, 169 Florida, 169, 297 Kentucky, 329 mentioned, 214, 271, 257 Missouri, 355 New Jersey, 169 properties of, 168, 169 Tennessee, 423 Ball-mills, described, 265 Baltimore County, Md., 336, 337 Barbour, E. H., cited, 362 Barium, adsorption by clay, 163 Barlow, W. Va., 446 Barringer, cited, 81 Barrington, R. I., 415 Basalt, as source of malthacite, 460 Bath brick, 199 Bath-tubs, manufacture of, 276 Baton Rouge, La., 331 Bauxite, 51, 167 Bay City, Mich., 345 Beattystown, N. J., 364 Beaumont, Tex., 431 Beaumont clays, Tex., 431 Beaver County, Okla., 400 Beaver County, Penn., 405, 407, 411 Beaver River region, Pa., 405, 407, 408, 413 Bedford, Ohio, 392 Bedford shale, 392 Bell, cited, 2 Bellaire, Ohio, 398 Belmont, Mass., 341 Belmont County, Ohio, 398 Benezette, Pa., 406 Bennington, Vt., 333 Ben's Run, Pa., 406 Ben ton County, Ind., 313 Ben ton group, 389, 458 Bentonite, described, 457, 458 INDEX 471 Bentonite, uses of, 458 Berdel, cited, 83 Berkeley County, W. Va., 442 Berlin, Conn., 295 Bermuda Hundred, Va., 437 Beryl, kaolinization of, 4 Beverly, Mass., 342 Beyer, S. W., cited, 123, 127, 137, 318 Bibbville, Ala., 283 Biedermann, cited, 98 Big Stone City, S. Dak., 420 Biotite, as source of kaolinite, 47 mentioned, 41, 71, 131 occurrence in clay, 54 Birmingham shale, W. Va., 446 Bfachof, cited, 101, 145 Bismarck, N. Dak., 390 Bituminous matter, Texas clay, 427 Black coring, 90 Black Lick, Pa., 406 Black River Falls, Wis., 452 Blair County, Pa., 407 Blake, cited, 48, 51, 97 Blandford, Mass., 340 Bleininger, A. V., cited, 190 Block House Run, Pa., 411 Blue Ball, Pa., 406 Bluff deposit, Neb., 363 Bolivar, Pa., 411 Bollinger County, Mo., 354= Bordentown, N. J., 370 Boring methods, 203 Bostick's Mills, N. C., 385 Boston, Mass., 341 Boulder, Colo., 290 Bourry, cited, 163 Bowlder-clays, 20 Boyd County, Ky., 329 Brady's Run, Pa., 406 Brandon, Vt., 333 Brandy wine Summit, Pa., 402 Brick, common, denned, 218 enameled, denned, 218 front, denned, 218 glazed, denned, 218 manufacture of, 218 soft- mud, characteristics of, 227 stiff-mud, characteristics of, 228 Brick-clay, adobe, 186 Alabama, 283 Arizona, 286 Arkansas, 285 California, 286, 289 Colorado, 290 common, analyses of, 185 physical tests of, 186 properties of, 185 Connecticut, 295 District of Columbia, 296 enameled, 191 Florida, 297 Illinois, 304 Brick-clay, Indiana, 307, 309, 313 Indian Territory, 315 Iowa, 316, 318, 322 Kentucky, 328 Maryland, 335, 338 Massachusetts, 341 Michigan, 345 Minnesota, 348 Missouri, 359 Nebraska, 363 New Mexico, 373 New Jersey, 364, 371 New York, 378 North Carolina, 385, 386 North Dakota, 390 Ohio, 392 Oklahoma, 400 Pennsylvania, 402, 413 pressed, analyses of, 188 flashing of, 189 physical tests, 188, 189 properties of, 188 Rhode Island, 415 Tennessee, 421 tensile strength, 122 Texas, 426, 427, 428, 431 Utah, 434 Virginia, 434, 437 Washington, 441 West Virginia, 442, 445, 446 Wisconsin, 452, 455, 456 Wyoming, 457 Brick-manufacture, burning, 236 drying, 232 molding, 220 preparation, 218 Bridgeboro, N. J., 370 Bridgeport, Tex., 426 Bridgeton, N. J., 371 Briquettes, tensile strength, 120 Bronson, Mich., 346 Brookville, Pa., 406 Brookville clay, 394, 395, 405 Bryson City, N. C., 385 Buchanan County, Iowa, 318 Buckley, cited, 25, 41, 455 Buffalo, N. Y., 378 Burlington, N. J., 370 Burlington shale, Mo., 355 Burning clay, changes occurring in, 156 dehydration period, 157 oxidation period, 158 volatilization during, 160, 161 vitrification period, 159 Butler County, Pa., 402 Cairo, N. Y., 376 Calcareous clays, Texas, 431 Wisconsin, 455 Michigan, 344 472 INDEX Calcite, 41, 55, 76, 98, 136 Calhoun, Mo., 181 Calhoun County, Iowa, 321 California, clays described, 286 fullers' earth in, 462 references on, 289 Tertiary clays, 289 Calumet County, Wis., 455 Cambria, Wyo., 457 Cambrian clays, 283, 316, 354, 355 Cambridge, Mass., 341 Cambridge limestone, West Virginia, 446 Cambro-Silurian, 198, 434 Camden, N. J., 370 Camden, S. C., 415, 416 Cameron, cited, 2 Cameron County, Pa., 402 Cancrinite, solubility of, 2 Cannel, Tex., 428 Canton, Ohio, 395, 396 Canton, N. C., 385 Cape Girardeau County, Mo., 354 Cape May formation, N. J., 371 Carbon, asphaltic, 88 effects on clay, 88 Carbon County, Pa., 402 Carbon County, Wyo., 458 Carbonaceous clay, Tex., 426 Carbonaceous matter, as coloring agent, 161. See Carbon Carbondale, Cal , 289 Carbon dioxide, relating to weathering, 2, 4 Carboniferous clays, Indiana, 309 Iowa, 318 Kansas, 326 Kentucky, 328 Maryland, 335 mentioned, 39, 55, 178, 179, 183, 185, 191, 192 Michigan, 345 Mississippi, 352 Missouri, 356 Pennsylvania, 402 Tennessee, 421 Texas, 426 Virginia, 437 West Virginia, 442 Carboniferous shales, siderite in, 55 Carclazite, 211 Carlisle shale, Colo., 290 Carroll County, Ohio, 396 Carter County, Ky., 329 Cassville coal, 398 Casting pottery, 269 Catskill shale, W. Va., 442 Cecil County, Md., 334, 336, 337 Cedar County, Iowa, 318 Ceredo, W. Va., 446 Chagrin shale, Ohio, 392 Chamberlin, T. C., cited, 41 Champlain Valley, N. Y., 378 Chandler, Okla., 400 Chanute, Kan., 326 Charlestown, W. Va., 442, 446 Chaser-mills, 240, 265 Chemical analysis of clays, 58 Chemical changes in clays, 33 Chemical composition, relation to fusibil- ity, 139 Chemical properties of clays, 40 Chemung shale, New York, 376 West Virginia, 442 Cheraw, S. C., 416 Cherryvale, Kan., 326 Chert, 52 Chester, Minn., 351 Chester County, Pa., 401 Chesterfield, S. C., 415 Chicago, 111., 304 China clay. See Kaolin Chittenden, Vt., 333 Chlorides, adsorption by clay, 164 Chlorite, 41 Chromolithography, 275 Cilly, Styria, 460 Cimolite, 51 Cincinnati shales, 304 Cisco, Tex., 426 Clarion clay, 406, 445 Clarke County, Wis., 452 Clay, absorption of water by, 86 adobe, 186 adsorptive power, 163 aeolian, 23 air-separation of, 214 air-shrinkage, 128 alkalies in, 82 ammonia in, 82 analyses of, 60 ball, 168 biotite in, 54 bowlder, 20 brick, 185 calcareous, 78 calcareous, uses of, 78 calcite in, 55 carbon in, effect of, 88 carbonates in, 1 changes in burning of, 156 chemical analysis of, 58 chemically combined water in, 87 chemical properties of, 40 chemical variation in, 60 classification of, 23 colluvial, 27 color of, 160, 161 delta, 25 definition of, 1 dolomite in, 57 drift, 20 enameled brick, 191 estuarine, 19 feldspar in, 53 fire, 170 INDEX 473 Clay, fireproofing, 192 fire-shrinkage, 129 flood*plain, 20 fusibility of, 137 garnet in, 57 glacial, 20, 360 glass-pot, 196 glauconite in, 57 gumbo, 195 gypsum in, 56, 78 hematite in, 54 hollow-brick, 192 hornblende in, 57 hydrous silica in, 70 hydroxides in, 1 i menite in, 56 iron compounds in, 72 iron in, coloring action of, 72 iron oxides in, 54, 71 kaolin, 165 kinds of, 165 lake, 20 lepidolite in, 54 lime in, 76 lime carbonate in, 76 lime silicates in, 78 limonite in, 54 littoral, 25 loess, 186, 360 magnesia in, 80 magnesite in, 57 magnetite in, 55 manganese in, 58 manufacturing methods, 217 marine, 19 mechanical analysis of, 108 meta-ssdimentary, 25 mica in, 53 mineral compounds in, 68 minerals in, 40 mining methods, 204 miscellaneous kinds of, 195 moisture in, 86 mottling of, 34 muscovite in, 54 origin of, 1 outcrops, 199 oxides in, 1 paint, 198 paper, 197 parent rock of, 1 paving-brick, 191 pelagic, 25 permeability, 163 physical properties of, 94 pipe, 196 plasticity of, 94 polishing, 199 Portland cement, 197 potash in, 82 preparation of, 213 pressed brick, 187 Clay, prospecting for, 199 pure, 8 pyrite in, 55 quartz in, 52 rare elements in, 58 rational analysis of, 61 residual, 11 rutile in, 56 sagger, 196 secondary character of, 1 sedimentary, 14 selenite in, 56 sewer-pipe, 183 siderite in, 55 silica in, 68 silicates in, 1 slip, 193 soda in, 82 soluble salts in, 90 specific gravity of, 136 statistics, 288 stoneware, 180 swamp, 20 tensile strength of, 120 terra-cotta, 182 texture of, 108- titanium in, 84 transported, 14 tourmaline in, 57 ultimate analysis of, 58 ultramarine, 199 uses of, 217 vanadiates in, 57 vivianite in, 58 wad, 197 ware, 196 washing, 213 "" water in, 86 weathering of, 104 Clay- deposits, change of color, 35 chemical changes in, 33 classification of, 23 concretions in, 35 consolidation of, 35 discoloration of, 34 erosion of, 30 exploitation of, 203 faulting of, 28 folding of, 28 leaching of, 35 mechanical changes in, 28 secondary changes in, 28 softening of, 35 tilting of, 28 Clay Marl series, 370 Clay-mining, 212 Clay-products, statistics, 278 Clay -slides, 205 Clay substance, 5 Clayton, Mass., 340 Clayton, Wash., 441 Cleveland, Ohio, 392 474 INDEX Cleveland shales, Ohio, 392 Cliffwood clays, New Jersey, 369 Clinton shale, New York, 376 Pennsylvania, 402 West Virginia, 442 Cloverport, Ky., 329 Coal, Wyoming, clays with, 457 Coal-measures, 303, 321, 329, 356, 393 Coffeyville, Kan., 326 Cohansey clay, New Jersey, 370, 371 Cold water, Mich., 346 Coldwater shales, 346 Collier, W. Va., 446 Collins, cited, 5, 210 Colloids, 1, 99 Colluvial clays, 27 Collyrite, 51 Color of clays, 161 Colorado, clays described, 289 mentioned, 179, 191 Mesozoic clays, 290 Pleistocene clays, 290 references on, 290 Columbia, S. C., 415, 416 Columbian formations, 296, 331, 337, 413, 415, 437 Columbiana County, Ohio, 396 Columbus, Ga., 301 Columbus, Ohio, 392 Common brick, 185 Concho County, Tex., 426 Concretions in clay, 35, 36, 427 limonite, 54 siderite, 55 Conduit clay, New York, 376 Conduits, manufacture of, 251 mentioned, 179, 251 Conemaugh series, 336, 398, 411, 446 Cones, Seger, 148 Connecticut, clays described, 293 Pleistocene clays, 295 references on, 296 Conoquenessing sandstone, Ohio, 393, 394 Converse, Wyo., 458 Cooper, Tex., 428 Cook, G. H., cited, 51, 98, 104 Cooper County, Mo., 354 Copper, adsorption by clay, 164 Copper Queen mine, clay in, 286 Corning, N. Y., 376 Cornwall, England, kaolin at, 5 Cornwall stone, analysis of, 11 Corona, CaL, 289 Corsicana, Tex., 428 Corunna, Mich., 345 Corundum-wheels, clay in, 199 Coshocton County, Ohio, 395 Cowley, Wyo., 458 Cox, E. T., cited, 310 Cramer, cited, 85, 141, 148 Crawfordsville, Ind., 309 Cremiatschenski, cited, 98 C. C. ware, defined, 262 Cretaceous clays, Iowa, 321 Kansas, 327 Maryland, 336 mentioned, 28, 41, 57, 161, 169, 179, 183, 185, 191, 197, 289, 301 Minnesota, 348 Mississippi, 352 Missouri, 355 Nebraska, 363 New Jersey, 366 New York, 378 North Dakota, 389 sedimentary clays of, 17 South Dakota, 419 Texas, 426 Wyoming, 457 Cretaceous fullers' earth, 465 Cripple Creek, Colo., kaolin at, 6 Cross, W., cited, 6 Crook County, Wyo., 458 Crucibles, 179 Crushers, described, 219 Cromwell, Conn., 295 Cumberland City, Tenn., 421 Cumberland County, Pa., 402 Currier, Tenn., 423 Cushman, A. S., cited, 101, 103, 104 Custer, S. Dak., 419 Cyanite, as source of kaolinite, 47 D Dakota group, 290, 321, 400, 419 Dallas, Tex., 427 Dana, E. S., cited, 48, 50, 460 Danversport, Mass., 342 Darlington clay, 407 Darton, N. H., cited, 296, 458 Daubree, cited, 6, 97 Day, D. T., cited, 461, 466 Decatur County, Ga., 461 Delage, cited, 41 Delaware, clays described, 296 mentioned, 198 Delaware County, Pa., 401 Dellslow, W. Va., 446 Delta-clays, 25 Demond, cited, 155 Denton, Tex., 427 Denver Basin, clays of, 290 De Smet, S. Dak., 420 Detroit, Mich., 346 Devonian shales or clays, Iowa, 318 Kentucky, 328 Maryland, 325 mentioned, 28, 179, 185, 191 Michigan, 345 Mississippi, 352 Ohio, 392 Pennsylvania, 402 West Virginia, 442 INDEX 475 Diatomaceous earth, Virginia, 437 Dick, cited, 42 Dickinson, N. Dak., 389 Discoloration by vanadiates, 57 Disintegrators, described, 219 mentioned, 251, 252 District of Columbia, clays of, 296 Dolomite, mentioned, 41, 76 occurrence in clay, 57 Dorsey, Md.,335 Double coal brick, 239 Down-draft kilns, 253 Drain-tile clay, Connecticut, 295 Iowa, 321 Kansas, 326 Missouri, 359 New Jersey, 371 New York, 376, 378 North Carolina, 385 Ohio, 391, 392 Drain-tile manufacture, 247 Dreux, clay from, 48 Drift-clays, 20 Drying-floors, 251 Drying -tunnels, described, 232 mentioned, 252, 270 Dry pans, described, 219 mentioned, 240, 251, 252, 257 Dry-press brick, 290 process, described, 231 mentioned, 252, 262 Dunkard series, 398, 449 Durand, Wis., 452 Dutch kilns, 239 E Eagle Ford formation, Tex., 427 Eagle Pass, Tex., 427, 428 Earthenware, denned, 262 mentioned, 182 red, burning of, 270 Earthen ware -clay, Connecticut, 295 Iowa, 316, 318 Massachusetts, 342 Michigan, 345 Pennsylvania, 413 East Liverpool, Ohio, 407 Eau Claire, Wis., 452 Eden shale, Ohio, 391 Edgar, Fla., 96, 297 Edwards County, Tex., 426 Edwards limestone, kaolin in, 426 Ehrenbergite, compared with bentonite, 458 Elgin, Tex., 431 Elk County, Pa., 402 Elkins, W.' Va., 442 Ellerslie, Md., 335 Elmendorff, Tex., 431 Elmira, N. Y., 378 El Reno, Okla., 400 Elsinore, Cal., 289 Enameled -brick clays, 191 Encaustic tile, 258 Eocene, 57, 352, 416, 437 coals, clay with, 428 Epidote as source of kaolinite, 47 Erosion of clays, 30 Escanaba, Mich., 346 Essex County, Mass., 340 Estuarine clays, 19, 371, 378, 455 Excavation, methods of, 204 F Fair burn, S. Dak., 462 Fargo, N. Dak., 390 Farrandsville, Pa., 406 Faulting in clay-deposits, 28 Fayence, architectural, 254 denned, 262 Fayette County, Pa., 406, 407 Fayetteville, Pa., 385 Feldspar, adsorptive power, 163 composition of, 53 mentioned, 6, 11, 41, 47, 48, 53, 68, 70, 76, 77, 83, 84, 136, 257, 261, 275, 385 occurrence in clay, 53 reactions in kaolinization of, 47 Feldspar beds, New Jersey, 369 Fernbank, Ala., 283 Ferric oxide, determination of, 65. See Iron oxide Ferriferous coal under-clay, 406 Ferriferous limestone-clay, 394, 395 Ferris, Tex., 428 Ferrous oxide, determination of, 66 Feuerfestigkeits-Quotient, 145 Filter-press, 214, 264, 265 Fire-brick, cone of firing, 253 Colorado, 290 Connecticut, 295 manufacture of, 252 requirements of, 253 shapes of, 253 texture, 253 Weber's experiments, 253 Fire-clay, Alabama, 283 association with coal, 179 chemical composition, 170 Colorado, 290 definition of, 170 Delaware, 296 distribution, geographic, 177 geologic, 179 for glass pots, 179 Indiana, 312 Iowa, 321 Kentucky, 329 Maryland, 335, 336, 337 mentioned, 214 476 INDEX Fire-clay, Mexico County, Mo., 356 Missouri, 356, 359 New Jersey, 174, 369, 371 New Mexico, 373 New York, 378 North Carolina, 385 Ohio, 392, 394, 395, 397 Pennsylvania, 401, 402, 405, 406, 407, 411 pholerite, 51 properties of, 170, 177 St. Louis, properties of, 356 silica-alumina ratio, 173 silica in, effects of, 170 South Dakota, 419 Tennessee, 421, 422 tensile strength, 122 Texas, 427, 428, 431 titanium in, effect of, 176 United States, distribution, 177 uses of, 179 Utah, 434 vanadates in, 57 Virginia, 437 Washington, 441 West Virginia, 445, 446 See also Flint-day Fireproofing, defined, 247 Fireproofing clay, analyses of, 193 Indiana, 312 Massachusetts, 342 mentioned, 313, 437 New Jersey, 193, 364 New York, 376 Ohio, 392 physical tests, 194 properties of, 192 Fire- shrink age, cause of, 129 range of, 129 relation to texture, 131 temperature of, 129 Flashing bricks, 189 Flint, 52, 261, 271, 275 Flint- clay, Alabama, 283 defined, 177 Kentucky, 392 Maryland, 385 mentioned, 40 Missouri, 354, 355 Ohio, 396, 397 origin, 354 Pennsylvania, 406 tensile strength, 122 West Virginia, 441, 445, 446 Flood-plain clays, 20 Floor-driers, 236, 252 Floor- tile, classification of, 258 manufacture of, 258 mentioned, 179, 258 properties of, 258 raw materials, 261 Florida, ball-clay, 297 Florida clays described, 297 fullers' earth, 461 . references on, 297 Flower-pot clay, California, 289. See Earthenware Flue-lining clay, Ind., 313 Fluorine as kaolinizing agent, 5 Fluxes defined, 59 Folding in clay-deposits, 28 Fond du Lac, Wis., 455 Fores tdale, Vt., 333 Forschammer, cited, 2 Fort Smith, Ark., 285 Fort Worth, Tex., 427 Fox Hills group, S. Dak., 389 Fredericksburg, Va., 437 Frostburg, Md., 335 Fullers' earth, Arkansas, 462 California, 462 defined, 460 distribution, 461 Georgia -Florida district, 461 mining and uses, 466 . New York, 462 petrographic characters, 461 production, 466 properties, 460 South Dakota, 462 Southern States, 462 Fulton, Mo., 356 Fusibility, Bischof's formula, 145 classification based on, 154 complete vitrification, 138 Cramer's experiments, 141 expression of, 145 factors influencing, 137 incipient vitrification, 138 Lud wig's experiments, 142 measurement of, 147 oxidation, relation to, 145 rate of softening, 139 relation to chemical composition. 139 homogeneity, 144 Richter's experiments, 140 Seger cones, 148 Seger's formula, 146 texture, relation to, 144 viscosity, 138 Wheeler's formula, 146 See Pyrometers Fusibility-factor, 147 Fusion formation, S. Dak., 419 G Gabbro, 1, 400 Gadsden County, Fla., 461 Galena-Trenton formation, Iowa, 316 Galesburg, 111., 304 Gallia, Ohio, 398 Gallipolis, Ohio, 398 INDEX 477 Garnet, as source of kaolinite, 47 mentioned, 68, 70, 71, 76, 83, 385 occurrence in clay, 57 Garrett County, Md., 335 Gas-retorts, 179, 196 Gay Head, Mass., 341 Geary, Okla., 400 Geijsbeek, S., cited, 423 Georgia, clay, minerals in, 41 clays described, 298 coastal plain clays, 301 fullers' earth in, 461 halloysite in, 49 mentioned, 179, 197 Pre- Cambrian clays, 298 references on, 303 Germany, 180 Gibbsite, 167 Glacial clay, Missouri, 360 Rhode Island, 415 South Dakota, 420 Washington, 441 Wisconsin, 455 Wyoming, 457. See also Pleistocene Glass-pot clay, 179 Glauconite, analysis of, 57 as coloring agent, 161 clays, 57, 68, 70, 71, 83, 427, 431 Glazes, Bristol, 271 porcelain, 275 pottery, 271, 272 salt, 271 terra-cotta, 257 Glen Allen, Mo., 167, 354 Gneiss, 278, 334, 340, 434, 452 Golden, Colo., 28, 290 Goldsboro, N. C., 385 Graham, Tex., 426 Grand Gulf formation, Ala., 283 Grand Junction, Tenn., 422 Grand Rapids, Mich., 345 Grand Rapids, Wis., 452 Granite, change to clay, 7 disintegration of, 2 mentioned, 278, 400 Grant County, W. Va., 442 Great Valley, clays in, 401, 434 Green Bay, Wis., 455 Green brier County, W. Va., 442 Greenford, Ohio, 395 Green Lake County, Wis., 455 Greensand. See Glauconite Greensand, Va., 437' Greensboro, N. C., 385 Greenup County, Ky., 329 Greenville, Tex., 428 Griffin, cited, 89 Grimsley, cited, 26, 442, 445 Grinding, effect on plasticity, 104 Grog, 132 Gross -Almerode, 180 Grout, cited, 26, 102, 103, 104 Grover, N. C., 385 Guillemin, cited, 50 Gumbo-clay, chemical composition, 196 Iowa, 322 Kansas, 327 Missouri, 122 physical properties, 196 tensile strength, 122 Gypsum, decomposition temperature, 56 effect on clay, 78 mentioned, 56, 76, 79, 98, 345, 389, 427 occurrence in clay, 56 H Hackensack, N. J., 19, 371 Halcyon, Wis., 452 Halle, Germany, kaolin at, 6 Halloysite, analyses of, 49 dehydration temperature, 52 Georgia, 49 Missouri, 41, 49 properties of, 48 referred to, 8, 40, 41, 167 Hall Station, N. C., 385 Hamilton shales, 345, 376, 442 Hammond, W. Va., 445 Hampshire County, W. Va., 442 Hand -wedging, 265 Hanover, Ohio, 392 Hardy County, W. Va., 442 Harford County, Md., 336, 337 Harmonville, Pa., 413 Harper's Ferry, Va., 434 Hauyne, as source of kaolinite, 47 Haverhill, Mass., 342 Ha worth, E., cited, 98, 327 Haydenville, Ohio, 394, 396 Hecht, cited, 148 Hematite, 54, 71 Henderson, Tex., 431 Henry County, Missouri, 359 Henry County, Tennessee, 423 Henry County, Virginia, 434 Herzfeld, cited, 98 Hice, R. R., cited, 407 Hico, Tenn., 422 Hightstown, N. J., 370 Hirsch, cited, 163 Hocking County, Ohio, 394, 395 Hofman, H. O., cited, 155 Hollow blocks, defined, 248 Hollow bricks, defined, 248 Hollow Rock, Tenn., 422 Hollow ware, advantages of, 251 manufacture of, 247 sizes, 248 Hollow-ware clays, 304, 316, 321, 359, 407. See also Fire-proofing day Holly Springs, Miss., 352 478 INDEX Holyoke, Mass., 341 Horaewood sandstone, West Virginia, 442 Hope Station, Pa., 406 Hopkins, T. C., cited, 401, 402 Hornblende, kaolinization of, 4 occurrence in clay, 57 referred to, 41, 68, 70, 71, 83 Hornellsville, N. Y., 376 Hot Springs, S. Dak, 419 Hottinger, A., cited, 81 Houston, Tex., 431 Howard County, Md., 337 Howell County, Md., 354 Hudson River shales, 39, 342, 364, 376, 402, 452 Hudson Valley, 19, 378, 381 Huntington County, Pa., 402 Huron, Ind., 309 Huron County, Mich., 345 Huron shale, Ohio, 392 Hydrated aluminum silicate, 4, 5 Hydrolysis, 2 Hydromica slates, as source of kaolin, 401 Hydrous silica, effect on clay, 70 Illinois, clays described, 303 Coal-measure shales, 304 drift-clays, 304 mentioned, 179, 191, 192 Ordovician clays, 304 references on, 307 Tertiary clays, 304 Ilmenite, occurrence in clay, 56 Impure shales, Missouri, properties of, 359 Independence, Ohio, 392 Independence limestone, 327 Indian Territory, clays described, 315 Indiana, Carboniferous shales, 309 clays described, 307 coal-measures, clays and shales, 311 Devonian shales, 307 indianaite, 309 Lower Carboniferous shales, 307 mentioned, 165, 179, 183, 192, 212 Ordovician shales, 307 Pleistocene clays, 313 references on, 313 Silurian shales, 307 Indianaite, analyses of, 50 Indiana, 309 origin of, 310 properties of, 50 referred to, 8 In key, v., B., cited, 6 Interlocking tile, 254 lola limestone, Kan., 327 lone, Cal., 289 lone formation, 289 Ionia, Mich., 346 Iowa, Cambrian shales, 316 Carboniferous shales, 318 clays described, 316 coal- measure clays and shales, 321 Cretaceous clays, 321 Devonian shales, 318 mentioned, 123, 127, 137, 179 Ordovician clays, 316 Pleistocene clays, 322 references on, 322 Silurian shales, 316 Iron compounds, coloring action, 72 effect of reduction on, 75 effect on clay, 72 oxidation of, 74 Iron ores in clay, 54 Iron oxide, coloring action of, 159, 161, 162 effect on adsorption, 76 effect on clay, 71 fluxing action of, 75 in residual clay, 12 mentioned, 137, 198 ^ relation to flashing, 189 sources of, 71 Ironstone china, 262 Jackson Bluff, Fla., 297 Jackson County, Ky., 329 Jackson County, Wis., 452 Jackson, Term., pottery at, 422 Jacksonville, Fla., 297 James River, Va., 437 Jauchau Fu, kaolin from, 8 Jefferson County, Ohio, 396 Jefferson County, W. Va., 442 Jennings shale, Maryland, 335 Jewettville, N. Y., 376 Jiggering, 266 Johnson, cited, 48, 51, 97 Johnson County, Wyo., 458 Johnstown, Pa., 406 Jollying, 266 Josingsf j ord, kaolin at, 3 Juniata County, Pa., 402 Jurassic, fullers' earth in, 462 Jura-Trias, Maryland, 336 Kansas, Carboniferous shales, 326 clays described, 326 Cretaceous, 327 Pleistocene clays, 327 references on, 327 Triassic clays, 327 Kansas City, Mo., 189 Kasai, cited, 100 INDEX 479 Kaolin, adsorptive power, 163, 164 Alabama, 278 analyses of, 4, 168 Arkansas, 285 china, 11 chemical composition, 167 Colorado, 6 Cornwall, England, 5 defined, 8 dehydration temperature, 52 Delaware, 11, 296 depth of, 6 derivation of name, 8 distribution of, 167 European, sources of, 165 garnet in, 57 Halle, Germany, 6 impurities in, 167 Indiana, 309 Johnson and Blake's definition, 48 Maryland, 334 Massachusetts, 340 mentioned, 11, 83, 84, 100, 198, 214, 251,271, 298,460 North Carolina, 6, 167, 385 Oklahoma Territory, 400 origin of, 165 Pennsylvania, 6, 401 physical tests of, 167 refractoriness of, 47 St. Anstell, England, analysis of, 6 St. Yrieux, France, analysis of, 11 South Dakota, 419 Tennessee, 421 tensile strength, 122 Texas, 40, 50, 426 tourmaline in, 57 uses of , 168 Utah, 434 Vermont, 333 Virginia, 167, 434 Zettlitz, Bohemia, 6 Kaolin-beds, so-called, New Jersey, 369 Kaolinite, defined, 8 described, 42 Johnson and Blake's definition, 48 mentioned, 3, 40, 41, 50, 51, 69, 98, 136, 167, 170 minerals yielding, 47 Missouri, 355 Kaolinization by pneumatolysis, 5 defined, 3 shrinkage accompanying, 47 Kaolin mining, 209, 210, 211 Kauling, 8 Kent's Island, Mass., 340 Kentucky, Carboniferous clays, 328 clays described, 328 Devonian clays, 328 mentioned, 169, 178, 179 Ordovician clays, 328 Pleistocene clays, 329 Kentucky, references on, 330 Tertiary, 329 Kern County, Cal., fullers' earth in, 462 Key port, N. J., 370 Kilns, continuous, 239 described, 236 down- draft, 239 mentioned, 251, 252, 258 pottery, 272 Kinderhook shales, Iowa, 318 Kingman, Kan., 327 Kingsland, N. J., 364 King-te-chin, porcelain of, 8 Kingwood, W. Va., 446 Kinkora, N. J., 370 Kittanning, Pa., 406 Kittanning clays, W. Va., 445 Knight, W. C., cited, 457 Knobstone shales, Indiana, 307 Knop, cited, 50 Knox dolomite, Tennessee, 421 Kohler, cited, 164 Koninck, cited, 50 Kovar, cited, 85 Kreischerville, N. Y., 378 Kummer, Wash., 441 Labradorite, kaolinization of, 4 Lacka wanna County, Pa., 402 La Crosse, Wis., 456 Lacustrine clays, Wisconsin, 455 Ladd, G. E., cited, 24, 41, 103, 105 Lafayette sands, Tenn., 422 Lagatu, cited, 41 La Junta, Colo., 290 Lake -clays, 20 Lake County, Ind., 313 Lampasas County, Tex., 426 Lancaster, N. Y., 378 Langenbeck, cited, 105 Laporte County, Ind., 313 Laramie County, Wyo., 458 Laramie clays, North Dakota, 389 South Dakota, 419 Laredo, Tex., 428, 431 Las Vegas, N. Mex., 373 Lawrence County, Ind., 50, 309 Lawrence County, Ky., 329 Lawrence County, Mo., 354 Lawrence County, Ohio, 396 Lawrence County, Pa., 405 Lawrence shales, 327 Lead, S. Dak., 420 Lead salts, adsorption by clay, 163 Leaky, Tex., 50, 426 Le Chatelier, H., cited, 48, 51, 52 Leda clays, 41 Lehi, Utah, 434 Leon County, Fla., 461 480 INDEX Lepidolite, occurrence in clay, 54 solubility of, 2 Lesquereaux, cited, 310 Leucite, as source of kaolinite, 47 solubility of, 2 Leucoxene, 56 Lignite, 389 with fire-clay, S. Dak., 419 Lignitic clays, Tex., 428 Lime, adsorption by clay, 163 as coloring agent, 159, 162 determination of, 65 effect on clays, 76 effect on iron coloration, 73 source of, in clay, 76 Lime carbonate, bleaching effect, 77 decarbonation temperature, 76 effect on clay, 76 relation to vitrification, 77 Lime silicates, effect on clay, 78 Limestone, alteration to clay, 7 as source of kaolin, 165 Limonite, mentioned, 41, 71, 193, 203 occurrence in clay, 54 Vermont, 333 Lincoln, Cal., 289 Lincolnton, N. C., 385 Linder, cited, 97 Lindgren, cited, 6, 289 Linn County, Iowa, 318 Little Falls Station, Wash., 441 Little Rock, Ark., 285 Littoral clays, 25 Lloyd, Tex., 427 Loess, analyses of, 187 distribution, 186 Iowa, 322 mentioned, 186, 304 Missouri, 360 Nebraska, 363 tensile strength, 122 Wisconsin, 456 Wyoming, 457 Logan shale, Ohio, 392 Log-washer, 162 Long Island, N. Y., 378 Lorraine shale, Ohio, 391 Los Angeles, Cal., 289 Louisiana, clays described, 331 references on, 332 Lower Barren Measures. See Conemaugh series Lower Carboniferous, Missouri, 355 Ohio, 392, 394 West Virginia, 442 Lower Cretaceous, New Jersey, 366 Texas, 426 Lower Freeport clay, Ohio, 394, 397 Pennsylvania, 408 Lower Kittanning clay, Ohio, 394, 395 Pennsylvania, 406, 407 West Virginia, 445 Lower Mercer clay, Ohio, 393, 394 iron ore, Ohio, 393 limestone, Ohio, 393 Lower Productive Measures. See Alle- gheny series Lucas, cited, 100 Ludwig, cited, 142 Lunette pyrometer, 153 Luzerne County, Pa., 402 Ai McConnellsville, N. Y., 462 McKean County, Pa., 402 Mt. Savage fire-clay, Pennsylvania, 405 West Virginia, 442 Mt. Savage, Maryland, 335 Mackenzie, Tenn., 422 Mackler, cited, 80, 91 Macon, Ga., 301 Magnesia, determination of, 65 effect on clay, 80, 81 Mackler's experiments with, 80 Magnesite, occurrence in clay, 57 Magnesium, adsorption of, by clay, 163 Magnetite, 41, 55, 71 Mahoning sandstone, West Virginia, 446 Maine, clays described, 333 Majolica, defined, 262 Malakoff, Tex., 431 Malthacite, 460, 461 Manganese, in clay, 58, 198 Vermont, 333 Mangum, Okla., 400 Manitowoc County, Wis., 455 Mansfield sandstone, 309, 311 Manufacture of, bricks, 218 conduits, 251 drain-tile, 247 fire-brick, 252 floor-tile, 258 hollow ware, 247 pottery, 262 roofing- tile, 254 sewer- pipe, 240 terra-cotta, 254 Maple Shade, N. J., 370 Maquoketa shale, 316 Marathon County, Wis., 452 Marble, adsorptive power of ground, 163 Marine beds, Texas, 431 Marine clays, 19 Marion County, Tenn., 421 Marly clays, Indiana, 313 Texas, 427 Marquette, Mich., 346 Marshall clays, Michigan, 345 Marshall County, Miss., 352 Martha's Vineyard, Mass., 341 Martin County, Ind., 309 Martinsburg shale, West Virginia, 442 INDEX 481 Martins ville, Ind., 309 Maryland, Algonkian clays, 334 Arundel clays, 337 Carboniferous shales, 335 clays described, 334 Cretaceous clays, 336 Devonian shale, 335 glauconite in, 57 Jura- Trias clays, 336 mentioned, 58, 101, 178, 179, 191, 198, 212 Patapsco clays, 337 Pleistocene clays, 337 Raritan clays, 337 references on, 339 Silurian shales, 334 Tertiary clays, 337 Massachusetts, clays described, 340 Cretaceous and Tertiary clays, 341 kaolins, 340 Pleistocene clays, 341 references on, 342 Mason City, Iowa, 318 Masontown, W. Va., 446 Massillon sandstone, Ohio, 393 Matawan, N. J., 370 Matawan formation, 336 Mauch Chunk shale, 335, 402, 442 Maxville limestone, clay in, 392 Maynard ville, Tenn., 423 May's Landing, N. J., 371 Mecca, Ind., 313 Mechanical analysis, Beaker method, 110 centrifugal method, 115 described, 108 Hilgard method, 114 Iowa clays, 127 New Jersey clays, 125 residual clays, 14 Schoene's method, 113 Medford, Mass., 341 Medina shale, 376, 442 Meigs County, Ohio, 398 Mellor, J. W., cited, 103 Menomonie, Wis., 456 Mercer clay, Pa., 402 Mercer County, Pa., 405 Merill, G. P., cited, 41, 49, 128, 461 Merillan, Wis., 452 Mertztown, Pa., 401 Mesozoic, 52, 285 Meta-sedimentary clays, 25 Mexico, Mo., 356 Mica, occurrence in clay, 53 compared with kaolin, 47 mentioned, 2, 68, 70, 210, 385 Michigan, Carboniferous shales, 345 clays described, 342 Devonian shales, 345 mentioned, 56, 78, 179 Pleistocene, 346 references on, 347 Michigan, Silurian shales, 342 Michigan shale formation, 345 Microcline, adsorptive power of, 164 as source of kaolinite, 47 Middle Kittanning clay, Ohio, 394, 397 Pennsylvania, 407 West Virginia, 445 Middletown, Conn., 295 Millard County, Utah, 434 Milldale, Conn., 295 Millersburg, Ohio, 394 Millsap, Tex., 426 Millville, N. J., 371 Mineral County, W. Va., 442 Minerals in clay, 40 Mingo clay, Ohio, 394 Mingo County, W. Va., 446 Mining clay, 205 Minneapolis, Minn., 351 Minnekata, S. Dak., fullers' earth at, 463 Minnesota, clays described, 348 Cretaceous clays, 348 Ordovician clays, 348 Pleistocene clays, 351 Pre- Cambrian clays, 348 references on, 351 residual clays, 348 Minorsville, Neb., 363 Minot, N. Dak., 390 Miocene clays, 83, 437 Mississippi clays, described, 352 references on, 352 Mississippian, 354 Missouri, ball-clays, 355 clays described, 352 Coal- measure clays, 356 fire-clays, 356 flint-clays, 40, 354 halloysite, 41, 49 kaolins, 354 mentioned, 122, 137, 167, 169, 178, 179, 180, 181, 183, 212 Palaeozoic limestone clays, 354 pholerite, 51 Pleistocene clays, 360 references on, 360 stone ware -clays, 355, 359 Tertiary clays', 360 Miston, Miss., 352 Mogadore, Ohio, potteries, 394 Molding pottery, 266 Monkton, Vt., 333 Monmouth formation, 336 Monongahela series, Ohio, 398 West Virginia, 446 Monroe County, Ohio, 398 Monroe County, W. Va., 442 Montague, Tex., 426 Montezuma, Ind., 313 Montgomery County, Iowa, 321 Montmorillonite, 51, 52 Moraine clays, 346, 378 482 INDEX Morgan County, Mo., 354 Morgan town, N. C., 385 Morgan town, W. Va., 446 Morristown, Tenn., 423 Mound City, 111., 304 Mounds ville, W. Va., 446 Mount Holly, N. C., 385 Mount Savage clay, Ohio, 393, 394 Moxahala, Ohio, 397 Muscovite, fluxing action of, 83 mentioned, 2, 41, 83, 136, 167 occurrence in clay, 54 solubility of, 2 Muskingum County, Ohio, 394, 395, 396 Nacogdoches, Tex., 431 Nacrite, defined, 51 Nageli, cited, 99 Nan tucket, Mass., 341 Narragansett Bay, R. I., 415 Natrona County, Wyo., 458 Nebraska, Carboniferous clays, 362 clays described, 362 Cretaceous clays, 363 loess, 363 references on, 364 Nebraska City, Neb., 362 Neocene, 289 Nephelinite, as source of kaolinite, 47 solubility of, 2 New Albany, Ind., 309 Newark, Ohio, 392 New Boston, Tex., 428 New Brighton, Pa., 407 New Brighton clay, 407 New Cumberland, W. Va., 445, 446 Newell, 155 New Hampshire, clays described, 333 New Jersey, Cambrian clays, 364 clays described, 364 Cretaceous clays, 366 glauconite in, 57 mentioned, 39, 55, 84, 123, 125, 137, 169, 174, 179, 181, 183, 188, 192, 196, 205 pholerite in fire-clays of, 51 Pleistocene clays, 371 Ordovician shales, 364 references on, 373 Tertiary clays, 370 Triassic shales, 364 New Lexington, Ohio, 395 New Mexico, clays of, 373 Newton County, Ind., 313 Newtonite, properties of, 51 New Ulm, Minn., 351 New York, clays described, 375 Cretaceous clays, 378 fullers' earth in, 462 New York, clays mentioned, 39, 56, 181, 191, 192 Paleozoic shales, 375 Pleistocene clay, 378 references on, 382 residual clays, 375 Tertiary clays, 378 Niagara shale, N. Y., 376 Niobrara formation, N. Dak., 389 Norfolk, Va., 437 North Carolina, clays described, 382 fullers' earth in, 462 kaolins, 385 mentioned, 6, 57, 69, 167 references on, 388 residual clays, 385 sedimentary clays, 385 North Dakota, clays described, 389 Cretaceous clays, 389 Laramie clays, 389 Pleistocene clays, 390 references on, 390 Tertiary clays, 389 Northeast, Md., 334 Northport, N. Y., 181 Oakfield, Wis., 455 Oak Hill, Ohio, 397 Oak Level, Va., 167 Oaxanna, Ala., 283 Ocher, 198 Odernheimer, cited, 35 Ohio, Allegheny series clays, 394 Brookville clay, 394 clays described, 390 Coal -measure clays, 392 Conemaugh series clays, 398 Devonian shales, 392 Dunkard series, 398 ferriferous limestone clay, 395 Lower Carboniferous clays, 392 Lower Freeport clay, 397 Lower Kittamiing clay, 395 Lower Mercer clay, 394 mentioned, 84, 178, 179, 191, 192 Middle Kittanning clay, 397 Monongahela series, 398 Mount Savage clay, 394 Ordovician, 390 Pleistocene, 398 Pottsville series, 393 Putnam Hill clay, 394 Quakertown shale, 393 references on, 399 Sharon shales, 393 Silurian, 390 Upper Freeport clay, 397 Upper Mercer clays, 394 Ohio River region, Pa., 407, 408, 413 INDEX 483 Ohio shale, Ohio. 392 Oklahoma clays described, 400 Olciie.vsky, cited, 97, 98, 101 Oletangy saale, Ohio, 392 Oligocene, fullers' earth in, 462 Oligoclase, solubility of, 2 Olive Hill, Ky., 329 Ontario, Medina brick shale in, 376 Oolite, Okla., 316 Open yards . described, 232 Ordovician clays, Kentucky, 328 Iowa, 316 limestone residuals, 452 Minnesota, 348 Missouri, 355 Ohio, 390 Wisconsin, 452 Oread limestone, 327 Ore Hill, Pa., 401 Orthoclase, 41, 83 adsorptive powers, 164 as source of kaolinite, 47 effect of fluorine on, 5 kaolinization of, 3 reaction with water, 3 solubility of, 2 Orton, E., cited, 73, 89, 97, 180, 392 Orton, Jr., K, cited, 23, 26, 123, 124, 392 Osgood shale, Ohio, 391 Ouachita County, Ark., 285 Owen County, Ind., 309 Owosso, Mich., 345 Paint-clay, Missouri, 354 properties of, 198 Palaeozoic clays, Georgia, 298 New York, 375 Pallet-driers, described, 232 referred to, 247, 251 Paper clays, Missouri, 354 Pennsylvania, 401 properties, 197 sources, 197 South Carolina, 416 Vermont, 333 Paris, Tex., 427 Parkers burg, W. Va., 449 Parkville, Pa., 406 Parrot River, England, 199 Patapsco, Md., 337 Patrick County, Va., 434 Patuxer.t, Md., 336 Paving-brick clays, composition of, 191, 192 Indiana, 312, 313 Iowa, 192, 321 Kansas, 326 Kentucky, 329 Maryland, 335 Michigan, 345 Paving -brick clays, Missouri, 359 Nebraska, 363 New York, 376, 378 Ohio, 392, 395, 397, 398 Pennsylvania, 402, 407, 413 properties of, 191 Texas, 426, 427, 431 Virginia, 437 West Virginia, 445, 446 Wisconsin, 452 Peaceburgh, Ala., 283 Pegmatite, as source of kaolin, 165, 402 referred to, 11, 340, 385 Pegram, Ala., 283 Pelagic clays, 25 Pembina, N. Dak., 389 Pendleton County, W. Va., 442 Pennsylvania, Allegheny series clays, 405 Alton fire-clay, 402 Brookville clay, 405 clays described, 401 Darlington clay, 407 Devonian shales, 402 Carboniferous clays, 402 Clarion clay, 406 Conemaugh series clays, 411 ferriferous coal under- clay, 406 kaolin, 6 Lower Barren Measures, 411 Lower Freeport clay, 408 Lower Kittanning clay, 406 Mount Savage fire-clay, 405 Mercer fire-clay, 402 Middle Kittanning clay, 407 Monongahela series clays, 413 Pleistocene clays, 413 Pottsville clays, 402 references on, 414 referred to, 39, 84, 178, 179, 180, 183, 191, 192, 198, 212 residual clays, 401 Sharon upper coal fire-clay, 405 Silurian shales, 402 Upper Coal-measures, 413 Upper Freeport clay, 41 1 Upper Kittanning clay, 407 Pennsylvania clays, Indian Territory, 315 Oklahoma, 400 Penn Yan, N. Y., 376 Penrose, cited, 6 Permeability of clay, 163 Permian clays, Indian Territory, 315 Nebraska, 362 Oklahoma, 400 West Virginia, 449 Perry County, Ohio, 395 Perry County, Pa., 402 Perth Amboy, N. J., 209 Peru, Neb., 363 Petersburg, Va., 437 Pe-tun-tse, 11 Phenolphthalein, 2 484 INDEX Philadelphia, Pa., 413 Phlogopite, solubility of, 2 Pholerite, in fire-clays, 51 in Missouri clays, 51, 355 properties of, 50 referred to, 40, 167 Physical properties of clay, 94 Physical tests of clays, Alabama, 284 Georgia, 303 Maryland, 339 Michigan, 347 Missouri, 361 New Jersey, 374 New York, 381 North Carolina, 387 Texas, 431 Virginia, 438 West Virginia, 450 Piedmont, W. Va., 445 Piedmont region, residual clays of, 12 Pierre shales, North Dakota, 389 South Dakota, 419 Pike County, Ark., 285 Pine Grove, Pa., 402 Pinkerton Point, Pa., 406 Pinson, Tenn., 422 Pipe-clay, defined, 196 Pipe-press, described, 240 Pittsburg, Kan., 326 Pittsburg, Pa., shales at, 411 Pitteburg coal, clay parting in, 413 referred to, 398, 411, 446 Plagioclase, as source of kaolmite, 3, 47 mentioned, 41 Plasticity, ball theory of, 99 cause of, 96 colloid theory of, 99 defined, 94 effect of bacteria on, 104 effect of weathering on, 104 molecular attraction theory of, 103 plate theory of, 97 relation to tensile strength, 120 texture theory of, 96 water necessary for developing, 95 water-of-h yd ration theory, 96 Platteville, Wis., 455, 456 Pleistocene clays, Alabama, 283 Colorado, 290 Connecticut, 295 Indiana, 313 Iowa, 322 Kansas, 327 Maryland, 337 mentioned, 52, 58, 185, 192, 285, 295 Michigan, 346 Minnesota, 351 Mississippi, 352 Missouri, 360 New Jersey, 371 New York, 378 North Dakota, 390 Pleistocene clays, Ohio. 398 Pennsylvania, 413 South Dakota, 419 Texas, 431 West Virginia, 437, 449 Wisconsin, 455 Pleistocene fullers' earth, 465 Plymouth, Vt, 333 Plymouth County, Iowa, 321 Pocahontas County, \\ . Va., 442 Polishing clay, 199 Pomona, N. C., 385 Porcelain, bone, defined, 272 electrical, 275 manufacture of, 271 spar, defined, 272 Porcelain-clay. See Kaolin Porosity, discussion of, 134 formula for calculating, 136 of Iowa clays, 135 practical bearing of, 135 Portage County, Ohio, 394 Portage County, Wis., 452 Portage shale, New York, 376 Porter County, Ind., 313 Port Huron, Mich., 346 Portland-cement clay, analyses, 198 properties of, 198 Port Murray, N. J., 364 Portsmouth, Chio, 392 Potash, in clay, 82 Pot-clay, 196, 214 Potomac clays, 296, 336, 352, 415 Potsdam, residual clay from, 12 Potsdam sandstone, A\ isconsin, 452 Potsdam shales, Wisconsin, 452 Pottery, bath-tubs, 276 china, defined, 262 classification, 262 common earthenware, defined, 262 C. C. ware, defined, 262 fayence, defined, 262 ironstone china, 262 majolica, defined, 262 Rockingham ware, defined, 262 sanitary ware, 276 semi-porcelain, 262 semi-vitreous ware, 262 stoneware, defined, 262 wash-tubs, 276 white granite ware, defined, 262 white ware, 262 yellow ware, defined, 262 Pottery clays, California, 289 Illinois, 304 Kentucky, 328 Maryland, 337 Massachusetts, 341 Nebraska, 363 Ohio, 394, 395, 396 Pennsylvania, 406, 407 South Dakota, 419 INDEX 485 Pottery clays, Tennessee, 421, 422 tensile strength of, 122 Texas, 426 See also Stoneware, Ball-clays, and Kaolin Pottery manufacture, 263 Potts ville, Md., 335 Potts ville, Pa., 402 Pottsville series, Pennsylvania, 393 West Virginia, 442 Pre-Cambrian clays, residual, 12 Georgia, 298 Minnesota, 348 Tennessee, 421 Wisconsin, 452 Pressed-brick clays, Indiana, 312 Iowa, 321 Kansas, 326 Maryland, 337 Massachusetts, 342 Minnesota, 348 New York, 376 Ohio, 392, 395 Pennsylvania, 406 Texas, 426, 428 Wisconsin, 456 Pressing, 269 Preston County, Virginia, 442 Prince George County, Md., 336, 337 Princeton, Minn., 351 Prochlorite, 41 Prosser, cited, 327, 392 Pug- mill, described, 220 mentioned, 240, 247, 252, 257, 265, 266 Pulaski County, Ark., 285 Pulaski County, 111., 304 Pulaski County, Ky., 329 Putnam Hill clay, Ohio, 394 Pycnometer, 137 Pyrite, mentioned,36, 71, 193, 311, 389, 427 occurrence in clay, 55 temperature of desulphurization, 74 weathering of, 55 Pyrometer, Lunette, 154 Seger cones, 148 thermo-electric, 153 Wedge wood, 154 Pyrophyllite, dehydration temperature, 52 mentioned, 51, 98 Pyroxene, 41 Q Quakertown clay and shale, Ohio, 393 Quakertown coal, Ohio, 393 Quartz, effect on clay, 53 origin, 4 referred to, 11, 41, 47, 48, 69, 77, 83, 136, 170, 210, 257, 385 weathering of, 4 Quartzite, as source of kaolin, 165, 293 Quaternary. See Pleistocene fullers' earth in, 462 Queen's Run, Pa., 406 R Racine, Wis., 455 Raleigh County, W. Va., 446 Rancocas formation, Md., 336 Randolph County, W. Va., 442 Ransome, F. L., cited, 6, 286 Rapid City, S. Dak., 419, 420 Rare elements in clay, 58 Raritan formation, Maryland, 336 New Jersey, 366 Rational analysis, compared with ulti- mate analysis, 62 described, 61 method of making, 66 Reading, 'Pa., 402 Rectorite, properties of, 51 Red Oak, Iowa, 321 Red Mountain, Colo., kaolinite crystals, 42 Red Wing, Minn., 348 Reeds ville, W. Va., 446 Re-pressing process, 232 Residual clays, analyses of, 13 Appalachian region, 12 California, 286 color of, 12 Connecticut, 293 defined, 7 depth of, 12 distribution of, 12 form of deposit, 11 from granite, 7 from limestone, 7 from pegmatite veins, 11 Georgia, 298 Indiana, 307 Maryland, 334, 335 Massachusetts, 340 mechanical analyses, 14 Minnesota, 348 Missouri, 354 New Jersey, 364 New York, 375 North Carolina, 385 origin of, 7 Pennsylvania, 401 Piedmont region, 12 rate of formation, 12 South Carolina, 415 Tennessee, 421 United States, 12 Vermont, 333 Virginia, 434 Washington, 441 West Virginia, 442 Wisconsin, 12, 452 Retort-clay, 196 486 INDEX Rhode Island, clays described, 415 references on, 415 Richmond, Va., 98, 437 Richmond shale, Ohio, 391 Richter, cited, 140, 142, 143 Richthofen, v., cited, 8 Ries, cited, 101, 104, 125, 137, 144, 461, 466 classification of, 27 Riley, Ind., 313 Ring -pits, 220, 252 Rochester, N. Y., 376 Rock Castle County, Ky., 329 Rockford, Iowa, 318 Rockingham ware, defined, 262 manufacture of, 270 Rockingham ware clay, Ohio, 397 Rock Run, Ala., 283 Rockwell, G. A., cited, 155 Rohland, P., cited, 100 Rolls, described, 219 Roman tile, 254 Roofing-tile, described, 254 manufacture of, 254 varieties of, 254 Roofing-tile clays, Illinois, 304 Kansas, 326 Missouri, 359 New York, 378 Ohio, 393 West Virginia, 446, 449 Rosenbusch, cited, 42 Rosenhayn, N. J., 371 Rosier, cited, 6, 47 Rusk, Tex., 431 Russell, I. C., cited, 186 Rutile, occurrence in clay, 56 S Sac County, Iowa, 321 Safford, J. M., cited, 421, 422 Sagger-clay, defined, 196 Ohio, 397 Saggers, 262, 272 Saginaw, Mich., 345, 346 St. Austell, England, kaolin at, 6 St. Charles, Mich., 345 St. Joseph County, Ind., 313 St. Louis, Mo., 84, 356 St. Louis clay, silica in, 69 Salem, Mass., 342 Salina, Kan., 327 Salina, Pa., 411 Salina shales, gypsum in, 56 New York, 376 Salisbury, R. D., cited, 41 Saltzburg sandstone, W. Va., 446 Saluda shale, Ohio, 391 San Antonio, Tex., 431 San Bernardino County, Cal., fullers' earth, 462 Sand, effect on shrinkage, 129 Sand-blast, 257 Sandstone, residual clay from, 12 Sand-wheels, 213 Sandy Ridge, Pa., 406 Sandy Run, Pa., 402 Saspamco, Tex., 431 Sayreville, N. J., 369 Scapolite, as source of kaolinite, 47 solubility of, 2 Schist, as source of kaolin, 165 formation of, 36 referred to, 434, 452 Schlossing, cited, 100 Schorl, 210 Schrotterite, 51 Sciotoville, Ohio, 329, 392 Scranton, Ohio, 395 Scumming, 157 Sebewaing, Mich., 345 Sections, Bellaire, Ohio, 397 Brazil, Ind., 311 Currier, Tenn., 423 Edgar, Fla., 297 Fairburn, S. Dak., 462 Georgia fullers' earth, 462 Grand Junction, Tenn., 422 Indiana Coal-measures, 311 kaolin -deposit, 13 Lewis ton, Ga., 301 New Cumberland, W. Va., 445 residual clay -deposit, 7 Upper Ohio River, 405 Zanesville, Ohio, 395 Sedimentary clays, described, 14 classification of, 18 Cretaceous, 17 distinguished from residual, 17 estuarine type, 19 flood -plain type, 20 lake type, 20 marine type, 19 origin, 14 structural irregularities, 17 swamp type, 20 Tertiary, 17 variations in, 17 Seger, H., cited, 73, 74, 77, 85, 94, 101, 104, 148, 174 Seger cones, 148 Selenite, 56 Semi-dry press process, described, 231 Semi-porcelain, defined, 262 Semi-vitreous ware, defined, 262 Semper, cited, 6 Serpentine, as source of clay, 1 Settling-tanks, 214 Sewanee coal, fire-clay with, 421 Sewell, Md., 337 Sewer-pipe clays, described, 183 distribution, 185 Indiana, 309, 312, 313 INDEX 487 Sewer .pipe clays, Indian Territory, 316 Maryland, 337 Micuigan, 345 Missouri, 359 North Carolina, 386 Ohio, 392, 393, 397 Pennsylvania, 411 properties of, 183 Texas, 431 Washington, 441 West Virginia, 445 Sewer-pipe manufacture, 240 Shaftsbury, Vt, 333 Shale, adsorptive power, 164 formation of, 164 tensile strength, 122 Sharon clay, Ohio, 393 Pennsylvania, 405 Sharon coal, Ohio, 393, 394 Sharon sandstone, Ohio, 393 Sharon shale, Ohio, 393 Shawano, Wis., 455 Sheboygan, Wis., 455 Shenandoah limestone clay, W. Va., 442 Shepherdstown, W. Va., 442 Sherman, Tex., 427 Shingle tile, 254 Shirley's Mills, Ala., 283 Shrinkage, cubic, Iowa clays, 135 measurement of, 132 See also Air- and Fire-shrinkage Siderite, decarbonation temperature, 74 forms of, 55 occurrence in clay, 55 referred to, 71 Sienna, 198 Sieverxi, S. C., 416 Silica, amount in clays, 69 combined, 68 determination of, 65 effect on clay, 69 fluxing action, 70, 140 free, 68 hydrous, 70 minerals containing, 68 Silica brick, Pa., 402 Sillimanite, as source of kaolinite, 47 Silurian clays, Indian Territory, 316 Iowa, 316 Kentucky, 328 Maryland, 335 Michigan, 342 New York, 376 Ohio, 390 Pennsylvania, 402 Slaking clays, 162 Slip-clays, analyses of, 195 fluxes in, 195 New York, 195 properties, 193 Texas, 431 uses, 195 Slip pump, 214 Smectite, 460, 461 Smith, J. L., cited, 50 Smith ville, Tenn., 421 Smock, J. C., cited, 137 Snyder County, Pa., 402 Soak-pit, described, 220 Socorro, N. Mex., 373 Soda, effect on clay, 82 minerals serving as source, 82 Sodalite, as source of kaolinite, 47 Soft- mud process, 220, 252 Solubility of minerals, 2 Soluble salts, 90, 182, 345 origin of, 90 prevention of, 92 quantity in bricks, 91 South Amboy, N. J., 181, 369 South Amboy fire-clay, 369 South Carolina, clays described, 415 coastal plain clays, 41 ii fullers' earth, 462 referred to, 179, 198 residual clays, 415 white clays, 416 South Dakota, clays described, 419 fullers' earth, 462 references on, 420 South Hadley, Mass., 341 South Haven, Mich., 346 South Mountain, Pa., white clay, 401 South River, N. J., 369 Specific gravity, discussion of, 136 determination of, 137 Iowa clays, 137 minerals in clay, 136 Missouri clays, 137 New Jersey clays, 137 Spencer, J. W., cited, 301 Spilman, W. Va., 446 Spodumene, solubility of, 2 Springs, relation to clay-beds, 163, 199 Stafford Court House, Md., 437 Stark County, Ohio, 394, 395, 396 Starke County, Ind., 313 Staten Island clay, rutile in, 56 Steindorfel, 460 Steubenville, Ohio, 398 Stevens Point, Wis., 452 Stewart County, Tenn., 421 Stiff-mud machine, 254 Stiff-mud process, described, 228 referred to, 247, 251, 252 Stockbridge, Wis., 455 Stockton, Cal., 289 Stone Mountain, Ga., halloysite at, 49 Stoneware, defined, 262 manufacture, 270 Stoneware-clay, chemical composition, 180 Connecticut, 295 Delaware, 296 Indiana, 312 488 INDEX Stone ware -clay, Iowa, 321 Kansas, 326 Maryland, 337, 338 Minnesota, 348 Mississippi, 352 Missouri, 181, 355, 359, 360 New Jersey, 181 New York, 181, 378 North Carolina, 386 Ohio, 180, 395, 397 physical properties, 180 physical tests, 181 Texas, 181, 427, 428, 431 uses, 182 Stover, E. C., cited, 104 Stream-clays, Wisconsin, 455 Strontium, adsorption by clay, 163 Structural features, sedimentary clays, 17 Sub-Carboniferous, Missouri, 355 Suffolk, Va., 437 Sullivan, adsorption experiments of, 164 Sulphates, adsorption by clay, 164 in clay, 91 Sulphur, in clay, 55 determination of, 66 scumming caused by, 157 Sulphur Springs, Tex., 428 Summers County, W. Va., 442 Summit County, Ohio, 394 Summit Station, Ohio, 392 Sunday Creek Valley, Ohio, 398 Swallows Falls, Md., 335 Swamp-clays, 30 Sylva, N. C., 385 Sylvan shale, 316 Synclines, 29 Syracuse, N. Y., 376 Table Rock, Neb., 363 Talc, 98 Tallahassee, Fla., 297 Tannin, adsorption by clay, 164 Taunton, Mass., 341 Taylor, Tex., 428 Taylor, Wash., 441 Taylorite, 458 Taylor-Navarro marls, Texas, 427 Tennessee, alluvial clays, 423 Carboniferous clays, 421 clays described, 420 Palaeozoic clays, 421 Pre-Cambrian clays, 421 references on, 424 referred to, 169 Tertiary clays, 422 Tensile strength, Beyer and Williams' ex- periments, 127 cause of, 123 definition, 120 effect of mixtures on, 127 measurement of, 120 Tensile strength, Missouri clays, 122 Orton's experiments, 123 practical bearing, 120 range in difterent clays, 122 relation to plasticity, 120 relation to texture, 123 Ries' experiments, 125 stone ware -clays, 123 Texas clays, 123 Terrace-clays, Pennsylvania, 413 Texas, 431 West Virginia, 449 See Flood- plain clays Terra- cotta, denned, 254 fayence, 254 manufacture of, 254 referred to, 179, 182 Terra-cotta clays, described, 182 distribution, 183 Maryland, 337 Missouri, 359 Massachusetts, 340 Nebraska, 363 New Jersey, 371 properties of, 182 tests of, 182, 184 Washington, 441 Terra-cotta lumber, denned, 248 Terra-cotta lumber clay, Pennsylvania, 413 Terra Haute, Ind., 313 Tertiary clays, Alabama, 283 Florida, 297 Kentucky, 329 Maryland, 337 Mississippi, 352 Missouri, 360 New Jersey, 370 New York, 378 North Dakota, 389 Oklahoma, 400 referred to, 28, 169, 179, 185, 197, 285, 289 sedimentary, 17 South Dakota, 419 Texas, 428 Tennessee, 422 Virginia, 437 Washington, 441 Wyoming, 457 Tertiary, fullers' earth in, 465 Tesserse, 258 Texas, calcareous clays, 56 Carboniferous clays, 426 clays described, 424 Cretaceous clays, 426 lignitic clays in, 428 Pleistocene, 431 references on, 433 referred to, 78, 84, 123, 165, 167, 179, 181 Tertiary clays, 428 Thermal waters, kaolinization by, 6 INDEX 489 Thompson, Minn., 348 Thornton, W. Va., 446 Thurber, Tex., 426 Tile. See Drain-, Poor-, Roofing-, and Wall-tile. Tile clays, Illinois, 304 Indiana, 307, 313 Indian Territory, 315 Io,va, 316, 318 Tennessee, 421, 422 Wisconsin, 455 Tioga County, Pa., 407 Tioiesti coal, Ohio, 393 Tionesta sandstone, Ohio, 393 Tishomingo County, Miss., 352 Titanite, 41 Titinium, determination of, 66 effect on clay, 84 in fire-clays, 176 range of, fn clays, 84 Toil, J. E., cited, 419 Toniwanda, N. Y., 378 Topiz, kaolinization of, 4, 47 Topeka, Kan., 326 Tounnaline, in c-lays, 41 in kaolin, 57,210 Tracy City, Tenn., 421 Transported clays, 14 Trenton, N. J., 370 Trenton limestone, Missouri clay in, 355 Triassic clays, Kansas, 327 New Jersey, 39, 364 North Carolina, 386 Virginia, 437 Troy, N. C., 385 Tucker County, W. Va., 442 Tuscaloosa, Ala., 283 Tuscarawas County, Ohio, 394, 395, 396 U Uffmgton shales, W. Va., 446 Ultimate analysis, explained, 59 interpretation of, 59 method of making, 64 Ultrimirine clay, 199 Union City, Mich., 346 Union County, Pa., 402 Union Furnace, Ohio, 394 Unite 1 States, residual clays in, 12 Up-draft kilns, 236 Upper Barren Measures. See Dunkard series Upper Coal -measures. See Monongahela series Upper Cretaceous, New Jersey, 370 Texas, 426, 428 Upper Freeport clay, Ohio, 397 West Virginia, '446 Upper Freeport coal, 411 Upper Kittanning clay, Pennsylvania, 407 Upper Marlboro, Md., 337 Upper Mercer coal, Ohio, 393 Upper Mercer fire-clay, Ohio, 393, 394 Upper Mercer limestone, Ohio, 393 Upper Productive Measures. See Monon- gahela aeries Upshur County, W. Va., 446 Valley Head, Ala., halloysite at, 49 Vanadiates, in clay, 57 Van Bemmelen, cited, 99 Vandalia, Mo., 356 Van Hise, C. K., cited, 47 Vanport limestone clay, Ohio, 395 Vaughan, T. W., cited, 461, 462 Vegetation of clay-soil, 200 Vermilion, S. Dak., 420 Vermont, clays described, 333 references on, 333 Verne, Mich., 345 Vintpn County, Ohio, 395 Virginia, Carboniferous clays, 437 clays described, 434 Conemaugh series clays, 446 diatomaceous earth, 437 fullers' earth, 462 Pleistocene clays, 437 references on, 441 referred to, 57, 84, 167 residual clays, 434 Tertiary clays, 437 Triassic clays, 437 Vitrification, relation to color, 162. stages of, 138 Vivianite, in clays, 58 Vogt, G., cited, 47, 104 Vogt, J. H. L., cited, 3, 4 Volume, determination of, 132 Volumeter for specific gravity determina- tion, 133 Segers', described, 137 Von Buch, cited, 6 W Waco, Ky., 328 Waco, Tex., 427 Wad-clay, defined, 197 referred to, 272 Walhalla, N. Dak., 390 Wallingford, Vt, 333 Wall-tile, manufacture of, 261 referred to, 198, 261 Ware-clay, defined, 196 Washing clay, 213 Washington, clays described, 441 references on, 441 Washington County, Ohio, 398 Washington, D. C., 296, 437 490 INDEX Wash-tubs, manufacture of, 276 Water, absorption of, by clay, 86 cneuiically coin Dined, 87 effect of, on clay, 86 effect on black coring, 90 mechanically combined, 86 relation to weathering, 2 Waupaca County, Wis., 455 Waushara County, Wis., 455 Way, T., cited, 99, 163 Weatherford, Tex., 426 Weathering, effect on plasticity, 104 processes, 1 Webb County, Tex., 428 Webster, N. C., 96, 167, 385 Wedgewood pyrometer, 154 Wedging-tables, described, 266 Weldon, N. C., 385 Wellsburg, W. Va., 446 West Cornwall, Conn., 293 West Mills, N. C., 385 Westmoreland County, Pa., 407, 411 Weston County, Wyo., 458 West Virginia, Carboniferous clays, 442 clays described, 442 Devonian clays, 442 Dunkard clays, 449 Lower Carboniferous clays, 442 Monongahela series clays, 446 Pleistocene clays, 449 references on, 451 referred to, 178, 179 Silurian clays, 442 Wet pan, described, 220 referred to, 240, 251, 252, 257 Wheeler, A. H., cited, 41, 49, 51, 95, 97, 98,* 104, 121, 122, 131, 137, 138, 146, 191, 196, 354 classification of, 24 White, I. C., cited, 398, 406 White granite ware, defined, 262 Whiteware, decoration of, 275 defined, 262 manufacture of, 271 White-ware clay, Missouri, 354. See also Kaolin Whitewash, 157 prevention of, 92 See Soluble salts Whitney, M., cited, 96 Whitneys, N. J., 371 Williams, I. A., cited, 123, 127, 137, 192, 251, 318 Wilkesboro, N. C., 385 Williamsport, Pa., 402 Willow Station, Ohio, 392 Will's Valley, Ala., 283 Wilmington, Tel., 296 Wilmont, Va., 437 Windom, N. Y., 376 Wisconsin, clays described, 451 minerals in, 41 Pleistocene clays, 455 references on, 456 referred to, 56, 78 residual clay in, 12, 452 sedimentary clays, 452 Wood County, Wis., 452 Woodbine formation, Tex., 427 Woodbridge, N. J., feldspar beds, 52 referred to, 196, 205, 209 Woodbridge fire-clay, 369 Woodbury County, Iowa, 321 Woodland, Pa., 406 Woodmansie, IS T . J., 371 Woodstock, Ala., 283 Woods town, N. J., 83 Woodward County, Okla., 400 Woolsey, cited, 407 Wrenshall, Minn., 351 Wyoming, clays described, 457 references on, 458 referred to, 128 Wyoming County, W. Va., 446 Yellow ware, clays for, 182, 397 defined, 262 manufacture of, 270 Zeolites, solubility of, 2 Zettlitz, Bohemia, 84, 100 kaolin at, 6 Zimmer, W. H., cited, 70, 153 Zinc-retorts, 179, 196 Zoisite, as source of kaolinite, 47 Zschokke, cited, 94, 99, 103 SHORT-TITLE CATALOGUE OF THE PUBLICATIONS OF JOHN WILEY & SONS, NEW YORK, LONDOK: CHAPMAN & HALL, LIMITED. ARRANGED UNDER SUBJECTS. Descriptive circulars sent on application. Books marked with an asterisk (*) are sold at net prices only, a double asterisk (**) books sold under the rules of the American Publishers' Association at net prices subject to an extra charge for postage. All books are bound in cloth unless otherwise stated. AGRICULTURE. Armsby's Manual of Cattle-feeding I2mo, Si 75 Principles of Animal Nutrition. . . e 8vo, 4 oo Budd and Hansen's American Horticultural Manual: Part I. Propagation, Culture, and Improvement i2mo, Part II. Systematic Pomology i2mo, Downing's Fruits and Fruit-trees of America 8vo, Elliott's Engineering for Land Drainage I2mo, Practical Farm Drainage \. i2mo, Graves's Forest Mensuration 8vo, Green's Principles of American Forestry i2mo, Grotenfelt's Principles of Modern Dairy Practice. (Woll.) I2mo, Kemp's Landscape Gardening I2mo, Maynard's Landscape Gardening as Applied to Home Decoration i2mo, * McKay and Larsen's Principles and Practice of Butter-making 8vo : Sanderson's Insects Injurious to Staple Crops I2mo, Insects Injurious to Garden Crops. (In preparation.) Insects Injuring Fruits. (In preparation.) Stockbridge's Rocks and Soils 8vo, 2 50 Winton's Microscopy of Vegetable Foods 8vo, 7 50 Woll's Handbook for Farmers and Dairymen i6mo, i 50 ARCHITECTURE. Baldwin's Steam Heating for Buildings I2mo, 2 50 Bashore's Sanitation of a Country House I2mo, i oo Berg's Buildings and Structures of American Railroads 4to, 5 oo Birkmire's Planning and Construction of American Theatres 8vo, 3 oo Architectural Iron and Steel 8vo, 3 50- Compound Riveted Girders as Applied in Buildings 8vo, 2 oo Planning and Construction of High Office Buildings 8vo, 3 50 Skeleton Construction in Buildings 8vo, 3 oo Erigg's Modern American School Buildings 8vo, 4 oo I Carpenter's Heating and Ventilating of Buildings 8vo, 4 oo Freitag's Architectural Engineering 8vo, 3 50 Fireproofing of Steel Buildings 8vo, 50 French and Ives's Stereotomy 8vo, 50 Gerhard's Guide to Sanitary House-inspection ibmo, oo Theatre Fires and Panics I2mo, 50 *Greene's Structural Mechanics 8vo, 50 Holly's Carpenters' and Joiners' Handbook i8mo, 75 Johnson's Statics by Algebraic and Graphic Methods 8vo, 2 oo Kidder's Architects' and Builders' Pocket-book. Rewritten Edition. i6mo,mor., 5 oo Merrill's Stones for Building and Decoration 8vo, 5 oo Non-metallic Minerals: Their Occurrence and Uses 8vo, 4 oo Monckton's Stair-building 4*0, 4 oo Patton's Practical Treatise on Foundations 8vo, 5 oo Peabody's Naval Architecture 8vo, 7 50 Rice's Concrete -block Manufacture 8vo, 2 oo Richey's Handbook for Superintendents of Construction i6mo, mor., 4 oo * Building Mechanics' Ready Reference Book. 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Boiler's Practical Treatise on the Construction of Iron Highway Bridges. .8vo, 2 oo * Thames River Bridge 4to, paper, 5 oo Burr's Course on the Stresses in Bridges and Roof Trusses, Arched Ribs, and Suspension Bridges 8vo, 3 50 Burr and Falk's Influence Lines for Bridge and Roof Computations 8vo, 3 o Design and Construction of Metallic Bridges 8vo. 5 oo Du Bois's Mechanics of Engineering. Vol. II Eirall 4to, 10 co Foster's Treatise on Wooden Trestle Bridges 4to, 5 oo Fowler's Ordinary Foundations 8vo, 3 50 Greene's Roof Trusses 8vo, i 25 Bridge Trusses 8vo, 2 50 Arches in Wood, Iron, and Stone 8vo t 2 50 Howe's Treatise on Arches 8vo, 4 oo Design of Simple Roof- trusses in Wood and Steel 8vo, 2 oo Symmetrical Masonry Arches 8vo, 2 50 Johnson, Bryan, and Turneaure's Theory and Practice in the Designing of Modern Framed Structures Small 4to, 10 oo Merriman and Jacoby's Text-book on Roofs and Bridges: Part I. Stresses in Simple Trusses 8vo, 2 50 Part II. 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