> OF THF UNIVERSITY Jl 11 1 I ECONOMIC GEOLOGY OF THE UNITED STATES BY HEINRICH RIES, A.M., PH.D. ASSISTANT PROFESSOR OF ECONOMIC GEOLOGY AT CORNELL UNIVERSITY THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1905 All rights reserved COPYRIGHT, 1905, BY THE MACMILLAN COMPANY. Set up and electrotyped. Published November, 1905. Nortoaoti $wgg J. S. Cashing & Co. Berwick & Smith Co. Norwood, Mass., U.S.A. PREFACE THE following work on the Economic Geology of the United States covers essentially the ground which is gone over in the elementary course in this subject in Cornell University, but it is hoped that it will prove useful as a text-book in other colleges. The mode of arrangement is markedly different from that found in other books on the same subject, in that the non- metallic minerals are discussed first and the metallic minerals last. This, to the author, seems the most desirable method of treatment, for the reason that the non-metallics are not only the most important, the value of their production having exceeded the metallics by over one hundred and fifty million dollars in 1903, but also because it leads from a discussion of the simpler to the more complex forms of mineral deposits. It has rtot been thought desirable to include a chapter on geologic and physiographic principles, since the space which could be allotted to it is altogether too small, and, more- over, the study of economic geology presupposes a knowl- edge of geology and mineralogy on the part of the student. While the references given at the end of each chapter do not include every paper that has been written on the subject to which they refer, still it is believed that they are suffi- ciently numerous to permit one to follow out the subject in considerable detail if he so desire. In the preparation of the manuscript all available sources of information have been freely drawn upon, and the num- bers in parentheses in the text refer to the numbered refer- ences at the end of each chapter. v VI PREFACE All statistical figures, unless otherwise stated, are taken from the reports of the United States Geological Survey. Descriptions of mineral occurrences in foreign countries are not included, except in a few cases where the deposits serve as an important if not the only source of supply for the United States. The writer wishes to express his thanks to Professor R. S. Tarr for examination and criticism of much of the manu- script, and to W. E. McCourt, Instructor in Geology, and H. Leighton, Assistant in Geology, for aid in the preparation of drawings and statistical tables. For the loan of photo- graphs or cuts acknowledgments are due to Messrs. H. F. Bain, J. E. Spurr, J. M. Boutwell, G. H. Eldridge, W. Lind- gren, F. H. Oliphant, and J. H. Pratt of the United States Geological Survey ; Professor A. C. Lane, Michigan Geologi- cal Survey ; Dr. D. H. Newland, New York State Museum ; Professor C. C. O'Harra, South Dakota School of Mines; Professor E. A. Smith, Alabama Geological Survey ; Pro- fessor G. H. Perkins, Vermont Geological Survey ; Dr. H. B. Kiimmel, New Jersey Geological Survey ; Dr. W. B. Phillips, Texas Geological Survey; Dr. G. P. Merrill, United States National Museum; also to Messrs. H. W. Turner, F. S. Witherbee, A. W. Sheafer, L. Martin, Wiley & Sons, Ver- mont Marble Co., and Bedford Quarries Co. CORNELL UNIVERSITY, ITHACA, N.Y., June, 1905. CONTENTS PAGE PREFACE '. . . v CONTENTS vii LIST OF ILLUSTRATIONS xv LIST OF ABBREVIATIONS . xxi PAET I NON-METALLIC MINERALS CHAPTER I COAL 3-38 Kinds of coal, 3 ; Peat, 3 ; Lignite, 4 ; Bituminous coal, 4 ; Cannel coal, 5 ; Semi-bituminous coal, 5 ; Anthracite coal, 5 ; Proximate analysis of coal, 6 ; Origin of coal, 9 ; Conditions of vegetable accumulation, 10 ; Chemical changes occurring during coal forma- tion, 12 ; Effect of heat and pressure, 14 ; Structural features of coal beds, 15 ; Outcrops, 15 ; Associated rocks, 16 ; Variations in thickness, 16 ; Other irregularities, 17 ; Coal fields of the United States, 18; Geologic distribution of coals in the United States, 19; Appalachian field, 20 ; Bituminous area, 21 ; Character of Appa- lachian bituminous coals, 22 ; Pennsylvania anthracite field, 22 ; Rhode Island field, 25 ; The Triassic field, 25 ; Eastern Interior field, 26 ; Northern Interior field, 27 ; Western Interior field and southwestern fields, 28 ; Western Interior field, 29 ; Southwestern field, 29 ; Gulf states lignite area, 30 ; Rocky Mountain fields, 30 ; The Pacific Coast fields, 31 ; Alaska, 32 ; Production of coal, 33 ; Production of coke, 35 ; References on coal, 35 ; References on peat, 38. CHAPTER II PETROLEUM, NATURAL GAS, AND OTHER HYDROCARBONS . History of petroleum development, 39 ; History of natural gas development, 40 ; Properties of petroleum, 40; Properties of natural gas, 42 ; Mode of occurrence, 43 ; Pressure of oil and gas wells, 44 ; Origin, 46 ; Inorganic theory, 46 ; Organic theory, 47 ; Geological vii Viii CONTENTS distribution of petroleum and natural gas, 48 ; Distribution of petroleum in the United States, 48 ; Appalachian field, 48 ; Ohio- Indiana field, 50 ; Texas-Louisiana oil fields, 51 ; Kansas, 52 ; Cali- fornia, 52 ; Wyoming, 53 ; Colorado, 53 ; Alaska, 54 ; Distribution of natural gas in the United States, 54 ; New York, 54 ; Pennsyl- vania, 54 ; West Virginia, 55 ; Ohio, 55 ; Indiana, 55 ; Kansas, 55 ; Uses of petroleum, 56 ; Uses of natural gas, 56 ; Oil shales, 56 ; Solid bitumens, 57 ; Occurrence, 57 ; Asphaltites, 58 ; Albertite, 59 ; Anthraxolite, 59 ; Ozokerite, 59 ; Grahamite, 59 ; Lake asphalt, 59 ; Uintaite or gilsonite, 59 ; Manjak, 59 ; Bituminous rocks, 60 ; Analyses, 60 ; Uses, 61 ; Production of petroleum, natural gas, and asphaltum, 61 ; References on petroleum, 66 ; References on natural gas, 67 ; References on oil shale, 67 ; References on as- phaltum, 67. CHAPTER III BUILDING STONES 69-91 Properties of building stones, 69 ; Color, 70 ; Texture, 70 ; Den- sity, 70 ; Hardness, 71 ; Strength, 71 ; Crushing strength, 72 ; Transverse strength, 72 ; Porosity and ratio of absorption, 73 ; Resistance to frost, 73 ; Resistance to heat, 73 ; Structural features affecting quarrying, 74 ; Bedding planes, 74 ; Granites, 75 ; Char- acteristics of granites, 75 ; Distribution of granites in the United States, 76 ; Eastern crystalline belt, 77 ; Central states, 77 ; West- ern states, 77 ; Uses of granite, 77 ; Miscellaneous igneous rocks, 78 ; Limestones and marbles, 78 ; General characteristics, 78 ; Varieties of limestones, 79 ; Distribution of limestones in the United States, 80 ; Distribution of marbles in the United States, 81 ; Onyx marbles, 83 ; Serpentine, 83 ; Sandstones, 84 ; General properties, 84 ; Varieties of sandstone, 85 ; Distribution of sand- stones in the United States, 86 ; Uses of sandstones, 87 ; Slates, 87 ; General characteristics, 87 ; Distribution of slates in the United States, 88 ; Uses of slate, 89 ; Production of building stones, 89 ; References on building stones, 90 ; References on onyx marble, 91. CHAPTER IV CLAY 92-108 Definition, 92 ; Residual clays, 92 ; Sedimentary clays, 93 ; Marine clays, 94 ; Flood-plain clays, 94 ; Lake clays, 94 ; Glacial clays, 94 ; ^Eolian clays, 94 ; Properties of clay, 95 ; Chemical properties, 95; Physical properties, 96; Plasticity, 96; Tensile strength, 96 ; Shrinkage, 96 ; Fusibility, 97 ; Specific gravity, 97 ; CONTENTS i x PAGE Chemical composition, 97 ; Classification of clay, 98 ; Kinds of clay, 99 ; Geological distribution, 100 ; Distribution of clays in the United States by kinds, 100 ; Kaolins, 100 ; Fire clays, 102 ; Pot- tery clays, 103 ; Brick and tile clays, 104 ; Miscellaneous clays of importance, 104 ; Uses of clay, 105 ; Production of clay, 105 ; References on clay, 106. CHAPTER V LIME AND CALCAREOUS CEMENTS ....... 109-123 Composition of limestone, 109 ; Changes in burning, 110 ; Lime, 110; Hydraulic cements, 111; Pozzuolano cements, 111; Hy- draulic limes, 112 ; Natural rock cements, 112 ; Portland cement, 113 ; Distribution of lime and cement materials in the United States, 116 ; Limestone for lime, 116 ; Hydraulic limes, 117 ; Natural rock cement, 117 ; Portland cements, 118 ; Uses of lime, 119 ; Uses of cement, 119 ; Production of cement, 120 ; References on lime and cement materials, 121. CHAPTER VI SALINES ' . . . . . . 124-138 Salt, 124 ; Occurrence of salt in sea and lake waters, 124 ; Rock salt, 125; Origin of rock salt, 125; Natural brines, 127; Salt marshes and soils, 127 ; Distribution of salt in the United States, 127; New York, 127; Michigan, 129; Other eastern states, 129; Louisiana, 129 ; Kansas, 130 ; Other western states, 130 ; Extrac- tion, 131 ; Uses, 132 ; Production of salt, 132 ; References on salt, 134; Borax, 134; Borax minerals, 134; Distribution in United States, 134 ; Uses, 134 ; Production of borax, 136 ; References on borax, 136 ; Sodium sulphate, 136; References, 137 ; Sodium car- bonate, 137 ; References, 137 ; Soda niter, 137 ; References, 138. CHAPTER VII GYPSUM 139-146 Gypsum, 139 ; Anhydrite, 139 ; Origin of gypsum, 139 ; Gypsite, 140 ; Distribution in the United States, 140 ; Iowa, 140 ; Kansas, 141 ; Michigan, 142 ; New York, 142 ; Other occurrences, 142 ; Analyses, 143 ; Uses, 143 ; Production of gypsum, 145 ; References on gypsum, 146. CHAPTER VIII FERTILIZERS 147-157 Phosphate of lime, 147 ; Apatite, 147 ; Amorphous phosphates, 147 j Florida phosphates, 148 ; Land pebble or matrix rock, 149 ; CONTENTS PACK River pebble, 149 ; South Carolina phosphates, 150 ; Tennessee phosphates, 150 ; Other phosphate occurrences, 153; Composition, 153 ; Uses, 154 ; Guano, 156 ; Greensand, 155 ; Production, 156 ; References on fertilizers, 157. CHAPTER IX ABRASIVES 158-166 Introductory, 158 ; Grindstones, 158 ; Whetstones and oilstones, 159 ; Buhrstones and millstones, 161 ; Pumice and volcanic ash, 161 ; Infusorial earth and tripoli, 162 ; Crystalline quartz, 163 ; Garnet, 163 ; Corundum and emery, 163 ; Artificial abrasives, 165 ; Production of abrasives, 165 ; References on abrasives, 166. CHAPTER X MINOR MINERALS 167-203 Asbestos, 167 ; Asbestos minerals, 167 ; Distribution, 167 ; Uses, 169 ; Production of asbestos, 169 ; References on asbestos, 169 ; Barite, 170 ; Uses, 170 ; Production, 170 ; References on barite, 171 ; Fluorspar, 171 ; Distribution in United States, 172 ; Uses, 173 ; References on fluorspar, 174 ; Fuller's earth, 174 ; Production of fuller's earth, 176 ; References on fuller's earth, 176 ; Glass sand, 176 ; References on glass sand, 178 ; Graphite, 178 ; Distribution of graphite in the United States, 178 ; Uses, 179 ; Production of graphite, 180 ; References on graphite, 181 ; Lithographic stone, 181 ; References on lithographic stone, 183; Lithium, 183; Mag- nesite, 183 ; References on magnesite, 184 ; Mica, 184 ; References on mica, 186 ; Mineral pigments, 186 ; Hematite, 186 ; Ochers, 186 ; Slate, 187 ; Gypsum, 187 ; Barite, 187 ; Asbestos, 188 ; Graphite, 188 ; Calcium carbonate, 188 ; Other paints, 188 ; Production of mineral pigments, 189 ; References on mineral paints, 189 ; Mold- ing sand, 189 ; References on molding sand, 190 ; Monazite, 190 ; Uses, 191 ; Production of monazite, 191 ; References on monazite, 191 ; Precious stones, 192 ; Diamond, 192 ; Ruby, 193 ; Sapphire, 193 ; Emerald, 193 ; Topaz, 194 ; Turquoise, 194 ; Garnet, 194 ; Opal, 195 ; Other precious stones, 195 ; Production of precious stones, 195 ; References on precious stones, 196 ; Sulphur and pyrite, 196 ; Sulphur, 196 ; Solfataric type, 196 ; Gypsum type, 197 ; Uses, 198; Production of sulphur, 198; References on sulphur, 199 ; Pyrite, 199 ; Distribution, 199 ; Uses, 200 ; References on pyrite, 200 ; Strontium, 200 ; Uses, 201 ; References on strontium, 201 ; Talc and soapstone, 201 ; Uses, 202 ; Pyrophyllite, 203 ; Production, 203 ; References on talc and soapstone, 203. CONTENTS CHAPTER XI PAGE WATER ............ 204-212 Mineral waters, 204 ; Distribution of mineral waters in the United States, 205 ; Production of mineral waters, 206 ; References on mineral waters, 207 ; Underground waters, 207 ; Ground water, 207 ; Artesian waters, 209 ; References on underground water, 211. CHAPTER XII SOILS AND ROAD MATERIALS ....... 213-219 Soils, 213 ; Origin, 213 ; Residual soils, 213 ; Transported soils, 213 ; Properties of soils, 213 ; Chemical properties, 214 ; Physical properties, 215 ; Distribution of soils in the United States, 216 ; References on soils, 216 ; Road materials, 217 ; References on road materials, 219. PART II METALLIC MINERALS OR ORES CHAPTER XIII ORE DEPOSITS .......... 223-250 Definition, 223 ; Gangue minerals, 223 ; Origin of ore bodies, 224 ; Ores of contemporaneous origin, 224 ; Concentration of ores in rocks, 225 ; Formation of cavities, 231 ; Precipitation of metals from solution, 232 ; Replacement or metasomatism, 233 ; Concen- tration by eruptive after-action or pneumatolysis, 234 ; Other- causes of precipitation, 235 ; Forms of ore bodies, 236 ; Fissure veins, 236 ; Other forms of ore deposits, 241 ; Secondary changes in ore deposits, 242 ; Weathering or superficial alteration, 242 ; Secondary deposition below water level, 244 ; Value of ores, 245 ; Classification of ore deposits, 246 ; References on ore deposits, 249. CHAPTER XIV IRON 251-277 Ores of iron, 251 ; Magnetite, 254 ; Distribution of magnetites in . the United States, 254; Non-titaniferous magnetites, 254; Other occurrences, 254 ; Titaniferous magnetites, 257 ; Magnetite sands, 258 ; Hematite, 259 ; Distribution of hematite ores in the United States, 259 ; Lake Superior region, 259 ; Clinton ore, 266 ; Other Xll CONTENTS PAGE hematite occurrences, 268 ; Limonite, 269 ; Bog ores, 269 ; Residual limonites, 270 ; Other occurrences, 271 ; Siderite, 272 ; Production of iron ores, 273 ; References on iron ores, 276. CHAPTER XV COPPER 278-302 Ores, 278 ; Impurities in copper ores, 280 ; Superficial alteration of copper ores, 280; Distribution of copper ores in the United States, 281 ; Montana, 282 ; Michigan, 287 ; Arizona, 290 ; Bisbee or Warren district, 290 ; Jerome district, 292 ; Clifton district, 293 ; Globe district, 294 ; Appalachian region, 294 ; Utah, 296 ; Cali- fornia, 297 ; Other occurrences, 298 ; Uses of copper, 298 ; Produc- tion of copper, 299 ; References on copper, 301. CHAPTER XVI LEAD AND ZINC 303-324 Ores of lead, 303 ; Ores of zinc, 303 ; Superficial alteration of lead and zinc ores, 305 ; Distribution of lead and zinc ores in the United States, 305 ; Lead alone, 306 ; Appalachian belt, 306 ; South- eastern Missouri, 306 ; Desilverized lead, 307 ; Zinc ores alone, 307 ; Eastern and southern states, 308; Sussex County, N.J., 308 ; Virginia and Tennessee, 310 ; Pennsylvania, 311 ; Lead and zinc ores of the Mississippi Valley region, 311 ; Upper Mississippi Valley area, 311 ; Ozark region, 314 ; Origin of the ores, 316 ; Rocky Mountain states, 318 ; Uses of lead and zinc, 319 ; Uses of lead, 319 ; Uses of zinc, 320 ; Production of lead and zinc, 321 ; Refer- ences on lead and zinc, 323. CHAPTER XVII GOLD AND SILVER 325-363 Ores of gold, 325 ; Ores of silver, 325 ; Mode of occurrence, 326 ; Weathering and secondary enrichment, 327 ; Classification, 327 ; Geological distribution, 329 ; Extraction, 329; Distribution of gold and silver ores, 331 ; Cordilleran region, 332 ; Pacific coast Creta- ceous gold-quartz ores, 332 ; Mother Lode belt, 333 ; Nevada County, 334 ; Central belt of gold-silver ores, 335 ; Mercur, Utah, 336 ; Other occurrences, 337 ; Eastern belt of Tertiary gold-silver veins, 337 ; Cripple Creek, 338 ; San Juan region, 341 ; Tonopah, Nev. , 343 ; Comstock Lode, Nev. , 344 ; Other occurrences, 345 ; . Auriferous gravels, 346 ; Black Hills region, 350 ; Homestake belt, CONTENTS xiii PAGE 351 ; Siliceous Cambrian ores, 352 ; Michigan region, 352 ; Eastern crystalline belt, 352 ; Alaska, 353; Uses of gold, 357 ; Uses of silver, 358; Production of gold and silver, 358; References on gold and silver, 360. CHAPTER XVIII SILVER-LEAD . 364-374 Silver-lead ores, 364 ; Leadville District, Colo., 364 ; Aspen, Colo., 367 ; Other occurrences, 369 ; Park City, Utah, 370 ; Tintic District, Utah, 372 ; Coeur d'Alene, Ido., 372 ; Montana, Nevada, etc., 373 ; References on silver-lead ores, 374. CHAPTER XIX ALUMINUM, MANGANESE, AND MERCURY ..... 375-395 Ores of aluminum, 375 ; Distribution of bauxite in the United States, 376 ; Georgia-Alabama, 377 ; Arkansas, 378 ,- New Mexico, 379 ; Uses of aluminum, 379 ; Uses of bauxite, 380 ; Production of bauxite and aluminum, 380 ; References on bauxite and alumi- num, 383 ; Manganese, 383 ; Manganese ores, 383 ; Origin, 384 ; Distribution of manganese ores in the United States, 384 ; Eastern area, 385 ; Arkansas, 387 ; Other United States occurrences, 387 ; Uses of manganese, 388 ; Production of manganese, 388 ; Refer- ences on manganese, 390 ; Ores of mercury, 390 ; Mode of occur- rence, 390 ; Distribution in the United States, 390 ; California, 391 ; Texas, 392 ; Origin, 393 ; Uses of mercury, 393 ; Production of mercury, 394 ; References on mercury, 395. CHAPTER XX MINOR METALS 396-417 Ores of antimony, 396 ; Distribution of antimony in the United States, 396 ; Uses, 397 ; Production of antimony, 397 ; References on antimony, 397 ; Arsenic, 398 ; References on arsenic, 398 ; Bis- muth, 399 ; Ores, 399 ; Distribution, 399 ; Uses and production, 399 ; Ores of chromic iron, 399 ; Origin of chromite, 400 ; Analyses, 400 ; Distribution of chromic iron in United States, 400 ; Uses, 401 ; Production of chromite, 402 ; References on chromic iron ore, 402 ; Molybdenum, ores and occurrences, 403; Uses of molybdenum, 403 ; Production of molybdenum, 403 ; References on molybdenum, 403 ; Nickel and cobalt, 403 ; Ores, 403 ; Distribution, 404; Eastern occurrences of nickel, 404 ; Other occurrences, 405 ; Uses of nickel, 405 ; Uses of cobalt, 406 ; Production, 406 ; References on nickel XIV CONTENTS and cobalt, 407; Platinum group of metals, 407.; Platinum, 407; Distribution in the United States, 407 ; Uses of platinum, 408 ; Pro- duction of platinum, 408 ; References on platinum, 409 ; Palladium, 409 ; Osmium, 409 ; Iridium, 410 ; Tin, 410 ; Ores, 410 ; Mode of occurrence, 410 ; Distribution in the United States, 411 ; Uses of tin, 412 ; Production of tin, 412 ; References on tin, 413 ; Titanium, 413 ; Ores, 413 ; Occurrence, 413 ; Uses, 414 ; References on tita- nium, 414 ; Tungsten, 414 ; Ores, 414; Occurrence, 415 ; Uses, 416 ; Production, 415 ; References on tungsten, 416 ; Uranium and vana- dium, 416 ; Ores, 416 ; Uses, 416 ; Production, 416 ; References on uranium and vanadium, 417. LIST OF ILLUSTRATIONS FIG. PAGE 1. Diagram showing changes occurring in passage of vegetable tissue to graphite .......... 13 2. Section in coal measures of western Pennsylvania, showing fire clay under coal beds 16 3. Section showing irregularities in coal seam. , split ; 6, parting of shale ; c, pinch ; d, swell ; e, cut out 17 4. Section of faulted coal seam 17 5. Section across Coosa, Ala. , coal field, showing folding and faulting characteristic of southern end of Appalachian coal field . . 20 6. Map of Pennsylvania anthracite field 23 7. Sections in Pennsylvania anthracite field 24 8. Coal breaker in Pennsylvania anthracite region . . . . 25 9. Section across Eastern Interior coal field 26 10. Shaft house and tipple, bituminous coal mine, Spring Valley, 111. . 27 11. Generalized section of Northern Interior coal field .... 28 12. Composite section showing structure of lower coal measures in Iowa 29 13. Section of anticlinal fold showing accumulation of gas, oil, and water 43 14. Map showing oil and gas fields of United States .... 49 15. Geological section in Ohio-Indiana oil and gas field ... 50 16. Section of Spindle Top oil field near Beaumont, Tex. ... 51 17. Section in Los Angeles oil field . . . . . . ' . 53 18. Map of asphalt and bituminous rock deposits of United States . 68 19. Section of Gilsonite vein, Utah 59 20. Map showing distribution of crystalline rocks (mainly granite) in United States 76 21. Map showing marble areas of eastern United States ... 81 22. Section showing cleavage and bedding in slate .... 87 23. Section in slate quarry with cleavage parallel to bedding, a, purple slate ; 6, unworked ; c and d, variegated ; e and /, green ; g and /&, gray green ; i, quartzite ; .?', gray with black patches . 88 24. Section showing formation of residual clay 93 25. Section of a sedimentary clay deposit 93 26. Map showing distribution of salt-producing areas in United States, compiled from various geological survey reports . . . 128 27. Map showing gypsum-producing localities of United States . . 141 28. Map of Florida phosphate deposits 148 29. Map of Tennessee phosphate areas 151 xv XVI LIST OP ILLUSTRATIONS PAGE FIG. 30. Vertical section showing geologic position of Tennessee phosphates 152 31. Map showing distribution of abrasives in United States . . .159 32. Section showing occurrence of corundum around border of dunite mass 164 33. Asbestos vein in serpentine ...... 168 34. Ideal section across a river valley, showing the position of ground water and the undulations of the water table with reference to the surface of the ground and bed rock 208 35. Geologic section of Atlantic Coastal Plain, showing water-bearing horizons .......... 210 36. Section from Black Hills across South Dakota, showing artesian well conditions 211 37. Replacement vein in syenite rock, War Eagle mine, Rossland, B.C. a, granular orthoclase with a little sericite ; 6, secondary biotite ; q, secondary quartz ; c, chlorite ; black, secondary pyrrhotite 234 38. Section of vein in Enterprise mine, Rico, Colo. The right side shows later banding due to reopening of the fissure . . . 237 39. Section showing change in character of vein passing from gneiss (0) to soft shale (_p) 238 40. Tabulation of strikes of principal veins in Monte Cristo, Wash., district 239 41. Linked veins ........... 240 42. Gash vein with associated "flats" and "pitches" Wisconsin zinc region 240 43. Section at Bonne Terre, Mo., showing ore disseminated through limestone ........... 241 44. Section through Copper Queen mine, Bisbee, Ariz., showing varia- ble depth of weathering 243 45. Map showing distribution of iron ores in United States . . . 253 46. Map of Lake Superior iron regions, shipping ports, and transporta- tion lines . . 259 47. Sections of iron ore deposits in Marquette range .... 260 48. Generalized vertical section through Penokee-Gogebic ore deposit and adjacent rocks, Colby mine, Bessemer, Mich. . . . 261 49. Generalized vertical section through Mesabi ore deposit and adja- cent rocks 262 50. Section of Clinton ore beds, Oxmoor, Ala. a, red sandstone, 5' ; &, yellow sandstone, 6' ; c, red sandstone, 15' ; d, ore, 22', upper 2' soft ; e, shale, 6' ; /, rich ore, 2' 6" . . . . 266 51. Section illustrating formation of residual limonite in limestone . 270 52. Map showing distribution of copper ores in United States . . 282 53. Map of Butte, Mont., district, showing distribution of veins and geology ........... 283 54. Section at Butte, Mont., showing mode of occurrence of the ore . 284 LIST OF ILLUSTRATIONS xvii PAGE FIG. 55. Section across Keweenaw Point . ... 287 56. Section showing occurrence of amygdaloidal copper, Quincy mine, Michigan 288 57. Geological section at Bisbee, Ariz. ..... 291 58. Generalized section of ore bodies at Bisbee, Ariz 292 59. Section of Morenci district. P, porphyry ; S, unaltered sediments ; F, fissure veins; M, metamorphosed limestone and shale; O, contact metamorphic ores ; R, disseminated chalcocite . 293 60. Section of ore body at Bully Hill, Calif 298 61. Map showing distribution of lead and zinc ores in United States . 305 62. Generalized section of southeastern Missouri lead region . . 306 63. Model of Franklin zinc-ore body 309 64. Section of Bertha zinc mines, Wythe County, Va., showing irregu- lar surface of limestone covered by residual clay bearing ore . 310 65. Section showing occurrence of lead and zinc ores in Wisconsin, with fissure ore in flats and pitches, and disseminated ore in oil rock . . . . . . . . . . . 312 66. Map of Ozark region . , . . . . . . . 314 67. Generalized section showing occurrence of lead and zinc ore in southwestern Missouri . . . . . -. . . 315 68. A typical hoisting outfit in the southwestern Missouri zinc region . 316 69. Map showing distribution of gold and silver ores in United States . 331 70. Map and section of portion of Mother Lode district, Calif. Pgv, river gravels, usually auriferous ; Ng, auriferous river gravels. Sedimentary rocks : Jw, mariposa formation (clay, slate, sand- stone, and conglomerate) ; Cc, calaveras formation (slaty mica schists). Igneous rocks : Nl, latite ; Nat, andesite tuffs, breccia, and conglomerate ; mdi, meta-diorite ; Sp, serpentine ; ma, meta-andesite ; aras, amphibole schist .... 334 71. Section illustrating relations of auriferous quartz veins at Nevada City, Calif . . . .335 72. Section at Mercur, Utah . *. . . . . . . . 336 73. Map of Colorado showing location of mining regions . . . 338 74. Section of vein at Cripple Creek, Colo 339 75. Geologic map of Telluride district, Colorado, showing outcrop of more important veins . . 342 76. Ideal cross section of rocks at Tonopah, Nev 343 77. Section of Comstock Lode. D, diorite ; Q, quartz ; V, vein matter in earlier diabase (Db) ; H, earlier hornblende andesite ; A, augite andesite 344 78. Generalized section of old placer, with technical terms, a, volcanic cap ; 6, upper lead ; c, bench gravel ; d, channel gravel . . 347 79. Section of Homestake Belt at Lead, S.D., showing relation of ancient and modern placers to Homestake Lode . . . 350 XV111 LIST OF ILLUSTRATIONS FIG. PAGE 80. Typical section of siliceous gold ores, Black Hills, S.D. . . . 351 81. Map showing mineral deposits of Alaska as far as known . . 354 82. Sketch map of Douglas Island, Alaska 355 83. Cross section through Alaska Treadwell mine on northern side of Douglas Island 356 84. Ideal section across Leadville district 366 85. Section of ore body at Aspen, Colo. 368 86. Diagrammatic section across a northeasterly lode at Rico, Colo., showing " blanket " of ore 369 87. Vein filling a fault fissure, Enterprise mine, Rico, Colo. . . 370 88. Section of lead-silver vein, CcEUr d'Alene, Ido 373 89. Geologic map of Alabama-Georgia bauxite region .... 377 90. Section of bauxite deposit, a, Residual mantle ; 6, Red sandy clay soil; c, Pisolitic ore; d, Bauxite with clay; e, Clay with bauxite ; /, Talus ; #, Mottled clay ; A, Drainage ditch . . 378 91. Map showing Georgia manganese areas ...... 385 92. Section in Georgia manganese area showing geologic relations of manganese, limonite, and ocher 386 93. Section of Batesville, Ark. , manganese region, illustrating geological structure and relation of different formations to marketable and non-marketable ore ........ 387 94. Map of California mercury localities 391 95. Map showing Texas mercury region 392 96. Section of cinnabar vein in limestone, Terlingua, Tex. . . . 393 97. Sketch map showing location of Carolina tin belt . . . .411 PLATES. I. Map showing distribution of coal hi United States. Frontispiece II. Fig. 1. Pit working (stripping) near Milnesville, Pa. The mammoth seam is uncovered in bottom of pit . . . 31 Fig. 2. Lignite seam, Williston, N.D 31 III. Fig. 1. General view of Tuna Valley, in Pennsylvania oil field 48 Fig. 2. View in Los Angeles, Calif., oil field. Such close spac- ing of oil derricks tends to hasten the exhaustion of the oil supply 48 IV. General view of Spindle Top oil field, Beaumont, Tex. . .51 V. Fig. 1. Quarry of bituminous sandstone, Santa Cruz, Calif. . 60 Fig. 2. Granite quarry, Hard wick, Vt. . . . . .60 VI. Quarry in limestone, Bedford, Ind. . . ... .80 VII. Marble quarry, Proctor, Vt 82 VIII. View of green slate quarry, Pawlet, Vt. ..... 88 IX. Bank of sedimentary clay, Woodbridge, N.J. This section affords at least five kinds of clay 103 X. Fig. 1. Quarry of natural cement rock, Cumberland, Md. . 117 Fig. 2. Marl pit at Warners, N.Y. The dark streaks are peat and the marl is underlain by clay .... 117 XI. Fig. 1. Interior view of salt mine, Livonia, N.Y. . . . 129 Fig. 2. Borax mine near Daggett, Calif. .... 129 XII. Fig. 1. Gypsum quarry, Alabaster, Mich. Shows gypsum overlain by glacial drift. The dump in foreground is over- burden removed from gypsum 139 Fig. 2. Rock phosphate mine near Ocala, Fla. . . .139 XIII. Fig. 1. Grindstone quarry, Tippecanoe, Ohio . . . .159 Fig. 2. Corundum vein between peridotite and gneiss, Corun- dum Hill, Ga 159 XIV. Fig. 1. View of open cut in magnetite deposit, Mineville, N.Y. The pillars are ore left standing to support the gneiss hanging wall ...... 254 Fig. 2. General view of magnetic separating plants and shaft houses, Mineville, N.Y 254 XV. Fig. 1. Iron mine, Soudan, Minn. Shows old open pit with jasper horse in middle 261 Fig. 2. Outcrop of Clinton iron ore, Red Mountain, near Birmingham, Ala 261 xix XX PLATES PLATE PAGB XVI. General view of Mountain Iron mine, Mesabi Range, Minn. Shows mining of ore with steam shovels and covering of (a) glacial drift . . 264 XVII. Fig. 1. Pit of residual limonite, Shelby ^ Ala 270 Fig. 2. Old limonite mine, Ivanhoe, Va., showing pinnacled surface of limestone which underlies the ore-bearing clay. The level of surface before mining began is seen on either side of excavation ........ 270 XVIII. Anaconda group of mines, Butte, Mont. ..... 285 XIX. Fig. 1. Smelter of Clifton Copper Co., Clifton, Ariz. . . 293 Fig. 2. View of Bingham Canon, Utah 293 XX. Fig. 1. Kennedy mine on the Mother Lode near Jackson, Calif 333 Fig. 2. Auriferous quartz veins in Maryland mine, Nevada City, Calif 333 XXI. Fig. 1. View of Independence mine and Battle Mountain, Cripple Creek, Colo 340 Fig. 2. General view of region around Tonopah, Nev. . . 340 XXII. Fig. 1. Hydraulic mining of auriferous gravel. The sluice box in foreground is for catching the gold .... 348 Fig. 2. An Alaskan placer deposit ...... 348 XXIII. Homestake mills, hoists and open cuts at Lead, S.D. . 351 XXIV. Fig. 1. General view of Rico, Colo., and Enterprise group of mines 369 Fig. 2. Ontario mine, Park City, Utah 369 XXV. Fig. 1. Bauxite bank, Rock Run, Ala. . . . . .376 Fig. 2. Furnace for roasting mercury ore, Terlingua, Tex. . 376 ABBREVIATIONS USED In the references at the end of each chapter, the volume numbers are given in Roman numerals. Numbers following a : indicate page numbers. The date of publication follows these, and is separated from them by a comma. Ala. Ind. and Sci. Soc., Proc. Alabama Industrial and Scientific Society, Proceedings. Amer. Geol. American Geologist. Amer, Inst. Min. Eng., Trans. American Institute Mining Engineers, Transactions. Amer. Jour. Sci American Journal of Science. Col. Sci. Soc., Proc. Colorado Scientific Society, Proceedings. Eng. and Min. Jour. Engineering and Mining Journal. Geol. Soc. Amer., Bull. Geological Society of America, Bulletin. Jour. Geol. Journal of Geology. Min. and Met. Mining and Metallurgy. Min. and Sci. P. Mining and Scientific Press. Min. Indus. Mineral Industry. Min. Mag. Mining Magazine. Mo. Geol. Surv. Missouri Geological Survey. N. Y. Acad. Sci., Trans. New York Academy of Science, Transactions. jV. Ca. Geol. Surv. North Carolina Geological Survey. Sch. M. Quart. School of Mines Quarterly. U. S. Geol. Surv., Mon. United States Geological Survey, Monograph. U. S. Geol. Surv., Ann. Eept. United States Geological Survey, Annual Report. Zeitsch. f. Prak. Geol. Zeitschrif t fur Praktische Geologic. xxi PAET I NON-METALLIC MINERALS CHAPTER I COAL Kinds of Coal. There is such an intimate gradation be- tween vegetable accumulation now in process of formation and mineral coal that it is generally admitted that coal is of vegetable origin. By a series of slow changes (p. 12), the vegetable remains lose -water and gases, the carbon becomes concentrated, and the materials assume the mineralized ap- pearance of coal. To the stages of this process names are given, four of which peat, lignite, bituminous coal, and anthracite coal are commonly known. Peat (79-83). This, which may represent the first stage in coal formation, is formed chiefly by the growth of the bog moss, sphagnum, in moist places. A section in a peat bog, from the top downward, shows : (1) a layer of living moss, and other plants ; (2) a layer of dead moss fibers, whose structure is clearly recognizable, and which grades into (3) a layer of fully formed peat, a dense brownish black mass, in which the vegetable struc- ture is often indistinct. The following analyses show the difference in composition of the different layers. They also show that while during this change the hydrogen and oxygen diminish, the carbon increases in proportion. 3 ECONOMIC GEOLOGY. OF THE UNITED STATES MATERIAL CARBON HYDROGEN OXYGEN NITROGEN Sphagnum 49 88 6.54 42.42 1.16 Porous, light brown sphag- num peat . 50 86 5.8 42.57 77 Porous, red brown peat . . 53.51 5.9 40 .59 Heavy brown peat .... 56.43 5.32 38 .25 Heavy black peat .... 59.7 5.7 33.04 1.56 Lignite. This substance, also called brown coal, repre- senting the second stage in coal formation, is brownish black or black in color, and often shows a brilliant luster, conchoidal fracture, and brown streak. Where the lumps have formed from trunks or other large, woody masses, the vegetable structure is often clearly visible. It burns readily, but with a long, smoky flame, and hence with lower heating power than the true coal. Because of the large amount of mois- ture, it often dries out on exposure to the air, and rapidly disintegrates to a powdery mass. The lignites have been found in the more recent geological periods. Because of the greater age and the greater compression of the vegetable matter, due to the pressure of overlying strata, lignite resembles true coal more closely than peat. In fact, in favorable situations, the altera- tion of Tertiary and Cretaceous coals has proceeded as far as to trans- form them beyond the stage of lignite. Jet is a coal-black variety of lignite, with resinous luster and sufficient density to permit its being carved into small ornaments. It is obtained on the Yorkshire coast of England, where a single seam produced 5180 pounds, valued at $1250. According to Phillips, jet is simply a conif- erous wood, still showing the characteristic structure under the micro- scope. (" Geology of England and Wales," p. 278.) Bituminous Coal. This represents the third stage in coal formation. It is denser than lignite, deep black, compara- COAL 5 tively brittle, and breaks with cubical, or sometimes con- choidal, fracture. On superficial inspection it usually shows no trace of vegetable remains ; but in thin sections examined under the microscope, traces of woody fiber, lycopod spores, etc., are commonly seen. Bituminous coal burns readily, with a smoky flame of yellow color, but with much greater heating power than lignite. It does not disintegrate on ex- posure to air as readily as lignite does. Most bituminous coal is of earlier age than lignite ; but where the two occur in the same formation, as in parts of the West, the lignite is commonly in horizontal strata, while the bituminous coal occurs in areas of at least slight disturbance. When freed of their volatile hydrocarbons and other gaseous constitu- ents by heating to redness in an oven, many bituminous coals cake to a hard mass called coke. Since some bituminous coals do not possess this characteristic, it is customary to divide these coals into coking and non- coking coals. Oannel coal is a compact variety of non-coking bituminous coal with a dull luster and conchoidal fracture. Owing to its unusually high percentage of volatile hydrocarbons, upon which its chief value depends, cannel coal ignites easily, burning with a yellow flame. (See analysis No. 14.) Semi-bituminous is a name applied to certain varieties in- termediate between bituminous and anthracite coal. Anthracite Coal. This coal is black, hard, and brittle, with high luster and conchoidal fracture. It represents the last stage in the formation of coal, and shows no traces of vegetable structure within its mass, although plant impressions are often abundant in the rocks immediately above and below it. Anthracite has a lower percentage of volatile hydrocarbons and higher percentage of fixed 6 ECONOMIC GEOLOGY OF THE UNITED STATES carbons than any of the other varieties (p. 8). On this account, it ignites much less easily and burns with a short flame, but gives great heat. The geological distribution of anthracite is more restricted t*aan that of bituminous coal and, in fact, its occurrence is often more or less intimately connected with dynamic disturbances. Proximate Analysis of Coal. An elementary analysis of coal (see p. 14) is of comparatively little practical value. Therefore proximate analyses are commonly employed, in which the probable method of combination of the elements is given. By the proximate method the elements in the coal are grouped as moisture, volatile hydrocarbons, fixed carbon, ash, and sulphur. The following table gives the proximate analysis of a number of coals from all parts of the United States. The analyses are arranged in the following order: Peat, Lignite, Bituminous Coal, . Anthracite. PROXIMATE ANALYSES OF COAL LOCALITY Moisture Volatile Hydro- carbon Fixed Carbon Ash Sulph. Fuel Ratio 1. Peat 20.22 52.31 24.52 .47 Dismal Swamp 2. Newcastle .... 13.59 32.31 48.32 5.78 .164 1.49 Washington 3. Kootznaboo . . . 2.41 44.75 47.93 4.88 .67 1.07 Alaska 4. Rockdale .... 33.63 46.78 7.45 12.14 .99 .15 Texas 5. Lignite 22.95 23.64 43.31 5.10 . . . 1.51 S. Platte field, Col. 6. Lignite 21.11 28.55 44.98 5.01 1 KQ E. field, Montana J. _>O COAL LOCALITY Moisture Volatile Hydro- carbon Fixed Carbon Ash Sulph. Fuel Ratio 7 Lignite . . 10.80 43.10 38.57 7.53 Q7 .O/ Corral Hollow, Cal. 8. Brookville Coal . . 1.47 17.93 75.508 4.525 .567 4.21 Conemaugh, Cam- bric Co. 9. Pittsburg Coal . . . 1.26 31.79 57.79 7.16 .79 1.81 Connelsville, Fay- ette Co. 10. Hocking Valley Coal 5.93 36.48 52.41 5.13 1.09 1.44 Ohio 11 Warrior . . . 4.83 18.95 72.76 3.28 .17 q oq Jeff. Co., Ala. O. OO 12. Jellico .... 4.40 31.56 61.87 1.86 .31 1.96 Campbell Co., Tenn. 13. Brazil Block Coal . 13.82 35.16 49.96 1.06 1.47 1.42 Brazil, Ind. 14. Cannel Coal . . . 1.47 49.08 26.35 23.10 1.48 .53 Cannelburg, Ind. 15. Bituminous Coal . . 5.50 39.50 54.60 5.40 . . . 1.38 Belleville, 111. 16 Butler 30.66 54.94 11.00 2.544 1.71 Kentucky 17. Owasso Coal Comp'ny 7.58 35.70 52.96 3.76 1.50 1.48 Owasso, Mich. 18. Saginaw Company . 5.82 39.79 45.15 9.24 3.83 1.13 Verne, Mich. 19. Fort Dodge . . . 7.48 39.52 45.54 8.44 5.28 1.15 Iowa 20. Lexington .... 9.24 29.01 42.19 15.18 4.38 1.45 Missouri 21. Hartshorne Coal . . 1.68 41.00 51.91 5.41 2.72 1.26 Hartshorne, I.T. 22. Gwyn's shaft . . . .892 14.57 77.09 6.24 1.19 5.28 Sebastian Co., Ark. 23. Semi-bituminous . . 1.10 11.27 72.83 12.04 2.74 6.46 Johnson Co., Ark. 24. Coal No. 1. . . . .88 31.57 56.81 8.93 1.47 1.79 Thurber, Texas 25. Coking Coal . . . .75 31.13 57.07 11.05 1.80 Raton field, Col. ECONOMIC GEOLOGY OF THE UNITED STATES LOCALITY Moisture Volatile Hydro- carbon Fixed Carbon Ash Sulph. Fuel Katio 26. Newcastle .... 7.992 29.031 53.806 8.023 1.148 1.85 Washington 27. Bituminous Coal . . 6.21 31.32 52.47 11.10 . . . 1.65 Canyon City, Col. 28. Anthracite .... 1.58 6.70 87.46 4.26 .58 13.05 Crested Butte, Col. 29. Anthracite .... 2.90 3.18 88.91 5.21 . . . 27.96 Cerillos field, New Mexico 30. Mammoth .... 3.163 3.717 81.143 11.078 .899 21.83 W. Middle field, Pa. 31. Mammoth .... 3.421 4.381 83.268 8.203 .727 19.00 N. Middle field, Pa. The moisture can be driven off at 100 C. and is usually highest in peat and lignite ; the volatile hydrocarbons are the easily combustible elements, and decrease toward the anthracitic end of the series; the fixed carbon burns with difficulty and is highest in the anthracite coals. The ash represents noncombustible mineral matter and bears no direct relation to the kind of coal ; and the same is true of sulphur, which is present as an ingredient of pyrite or gypsum. The value of coal for fuel or other purposes is determined mainly by the relative amounts of its fuel constituents, viz. the volatile hydro- carbons and the nonvolatile or fixed carbons. The fuel value, or fuel ratio, is determined by dividing the fixed carbon percentage by that of the volatile hydrocarbons. The fixed carbon represents the heating element of the coal, while the volatile hydrocarbons burn easily, but have little heating power. The heating power and fuel ratio will, therefore, increase together. This increase in the heating power of the coal is only true, however, up to a certain point, after which the difficulty in making the coal burn offsets the extra amount of heat developed. Coals with a high percentage of fixed carbon develop great heating power, while those lower in fixed carbon and high in volatile hydrocarbons lack in heating power, but are free burning. COAL 9 Moisture is a nonessential constituent of coal. It not only dis- places so much combustible matter, but requires heat for its evapo- ration. When present in large amounts it often causes the coal to disintegrate while drying out. It ranges from 1 per cent in anthracite to 20 or 30 per cent in lignites. Ash also displaces combustible matter, but otherwise it is in most cases an inert impurity. The clinkering of coal is commonly due to a high percentage of fusible impurities in the ash, and for metallur- gical work the composition of the ash often has to be considered. The following analyses will also serve to illustrate the composition of the ash: ASH ANALYSES Si0 2 A1 2 8 Fe 2 3 CaO MgO Mn0 2 S0 3 Alka- lies. Chlo- rine P,0 5 Peat, average of several . . . 25.50 5.78 18.70 24.00 3.20 7.50 1.72 .60 2.56 Lignite .... 30.14 13.48 11.70 23.59 .88 3.32 14.22 Bituminous Coal 34.32 14.62 22.94 14.85 1.42 1.16 10.97 Sulphur is an objectionable impurity in steaming coals on account of its corrosive action on the boiler tubes. It is also undesirable in coals to be used for metallurgical purposes and gas manufacture. Origin of Coal (4). It has been shown that there are gradations between unquestioned plant beds and mineral coal, and that coal, besides containing the same materials as plant tissue, often shows the presence of plant fibers, leaves, stems, seeds, etc. Moreover, stumps or trunks of trees are sometimes found standing upright in the coal, with their roots penetrating the underlying bed of clay (5), just as trunks of trees at present stand in bogs. While these facts point unmistakably to a vegetable origin of coal, it is less easy to understand the exact manner in which the great accumulations of vegetable matter have been made, and the changes from plant tissue to mineral 10 ECONOMIC GEOLOGY OF THE UNITED STATES coal. Each of these points, therefore, demands further consideration. Conditions of Vegetable Accumulation (4). At present there are several conditions under which plant remains accumulate to considerable depth over areas in some cases of large size. All of these are closely associated with water, either fresh or salt, because plant remains falling in water have their decay so retarded by the exclusion of air that accumulation is possible. Of these the following are the most important : (1) accumulation due to algse on the sea bottom beneath a sargasso sea ; (2) marine swamps, including salt marshes and mangrove swamps ; (3) delta deposits; (4) peat bogs; (5) coastal plain marshes. While accumulations made in any one of these ways may form coal beds, and while individual beds may be formed which are due to any of these causes, to many of them there are such objections as to render them extremely improbable as general explanations for the great number of widely extended deposits of coal. The theory of accumu- lation from deposits of algae, for example, demands deep water of an open ocean for the circulation of ocean cur- rents. But most coal beds are evidently formed either on the land or else in shallow water of lakes, lagoons, or sea- coast swamps. To the theory of various swamps there are two serious objections : (1) that in such deposits as are now forming, the currents are bringing more fragmental sediments than are commonly present in coal beds ; (2) that at present only one kind of tree, the mangrove, is adapted to growth in salt water. It is, of course, possible that in earlier ages the number of trees adapted to this mode of life was far greater. COAL 11 Streams are bringing plant remains to lakes or oceans and incorporating them in their deltas ; but nowhere are such extensive accumulations now forming as to make large coal fields in this manner. Moreover, the amount of sedi- ment brought in such places would seem to exclude the possibility of the deposit of large areas of vegetable mat- ter free from a great admixture of sediment. The combi- nation of this source of vegetable supply with that caused by the growth of marine or fresh- water swamp plants in the delta lagoons would increase the chances of the forma- tion of coal beds by this means; but even with this addi- tion, it seems impossible to accept this as a general theory for the formation of extensive beds of coal. It is a well-known fact that thick deposits of vegetable matter, often covering areas of several square miles, are formed in the peat bogs that in so many places represent the last stage of lake or pond filling in cool, temperate climates. Each of these bogs would, under favorable circumstances, change to a bed of coal, and some of them are extensive enough to form coal beds of large size. But such bogs are, compared to our larger coal fields, far too limited in area to admit of the acceptance of this explana- tion to account for great coal fields without assuming far more widespread bog-forming conditions than any at present known. Perhaps the most perfect resemblance to coal-forming condition is that now found on such coastal plain areas as that of southern Florida and the Dismal Swamp of Virginia, North Carolina. Both of these areas are very level, though with slight depressions in which there is either standing water or swamp conditions. In both regions there is such 12 ECONOMIC GEOLOGY OF THE UNITED STATES general interference with free drainage that there are exten- sive areas of swamp, and in both there are beds of vegetable accumulations. In each of these areas there is a general absence of sediment and therefore a marked variety of vege- table deposit. If either of these areas were submerged be- neath the sea, the vegetable remains would be buried and a further step made toward the formation of a coal bed. Re- elevation, making a coastal plain, would permit the accumula- tion of another coal bed above the first, and this process might be continued again and again. In support of the theory that coal was accumulated in some such situation as this, are a number of facts : (1) the coal beds occur over wide areas in sediments which were deposited near land borders and which may therefore have been again and again raised above sea level to form extensive coastal plains ; (2) there are evidences of land conditions re- vealed in the workings of some mines ; (3) the enormous area of some coal fields call for some such widespread condi- tions as coastal plains might provide ; (4) the slight admix- ture of sediment indicates the absence of conditions of sediment supply, e.g. rivers, waves, tidal currents, and wind- formed currents ; (5) vegetable accumulations made in such situations would require but slight changes in land level to be buried beneath sedimentary strata as the coal beds have been. Chemical Changes occurring during Coal Formation. Dead plant tissue when exposed to the air oxidizes rapidly and decays, all of the gaseous elements passing off, leaving only the mineral matter which the plant tissue contained. The exclusion of air caused by the presence of water, as in a pond or a swamp, greatly retards oxidation ; but, as it slowly COAL 13 proceeds the oxygen, nitrogen, and hydrogen of the plant tissue, together with some of the carbon pass off in the form of carbon dioxide (CO 2 ), carbon monoxide (CO), marsh gas (CH 4 ), and water. As a result, as the process continues an increasing percentage of carbon is left behind. The change is also accompanied by a change in color to deep brown, and finally to black. The changes that take place in the passage of vegetable matter into coal are graphically shown in the following dia- gram prepared by the late Professor Newberry : VEGETABLE TISSUE PEAT LIGNITE BITUM. COAL ANTHRACITE FIG: 1. Diagram showing changes occurring in passage of vegetable tissue to graphite. After Newberry. In this diagram the rectangle ABOD represents a given volume of fresh vegetable matter, which contains a small percentage of mineral matter, the rest being organic sub- stances consisting roughly of 50 per cent carbon (EFCD) and 50 per cent hydrogen, oxygen, and nitrogen (ABEF). In the change from fresh vegetable tissue to peat, part of these four elements pass off as gaseous compounds, so that the remaining volume of peat is less (BGDH) than the origi- nal volume of vegetable matter (ABCD). Since, however, H, O, and N have passed off in larger amounts than the carbon, the percentage of the latter in the peat will be higher than it was in the fresh plant tissue. (Compare BFGI and 14 ECONOMIC GEOLOGY OF THE UNITED STATES FIDH with ABEF and EFCD.) The actual weight of mineral matter will be the same, but its percentage will be larger. This change continued will result finally in anthra- cite, the last of the coal series, in which the per cent of carbon (LKMN) is high and that of the other organic elements low (JKL). The amount of compression that occurs in such changes as those illustrated in the diagram may be under- stood when it is stated that it is estimated that from 16 to 30 feet of peat are required to make one foot of true coal. The following analyses of various grades of coal from peat to anthracite clearly illustrate this gradual concentration of carbon by loss of volatile elements. ELEMENTARY ANALYSES OF COALS c. H. o. H. s. Ash Mois- ture Peat 59.47 6.52 31.51 2.51 22 Lignite ... . . . 58.44 4.97 16.42 1.30 Bituminous coal . 68 13 6.49 583 2.27 2.48 12.30 Breckenridge Co., Ky. Bituminous coal 73 80 5 79 16.58 1 52 .41 1.90 Ohio Bituminous coal Clay Co., Ind. Anthracite 82.70 90.45 4.77 2.43 9.39 2.45 1.62 .45 1.07 4.67 East Pa. Effect of Heat and Pressure. While the first stage in coal formation is brought about simply by the exclusion of air, for further development pressure seems necessary. Even in peat beds the lower layers are under the gentle pressure of the upper layers ; but peat is not changed even to lignite until buried under many feet of sediments. Great pressure, possibly aided by heat, seems necessary for the COAL 15 change from lignite to bituminous coal ; and long periods of time are apparently required for the slow changes to take place. That heat may sometimes have been present is indi- cated by the evidence of rock folding that is sometimes, though by no means invariably, present in bituminous coal areas. Most of the anthracite coal in the United States occurs in the highly folded Appalachians of Pennsylvania. Such fold- ing must have been productive of much heat and pressure, and that the folding has produced the anthracite is by many believed to be proved by the fact that these coal beds pass into bituminous coal when traced southward or westward into areas of less disturbances. This view is questioned by some geologists, especially J. J. Stevenson, who has argued that the anthracite has not been developed from bituminous coal by metamorphism, but that the volatile constituents were partly removed by longer exposure of the vegetable matter to oxidation before burial (7). There are some cases, as in the Cerillos coal field of New Mexico (50), where anthracite probably has been produced by heat. Here a bituminous coal has been deprived of its volatile matter and converted into anthracite in those -por- tions of the bed near an intrusion of andesite. A similar change has taken place in the Crested Butte district of Colorado (29)-. Structural Features of Coal Beds. Outcrops (13). The outcrop of a coal bed is usually easily recognizable on account of its color and coaly character; but unless the exposure is a rather fresh one, the material is disintegrated and mellowed, the wash from it mingling with the soil, and 16 ECONOMIC GEOLOGY OF THE UNITED STATES Coal FireClay Coal Fire Clay Coal if the outcropping bed is on a hillside, often extending some feet down the slope. This weathered outcrop has been termed the " smut " or " blossom " by coal miners. In areas where the beds have been tilted and the slopes are steep, the outcrops of coal can usually be easily traced ; but in regions where the dip is low and the surface level, the search for coal is often attended with difficulty, which is increased if the country is covered with glacial drift. In such cases boring or pit- ting is commonly resorted to. Associated Mocks. Most coal beds are interbedded with shales, clays, or sand- stones, though conglomerates or limestones are at times also found in close proximity. Coal beds are often underlain by a bed of clay, which in some regions is of refractory character (Fig. 2); but the widespread belief that all these under clays are fire clays is unwarranted. Variations in Thickness. Coal beds or FIG. 2. Section in coal measures of "seams" are rarely of uniform thickness western Pennsylva- nia, showing fire over large areas; indeed, a bed which is clay under coal <. /v . i i -, beds. After Hop- * sumcient thickness to work in one mine may be so thin in a neighboring mine as to be scarcely noticeable. This irregularity is in some cases due to variations in thickness of vegetable accumulations, in other cases to local squeezing of the coal bed subsequent to its formation. These thinnings and thickenings are com- monly called "pinchings" and "swellings" (Fig. 3). In regions of pronounced folding, the coal beds are usually COAL 17 found in separate synclinal basins, the intervening anticlinal folds having been worn away. Other Irregularities. Splitting (Fig. 3) is a common feature of many coal seams. The Mammoth bed, so promi- nent in most of the anthracite basins of Pennsylvania, splits FIG. 3. 'Section showing irregularities in coal seam, a, split; 6, parting of shale; c, pinch; d, swell; e, cut out. into three separate beds in the Wilkesbarre basin. .This splitting is caused by the appearance of beds of shale (called "slate" by coal miners), which often become so thick as to split up the coal seam into two or more beds. When narrow, such a bed of slate is called a parting. The Pitts- burg seam of western Pennsylvania shows a fire-clay parting or "horseback" (Fig. 3) from six to ten inches thick over many square miles. In addition to these " slate " partings, which run parallel with the bed- ding, others are often encountered which cut across the beds from top FIG. 4. Section of faulted coal seam. After Keyes, la. Geol Surv., II: 86, 1894. to bottom. These in some cases represent erosion channels, formed in the coal during or subsequent to its formation, and later filled by the deposition of sand or clay. In other 18 ECONOMIC GEOLOGY OF THE UNITED STATES cases they are due to the filling of fissures formed during the folding of the strata. Faulting (Fig. 4) is not an uncommon feature of coal beds, and the coal is sometimes badly crushed on either side of the line of fracture. The amount of throw and the num- ber and kind of faults may vary, so that one might expect normal, reverse, overthrust, and even step faults. Coal Fields of the United States (PI. I). Coal in com- mercial quantities occurs in twenty-seven of the forty-seven states and territories as well as in Alaska. These occur- rences can be grouped into nine well-marked fields, as follows : (1) Appalachian, including parts of Pennsylvania, Ohio, Maryland, Virginia, West Virginia, Eastern Ken- tucky, Tennessee, Georgia, and Alabama . . 71,291 sq. mi. (2) Rhode Island Very small. (3) Atlantic Coast Triassic, including parts of Virginia and North Carolina . . . . . . 1070 sq. mi. (4) Eastern Interior, including parts of Indiana, Illinois, and western Kentucky 58,000 sq. mi. (5) Northern Interior, including parts of Michigan . 11,300 sq. mi. (6) Western Interior, including parts of Iowa, Missouri, Nebraska, and Kansas 66,200 sq. mi. (7) Southwestern field, including parts of Indian Terri- tory, Arkansas, and Texas . .... 27,876 sq. mi. (8) Rocky Mountain field, including parts of South Da- kota, Montana, Idaho, Wyoming, Utah, Colorado, and New Mexico 43,610 sq. mi. (9) Pacific Coast, including parts of Washington, Oregon, and California 1050 sq. mi. The above grouping does not include the areas of lignite- bearing formations, although these are shown on the map COAL 19 (PL I). According to Hayes there are in Montana, the Dakotas, and Wyoming, approximately 56,500 square miles of lignite-bearing formations, chiefly of Cretaceous age. A series of fields in the Tertiary of Alabama, Mississippi, Louisiana, Arkansas, and Texas cover approximately as large an area. The estimates given above are of course only approximate, and some of these fields may be extended in the future by the development of areas now classed as unproductive. This applies especially to those in which the coal lies too deep to be profitably mined at present. It is a noteworthy fact that the production of the fields is by no means propor- tional to their areas. (Compare above list with table, p. 34.) Proximity to markets, value of the coal for fuel, and relative quantity of coal per square mile of productive area, are factors of importance in determining the output of a field. Geologic Distribution of Coals in the United States. The coal-bearing formations of the United States range in age from Carboniferous to Tertiary. Carboniferous coals occur east of the 100th meridian, Cretaceous coals between the 100th and 115th meridian, and the Tertiary coals chiefly between the 120th meridian and the Pacific coast. Excep- tions to this distribution are the occurrence of a small area of Triassic coals in Virginia and North Carolina, and a large Tertiary area of lignite in the Gulf States. This indicates that during the coal-forming periods there was in North America a slow westward shifting of the zone in which conditions favorable to coal formation occurred, the only exceptions being those mentioned above. The Carboniferous coals are commonly grouped into several well-marked and clearly separated areas; but this isolation is probably the result of folding and erosion, all 20 ECONOMIC GEOLOGY OP THE UNITED STATES excepting the Michigan field having apparently been origi- nally continuous. To a certain extent the same is true d % of the Rocky Mountain coal fields. These have often been seriously dis- turbed by post-Cretaceous uplifts, which in many instances have im- proved the qualities of the coal. As a whole, the Tertiary coals are medium to low grade, though in some sections, notably in Washington, they are of excellent quality. 3 S2 5 S feS il = C ~ I - B < 8 -e 3 Appalachian Field (12, 15, 18, 55, 58, 60, etc.). This, the most important coal field in the United States, ex- tends 850 miles, from northeastern Pennsylvania to Alabama, and about 75 per cent of its area contains work- able coal. At the southern end the coal measures pass beneath the coastal plain deposits, and they may connect with the Arkansas coal measures be- neath the Mississippi embayment. Being closely associated with the Appalachian Mountain uplift, the coal measures of this region partake of the structural features of the Appalachian belt. Thus, while the strata of the western portion are either horizontal or only slightly bent, those farther east are often highly folded (Fig. 7), and in the southern 5 l *l O y COAL 21 Appalachians the strata are both folded and faulted (Fig. 5). Extensive erosion following the folding of the coal meas- ures has resulted in the development of a number of basins. The coal measures of the Appalachian field consist of a great thickness of overlapping lenses of conglomerate, sand- stone, shale, coal, and some limestones, and owing to this lenticular character of the deposits, and to local thickenings, it is difficult to trace individual beds of coal over wide areas, or to correlate sections at widely separated points. The middle Carboniferous, or Pennsylvanian, includes most of the coal beds of the Appalachian area, and is divided into the following five major subdivisions which are recognizable throughout the field : (1) Dunkard or Upper Barren Measures; (2) Monongahela or Upper Productive Measures ; (3) Conemaugh or Lower Barren Measures ; (4) Alleghany or Lower Productive Measures ; (5) Pottsville or Serai Conglomerate. This classic section was first worked out in Pennsylvania, and has since been identified in other parts of the Appa- lachian field. At the time it was made, the second and fourth members were thought to be the only ones carrying coal, and hence the name " Productive " ; but since then the Pottsville has been found to be locally productive, and a few seams have been found even in the Barren Measures. The Appalachian field is divisible into two parts of very unequal size : (1) the anthracite field of northeastern Pennsylvania ; and (2) the bituminous area, which occu- pies the balance of the field. Bituminous Area (15, 20). In western Pennsylvania, where we have the type section of the Carboniferous of eastern 22 ECONOMIC GEOLOGY OF THE UNITED STATES America, about 95 per cent of the coal mined comes from the Alleghany and Monongahela groups, though beds of coal are found as high as the Dunkard and as low as the Pottsville. While most of the coal beds are of limited extent, the celebrated Pittsburg bed, at the base of the Monongahela, has an average thickness of 6 feet over an area of 50 miles square. Its original capacity, estimated to be 10,000,000 tons of available coal, makes it one of the most important bituminous coal beds in the world. This same bed is recognizable and important in Ohio and Mary- land. In the southern portion of the Appalachian field, the coal beds lie in the Pottsville, which here is much thicker than farther north, reaching a maximum thickness of 5000 to 6000 feet, as against 300 feet in western Pennsylvania, and most of the workable coal occurs in its upper portion. Character of Appalachian Bituminous Coals. The coals of this field differ greatly from place to place. In general there is a decrease in volatile hydrocarbons from the west toward the east and southeast. Good coking coals are found throughout the field. Those of Maryland are semi-bituminous, and have a high reputation for steaming purposes ; but those of Pennsylvania include many coking coals, and are hence of further value in smithing, and coke and gas manufacture. While much of the coke is used locally by the great metallurgical establish- ments, a large amount is also shipped to other states, even in the far Northwest. The markets for these coals are chiefly in the South where, excepting along the seacoast, they come into successful competition with the Penn- sylvania anthracite for domestic purposes. In the north and northwest they compete less successfully with coals from the interior fields. Pennsylvania Anthracite Field (18). This field (Fig. 6) lies in the eastern central part of the state, covering an area COAL 23 of about 3300 square miles, about one-seventh of which is underlain by workable coal measures. Intense folding (Fig. 7) has placed some of the coal in the synclinal troughs where it has been preserved from erosion which has removed the coal from the intervening anticlines. Therefore the anthracite is found in a number of more or less separated narrow basins. It has been estimated that from 94 to 98 per cent of the coal originally depos- ited has been removed from this field by denudation. The coal measures of the anthracite district consist of beds of sandstone, shale, and clay, with coal beds at intervals varying from a few feet to several hundred feet, though rarely exceed- ing 200 feet. The coal beds, which vary in thick- ness from a few inches to 50 or 60 feet, occur through- out the entire section of the coal measures, but are most important in the lower 300 to 500 feet. Beneath the Pro- ductive Measures is the hard Pottsville conglomerate, which forms an important stratigraphic horizon, recogniz- able by its lithological character and bold outcrops. Local variations in the coal beds, and lack of uniformity in naming them, have rendered their correlation in the different fields more or less difficult. FIG. 6. Map of Pennsylvania anthracite field. After Stoek, U. S. Geol. Surv., 22dAnn. Rept., Ill . 24 ECONOMIC GEOLOGY OF THE UNITED STATES The position of the coal beds and physical characteristics of the coal have necessitated the use of special methods of mining and of treat- ment after mining. Sharpness of folding and steep dips prevail, these introducing many mining problems not found in bituminous regions. When brought to the surface, it consists of lumps varying in size and mixed with more or less shaly coal, called "bone," so that, before ship- ment to market, it is necessary to break, size, and sort it. This is done 12* 1 1 ~T l| jj F 2 5 fS -3 J 4 3 i i j --s +18139 + j a p fe Oieck Ridg* 'X IMP Above Tide Section (A) Near Hazleton 3 Trwckow Basin ?? hi JS !? M 1 2 |lHeHKHch.aB M ,n S1 >' ftA "f"| 3? R| ""< - 3 8 5 = Cull Run Be Lansford Baaine . Ami- \ / 1000 Above Iid Section (C)across the anther Creek Basin FIG. 7 . Sections in Pennsylvania anthracite field. After Stoek, U. S. GeoL Surv., 22d Ann. Kept., Ill: 72. in a coal breaker (Fig. 8), in which the coal is crushed in rolls, and sized by screens, while the slate is separated either by hand, automatic pickers, or jigs. These breakers are a prominent feature of the anthracite region, and much money has been spent in increasing their efficiency. As the result of years of mining, the refuse from the breakers, consisting of a fine coal-dust and bone, termed " culm," has accumulated in enormous piles. Much of it is now being washed to save the finer particles of clean coal ; and much is also washed into the mines to support the roof, so that the pillars of coal, originally left for that purpose, can be extracted. COAL 25 On account of its cleanliness and high fuel ratio, anthra- cite coal is much prized for domestic purposes. Most of that mined is marketed in the eastern and middle states, although small quantities are shipped to the western states, especially those that can be reached by way of the Great Lakes. FIG. 8. Coal breaker in Pennsylvania anthracite region. Rhode Island Field (63, 64). A small area of metamorphosed, folded, and faulted Carboniferous occurs in the Narragansett Bay region of Rhode Island, extending up into Massachusetts. The inclosing strata of conglomerate and clay are often changed to schist, and the coal to a form of anthracite so nearly pure carbon as to be exceedingly difficult to burn. In fact, in places the coal has been metamorphosed to graphite. Attempts to utilize this have not met with much success on account of the high percentage of impurities which the material contains. The Triassic Field (52). This coal field which is more important historically than economically, having been worked as early as 1700, includes several small steep-sided basins lying in the Piedmont region of Virginia and North Carolina. It is probable that the coal-bearing beds of the several areas, originally horizontal, were formerly continuous, having been separated by folding, faulting, and denudation. In addition to this, the coal is cut by dikes and sheets of igneous rock, which have locally altered it to natural coke or carbonite. 26 ECONOMIC GEOLOGY OF THE UNITED STATES il Eastern Interior Field (13, 32). This field is an oval, elongated basin (Fig. 9) extending northeast and southwest, with the marginal beds dipping gently toward the lowest portion, which lies in Illinois, where the beds are nearly horizontal. The coal-bearing rocks rest uncom- formably on lower Carboniferous, Devo- nian, and Silurian strata, the basal member being a sandstone probably tlie equivalent of the Pottsville. The entire section of coal-bearing rocks, attaining a thickness of 1200 feet, belongs to the Coal Measures, although the upper part may be of Permian age, and the highest workable coal beds are classed as Freeport or Conemaugh. The coal seams occur in the lower portion of the section, and hence out- crop around the margin, and the mining operations are confined to a narrow belt, because near the center of the basin the coal beds underlie too great a thick- ness of unproductive strata to permit of profitable working under present conditions. Great difficulty has been encountered in attempts at correlation of the coal beds of different parts of the field, be- cause of the varying section shown COAL 27 from place to place, and lack of continuity of the beds. In consequence, the custom has arisen of giving the coal beds numbers instead of names. In Indiana coal is found in at least twenty horizons with workable beds in not less than eight ; but at any given point the number of workable beds never exceeds three, and in places there is only one. One of the Indiana coals is known as " block coal," the name arising from the fact that the presence of joint planes at right angles causes the coal to break into blocks. There are many coal beds in Illinois worked at depths of from 50 to 200 feet or more; but there is a marked absence of stratigraphic knowledge regarding this part of the field. In Kentucky, on the other hand, there are only two workable coal beds of decided importance, and fully 75 per cent of the coal produced in the strata comes from the upper of these. This bed is so persistent that it underlies a part of the whole of 8 counties, with an average thickness of 5 feet and at a depth commonly less than 200 feet. The coals of the eastern interior field, although varying widely in quality, are all bituminous. On account of their higher percentage of ash and sulphur, they are little used for coking. Most of the coal used in and near this field is supplied from it ; but even within the field the Appalachian coals enter into competition. The Cannel coal found near Carmelsburg, Kentucky, which is the only good gas producer found in this field, finds a ready market. Northern Interior Field (43). This field forms a large basin in which the coal dips irregularly from the margin toward the center (Fig. 11), but on account of the heavy FIG. 10. Shaft house and tipple, hituminous coal mine, Spring Valley, 111. 28 ECONOMIC GEOLOGY OF THE UNITED STATES mantle of glacial drift it has been difficult to determine its exact boundaries, and prospecting is necessarily done by means of drilling. The coal measures attain a total thickness of 600 to 700 feet in the center of the basin, and include 7 horizons of workable coal with an average thickness of 2 feet and rarely exceeding 4 feet. Coal is found near the center of the basin at depths of 400 feet or more, though the beds that are mined are mostly 200 tact FIQ. 11. Generalized section of Northern Interior coal field. After Lane, U. S. GeoL Surv., 22d Ann. Rept., Ill: 316. at depths of 100 to 150 feet. All the coals are bituminous and used chiefly for fuel, but some are coking, and others will probably prove of value for gas manufacture. Western Interior Field and Southwestern Fields (14). These two fields form a practically continuous belt of coal- bearing formations, extending from northern Iowa south- westward for a distance of 880 miles into central Texas. Throughout most of this area the beds lie horizontal, or have a gentle westward dip averaging 10 to 20 feet per mile. A notable exception is found in the beds of eastern Indian Territory and Arkansas which are rather strongly folded, reminding one of the Pennsylvania anthracite area. COAL 29 Western Interior Meld. The coal measures, composed of limestones, sandstones, shales, fireclays, and coal beds, rest unconformably on the Mississippian and dip westwardly under beds of Permian, Cretaceous, and Pleistocene (Fig. 12). Toward the south and west the beds increase in thickness, the maximum being 1000 feet in Iowa (36) and 3000 in Kansas (37). Most of the coal mined in this field comes from the lower part of the coal measures where the beds are irregular in FIG. 12. Composite section showing structure of lower coal measures of Iowa. After Keyes, la. Geol. Surv., I: 105. thickness and distribution, in consequence of deposition on a very uneven surface. All the coals of. this field are essentially bituminous and used chiefly for steaming and heating purposes, being of no value for either coking or gas making. Some of the seams will coke, but there is no demand for the product, and the sulphur and ash are too high for gas making. Southwestern Field. While it is known that there is much good coal in this field, full development has not been undertaken in most parts of it. The Indian Territory coals (34, 35), of which there arc 7 important beds in a section of 4500 feet of shales and sandstone, are both folded and faulted. These coals, as well as those of Texas (69), where there are three workable beds, are all bituminous; 30 ECONOMIC GEOLOGY OF THE UNITED STATES but in the eastern end of the Arkansas (25) field there is anthracitic coal of probable Permian age. The coal from this field finds its most important market in the South, though some is sent North. The Texas coals are of especial importance on the railways, being used as far west as the Pacific coast. It has, however, found a serious competitor in the Texas crude petroleum ; but it remains to be seen whether this competition will be lasting. On account of the value for domestic purposes the anthra- cite finds an important market to the northward. Gulf States Lignite Area (9). There is a narrow lignite- bearing belt extending across the lower part of Alabama and Mississippi; and another much larger belt extending from near Little Rock, Arkansas, southwestward across the northwestern corner of Louisiana (42), and in a narrowing belt across Texas. Both of these are of Eocene age. The lignites are usually high in moisture and ash, the best grade being that mined in the lower end of the area, near Laredo on the Rio Grande. A small field of Cretaceous lignitic coal has been devel- oped around Eagle Pass on the Rio Grande (70). This is an extension of the Mexican field, but is of poorer quality. Rocky Mountain Fields (17). These cover a broad area, extending from the Canadian boundary southward into New Mexico, a distance of about 1000 miles, and includ- ing over 50 fields of various size and irregular shape. Most of the beds lie within the mountainous region, but at the northern end of the area, in Wyoming and the Dakotas, the coal fields extend eastward under the plains for some OF THE " - or PLATE II FIG. 1. Pit working (Strippings) near Milnesville, Pa. The Mammoth seam is uncovered in bottom of pit. FIG. 2. Lignite seam, Williston, N.D. After Babcock photo. COAL 31 distance. The age of the coal ranges from Cretaceous to Tertiary, though most of it belongs to the former. While portions of this enormous area of coal-bearing strata are only slightly disturbed, mountain-building forces and igneous intrusions have affected a large proportion of the region, often materially changing the character of the coal. Thus, while in undisturbed portions of the field the beds are lignitic (PI. II, Fig. 2), in the disturbed parts they have been altered to bituminous and even to anthracite coal. Some of the bituminous coals produce an excellent quality of coke. Colorado (29, 30) is the most important coal-producing state of the Rocky Mountain region. This is due, not only to the quality of its coals, but also to the presence within the state of extensive metal- lurgical industries. The Raton field, in the southeastern part of the state and extending into New Mexico (50, 51), is at present the most important producer. Like many of the fields of this region the age of these is Laramie, and the beds are both folded and faulted. They are, moreover, crossed by igneous intrusions which have in some places produced natural coke, but in others destroyed the value of the coal. In a section of from 3000 to 4500 feet of Laramie strata there are 40 coal beds, only a few of which are, however, workable. There are both coking and semi-coking coals, and some anthracite. In Montana (45, 46, 47) the coals range in age from Triassic to Ter- tiary, and in quality from lignite to bituminous. The coals of Wyoming, which occupy a very large area, show the same range in quality, but are more commonly lignite because found to so large an extent in re- gions of slight disturbance. The Utah coals are prevailingly semi- bituminous, and those of the two Dakotas lignitic. The Pacific Coast Fields (16). Tertiary coals, partly bituminous, though mainly lignitic, occur scattered over a wide area in the states of California (28), Washington (75), 32 ECONOMIC GEOLOGY OF THE UNITED STATES and Oregon (56, 57). The separate fields are limited in ex- tent, widely separated, and with a small total output. Of the four fields recognized in Washington, the most impor- tant lie directly east of Seattle arid Tacoma. The total thickness of coal-bearing sandstones and strata is about 10,000 feet, but important coal beds are found only in the lower 2000 feet. It is stated that there are 100 coal seams of sufficient thickness to attract the prospector ; and in a single district there may be from 5 to 10 workable beds. Since the quality of the coal varies with the extent of dynamic disturbance, there is considerable variation even in a single field, and, in fact, in a single mine. Both California and Oregon produce small quantities of lignitic coal of Tertiary age, but show no promise of becoming important producers. Indeed, the coal-trade conditions of the Pacific coast are unique. The local supply is not equal to the demand, and the Rocky Mountain fields are too far off to supply the Pacific coast with cheap fuel. Therefore much coal is imported, bringing about a competition in San Francisco from many countries, including England, Wales, Scotland, Australia, Japan, and British Columbia. These foreign coals are all of better quality than the Pacific coast coals, and they can be imported with low freight rate as ballast in wheat-carrying vessels that come to San Francisco for cargoes. These coal imports form three-quarters of the total import coal tonnage of the United States; but since 1895 -there has been a steady decrease in the importation of coal and an increase in the Pacific coast production. Alaska (23,24). Although Alaskan coal was first mined in 1852 at Port Graham, the resources of the region are still but little known and slightly developed. The ex- plorations for gold during the last few years, together with the field work done by the United States Geological COAL 33 Survey, have proved that coal is widely distributed in the Alaskan Territory (Fig. 81). So far as known the coal beds are all in Mesozoic and Tertiary formations. While most of the coal is lignitic, there is considerable bitumi- nous coal and some semi-anthracite. Coal mining has been carried on at a numbey of localities, especially along the rivers and coast. The higher grade coals along the coast, par- ticularly in the southern part where shipments can be made throughout the year, will doubtless be developed with profit in the near future. Coals in the Yukon Valley, though of low grade and variable character, bring $15 a ton at the mines because of the local demand in the mining camps. The effect of such a local demand on the coal is even more strikingly shown by the fact that the semi-bituminous coal near the Cape Nome gold field sold, at times, for as much as $100 per ton. Production of Coal. While coal mining in the United States began at an early date, the figures of production for the first few years are more or less incomplete. The phe- nomenal growth of the coal-mining industry is well shown, however, by the following figures : YEAR QUANTITY SHORT TONS YEAR QUANTITY SHORT TONS 1868 31 648,960 1890 157,770,963 1870 36 806 560 1895 193,117,530 1875 59 088 320 1900 .... 269,684,027 1880 76 157 944 1903 .... 357,356,416 1885 111 159 795 The production and value of the coal produced by the 12 largest producers in point of output since 1901 has been as follows: 34 ECONOMIC GEOLOGY OF THE UNITED STATES 1901 1902 1903 STATE QUANTITY QUANTITY QUANTITY SHORT VALUE SHORT VALUE SHORT VALUE TONS TONS TONS Pennsylvania : Anthracite 67,471,667 112,504,020 41,373,595 76,173,586 74,607,068 152,036,448 Bituminous 82,305,946 '81,397,586 98,574,367 106,032,460 103,117,178 121,752,759 Illinois 27,331,552 28,163,937 32,939,373 33,945,910 36,957,104 43,196,809 West Virginia 24,068,402 20,848,184 24,570,826 24,748,658 29,337,241 34,297,019 Ohio 20,943,807 20,928,158 23,519,894 26,953,789 24,838,103 31,932,327 Alabama 9,099,052 10,000,892 10,354,570 12,419,666 11,654,324 14,246,798 Indiana 6,918,225 7,017,143 9,446,424 10,399,660 10,794,692 13,244,817 Colorado 5,700,015 6,441,891 7,401,343 8,397,812 7,423,602 9,150,943 Kentucky 5,469,986 5,213,076 6,766,984 6,666,967 7,538,032 7,979,342 Iowa 5,617,499 7,822,805 5,904,766 8,660,287 6,419,811 10,563,910 Maryland 5,113,127 5,046,491 5,271,609 5,579,869 4,846,165 7,189,784 Kansas 4,900,528 5,991,599 5,266,065 6,862,787 5,839,976 8,871,953 Tennessee 3,633,290 4,067,389 4,382,968 5,399,721 4,798,004 5,979,830 Grouping the output by fields, the overwhelming impor- tance of the Appalachian field is well seen. PRODUCTION OF COAL IN UNITED STATES BY FIELDS FROM 1901-1903 FIELD 1901 SHORT TONS 1902 SHORT TONS 1903 SHORT TONS Anthracite (Pa., Colo., N. Mex.) Triassic 67,538,536 12000 41,467,532 39206 74,679,799 35,393 Appalachian 150 501 214 173 274 861 185 600 161 Northern 1 241 241 964718 1,367 619 Eastern Interior 37 450 871 46 133 04 52 130 856 19,665,985 20,727,495 23,171,692 Rocky Mt 14,090,362 16,149,545 16,981,059 2,799,607 2,834,058 3,389,837 The average price of anthracite coal, per short ton, in 1903 was $2.04, while that of bituminous was |1.24. COAL 35 The exports in 1903 amounted to 2,008,857 long tons of anthracite, valued at 19,680,044, and 6,303,241 long tons of bituminous, valued at $17,410,385, PRODUCTION OF LEADING COAL-PRODUCING COUNTRIES COUNTRY SHORT TONS United States (1903) 357,356,416 Great Britain (1903) 257,974,605 Germany (1903) 178,916,600 Austria-Hungary (1902) 43,518,319 France (1903) 38,583,798 Belgium (1903) 26,312,805 Russia (1902) ........ 17,090,835 Japan (1901) 9,861,107 Production of Coke. The quantity of coke now produced annually in the United States is very large, and there is an extensive demand for it in smelting operations. In 1903 there were produced 25,262,360 short tons of coke from 39,410,729 short tons of coal, which gave an average yield of 64.1 per cent coke .per ton of coal, with the aver- age value of $ 2.63 per ton coke. This quantity was supplied by 77,188 coke ovens, and over 50 per cent of the supply came from Pennsylvania. In addition 1,882,394 short tons, or 7.4 per cent of the total production, was made in by- product coke ovens, the approximate percentage of by- products obtained from a ton of coal being: coal tar, 12.55 gallons; ammonia liquor, 14.4 gallons; ammonium sulphate, 17.6 pounds. REFERENCES ON COAL GENERAL. 1. Catlett, Amer. Inst. Min. Engrs., Trans. XXX : 559, 1901. (Coal outcrops.) 2. Bain, Jour. Geol. Ill: 646, 1895. (Structure of coal basins.) 3. Lesley, Manual of Coal and its Topography; Philadelphia, 1856. 4. Lesquereux, 2d Geol. Surv. Pa., Ann. Kept., p. 95, 1885. (Origin.) 5. Lyell, Amer, Jour. Sci. CLV : 353, 1843. 36 ECONOMIC GEOLOGY OF THE UNITED STATES (Upright trees in coal.) 6. Moffat, Amer. Inst. Min. Engrs., Trans. XV: 819, 1887. (Change of mine prop to coal.) 7. Steven- son, Geol. Soc. Amer. Bull., V : 39, 1893. (Origin Pa. anthracite.) 8. Wormley, Geol. Surv., Ohio, VI: 403, 1870. (Proximate and ultimate analysis.) See also Nos. 32, 32a, 37, 55. GENERAL AREAL REPORTS. 9. Hayes, U. S. Geol. Surv., 22d Ann. Kept., Ill: 1, 1903. (U. S. coal fields.) 10. MacFarlane, Coal Regions of America, 700 pp., 3d ed., 1877, New York. 11. Nich- olls, The Story of American Coals, 1897 (Phila.). 12. White, U.S. Geol. Surv., Bull. 65. (Bituminous field, Pa., Ohio, and W. Va.) 13. Series of papers on the several coal fields of the United States, in U. S. Geol. Surv., 22d Ann. Kept., Ill: 11-571, 1902, as follows: Ashley, p. 271. (Eastern Interior.) 14. Bain, p. 339. (Western Interior.) 15. Hayes, p. 234. (Southern Appalachians.) 16. Smith, p. 479. (Pacific coast.) 17. Storrs, p. 421. (Rocky Mountain field.) 18. Stoek, p. 61. (Pa. anthracite.) 19. Taff, p. 373. (Southwestern.) 20. White, Campbell, and Hazeltine, p. 125. (Northern Appalachians.) Alabama: 21. Gibson, Ala. Geol. Surv., 1890. (Cahaba field.) 22. McCalley, Ala. Geol. Surv., 1900. (Warrior field.) Alaska : 23. Ball, U. S. Geol. Surv., 17th Ann. Rept., 1 : 771, 1896u (Coal and lignite.) 24. Brooks, Ibid., 22d Ann. Rept., Ill: 521. Arkansas : 25. Taff, U. S. Geol. Surv., 21st Ann. Rept., II: 313. (Camden field.) Arizona: 26. Blake, Amer. Geol., XXI: 345, 1898. 27. Campbell, U. S. Geol. Surv., Bull. 225: 240, 1904. (Deer Creek -field.) California : See Pacific Coast Report referred to above and also various county reports in (28) llth Ann. Rept. Calif. State Mining Bureau. Colorado: 29. Eldridge, U. S. Geol. Surv., Geol. Atlas of the U. S., folio 9. (Anthracite.) 30. Hills, U. S. Geol. Surv., Min. Res., 1892, 319. Georgia: 31. McCallie, Ga. Geol. Surv., Bull. 4, 1904. (General.) Iowa: 32 a. Keyes, la. Geol. Surv., II: 1894. (General.) Indi- ana: 32. Ashley, Ind. Dept. of Geol. and Nat. Hist., 23d Ann. Rept., 1899: 1. Illinois: 33. Also Worthen and others, 111. Geol. Surv., 1 : 1866 ; III : 1868 ; IV : 1870 ; V : 1873 and VI : 1875. - Indian Territory : 34. Adams, Ibid., 21st Ann. Rept., II: 257, 1900. (Eastern Choctaw field.) 35. Taff, White, and Girty, U. S. Geol. Surv., 19th Ann. Rept., Ill : 423, 1898. (McAlester-Lehigh field.) Iowa: 36. Keyes, Iowa Geol. Surv., II: 536. Kansas: 37. Ha- worth and Crane, Kas. Univ. Geol. Surv., Ill: 13, 1898. Ken- tucky: 38. Moore, Ky. Geol. Surv., Ser. 2, IV, pt. XI: 423. (Eastern border and Western field.) 39. Lesley, Ky. Geol. Surv., IV: 443, 1858. (Eastern.) 40. Norwood, Ann. Rept., Inspector of Mines, 1901-1902. (Much general information.) 41. For analyses, see COAL 37 Ky. Geol. Surv., New Series, Chem. Kept., etc., pt. I, II, and III. Louisiana: 42. Harris, Prelim. Kept, on Geol. of Louisiana for 1899: 134. (Lignite.) Maryland: 42 a. Martin, Kept, on Alle- gheny Co. Michigan : 43. Lane, Mich. Geol. Surv., VIII : pt. 2. Missouri: 44. Winslow, Mo. Geol. Surv., 1891: 19-226. Montana: 45. Weed, Eng. and Min. Jour., LIII: 520, 542, and LV : 197, also Geol. Soc. Amer., Bull. Ill : 301, 1892. (Great Falls and Rocky Fork fields.) 46. Rowe, Amer. Geol., XXXII: 369, 1903. 47. Burchard, U. S. Geol. Surv., Bull. 225:276, 1904. (Lignites, Upper Missouri Valley.) Nebraska: 48. Barbour, Neb. Geol. Surv., I: 198, 1903. Nevada: 49. Spurr, U. S. Geol. Surv., Bull. 225: 289, 1904. New Mexico: 50. Johnson, Sch. of M. Quart., XXIV: 456. (Cerillos.) 51. Stevenson, N. Y. Acad. Sci., Trans. XV: 105, 1896. (Cerillos field.) North Carolina: 52. Woodworth, U. S. Geol. Surv., 22d Ann. Rept., Ill: 31, 1902. North Dakota: 53. Babcock, N. Dak. Geol. Surv., 1st Biennial Rept., 1901 : 56. 54. Wilder, Eng. and Min. Jour., 74: 674, 1902. (Lignite.) Ohio: 55. Orton, Ohio Geol. Surv., VII: 253. Oregon: 56. Diller, U. S. Geol. Surv., 17th Ann. Rept., I. (N. W. Ore.) 57. Diller, Ibid., 19th Ann. Rept., Ill: 309. (Coos Bay.) Pennsylvania : 58. d'ln- villiers, 2d Pa. Geol. Surv. Rept., 1885 and 1886. (Pittsburg re- gion.) 59. McFarlane, Coal Regions of America, 3d ed. ; New York, 1877. 60. Rept. MM. contains many analyses. 61. See also various county reports of same survey. 62. Final Summary Rept., Ill: pt. 1, and 2. Rhode Island: 63. Emmons, Amer. Inst. Min. Eng., Trans. XIII : 510, 1885. 64. Stevenson, Manchester Geol. Soc., Trans. XXIII: 127. (New Eng. fields.) South Dakota: 65. Todd, S. Dakota Geol. Surv., Bull. 1 : 159. Tennessee : 66. Duf- field, Eng. and Min. Jour., LXXIV : 442, 1902. (Cumberland Pla- teau.) 67. Safford, U. S. Geol. Surv., Min. Res., 497, 1892. Texas: 68. Dumble, Bull, on Lignites of Texas, Tex. Geol. Surv. (Lig- nites.). 69. Phillips, Univ. Tex. Mineral Surv., Bull. 3 : 137, 1902. (Coal and lignite.) 70. Vaughan, U. S. Geol. Surv., Bull. 164, 1900. (Rio Grande fields.) Utah : 71 . Forrester, U. S. Geol. Surv., Min. Res., 511, 1892. Vermont : 72. Hitchcock, Amer. Jour. Sci., ii, XV: 95, 1853. (Lignite at Brandon.) Virginia : 73. Camp- bell, U. S. Geol. Surv., Bull. Ill, 1892. (Big Stone Gap field.) 74. Woodworth, U. S. Geol. Surv., 22d Ann. Rept., Ill: 31, 1902. (Triassic coal.) Washington: 75. Landes and Ruddy, Wash. Geol. Surv., II; Willis, U. S. Geol. Surv., Ann. Rept., Ill: 393, 1898. (Puget Sound.) West Virginia: 76. White, West Va. Geol. Surv., II: 1903. Wyoming: 77. Fisher, U. S. Geol. Surv., Bull. 225: 293, 1904. 78. Knight, Min. Ind., Ill: 145, 1894. 38 ECONOMIC GEOLOGY OF THE UNITED STATES REFERENCES ON PEAT 79. Hies, N. Y. State Museum, 54th Ann. Kept., 1903. (N. Y., Origin and uses in general, Bibliography.) 80. Carter, Ont. Bur. Mines, Rept. for 1902. (General.) 81. Shaler, U. S. Geol. Surv., 12th Ann. Kept., p. 311. (Peat and swamp soils.) 82. Roller, Die Torfindustrie, Vienna, 1889. 83. Hies, Min. Res., U. S. Geol. Surv., 1901. (U. S.) THE RSITY r re*! CHAPTER II PETROLEUM, NATURAL GAS, AND OTHER HYDROCARBONS UNDER this head are included a number of hydrocarbon compounds, of complex and variable composition, ranging from the solid to the gaseous state, the series including four well-marked and well-known members; viz., natural gas, petroleum, mineral tar or maltha, and asphalt. The de- velopment of these products, and especially the first two, has been so remarkable and attended by such important economic results that it seems well to preface the follow- ing description by a brief outline of this history of their development. History of Petroleum Development. Petroleum has long been known in many parts of the world because of its pres- ence in bituminous springs or as a floating scum on the surface of pools. It was used at an early date on the walls of Babylon and Nineveh, and was obtained by the Romans from Sicily for use in their lamps. In the United States petroleum was mentioned by French missionaries even in 1635, and the early Pennsylvania settlers obtained small quantities by scooping out the oil from dug wells. Its discovery at greater depth on the western slope of the Alleghanies was made during the drilling of brine wells ; but its early use was chiefly a medicinal one until 1883, when attempts were made to purify it for use as a 39 40 ECONOMIC GEOLOGY OF THE UNITED STATES lubricant and illuminant. The beginning of the oil industry is usually considered to date from the sinking of a successful well by Colonel Drake on Oil Creek, Pennsylvania, in 1860. From this center prospectors spread out in all directions mak- ing valuable discoveries, until now petroleum production and refining rank among the leading industries of the country, the supply coming from many states. History of Natural Gas Development. Natural gas was discovered and first employed for economic purposes at Fredonia, New York, in 1824. In 1841 it was used in the Great Kanawah Valley as a fuel in salt furnaces, but its first extensive use began in 1872 at Fairview, Pennsylvania. It was used in 1885 for iron smelting at Etna Borough near Pittsburg, and in 1886 was piped nineteen miles from Murrayville to Pittsburg. Now natural gas is piped long distances to cities, being used as a fuel in many industries, as well as for domestic heating and lighting. Properties of Petroleum (1, 2, 7). Crude petroleum is a liquid of complex composition and variable color and den- sity. It consists of a mixture of hydrocarbons, the American petroleum belonging usually to the paraffin series although some has an asphaltic base. The Mississippi River forms a rough dividing line between fields containing oil with a paraffin base and those with an asphaltic base. In addition to these compounds, petroleum may contain a small per- centage of nitrogen and sulphur. The following are analyses of several petroleums from American and foreign localities: PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 41 ELEMENTARY ANALYSES OF PETROLEUMS LOCALITY PER CENT SPECIFIC C. H. 0. GRAVITY H 2 = l Heavy oil, W. Va Light oil, W. Va. 83.5 843 13.3 14 1 3.2 1 fi .873 QJ.1 9 Heavy oil, Pa. 849 137 I f\A .o^tU CQfi Light oil, Pa 8 9 14 8 q O QI a Parma, Italy 840 134 1 S froo Hanover, Germany . . . Galicia, Austria . 80.4 89 2 12.7 10 1 6.9 K 7 .892 Off) Light oil, Baku, Rus. . . . Heavy oil, Baku, Rus. . . Java 86.3 86.6 87 1 13.6 12.3 120 0.1 1.1 Q .O/U .884 .938 Q9Q Beaumont, Texas .... 86.8 13.2 .920 Petroleums commonly vary in specific gravity between .801 and .965, the following being some of the limits shown by American oils : SPECIFIC GRAVITY OF SOME AMERICAN PETROLEUMS STATE SPECIFIC GRAVITY GRAVITY BEAUME 1 Pennsylvania .801-.817 .816-.860 .835-1.000 .841-.873 .904-.925 .912-.945 .920-.983 46.2-42.6 42.8-32.5 38.8-10.0 37.6-30.0 24.8-31.1 23.3-11.9 21.9-12.3 Ohio "West Virginia . Beaumont, Texas Wyoming California The temperature at which crude petroleum solidifies ranges from 82 F., in some Burma oils, to several degrees below zero in certain Italian oils. The flashing point, or the lowest 1 A specific gravity of 1, compared with water, is 10 on the Beaume scale. 42 ECONOMIC GEOLOGY OF THE UNITED STATES temperature at which inflammable vapors are given off, may be as low as zero degrees in the Italian oils to as high as 370 F. in an oil found on the Gold Coast of Africa, but these are extreme limits. There is also a great range in the boiling point, which is 180 F. in some Pennsylvania oils and 338 F. in oils found at Hanover, Germany. The various liquid hydrocarbons making up crude petro- leum vary in their gravity and temperature of volatilization. The more important oils which can be separated from crude petroleum by distillation are gasoline, benzine, heavy naphthas, and residuum. Those with a paraffin base are generally lighter and more valuable on account of the higher quantity and quality of the naphthas, illuminating oils, and lubricating oils which they produce. Those with an asphalt base are of inferior quality and chiefly valuable for fuel. Their trans- portation by pipe lines is also more difficult. The percentage of the different distillates varies. The following average percentages of distillates were yielded by the oils of several fields in 1902 (Oliphant) : APPALACHIAN FIELD LIMA, IND. FIELD KANSAS FIELD Naphthas 20 1 10 Q 1Q Illuminating oils . 61 4 AQ. Q BO Lubricating and heavy oils . . Residuum 7.1 63 17.2 25 Loss from uncondensed products and water 51 230 7 Properties of Natural Gas. This consists chiefly of Marsh gas fire damp CH 4 . It is colorless, odorless, and burns easily, as well as somewhat luminously; but when mixed PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 43 with air, it is highly explosive. As is shown by the fol- lowing analyses, several other gases are commonly present in small quantities : ANALYSES OF NATURAL GAS HYDRO- GEN MARSH GAS OLEFI- ANT GAS CAR- BONIC OXIDE CAR- BONIC ACID OXTGEN NITRO- GEN PHURIC HYDRO- GEN Fostoria, O. 1.89 92.84 .20 .55 .20 .35 3.82 .15 Findlay, O. 1.64 93.35 .35 .41 .25 .39 3.41 .20 Muncie, Ind. 2.35 92.67 .25 .45 .25 .35 3.53 .15 Mode of Occurrence (4,5,6,8). Oil is rarely found without gas, and saline water is likewise often present. If the con- taining strata are horizontal, the oil and gas are usually irregularly scattered, but if tilted or folded, they collect at the highest point possible. It was the result of observa- C WATER CAPROCK a GAS . b OIL FIG. 13. Section of anticlinal fold showing accumulation of gas, oil, and water. After Hayes, U. S. Geol Surv., BulL 212. tions along this line that led I. C. White to develop what is known as the "Anticlinal Theory" (8). According to this theory, in folded areas the gas collects at the summit of the fold, with the oil immediately below, on either side, followed by water (Fig. 13). Unless there are secondary 44 ECONOMIC GEOLOGY OF THE UNITED STATES anticlines, the intervening synclines are liable to be barren of oil and gas. For this theory, as for others, it is necessary that the oil-bearing stratum shall be capped by a practically impervious one. Such anticlinal waves are found in the oil fields of the Appalachians, Indiana, western Ohio, and many other locali- ties. While this theory has been disputed, it may be con- sidered established for many localities. The rival theory advanced by Lesley and Ashburner, that the oil has accumu- lated in porous areas of rock, perhaps ancient shore-line deposits, may likewise apply in some cases. It supplies all the necessary conditions of a subterranean reservoir for the accumulation of oil in "pools." In the first discovered fields, the oil and gas were found in porous, sandy strata, varying from fine-grained, cemented sandstone to loose gravels. These strata were termed sands, and the area of porous oil sand was called the pool. Later discoveries in Ohio and Indiana showed that the gas and oil might occur in limestone also. The quantity of oil which a cubic foot of apparently dense rock can hold is often surprising. White (36) estimated that fairly productive sands may hold from six to twelve pints of oil per cubic foot, but that probably not more than three-fourths of the quantity stored in the rock is obtain- able. The ease with which the containing rock yields its supply of oil depends largely on the openness of the pores. Pressure of Oil and Gas Wells. Since both oil and gas usually occur in the earth under pressure, any break in the porous rock or reservoir which contains them allows them to escape, frequently giving rise to surface indications, and the force with which oil and gas oftentimes issue from a PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 45 well indicates the pressure under which they are confined. It is sometimes sufficient to blow out the drilling tools and casing, as well as to cause the oil to spout many feet into the air. There are several remarkable cases of the amount spouted by these gushing wells. One of these is the famous Lucas well at Beaumont, Texas, which in 1901 for nine days gushed a six-inch stream to a height of 160 feet, at the rate of 75,000 barrels per day. This, however, is small compared with the records of some Russian oil wells. Although many wells flow when first drilled, this does not usually continue long, and the oil then has to be brought to the surface by pumping. The depth of the wells drilled in the United States ranges from 250 to 3700 feet, and over 70 per cent of the total number drilled are located in Ohio and Pennsylvania. The maximum pressure which a well develops when closed has been called rock pressure. As a result of his studies in the Ohio-Indiana field, Orton (29) found that the rock pressure was the same as that of a column of water whose height was equal to the difference in elevation between the level of Lake Erie and that of the oil or gas bearing stratum. He therefore considered it to be hydrostatic pressure. This theory, while apparently applicable in many localities, was found to be inadequate to explain the great pressure shown in many shallow wells. In such cases, no doubt, as in many others, the pressure is due to the expansive force of the imprisoned gas. Either the drilling of additional wells or a drain by exces- sive use from wells already bored commonly causes a slow decrease in pressure in an oil or gas field. Thus in the natural-gas region of Findlay, Ohio, the rock pressure in 1885 was 450 pounds per square inch ; 400 in 1886 ; 360- 380 in 1887; 250 in 1889; 170-200 in 1890. Some West 46 ECONOMIC GEOLOGY OF THE UNITED STATES Virginia wells have shown a measured rock pressure of 1110 pounds per square inch and an estimated pressure of 2000 pounds. Origin. That the solid, liquid, and gaseous l^drocarbons are more or less closely related is evident from the fact that the gases given off by petroleum are similar to those pre- dominating in natural gas, while the exposure of many petroleums to the air results in a change to a viscous mass and finally to a solid, asphalt-like substance. It is a well- known fact that petroleum is rarely free from natural gas, although this gas may sometimes form alone, as in coal mines, or from decaying vegetation in stagnant pools. The origin of the hydrocarbon compounds, has been the subject of much speculation among both chemists and geologists, the former for a time arguing for an inorganic or mineral origin, the latter for an organic derivation. Inorganic Theory. Several theories have been advanced to account for an inorganic origin of oil, the most important of which, though not the earliest, was that of Mendel jeff, the Russian chemist. According to his theory, the interior of the earth contains metallic iron, as well as carbid of iron like that found in meteorites. Waters percolating down- ward through the earth's crust, on reaching the heated interior, become converted into steam, which, attacking the carbid of iron, forms hydrocarbons. These are forced to the surface by the expansive force of the steam. From a purely chemical standpoint, this theory is reason- able, but it does not accord with geologic facts. If petro- leum were found in this manner, we should expect to find it widely distributed through the oldest rocks of the earth's PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 47 crust. On the contrary, it is known in these rocks at only one locality, in Ontario, where a hard, compressed asphalt is found in crystalline rocks. It is significant that this material, which was probably originally petroleum, occurs in rocks which show evidence of having been originally stratified. Organic Theory. This considers that petroleum has been derived from either animal or vegetable matter by a process of slow distillation, although the exact changes involved are uncertain. There are several strong arguments in favor of it. (1) Petroleum is a combustible substance, and all other similar combustibles have originated organically. (2) It is possible to artificially produce, from either animal or vege- table substances, both gaseous and liquid, compounds which are closely analogous to those found in petroleum and natural gas. Fish oil, for example, will on distillation yield petroleum compounds, including illuminating oil, lubricating oil, benzine, and paraffin. (3) These substances occur in fossil-bearing rocks. (4) They are practically absent from the crystalline rocks. (5) In some places 'these substances occur in close proximity to fossils. (6) Natural gas is actually generated in coal seams. Some geologists, including Orton (4) and Newberry (Geol. Soc. Amer., Bull. I: 192), have believed that the formation of petroleum has taken place at low temperatures ; but others, including Peckam (6), have considered heat necessary. In the case of Appalachian oils, the folding of the strata is sup- posed to have supplied this heat. It seems doubtful whether either petroleum or natural gas have migrated any great distance through the strata subse- quent to their formation. When any movement has taken 48 ECONOMIC GEOLOGY OF THE UNITED STATES place through pores of the rock, it has probably been due to gravity separation, the gas rising to the highest point of the stratum while the oil settles. Geological Distribution of Petroleum and Natural Gas. Petroleum is widely distributed geologically, being found in rocks whose age ranges from the Ordovician to the most recent, the occurrences in Paleozoic strata being chiefly in eastern United States, those in post-Carboniferous strata in the western and southern states. Natural gas may show an equally wide geological distribu- tion, although in the United States the larger amount is now obtained from the Paleozoic formations. Distribution of Petroleum in the United States. The im- portant petroleum occurrences of the United States, so far as at present known, may be considered to belong to the seven following fields (Fig. 14) : (1) the Appalachian field, includ- ing New York, western Pennsylvania, eastern Ohio, West Virginia, Kentucky, and Tennessee; (2) the Ohio-Indiana field ; (3) the Texas-Louisiana field ; (4) the Kansas-Indian Territory field; (5) the Colorado fields; (6) the Wyoming fields; (7) the California fields. In addition to these there are scattered occurrences in Michigan, etc. (See map, Fig. 14.) Appalachian Field. This field, which supplied over 85 per cent of the oil produced in the United States in 1902, extends from southwestern New York (25) into West Virginia (37, 38) and is subdivided into several districts, each containing sev- eral "pools." The region is of interest historically and geo- logically, some of the earliest discoveries of oil having been made in it. The oil is obtained from sandstones and con- glomerates, ranging in age from the Upper Carboniferous PLATE III FIG. 1. General view of Tuna Valley, in Pennsylvania oil field. Photo, by F. H. Oliphant. FIG. 2. View in Los Angeles, Calif., oil field. Such close spacing of oil derricks tends to hasten the exhaustion of the oil supply. OF THE IVERSITY or PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 49 in the upper part of the field, to Middle Devonian in the lower portion, which underlie an area of probably 55,000 P It 02 T3 square miles. There are often several productive beds in a single formation, and 40 oil sands have been recognized in 50 ECONOMIC GEOLOGY OF THE UNITED STATES the entire section. This field, which is the most important in the United States, supplies a large amount of high-grade petroleum, and has a large output ; but apparently the pro- duction has practically reached its maximum. The petroleum- producing areas of Pennsylvania (31, 32) are divided into a number of districts, this division being based partly on quality and partly on county lines. Each district may be subdivided into pools. In the Clarendon and Warren County district is found some of the finest petroleum produced in the United TRENTON LIMESTONE UTICA SHALE HUDSON R. NIAGARA LIMESTONE LOWER UPPER OHIO SHALE NIAGARA SHALE HELDERBERG HELDERBERQ SHALE MEDINA CLINTON LIMESTONE LIMESTONE LIMESTONE SHALE FIG. 15. Geological section of Ohio-Indiana oil and gas fields. After Orton. U. S. Geol. Surv., 8th Ann. Kept., II. States, while the Franklin district is noted for the fine, natu- ral lubricating oil which it yields. In Kentucky (22) and Tennessee a limited amount of petroleum is obtained from Silurian rocks. The total number of wells drilled in the Appalachian field from 1877 to the end of 1903 was 137,679. Ohio-Indiana Field (16-18, 26-30). The discovery of oil and gas in the Trenton rocks of western Ohio in 1884 caused considerable excitement, since it showed the existence of petroleum in limestone, an exception to previously known conditions, and at a much lower geological horizon than any in which oil or gas had hitherto been found. This field "ti>V or THE A UNIVERSITY 1 PLATE IV PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 51 extends from Findlay in northwestern Ohio south westward into Indiana. The oil, which is dark and heavy, and con- tains a higher percentage of sulphur than the Pennsylvania oil, is found near the top of the porous, dolomitized portions of the Trenton limestones, at depths of about 1100 feet. The limestone, which shows several low folds (Fig. 15), is covered by the impervious Hudson River shales. Texas- Louisiana Oil Fields (33-35). These occur in a belt from 50 to 75 miles wide along the Gulf Coast from near the Mississippi River in Louisiana to a point about two thirds the way across Texas (Fig. 14). The nearly flat surface of this coastal plain is occasionally in- terrupted by low mounds or swells which seem to in- dicate favorable conditions for the accumulation of oil below the surface. Underlying this area is a series of Quaternary and Tertiary clays, sands, and gravels, with occasional limestones, having in general a gentle southeast- ern dip interrupted by low domes. The oil pools are all of small size, that at Beaumont, which is the best known, covering an area of about 200 acres (PI. IV). It was discovered in 1901, and within a year and a half 280 successful wells had been drilled. The oil rock, which lies from 900 to 1000 feet below the surface, is a very porous, crystalline dolomitic limestone, and the cap- LEGEND EH SAND m m SHALE^ GYPSUM SALT . DOLOMITE CLAY FIG. 16. Section of Spindle Top oil field near Beau- mont, Texas. After Fenneman, Min. Mag., XI: 317. 52 ECONOMIC GEOLOGY OF THE UNITED STATES rock is clay. The occurrence of gypsum and salt under- lying the oil rock in some of the wells is unique (Fig. 16). Many of the wells in this pool were gushers, but so great was the drain on this field that by the end of the first year after its discovery the pressure was considerably reduced, and in 1903 many of the wells had practically ceased producing, while others were yielding a mixture of salt water and oil. The production, however, is still considerable, although the supply is no doubt exhaustible. The coastal-plain oils have an asphaltic base, or are " heavy," and at times contain con- siderable sulphur. In 1903 many wells were being developed in the Sour Lake district about 20 miles northwest of Beaumont. The oil is heavy like that of Beaumont, but runs lower in sulphur. In Louisiana active drilling operations have been carried on in the region around Jennings, and one well yielded 20,000 barrels per day while it was gushing. The oil re- sembles that of Beaumont. The belt of Cretaceous rocks of central Texas has yielded both oil and gas at several localities, but the only important one is at Corsicana, where both. a light and heavy oil have been found in sands interbedded with dense clay shales. The two kinds of oil occur at different horizons. Kansas (19-21). In southeastern Kansas a dark green oil is obtained from the sugar sands near the bottom of the Cherokee shales, about 800 feet below the surface. A second horizon is found about 300 feet lower. California. There are a number of productive fields in California (10-12), all lying south of the latitude of San Fran- cisco. Altogether there are 10 or 12 horizons in the folded Tertiary strata, which have a, total thickness of 20,000 feet. The oil which is found in conglomerates, sandstones, and arenaceous shales, is, in the most productive areas, found closely associated with anticlines, but the strata are in many PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 53 FLEXURE places extensively faulted (Fig. 17), and it is doubtless to these faults that many of the California oil springs are due. By adding to the porosity of the rocks, the faulting has probably also increased the capacity of some of the oil reservoirs. In 1903 the Kern River field was the most productive in California. It has an area of 12 square miles, the oil being found at depths ranging from 200 to 300 feet in a series of lower Miocene sands inter- bedded with clay. The T, . -i p FIG. 17. Section in Los Angeles oil field. wells yield trom a tew After Watts ^ Calift state Min BureaUt barrels up to 600 per Buii.ii:i,\m. day, but are flowing usually for only a short period. The California oils, like those of Texas, have an asphaltic base, those found in the shale being generally lighter. Wyoming (39-41). This state contains 18 oil districts, most of which are but slightly developed and the geology imperfectly known. Most of them are in the Mesozoic strata, the balance in Upper Carboniferous, the oil being commonly found along the axes of anticlinal folds. The wells vary from 300 to 1500 feet in depth, and the oils are mostly lubricating, although a few contain considerable kerosene (39). Colorado. The oil at Florence (13, 15), in this state, is found in porous, sandy layers of Cretaceous age, at depths of from 1000 to 2000 feet, and, unlike most other occur- rences, in a synclinal trough. It is a heavy oil. Near Boulder (14) there is another oil field, recently developed, in which the oil is found at depths as great as 8800 feet. 54 ECONOMIC GEOLOGY OF THE UNITED STATES Alaska. Petroleum has been found at several localities in Alaska (Fig. 81), and the developmental work already done gives promise of a supply in the future (9,10). Distribution of Natural Gas in the United States. The distribution of natural gas is almost coextensive with that of petroleum, but the commercially important fields are fewer in number. The most important producing states are New York (51), Pennsylvania (54), Ohio (53), Indiana (45), and Kansas (47). New York. Gas is found in several formations, includ- ing the Medina and Oswego sandstones, Utica shale, and Potsdam sandstone, but the main supply is irregularly distributed through the Trenton limestones, showing no arrangement in belts or relation to folds. The pressure ranges from 10 or 20 pounds up to 1540 pounds, which is the highest reported from any field in the world. A simi- larly wide range exists in the volume of the wells. Pennsylvania. Gas is obtained from the same forma- tions that carry the oil. The Bradford district was the first developed, and formerly yielded gas of high pressure. Much is still obtained from McKean, Elk, and Warren counties. Extensive deposits were also found about Pitts- burg, and later to the south of it. Green and Washington counties now produce important supplies from a pool whose length is about 25 miles and width 3 to 4 miles, with pres- sure ranging from 800 to 1000 pounds. Although in recent years several new gas-bearing sands have been discovered in southwestern Pennsylvania, the enormous demand for the gas threatens exhaustion of the available supply at no very distant date. PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 55 West Virginia (see Petroleum references). This state is now the leading producer of natural gas in the United States, and is looked to as an important source of future supply for both Ohio and Pennsylvania, whose gas supply is slowly falling off. The main supply is obtained from the Gordon and Fifth sands of the Catskill formation, this being a higher horizon than that yielding the gas in the Bradford district of Pennsylvania. Immense quantities are obtained from the fields of Wetzel and Tyler counties, the wells being from 2700 to 3200 feet deep. Pipe lines are now run from this district to Pittsburg, and a line has been laid from Tyler County to Cleveland, Ohio. Un- fortunately, by allowing it to escape with the petroleum, many thousand cubic feet of gas have been wasted in this state. Ohio (52-53) . The Trenton limestone, which formerly supplied large quantities of natural gas, is now so nearly exhausted that little gas is obtained except by pumping. Some gas is obtained from the Clinton limestone of central and eastern Ohio, and small amounts from the Corniferous limestone ; but many towns in this state are now supplied by the West Virginia fields. Indiana (45,46). The gas fields of this state, covering about 2500 square miles, were formerly among the most important in the country, the gas being obtained from the Trenton limestone. The supply is, however, rapidly giving out, and its complete exhaustion is probable at no very distant date. Kansas (47-50). Southeastern Kansas and northern Indian Territory are underlain by what is probably an extensive field of shale gas. The supply comes from the Cherokee 56 ECONOMIC GEOLOGY OF THE UNITED STATES shale, and is now much used as a source of fuel in the local metallurgical and manufacturing industries. Some gas is obtained from eastern Kentucky. Scattered pockets of high -pressure gas have also been found at several localities in Texas and also in California. Uses of Petroleum. The two most important uses are for illuminating and lubrication; but the various distillates have special uses. Rhigolene is used as a local anaesthetic, gasoline is used as a fuel, and naphtha as a solvent for resins in making varnish and in oilcloth manufacture, while benzine is of value for cleaning and as a substitute for and an adulterant of turpentine. Astral oil and mineral sperm oil are special grades of illuminating oil with high flashing points. Crude petroleum is now much used for fuel purposes in engines, as along the Pacific coast and in the southwest, where good coal is so scarce that many of the locomotives are run by the use of crude oil. The paraffin residue is placed on the market for medicinal purposes under the name of vaseline, petroleum ointment, and cosmoline. It is also used in the manufacture of chew- ing gum and for electrical insulation. Uses of Natural Gas. Natural gas is widely employed as a fuel in factories, metallurgical establishments, glass works, cement plants, etc. For domestic purposes, such as heating, cooking, and lighting, it is also widely used. Its cheapness, cleanliness, and high calorific power, and the ease with which it can be used have been important factors in insuring its widespread selection for the above purposes. Oil Shales (55 a and &) . Shale containing sufficient petro- leum to permit its extraction by a process of distillation is PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 57 known as torbanite or kerosene shale. Such shales are found in the Carboniferous of New South Wales, Australia, New Zealand, and Scotland, and in the Cretaceous of Brazil. They are almost unknown in the United States. The fol- lowing analysis indicates the composition and richness of shale in hydrocarbons : MOIST VOLATILE HYDRO- CARBON FIXED CARBON ASH SULPHUR Rich shale, Joadja, N.S.W. . .16 89.59 5.27 4.96 .384 The oil can be obtained by distillation in retorts; but in view of the large available supplies of petroleum, obtainable in many parts of the world, the material at present has but little commercial value. It is distilled in New South Wales and also in Scotland. SOLID BITUMENS Occurrence (56-60, 66). Solid bitumens may be grouped according to their mode of occurrence, as (1) asphaltites, which represent the varieties free from sandy and clayey impurities, found filling either fissures or basins ; (2) bitu- minous rocks, in which the bitumen fills the pores of sand- stones, limestones, or other rocks. They are found over a wide range (Fig. 18), both geographically and geologically. A study of the deposits leads to the conclusion that these solid bituminous compounds have been derived from petro- leum (58, 59, 60), for the following reasons : In the asphal- tite deposits the solid bitumens are often associated with petroleum springs, or with fissures leading down to or toward petroleum-bearing strata. In some cases the asphal- tite not only fills such a fissure, but impregnates the wall 58 ECONOMIC GEOLOGY OF THE UNITED STATES rock to a distance of a foot or two on either side of the vein, indicating that the material came up through the fissure in a liquid condition, filling it, and even penetrating the wall rock. The bitumen in bituminous rocks may either have origi- nated from organic remains within the rock itself or have seeped into it from some neighboring pool. In either case the material seems originally to have been liquid petroleum which later solidified. FIG. 18. Map of asphalt and bituminous rock deposits of United States. After Eldridge, U. S. Geol. Surv., 22d Ann. Kept., IX. Asphaltites. There are several varieties of asphaltites, all black or dark brown in color, commonly with a pitchy odor, burning readily with a smoky flame, and insoluble in water, but soluble in ether, oil of turpentine, and naphtha. Their specific gravity ranges from 1 to 1.1. They are PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 59 closely related chemically and in their mode of occurrence, but differ somewhat in their behavior toward solvents, as well as in their fusibility. The most important varieties are described below. Albertite (61), a black bitumen with a brilliant luster and conchoidal fracture, a hardness of 1 to 2 and specific gravity 1.097, is found filling fissures in bituminous shales in New Brunswick. Anthraxolite (63) is a coaly, lustrous, black mineral, with a hardness of 3 to 4, and specific gravity of 1.965. It is found at Sudbury, Ontario, forming veins in a black fissile slate, but has also been described from other localities. Ozokerite (67), also termed mineral wax or native paraffin, is a waxlike hydrocarbon, yellow brown to green, translucent when pure, and of greasy feel. Its specific gravity is .955. While known to occur in Utah, the most important deposit is in Galicia. At the latter locality the Ozokerite is found forming veins from a few millimeters up to several feet in thickness in much-disturbed Miocene shales and sandstones. Grahamite (66) is a vein asphalt found in the Carboniferous of West Virginia. Lake Asphalt (71) is not found in the United States, but occurs in the famous pit or lake on the island of Trinidad, off the coast of Venezuela. Uintaite, or Gilsonite (66), is a black, brilliant bitumen, with conchoidal fracture, hardness 2 to 2.5, and specific gravity of 1.065 to 1.07. It is found filling a series of fissures, termed veins, in the Bridger beds of the Tertiary in eastern Utah, and, to a less extent, in western Colorado. One of these veins, the Duchesne, has been worked to a depth of 105 feet, and is traceable for about a mile, its width for half this distance being 3 to 4 feet. It is usually vertical and in places faulted. Maniak is the name applied to a bitumen FIG. 19. Section of Gil- resembling Uintaite, found on the island of sonite vein, Utah. Barbados. It is a hydrocarbon of high purity, ^ ^^ ndk black color, brilliant luster, and conchoidal frac- Ann. Kept., I: 932. 60 ECONOMIC GEOLOGY OF THE UNITED STATES ture, and forms seams from a quarter of an inch to 30 feet thick in a blue shale. The material brings $60 a short ton in New York. Bituminous Rocks (66). These are commonly classified according to the character of the containing rock, as bitu- minous sandstones, bituminous limestones, and bituminous schists. They are much more widely distributed than the asphaltites, being found in several geological horizons, and are worked in Kentucky (66), Indian Territory (66), and California (64). As illustrative of its mode of occurrence, we may men- tion the bituminous sandstone, which is extensively quar- ried near Santa Cruz, California (PI. V, Fig. 1). The rock, which is of blackish or brownish-black color, weather- ing to gray, occurs beneath the Monterey shales, sometimes resting directly on granites. The bitumen impregnates the heavy bedded sandstone immediately under the shale, and also the sand that fills cracks which extend up into the shale. These cracks, which vary in width from very minute size up to 25 or 30 feet, are sometimes traceable for several hundred feet, being at times of value as guides in finding the main bed. Analyses. The variable composition of asphaltites and bituminous rocks can be seen from the following table : ANALYSES OF ASPHALTITES AND MALTHA LOCALITY SOLUBLE IN CS 2 MINERAL MATTERS NON-BITUMINOUS ORGANIC MATTER Trinidad Lake Asphalt . Graham ite, W. Va. . . Gilsonite, Utah . . . Maltha, Kern. Co., Calif. 54.25 100.00 100.00 93.20 36.51 .10 5.77 9.24 .54 PLATE V FIG. 1. Quarry of bituminous sandstone, Santa Cruz, Calif. After Eldridge, U.S. Geol. Surv., 22d Ann. Rept., I. FIG. 2. Granite quarry, Hardwick, Vt, Photo, by G. H. Perkins. PETROLEUM, NATURAL GAS, OTHER HYDROCARBONS 61 ANALYSES OF BITUMINOUS ROCKS LOCALITY MOISTURE SOLUBLE INCS 2 CaC0 8 MgCOg SAND OB CLAY Ctilifornis, .... 2.50 20.20 3.00 7400 Kentucky .... 5.76 9422 Seyssel, France . . . 8.15 1 Q 91.70 K SO 97 01 4- QS Uses. Trinidad asphalt mixed with powdered rock and tar is much in use for pavements, and the bituminous rocks are employed for similar purposes. Ozokerite, known as Ceresin in its purified form, is used in the manufacture of candles, ointments, powders, as an adulterant of bees- wax, and combined with India rubber as an insulating material. The most important use of Uintaite and Manjak is for making low-grade and dipping varnishes, such as are used for iron work and baking Japans. Other uses to which the Uintaite at least has been put are for preventing elec- trolytic action .on iron plates of ship bottoms, coating masonry, acid-proof lining for chemical tanks, roofing pitch, insulating electric wires, as a substitute for rubber in com- mon garden hose, and as a binder pitch in making coal briquettes. Production of Petroleum, Natural Gas, and Asphaltum. The production of crude petroleum and natural gas for several years is given below : 62 ECONOMIC GEOLOGY OF THE UNITED STATES <*< CO US O (M Oi O CO t- a 3 SS ^ rH CO rH TjT CD" co" CM' 00 CO r- CM O CM 00 rH CO CM rH co H8 CO US rH 3). A great series of sedi- mentary and metamorphic rocks, composed chiefly of car- bonate of lime, or, in the case of dolomite, of carbonate of lime and magnesia, is included under the term limestone and marble. These rocks also contain varying, but usually small amounts of iron oxide, iron carbonate, silica, clay, BUILDING STONES 79 and carbonaceous matter. When of metamorphic character, various silicates, such as mica, hornblende, and pyroxene, may be present. These calcareous rocks vary in texture from fine-grained, earthy, to coarse-textured, fossiliferous rocks, and from finely crystalline to coarsely crystalline varieties. There is, also, great range in color, the most common being blue, gray, white, and black, but beautiful shades of yellow, red, pink, and green, usually due to iron oxides, are also found. Their crushing strength commonly ranges from 10,000 to 15,000 pounds per square inch, while their absorption is generally low. The mineral composition of limestone exerts a strong influence on its durability. Those limestones which are composed chiefly or wholly of carbonate of lime are liable to solution in waters containing carbon dioxide ; but dolo- mite limestones, especially coarse-grained ones, disintegrate rather than decompose. Streaks of mineral impurities cause the stone to weather unevenly. Pyrite is an especially inju- rious constituent, not only on account of its rusting, but also because the sulphuric acid set free by its decompo- sition attacks the stone. Black or gray limestones will sometimes bleach on exposure. Varieties of Limestones. In the geological sense limestones are of sedimentary origin, while marbles are of metamorphic character, but in the trade the term marble is applied to any calcareous rock capable of taking a polish. In addition to the different varieties of marble and the ordinary limestones there are certain kinds of calcareous rock to which special names are given, as follows : Dolomite, or dolomitic limestone, composed of carbonate of lime and magnesia, and to the eye alone often is indistinguishable from lime- stone. 80 ECONOMIC GEOLOGY OF THE UNITED STATES Oolitic limestone, composed of small, rounded grains of concretionary character. Travertine, or calcareous tufa, a limestone deposited from springs. It is often sufficiently hard and durable for building, but rarely occurs in deposits of large size. Stalactitic and stalagmitic deposits, formed on the roofs and floors of caves, respectively, are often of crystalline texture and beautifully colored, and, when of sufficient solidity, are known as onyx marble. Fossiliferous limestones is a general term applied to those limestones which contain many fossil remains. Under this heading are included crinoidal limestone and coral-shell marble. Coquina is a loosely cemented shell aggregate, like that found near St. Augustine, Florida. Chalk is a fine, white, earthy limestone, composed chiefly of forami- niferal remains. Distribution of Limestones in the United States. Lime- stones are found in many states, and in all geological for- mations from Cambrian to Tertiary, but those of the Paleozoic, which are much used in the Eastern and Central states, are more extensive and more massive than those of later formations. Although many large quarries have been opened to supply a local demand, the product is shipped to a distance from only a few localities. At present the sub-Carboniferous Bedford (18) oolitic limestone of Indiana (PI. VI) is, perhaps, the most widely used limestone in the United States. It occurs in massive beds from 20 to 70 feet thick, and is said to underlie an area of more than 70 square miles. Although soft and easily dressed, it has good strength, and has been used in many important cities of the United States. Cretaceous limestones are worked in' Kansas, Nebraska, and Iowa, although the most important sources are in the Paleozoic formations. PLATE VI ^^-^SS^. *V ,} *-' ^* -J"^^^. > OF THF " A f UNIVERSITY 1 V F ^/ Xt C A' \roR^]^f^ ^*'issttr---^i.-^s= s ^^ BUILDING STONES 81 Distribution of Marbles in the United States (3). While some variegated marble is produced in the United States, FIG. 21. Map showing marble areas of eastern United States. After Merrill. Stones for Building and Decoration. still most of those quarried are white, the greater part of the variegated stones being imported. The main supply 82 ECONOMIC GEOLOGY OF THE UNITED STATES comes chiefly from regions of metamorphic rock, the eastern crystalline belt being the principal producer (Fig. 21). Vermont (32, 33) leads all other states in marble produc- tion, supplying 80 per cent of all the marble used for ornamental work in the country. The most important and largest quarries are those at Proctor (PI. VIJ) and West Rutland, where a thick and steeply dipping bed of marble occurs between other limestones. The marble bed, which has a thickness of 150 feet at the top of the quarry, narrowing to 75 feet at the bottom, is divisible into a series of well-marked layers of varying thickness, quality, and color, white, blue, gray, and striped (33). Similar marbles are quarried in Massachusetts (3, 22) ? New York (3, 28), Maryland (21), and Georgia (15). A variegated red and white marble of some hardness is quarried at S wanton, Vermont (33), the brilliant red being caused by iron oxide, the white by calcite deposited in breccia cavities. The Trenton limestone in eastern Tennessee (3) supplies marbles of pinkish chocolate color with white variegation ; and certain layers are rendered peculiarly beautiful by the replacement of the fossils by calcite. It is used chiefly for interior decoration. Marble has been reported from various states west of the Mississippi, but as yet little quarrying has been done. That quarried in Inyo County, California, has attracted con- siderable attention in recent years. Most of the variegated marble used for interior decoration in this country is obtained from abroad, although ornamental stones of this class occur in the United States ; however, up to the present time few attempts have been made to place them on the market. This may be PLATE VII Marble quarry, Proctor, Vt. Photo., Vermont Marble Co. The banding of the rock is vertical. The horizontal lines are caused by the stone being quarried in benches. BUILDING STONES 83 due to the fact that few quarrymen care to assume the temporary expense which their introduction might involve. Onyx Marbles (37-40). Under this term are included two types of calcareous rock, one a hot-spring deposit, or travertine, formed at the surface, the other a cold-water deposit formed in limestone caves in the same manner as stalagmites and stalactites. Cave onyx is more coarsely crystalline and less transluscent than travertine onyx. The beautiful banding of onyx is due to the deposition of successive layers of carbonate of lime, while the colored cloudings and veinings are caused by the presence of metallic oxides, especially iron. Neither variety of onyx occurs in extensive beds, though both are widely distributed. Onyx is found in Arizona, California, and Colorado, but it has not been developed in any of these states except on a small scale. Most of the onyx used in the United States is obtained from Mexico, though small quantities are obtained from Egypt and north Algeria. The value of onyx varies considerably, the poorer grades selling for as little as 50 cents per cubic foot, while the higher grades bring $50 or more. The earliest-worked deposits were probably those of Egypt, which were used by the ancients for the manufacture of ornamental articles and religious vessels; and the Romans obtained onyx from the quarries of northern Algeria. Many of the travertine onyx deposits occur in regions of recent volcanic activity, and all of the known occurrences are of recent geological age. SERPENTINE Pure serpentine is a hydrous silicate of magnesia; but beds of ser- pentine are rarely pure, usually containing varying quantities of such impurities, as iron oxides, pyrite, hornblende, and carbonates of lime and magnesia. The purer varieties are green or greenish yellow, while the impure types are various shades of black, red, or brown. Spotted green and white varieties are called ophiolite or ophicalite. Serpentine is sometimes found in sufficiently massive form for use in structural or decorative work; but, owing to the frequent and irregu- lar joints found in nearly all serpentine quarries, it is difficult to obtain other than small-sized slabs. Its softness and beautiful color have led 84 ECONOMIC GEOLOGY OF THE UNITED STATES to its extensive use for interior decoration ; but since it weathers irregu- larly and loses luster, it is not adapted to exterior work. Though found in a number of states, most of the numerous attempts to quarry American serpentine have been unsuccessful. Considerable serpentine for ordinary structural work has been quarried in Chester County, Pennsylvania, and a variety known as Verdolite is worked near Easton, Pennsylvania. Quarrying operations are also under way in the state of Washington. SANDSTONES General Properties (1, 3). While most sandstones are composed chiefly of quartz grains, some varieties contain an abundance of other minerals, such as mica, or, more rarely, feldspar, which in rare cases may even form the predominating mineral. Pyrite is occasionally present, and varying amounts of clay frequently occur between the grains, at times in sufficient quantity to materially influence the hardness and dressing qualities of the stone. The hard- ness of sandstones, however, usually depends on the amount and character of the cement, varying from those having so small an amount of silica or iron oxide cement that the stone crumbles in the fingers to those quartzites whose grains are so firmly bound by silica that the rock resembles solid quartz. With these differences the chemical compo- sition varies from nearly pure silica to sandstone with a large percentage of other compounds. (For analyses, see Kemp's "Handbook of Rocks.") There are many colors among sandstones, but light gray, white, brown, buff, bluish gray, red, and yellow are most com- mon. In density sandstones range from the nearly imper- vious quartzites to the porous sandrocks of recent geologic formations, and consequently they show a variable absorption. BUILDING STONES 85 Most sandstones contain some quarry water, and those with appreciable amounts are softer and more easy to dress when first quarried ; but they cannot be quarried in freezing weather. The average specific gravity of sandstone is 2.3, and accordingly a cubic foot weighs about 140 to 150 pounds. On the whole, sandstones resist heat well and are usually of excellent durability, since they contain few minerals that easily decompose. When they disintegrate it is commonly by frost action. The injurious minerals are pyrite, mica, and clay. Pyrite is likely to cause discoloration on weather- ing ; the presence of mica tends to cause the stone to scale off if set on edge ; and clay may cause injury to the stone in freezing weather on account of its capacity for absorbing moisture. The value of a sandstone is often lessened by careless quarrying, or by placing it on edge in the building, thus exposing the bedding planes to the entrance of water. Varieties of Sandstone. With an increase in the size of their grains, sandstones pass into conglomerates on the one hand and with an increase in clay into shales. By an in- crease in the percentage of carbonate of lime they may also grade into limestones. On account of these variations, as well as the difference in color and the character of the cement, a number of varieties of sandstone are recognized, of which the following are. of economic value: arkose, a sandstone composed chiefly of feldspar grains ; flagstone, a thinly bedded, argillaceous sandstone used chiefly for paving purposes ; bluestone, a flag- stone much quarried in New York ; freestone, a sandstone which splits freely and dresses easily ; brownstone, a term formerly applied to sand- stones of brown color, obtained from the eastern Triassic belt, and since stones of other colors are now found in the same formation, the term has come to have a geographic meaning and no longer refers to any specific physical character. 86 ECONOMIC GEOLOGY OF THE UNITED STATES Distribution of Sandstones in the United States. Sand- stones occur in all formations from pre-Cambrian to Ter- tiary. They are so widely distributed that for local supply there are numerous small quarries in many states, but there are several areas which have been operated on an extensive scale, some of them for many years. Of these, one of the best known is the Triassic Brownstone belt, which extends from the Connecticut Valley in Massachusetts southwest- ward into North Carolina. Among the Paleozoic strata there are many sandstones, often massive, and usually dense and hard. Of these the Medina and Potsdam are specially important and much quarried in New York State (27, 28). The same forma- tions extend southward along the Appalachians and are available at several points. Devonian flagstones are ex- tensively quarried at several localities in New York and Pennsylvania. At the present time the Lower Carbon- iferous Berea sandstone of Ohio (29) is in great demand because of its light color, even texture, and the ease with which it is worked. Moreover, it has the peculiar property of changing to a uniform buff on exposure to the air. There are numerous other Paleozoic sandstones in the central states, among them the Potsdam which covers a wide area in Michigan and Wisconsin (35). Some of this stone is bright red in color. The Mesozoic and Tertiary strata of the West contain an abundance of sandstone strata, and quarries opened in many of them yield a good quality of stone. Though usually less dense and hard than the Paleozoic sandstones, they serve admirably for buildings in the mild or dry climates of the West. BUILDING STONES 87 Uses of Sandstones. The wide distribution of sandstones makes them an important source of local structural material. They are chiefly used for ordinary building work, and but little for massive masonry or monuments. The thin-bedded flagstones are much used for flagging, and some of the harder sandstones are split up for paving blocks. For other uses, see Abrasives. SLATES General Characteristics (3, 26). Slates are metamorphic rocks derived from clay or shale or more rarely from igneous rocks (11). Their value depends upon the presence of a well-defined plane of splitting, called cleavage (Fig. 22), de- veloped by metamorphism through the rearrangement and flattening of the original mineral grains and the development of mica- ceous minerals. The cleavage usually de- velops at a variable angle to the bedding planes which are often completely obliterated by the metamorphism. When not completely destroyed the bedding planes are marked by parallel bands, called ribbons, cutting across the planes of cleavage, but so perfect is the cleavage in the best slates that the rock readily splits into thin sheets with a smooth surface. Slates are commonly so fine grained that the mineral com- position is not evident to the eye, but the microscope re- veals the presence of many of the varied mineral grains found in shale, and in addition much chlorite, developed by QUARRY FLOOR FIG. 22. Section showing cleavage and bed- ding in slate. After Dale, U. S. Geol. Surv., 19th Ann. Kept., III. 88 ECONOMIC GEOLOGY OF THE UNITED STATES metamorphism. Owing to the presence of carbonaceous particles, most slates are black or bluish black, but green, purple, and red slates are also known. The specific gravity of slate is about 2.7, and a cubic foot weighs between 170 and 175 pounds. Most slates are fairly durable, though the presence of pyrite along the ribbons may lead to Some colored slates FIG. 23. Section in slate quarry with cleavage parallel to bed- their decay. ding, a, purple slate ; b, un- worked ; c and d, variegated ; fade Oil exposure to the Weather, e and/, green; g and h, gray . . . , , . , . , green ; i.quartzite;^, gray with Ut this change, which IS due to black patches. After Dale. the bleaching of certain minera l grains, does not necessarily result in loss of strength or disintegration. Distribution of Slates in the United States. Since slates are of metamorphic origin, they are limited to those regions in which the rocks are metamorphosed, and at present the greater part of our supply comes from the Cambrian and Silurian strata of the eastern crystalline belt of the Atlantic states. A series of quarries producing red, green, purple, and variegated slates are located in a belt of Cambrian and Hudson River strata along the border of New York (PL VIII) and Vermont (26,33). Black slates are quarried in Maine (3), New Jersey (3), Pennsylvania (3), Maryland (21), Georgia (3), and Virginia (3). Other producing states are Minnesota, California (11), and Arkansas (9). PLATE VIII View of green-slate quarry, Pawlet, Vt. Photo, by H. Ries. BUILDING STONES 89 Uses of Slate. Slate is best known as a roofing material, but it is also used for mantels, billiard-table tops, floor tiles, steps, flagging, slate pencils, acid towers, wash tubs, etc. The process of marbleizing slates for mantels and fireplaces is carried on at several localities. In quarrying slate there is from 40 to 60 per cent waste, which is greater than in any other building stone; but the introduction of channeling machines in quarrying has done much to reduce this. The discovery of a use for this waste has been an important problem, which has thus far been only partially solved. It is sometimes ground for paint, and attempts have been made to utilize it in the manufacture of bricks and Portland cement. Production of Building Stones. The production of build- ing stones by kinds for several years was as follows : PRODUCTION OF BUILDING STONES IN THE UNITED STATES 1900 1901 1902 1903 Granite and Trap . Marble .... $12,675,617 4,267,253 115,976,961 4,965,699 $18,257,944 5,044,182 $18,436,087 5,362,686 Slate 4,240,466 4,787,525 5,696,051 6,256,885 Sandstone and Bluestone . . . 6,471,384 8,138,680 10,601,171 11,262,259 Limestone . . 16,666,62s 1 21,747,061! 24,959,751 * 26,642,551 l Total .... 44,321,345 55,615,926 64,559,099 67,960,468 The value of the building stones produced by the several more important states, together with the kind of stone pro- duced chiefly in 1903, is given below. i Does not include limestone used as flux. 90 ECONOMIC GEOLOGY OF THE UNITED STATES PRODUCTION OF BUILDING STONES IN MORE IMPORTANT STATES IN 1903 TOTAL VALUE KIND PRODUCED CHIEFLY Pennsylvania . . $12,589,202 Limestone Vermont .... 5,889,208 Marble 3,611,140 Granite Ohio 5,280,472 Limestone New York . . . 5,182,850 Limestone Massachusetts . . 4,443,601 Granite Indiana .... 2,903,284 Limestone Georgia .... 1,577,134 Granite Maryland . . . 1,344,722 Granite All others . . . 42,821,613 In 1903 the slate exported was valued at 1628,612. REFERENCES ON BUILDING STONES GENERAL ON PROPERTIES. 1. Hermann, Steinbruchindustrie und Stein- bruch geologic, Berlin, 1899. Borntrager Bros. 2. Merrill, Min- eral Census, 1902. (Mines and Quarries.) 3. Merrill, Stones for Building and Decoration, 3d ed., New York, 1904. Wiley & Sons. For general information on properties and testing see also, 4. Buck- ley, Jour. Geol., VIII : 160 and 333, 1900. 5. Julien, Amer. Geologist, XXI : 397, 1898. 6. Merrill, Maryland Geol. Surv., II : 47, 1898. 7. Watson, Ga. Geol. Surv., Bull. 9-A, 1903. AREAL REPORTS. Alabama : 8. Smith, Eng. and Min. Jour., LXVI : 398. (General.) Arkansas: 9. Dale, U. S. Geol. Surv., Bull. 225: 414, 1904. (Slate.) 10. Hopkins, Ark. Geol. Surv., Ann. Kept., 1890; IV, 1893. (Marbles.) California: 11. Eckel, U. S. Geol. Surv., Bull. 225 : 417, 1904. (Slate.) 12. Jackson, Calif. State Min. Bureau ; 8th Ann. Kept. : 885, 1888. (General.) Colorado : 13. Lakes, Mines and Minerals, XXII : 29 and 62, 1901. (General.) 14. Merrill, Stones for Building and Decoration, New York, 1904. Georgia: 15. McCallie, Ga. Geol. Surv., Bull. 1, 1894. (Marbles.) 16. Watson, Ibid., Bull. 9-A, 1903. (Granites and Gneisses.) Indiana: 17. Hopkins, Ind. Geol. and Nat. Hist. Surv., 20th Ann. Kept. : 188, 1896. 18. Siebenthal, U. S. Geol. Surv., 19th Ann. Kept., VI : 292, 1898. (Bedford limestone.) 19. Thompson, Ind. Geol. and Nat. Hist. Surv., 17th Kept.: 19, 1891. (General.) Maine : 20. BUILDING STONES 91 Merrill, Stones for Building and Decoration. Wiley and Sons, New York, 1904. Maryland: 21. Matthews, Md. Geol. Surv., 11:125, 1898. (General.) Massachusetts: 22. Whittle, Eng. and Min. Jour., LXVI : 336, 1898. (General.) Michigan : 23. Benedict, Stone, XVII : 153, 1898. (Bayport district.) Missouri : 24. Buck- ley and Buehler, Mo. Bur. Geol. and Mines, Bull. 2, 1904. New Hampshire: 25. Hitchcock, 10,th Census U. S., X : 124, 1884. New York : 26. Dale, U. S. Geol. Surv., 19th Ann. Kept., Ill : 153, 1899. (Slate belt.) 27. Dickinson, N.Y. State Museum, Bull. 61, 1903. (Bluestone and other Devonian sandstones.) 28. Smock, N. Y. State Museum, Bull. 3, 1888. Ohio: 29. Orton, Ohio Geol. Surv., V : 578, 1884. (General.) Pennsylvania: 30. Hopkins, Penn. State College, Ann. Kept., 1895 ; Appendix, 1897. (Brownstones.) 31. Lesley, Tenth Census, U. S., X : 146, 1884. (General.) 31 a. South Dakota : Todd, S. Dak. Geol. Surv., Bull. 3 : 81, 1902. (General.) Vermont: 32. Perkins, Kept, of State Geologist on Mineral Industries of Vt., 1899-1900, 1900, 1903-1904; and 33. Re- port on Marble, Slate, and Granite Industries, 1898. Washington: 34. Shedd, Wash. Geol. Surv., II : 3, 1902. (General.) Wisconsin : 35. Buckley, Wis. Geol. and Nat. Hist. Surv., Bull. IV, 1898. (General.) Wyoming: 36. Knight, Eng. and Min. Jour., LXVI: 546, 1898. REFERENCES ON ONYX MARBLE 37. DeKalb, "Onyx Marbles," Trans., Am. Inst. Min. Engrs., XXV: 557, 1896. 38. Merrill, Stones for Building and Decoration (New York), 3d ed., 1904. 39. Merrill, Ann. Kept. U. S. Nat. Mus. (Washington), 1894. 40. Merrill, Min. Indus., Vol. II, "Onyx," 1894. CHAPTER IV CLAY Definition. Clay, which is one of the most widely dis- tributed materials and one of the most valuable commercially, may be defined as a fine-grained mixture of the mineral Jcao- linite (the hydrated aluminum silicate) with fragments of other minerals, such as silicates, oxides, and hydrates, and also often organic compounds (sometimes classed as col- loids), the mass possessing plasticity when wet and becom- ing rock hard when burned to at least a temperature of redness. Residual Clays (42). Clays are derived primarily and principally from the decomposition of crystalline rocks, more especially feldspathic varieties, and deposits thus formed will be found overlying the parent rock and grad- ing down into it. From its method of origin and position it is termed a residual clay (Fig. 24). All residual clays show a variable amount of kaolinite or clay-substance. This mineral, which is white in color, results from the decomposition of feldspar, either by weathering, or, less often, by the action of volcanic vapors. The decay of a large mass of pure feldspar would therefore yield a mass of white clay, but in most instances, the feldspar is asso- ciated with other minerals, such as quartz, mica, and hornblende, all of which, except the quartz, decay with the greater or less rapidity, and some of these, such as the hornblende, may likewise yield a hydrous aluminum silicate. Any ferruginous minerals in the rock will, in decomposing, form limonite, which stains the mass. 92 CLAY 93 Large masses of pure feldspar are rare, but feldspathic rocks, such as granite or syenite, are more common, and these will also decompose to clay; but, since the parent rock contains other minerals, such as quartz or mica, these will either remain as sand grains in the clay, or, by decom- position, will form soluble compounds, or iron stains. The decay of many rocks, for example, lime- stone and shale, in FlG - 24 - Section showing formation of residual clay, addition to the crys- After ffies, U. 8. Geol. Surv., Prof. Paper, 11: 16. talline rocks, produces a residuum of clay. Kaolin is a white-burning residual clay, but it is rare. The extent of a deposit of residual clay will depend on the extent of the parent rock and the topography of the land, which also influences its thickness. On steep slopes much of the clay may be washed away and residual clays are also rare in glaciated regions, for the reason that they have been swept away by the ice -erosion. They are consequently wanting in most of the Northern states, but abundant in many parts of the Southern states, where the older formations appear at the surface. Sedimentary Clays (42). With the erosion of the land surface the particles of residual clay become swept away to lakes, seas, or the ocean, where they settle down in the quiet water LOAMY CLAY CLAY SAND SAND AND GRAVEL BEDROCK' as a fine alumin- ous sediment, . i f . , ., FIG. 25. - Section of a sedimentary clay deposit. After j Hies, U. S. Geol. Surv., Prof. Paper, 11:18. o f sedimentary clay (Fig. 25). Such beds are often of great thickness and 94 ECONOMIC GEOLOGY OF THE UNITED STATES vast extent. With the accumulation of many feet of other sediments on top of them, they often become solidated either by pressure or by the deposit of a cement around the grains. Consolidated clay is termed shale, and this upon being ground and mixed with water often becomes as plastic as an uncon- solidated clay. Sedimentary clays may be divided into the following groups according to their mode of origin and form of deposit. Marine Clays. Formed by the deposition on the ocean floor of the finer particles derived from the waste of the land. Such ancient sea-bottom clays have been elevated to form dry land in all the con- tinents, in many cases forming consolidated clay strata, but elsewhere, especially in coastal plains, in uncon solidated condition. Extensive clay deposits are also formed in protected estuaries and lagoons along the sea coast. Flood-plain Clays. Formed by the deposition of clayey sediment on the lowlands bordering a river during periods of flood. Layer upon layer, this deposit builds a flood plain often of great extent and depth. Such areas of flood-plain clays are most extensive along the greater rivers and in the deltas which they have built in the sea. Lake Clays. Clay is deposited on the bottom of many lakes and ponds in the same manner as on the ocean bottom. Where the streams bring only fine particles the filling of a lake may be entirely of clay. Many lakes have been either drained or completely filled and their clays therefore made available. This is especially true of small, shallow lakes formed during the Glacial Period. Glacial Clays, commonly known as till or bowlder clay, a rock flour ground in the glacial mill in which rock fragments were worn down to clay by being rubbed together or against the bed rock over which the ice moved. When the ice melted, this deposit was left in a sheet of varying thickness and characteristics over a large part of the area which the ice covered. CLAY 95 jEolian Clays. Wind drifts drive clay about, and in favorable posi- tions causes its accumulation in beds. This is true of the Chinese loess, a wind-blown deposit derived from residual soils and drifted about in the arid climate of interior China. Some at least of the loess clays of the Mississippi Valley seem to have a similar origin, the source of the clay being glacial deposits ; in other cases loess seems to be a water deposit either in shallow lakes or else in broad, slowly moving streams. Properties of Clay. These are of two kinds, physical and chemical, and since they exercise an important influence on the behavior of the clay, the most important ones may be described. Chemical Properties (42). The number of common ele- ments which have been found in clays is great, and even some of the rarer ones have been noted ; but in a given clay the number of elements present is usually small, being commonly confined to those determined in the ordinary chemical analysis, which shows their existence in the clay, but not always the state of the chemical combination. The common constituents of a clay are silica, alumina, ferric or ferrous oxide, lime, magnesia, alkalies, titanic acid, and combined water. Organic matter, though often pres- ent, is usually in small amounts, and carbon dioxide is always found in calcareous clays. The effect of these may be noted briefly. Silica is most often present in the form of quartz grains; but it may also be contained in grains of undecomposed minerals. It aids in lowering the plasticity and shrinkage, and helps to increase the refractoriness at low temperatures. A clay high in silica (70 to 80 per cent) is usually sandy. Alumina, which is most abundant in white clays, is a refractory ingredient. Iron oxide acts as a coloring agent in both the raw and burned clay, small quantities coloring a burned clay 96 ECONOMIC GEOLOGY OF THE UNITED STATES buff, and larger amounts (4 to 7 per cent), if evenly distributed, turning it red. It also acts as a flux in burning. Whatever the iron compound present in the raw clay it changes to the oxide in burning. Lime, magnesia, and alkalies are also fluxing ingredients of the clay. The combined percentage of fluxing impurities is small in a refractory clay, and often high in a low grade one. Lime, if present in considerable excess over the iron, will, in burning, exert a bleaching effect on the iron. For this reason, highly calcareous clays, such as those in the Great Lake region, burn cream or buff. When lime is present in large amounts it also causes clay to soften more rapidly in firing than it otherwise would. Chemically combined water and organic matter both pass off at a temperature of very dull redness (450 to 650 C.). Their loss leaves the clay temporarily porous until fire shrinkage sets in. Titanic acid, though rarely exceeding 1 per cent, acts as a flux at high tempera- tures at least. Sulphur trioxide is rarely present in sufficiently high amounts to interfere with the successful burning of the clay. Physical Properties (42). These include plasticity, ten- sile strength, air and fire shrinkage, fusibility, and specific gravity. Plasticity may be defined as the property which clay possesses of forming a plastic mass when mixed with water, thus permitting it to be molded into any desired shape, which it retains when dry. This is an exceedingly important character of clay. Clays vary from exceedingly plastic, or " fat " ones, to those of low plasticity which are " lean " and sandy. Plasticity is probably due in part to fineness of grain, and in part to the presence of colloids. Tensile strength is the resistance which a mass of air-dried clay offers to rupture, and is probably due to interlocking of the particles. Tests show that the tensile strength of clays varies from 15 to 20 pounds per square inch up to 400 pounds or more per square inch. Many common brick clays range from 100 to 200 pounds. Shrinkage is of two kinds air shrinkage and fire shrinkage. The former takes place while the clay is drying after being molded, and is CLAY 97 due to the evaporation of the water, and the drawing together of the clay particles. The latter occurs during firing, and is due to a com- pacting of the mass as the particles soften under heat. Both are variable. In the manufacture of most clay products an average total shrinkage of about 8 or 9 per cent is commonly desired. Excessive air or fire shrinkage causes cracking or warping of the clay. To prevent this a mixture of clays is often used. Fusibility is one of the most important properties of clays. When subjected to a rising temperature, clays, unlike metals, soften slowly, and hence fusion takes place gradually. In fusing, the clay passes through three stages, termed, respectively, incipient fusion, vitrification, and viscosity. In the lower grades of clay, that is, those having a high percentage of fluxing impurities, incipient fusion may occur at about 1000 C., while in refractory clays, which are low in fluxing impurities, it may not occur until 1300 or 1400 C. is reached. The temperature interval between incipient fusion and vitrification may be as low as 30 C. in calcareous clays, or as much as 200 C. in some others. The recognition of this variation is of considerable practical importance, and vitrified products, such as paving bricks and stoneware, have to be made from a clay in which the three stages of fusion are separated by a dis- tinct temperature interval. The importance of this rests on the fact that it is impossible to control the temperature of a large kiln with- in a few degrees, and there must be no danger of running into a condition of viscosity in case the clay is heated beyond its point of vitrification. Specific gravity varies commonly from about 1.70 to 2.30. Chemical Composition. As might be expected from their diverse modes of origin, clays vary widely in their chemical composition. There is every gradation from those which, in composition, closely resemble the mineral kaolinite to those, like ordinary brick clays, in which there is a high percentage of impurities. This variation is shown in the following table : 98 ECONOMIC GEOLOGY OF THE UNITED STATES j j L >rd 1-5 i i |d M S ,4 S^ d gfS o u w ^ d " J H w 2 H B* *-" M cq K - > M - c _ a o g u j ^ g >r 2 gS SS Q K ^ K S S es K > S S < S ^^ o 2 & w < K tl J W fe- 12.42 f9.70 U.12 5.90 .80 3.55 2.78 } 6.24 2.49 3.74 .85 TiO 2 Ti0 2 MnO TiO 2 C0 2 C0 2 3.6 .96 .64 .78 20.46 4.80 MuO .76 Classification of Clay. It is possible to base a classifica- tion of clays either on origin, chemical and physical proper- ties, or uses. But since the subdivisions which can be made are not sufficiently distinct, each of these gives rise to a more or less unsatisfactory grouping. The following classifica- tion is based partly on mode of origin and partly on physical characters : 1. Residual clays. A. White-burning (kaolins, formed from feldspathic rocks). B. Colored-burning (formed from igneous, metamorphic, and many sedimentary rocks). 2. Clastic, or mechanically formed clays. A. Water formed (of variable extent, depending on locality and mode of deposit). a. White-burning (ball and paper clays). b. Colored-burning (brick and pottery clays). CLAY 99 B. Glacial clays (often stony; all colored-burning). C. Wind-formed clays (some loess). 3. Chemical precipitates (some flint clays). Kinds of Clays. Many kinds of clays are known by special names, the more important of which are the following : Adobe. A sandy, often calcareous, clay used in the west and south- west for making sun-dried brick. Ball clay. A white-burning, plastic, sedimentary clay, employed by potters to give plasticity to their mixture. Brick clay. Any common clay suitable for making ordinary brick. China clay. A term applied to kaolin (q.v.) . Earthenware clay. Clay suitable for the manufacture of common earthenware, such as flower pots. Fire clay. A clay capable of resisting a high degree of heat. Flint clay. A peculiar flintlike, fire clay, which when ground up and wet develops no plasticity. Chemically it differs but little, if at all, from the plastic fire clays. Moreover, the two often occur in the same bed, either in separate layers or irregularly mixed. Gumbo. A very sticky, highly plastic clay, occurring in the central states, and used for making burned-clay ballast (1). Kaolin. A white-burning residual clay, employed chiefly in manufacture of white earthenware and por- celain. Loess. A sandy, calcareous, fine-grained clay, covering thou- sands of square miles in the Central states, and of wide use in brick making. Paper clay. Any fine-grained clay, of proper color, that can be employed in the manufacture of paper. Pipe clay. A loosely used term applied to any smooth plastic clay. Strictly speaking, it refers to a clay suited to the manufacture of sewer pipe. Pottery clay. Any clay suitable for the manufacture of pottery. Retort clay. A plastic fire clay, used in making gas retorts. The term is a local one used chiefly in New Jersey. Sagger clay. A loose term applied to clays employed in making saggers ; they are of value for other purposes as well. Stoneware clay. A very plastic clay, which burns to a vitrified or stoneware body. Terra-cotta clay. Clay suitable for the manufac- ture of terra cotta. The term has no special significance, as a wide variety of clays are adapted to this purpose. 100 ECONOMIC GEOLOGY OF THE UNITED STATES Geological Distribution. Clays have a wider distribution than most other economic minerals or rocks, being found in all formations from the oldest to the youngest. The pre- Cambrian crystallines yield both white and colored residual clays, usually the result of weathering, though more rarely of solfataric action. In the Paleozoic rocks, deposits of shale, and sometimes of clay, are found in many localities ; and, since they are usually marine sediments, the beds are often of great extent and thickness. With the exception of cer- tain Carboniferous deposits, the Paleozoic clays are mostly impure. The Mesozoic formations contain large supplies of clays and shale suitable for the manufacture of bricks, terra cotta, stoneware, fire brick, etc. The Pleistocene clays are all surface deposits, usually impure, and individually of limited extent, although they are thickly scattered all over the United States. Their chief value is for brick and tile making. They have been accumulated by glacial action, on flood plains, in deltas, or iir estuaries and lakes. Distribution of Clays by Kinds. Kaolins (59). Since kaolins are derived only from crystalline or igneous rocks, their distribution is limited; indeed, at present the only deposits worked are in the eastern states. Being com- monly formed by the weathering of pegmatite veins, kaolin deposits have great length as compared with their width, which may be anywhere from 5 to 300 feet. Their depth ranges from 20 to 120 feet, depending on the depth to which the feldspar has been weathered. Quartz and white mica are often present in kaolin, and it is then frequently necessary to put the clay through a washing process CLAY 101 to remove these minerals. The difference between a washed and unwashed kaolin is well shown by the two following analyses, from which it is seen that the quartz contents have been considerably lowered, and that the washed product approaches more closely to the composition of kaolinite : CRUDE KAOLIN WASHED KAOLIN SiO 2 6 40 4^ 78 ALOo 26 51 36 4fi Fe O Q 1 14 OQ FeO . 1 08 CaO .57 50 MffO . .01 04 Alkalies 98 95 H 2 O , . IVloisture 8.80 25 13.40 205 Clay substance 100.66 6614 99.84 9394 North Carolina (44) and Pennsylvania (50, 52) are the most important kaolin-producing states, but deposits are also worked in Connecticut, Maryland (30), and Virginia (59). It is known to occur in Alabama (9). All of these deposits except that in Connecticut are found south of the limit of the glacial drift. The output from the American deposits is insufficient to supply the domestic pottery industry, and consequently many thousand tons are annually imported from England. Since this can be brought over as ballast, it is possible to put it on the American market at a low price. The best grades of kaolin sell for 110 to $12 per ton at Trenton, New Jersey, and East Liverpool, Ohio, these being the two most important pottery centers of this country. 102 ECONOMIC GEOLOGY OF THE UNITED STATES Fire Clays. Fire clays are found in the rocks of all systems, from the Carboniferous to the Tertiary, inclusive, with the exception of the Triassic. In the Lower Creta- ceous of New Jersey (42) there are many beds of refrac- tory clay, variable in thickness and closely associated with beds of less refractory character. They not only support a thriving local fire-brick industry, but serve also as a source of supply for factories in other states. Similar, but less extensive and less refractory, beds occur in strata of Cretaceous Age in the coastal plain of Maryland (30), Georgia (17), South Carolina (53), and Alabama (9). The most extensive, and among the most important, beds of fire clay are those found in the Carboniferous strata of Pennsylvania (48, 52), Ohio (46, 47), Kentucky (26, 27), Indi- ana (20), and Illinois (19). Those of the first two named states are on the average the most refractory. Here the fire clays are usually found underlying coal seams and often at well-marked horizons, especially in the Upper Productive Measures. The section given in Fig. 2 is fairly representative of their mode of occurrence. Those of Indiana and Illinois are so placed that one mine shaft is often used for extracting coal, fire clay, stoneware clay, and shale. The beds of refractory clay, found in the Carbon- iferous strata near St. Louis (38), are not only used in the manufacture of fire brick, but are, in some cases, found suitable, after washing, for mixture with imported Ger- man clays for the manufacture of glass pots. The Ter- tiary strata of Missouri also supply some refractory clays. PLATE IX CLAY 103 Fire clays are found in the Black Hills of South Dakota (54), in the Laramie beds of Colorado (13-15), and in California (12) ; but, except- ing near Denver, where used for making fire brick and assayer's appa- ratus, these deposits are as yet slightly developed. Pottery Clays. Under this heading are included several grades of clay, the kaolins, already described, being the purest and best suited to the manufacture of high grades of pottery. A second grade of pottery clay, the ball clay, is of limited distribution in the United States. A small quantity is found in the Cretaceous (PI. IX) of New Jersey (42), and a much larger amount in the Tertiary of western Kentucky (26, 27) and Tennessee (55), and southeastern Missouri (38) and Florida (59). As in the case of kaolin, the domestic supply is not sufficient to meet the demand, and large quantities of ball clay are imported from England. Stoneware clays form a third grade of pottery clays. Being usually of at least semi-refractory character, their distribution is essentially coextensive with that of fire clays; indeed, the two are often dug from the same pit or mine. Large quantities are obtained in New Jersey (42), western Pennsylvania (48), and eastern Ohio (47). Stoneware clays usually in the same area as .the fire clays are also obtained in Illinois (19), Indiana (20), Kentucky (26), Tennessee (55), Georgia (17), Alabama (9), and Texas (56); and they occur also in Missouri (38), Iowa (22), Colorado (14), and California (12), although little is known about these deposits. Many of the Pleistocene surface clays in various states are sufficiently dense-burning to be used locally by small stoneware factories. 104 ECONOMIC GEOLOGY OF THE UNITED STATES Brick and Tile Clays (59). None of our states lack an abundant supply of good brick and tile clays, and in many areas there are extensive deposits near the large markets, and often near tide water. In such cases the clay beds are exploited to an enormous extent. In the northeastern states the Pleistocene surface clays are found almost everywhere in great abundance, and are made use of in many places, especially near the large cities. In the Middle Atlantic states Columbian loams and clay marls are an important source of brick material. In Ohio, Illinois, and Indiana Pleistocene clays, in part of glacial, and in part of flood-plain origin, are much used for brick and tile. Impure Paleozoic shales are also used in places, especially in the manufacture of vitrified paving brick, thousands of which are made annually in Ohio. Northern Illinois, Michigan, and Wisconsin draw their main supply of brick clays from the calcareous lake deposits. Although glacial clays and flood-plain deposits are much used in the states west of the Mississippi, the loess which occurs over a wide area is probably even more important as a source of brick, while in the southwestern states loess and adobe are important. Residual clays, river silts, glacial clays, and other forms of clay are employed in brick making along the Pacific coast. Miscellaneous Clays of Importance. Paper clays of good quality are much sought for by paper manufacturers. At present the best ones are obtained from the Potomac formation of -North Carolina. A small amount of ylasspot clay (48), comes from western Pennsylvania and eastern Missouri ; but our chief supply is imported. Terra-cotta clays are obtained from the same areas that supply fire clays, New Jersey being the principal producer. CLAY 105 Uses of Clay. So few people have even an approxi- mate idea of the uses to which clays are put that it seems desirable to call attention to them briefly. In the following table an attempt has been made to do this : 1 Domestic. Pottery of various grades; Polishing brick, often known as bath bricks; Fire kindlers ; Majolica stoves. Structural. Brick; Tiles and Terracotta; Chimney pots ; Chimney flues; Door knobs ; Fireproof ng ; Copings; Fence posts. Hygienic. Closet boivls ; Sinks, etc. ; Sewer pipe ; Ventilating flues ; Foundation Blocks; Vitrified bricks. Decorative. Ornamental pottery ; Terracotta; Majolica; Garden furniture. Minor Uses. Food adulterants ; Paint filer ; Paper filing ; Electrical insulations ; Pumps ; Filling cloth ; Scouring soap ; Packing horses' hoofs ; Chemical apparatus ; Condensing worms ; Ink bottles ; Ultra- marine manufacture ; Emery wheels. Refractory Wares. Crucibles and other assaying apparatus ; Refractory bricks of various patterns ; Glass pots. Engineering Work. Puddle; Portland cement; Railroad ballast; Water conduits; Turbine wheels. Production of Clay. Owing to the fact that clays are usually manufactured by the producer, it is necessary to give the value of the product, no record being kept of value of the raw material. VALUE OF CLAY PRODUCTS IN UNITED STATES, 1901-1903 1901 1902 1903 Ohio . . . . $21,574,985 $24,249,748 $25,208,128 Pennsylvania . . New Jersey . Illinois ..... New York . . . Indiana .... Others 15,321,742 11,681,878 9,642,490 8,291,718 4,466,454 39,232,320 17,833,425 12,613,263 9,881,840 8,414,113 5,283,733 44,293,409 18,847,324 13,416,939 11,190,797 9,208,252 5,694,625 47,396,583 Total .... $110,211,587 $122,169,531 $130,962,648 Table compiled by R. T. Hill and modified by H. Ries. 106 ECONOMIC GEOLOGY OF THE UNITED STATES LEADING STATES IN PRODUCTION IN 1903 PER CENT OF TOTAL Common brick Pennsylvania . I 9 2 Front brick Pennsylvania . 19 7 Vitrified brick Ohio .... 2S8 Ornamental brick .... Fire brick . Ohio .... Pennsylvania . 4.7 464 Drain tile Ohio .... 247 Sewer pipe Ohio .... 38 6 Terra cotta Illinois . 25 6 Fireproofing New Jersey . 463 Hollow tile and block . . . Tile not drain Ohio .... Ohio 44.9 30 5 REFERENCES ON CLAY TECHNOLOGY AND PROPERTIES. 1. Bain, Min. Indus., VI: 157, 1898. (Clay ballast.) 2. Barber, The Pottery and Porcelain of the United States, 2d ed., N. Y., 1901 (G. P. Putnam's Sons), $5.00. 3. Bourry, Treatise on Ceramic Arts, N. Y. (Van Nostrand & Co.), London (Scott Greenwood & Co.), 1901. 4. Bischof, Die Feuer- festen Thone, 2d ed., Leipzig, 1895 (Quandt & Handel), 12 Mks. 5. Branner, Bibliography of Clays and the Ceramic Arts, U. S. Geol. Surv., Bull. 143, Washington, 1896. 7. Davis, A Practical Treatise on the Manufacture of Bricks, Tiles, and Terra Cotta, 2d ed., Philadel- phia, $5.00. 8. Wheeler, Vitrified Paving Brick, Indianapolis, 1895, (Clayworker Pub. Co.), $1.00. Many excellent papers in Transac- tions American Ceramic Society, Vols. 1-6 of which have appeared. See also Nos. 22, 30, 42, 43 for general properties and technology. AREAL REPORTS. Alabama : 9. Smith and Ries, Ala. Geol. Surv., Bull. 6, 1900. (General.) Arkansas: 10. Branner, Ark. Geol. Surv., Rept. for 1888. (Many analyses.) 11. Also Amer. Inst. Min. Engrs., Trans. XXVII: 42, 1898. (S. W. Ark.) California : 12. Johnston, Calif. State Mineralogist, 9th Ann. Rept.: 287, 1890. (General.) See also scattered notices in other annual reports. Colorado: 13. Eldridge, U. S. Geol. Surv., Mon. XXVII, 1896. (Denver Basin.) 14. Geijsbeek, Clay Worker, XXXVI : 424, 1901. (General.) 15. Ries, Amer. Inst. Min. Eugrs., XXII: 386, 1897. (Clays and Clay Industry.) Delaware : 16. Booth, Geol. of Dela- CLAY 107 ware: 94 and 106, 1841. Georgia : 17. Ladd, Ga. Geol. Surv., Bull. 6 A., 1898. (Cretaceous clays.) 18. Spencer, Ga. Geol. Surv., Paleo- zoic Group : 276, 1893. (N. W. Ga.) Illinois : 19. Many scattered references in volumes on Economic Geology of Illinois Geol. Survey, Resume of these in U. S. Geol. Surv., Prof. Pap. 11, 1903. Indiana: 20. Blatchley, Ind. Dept. Geol. and Nat. Hist., 20th Ann. Kept. : 23, 1896. (Carboniferous clays.) 21. Same author, 22d Ann. Rept. : 105, 1898. (N. W. Ind.) Scattered references in other annual re- ports. Iowa : 22. Beyer, Williams, and Weems, la. Geol. Survey, XIV: 29, 1904. Kansas: 23. Prosser, U. S. Geol. Surv., Mineral Resources, 1892: 731, 1893. 24. See also Reports on Mineral Resources of Kansas, Kas. Geol. Survey, 1897-1901. Kentucky: 25. Crump, Eng. and Min. Jour., LXIV : 89, 1897. 26. Ries, U. S. Geol. Surv., Prof. Pap. 11, 1903. 27. Many analyses in Ky. Geol. Surv., Chem. Rept. A, pts. 1, 2, and 3, 1885, 1886, 1888. Louisiana: 28. Clendenin, Eng. and Min. Jour., LXVI: 456, 1898. 29. Ries, Preliminary Report on Geology of La., I: 264, 1899. Maryland: 30. Ries, Md. Geol. Surv., IV, Pt. Ill: 205, 1902. Massachusetts: 31. Crosby, Technol. Quart., Ill : 228, 1890. (Kaolin at Blandford.) 32. Shaler, Woodworth, and Marbut, U. S. Geol. Surv., 17th Ann. Rept., 1 : 957, 1896. (R. I. and S. E. Mass.) 33. Whittle, Eng. and Min. Jour., LXVI: 245, 1898. Michigan: 34. Ries, Mich. Geol. Surv., VIII : Pt. I, 1903. (Clays and shales.) Minnesota : 35. Berkey, Amer. Geol., XXIX: 171, 1902. (Origin and distribution.) 36. Win- chell, Minn. Geol. Surv., Misc. publications, No. 8, 1881. (Brick clays.) Mississippi: 37. Eckel, U. S. Geol. Surv., Bull. 213: 382, 1903. (N. W. Miss.) Missouri: 38. Wheeler, Mo. Geol. Surv., XI, 1896. (General.) Nebraska: 39. Neb. Geol. Surv., I: 202, 1903.- New Hampshire : 40. Hitchcock and Upham, Report on Geology of New Hampshire, V: 85, 1878. New Jersey: 41. Cook, N. J. Geol. Surv., 1878. (Special Report on Clays.) 42. Kummel, Ries, Knapp, N. J. Geol. Surv., Final Reports, VI, 1904. New York: 43. Ries, N. Y. State Museum, Bull. 35, 1900. (General.) North Carolina: 44. Ries, N. Ca. Geol. Surv., Bull. 13, 1897. (General.) North Dakota : 45. Babcock, N. D. Geol. Surv., 1st Rept. : 27. (General.) Ohio: 46. Orton, Ohio Geol. Surv., VII: 45, 1893. (Geology.) 47. Orton, Jr., Ibid., p. 69. (Clay industries.) Pennsylvania : 48. Hopkins, Pa. State College, Ann. Repts. as follows, 1897, Ap- pendix. (W. Pa.) 49. Ibid., Append, to Rept. for 1899-1900. (Philadelphia and vicinity). 50. Ibid., 1898-1899. (S. E. Pa.) 51. Many analyses in 2d Pa. Geol. Surv., Rept. MM. : 257, 1879, and scattered references in Repts. H 5, H 4, C 4, C 5, etc. 52. Re- sume in U. S. Geol. Surv., Prof. Pap. 11 : 208, 1903. South Carolina : 108 ECONOMIC GEOLOGY OF THE UNITED STATES 53. Sloane, Bull. S. Car. Geol. Surv. (S. Car.) South Dakota: 54. Todd, S. D. Geol. Surv. ? Bull. 1 : 108. Tennessee : 55. Eckel, U. S. Geol. Surv., Bull. 213 : 382, 1903. (W. Tenn.) Texas : 56. See county reports issued by First Geol. Survey. United States : 57. Hill, U. S. Geol. Surv., Min. Res. 1891 : 474, 1893. 58. Ries, U. S. Geol. Surv., 18th Ann. Rept., IV : 1105, 1897. (Pottery Clays.) 59. Ries, U. S. Geol. Surv., Prof. Pap. 11, 1903. (Clays east of Mississippi River.) Vermont : 60. Nevius, Eng. and Min. Jour., LXIV: 189, 1897. (Kaolin.) 61. Ries, U. S. Geol. Surv., Prof. Pap. 11: 58, 1903. Washington: 62. Landes, Wash. Geol. Surv., II: 173, 1902. (General.) Wisconsin: 63. Buckley, Wis. Geol. and Nat. Hist. Surv., Bull. 7, Pt. I, Eco. Series 4, 1901. (General.) 64. Forth- coming bulletin by Ries. Wyoming : 65. Knight, Wyo. Experiment Station, Bull. 14, 1893. (General.) CHAPTER V LIME AND CALCAREOUS CEMENTS Composition of Limestones (35) . Limes and calcareous cements form an important class of economic products, obtained from limestones by heating them to a tempera- ture ranging from that of decarbonation to clinkering. The term limestone is applied to one of the main divi- sions of the stratified rocks so widely distributed, both geologically and geographically, and formed under such different conditions, that its composition varies greatly, this range of variation becoming appreciable from an inspection of the following table, which contains a few selected types : 1 TABLE OF LIMESTONE ANALYSES, INCLUDING THE MINERALS CALCITE AND DOLOMITE CaC0 3 MgC0 3 SiO 2 A1 2 3 Fe 2 3 H 2 O 1. Calcite .... 100.00 2. Dolomite . . . 54.35 45.65 3. White limestone, Adams, Mass. . 99.30 .49 .63 .55 4. Limestone, Lehigh Valley district, Pa 88.00 4.00 5.87 1. 59 5. Limestone, Coplay, Pa 67 14 2 90 18.34 7 49 3.92 1 Kemp, " Handbook of Rocks." 109 110 ECONOMIC GEOLOGY OF THE UNITED STATES CaC0 8 MgCO Si0 2 A1 2 3 Fe 2 8 H 2 6. Limestone, Cum- berland, Md. 41.80 8.60 24.74 16.74 6.30 7. Dolomite, Pleasant- ville, N.Y. . . 59.84 36.80 2.31 .40 .25 8. Magnesiari lime- stone, Rosendale, N.Y 45.91 26.14 15.37 11 .38 1.20 From this table it will be seen that limestones vary from rocks composed almost entirely of carbonate of lime, or of carbonate of lime and carbonate of magnesia, to others which are high in clayey or siliceous impurities. The presence of such impurities in large quantity usually imparts an earthy appearance to the limestone, and some- times even gives it a shaly structure. Marked variations in composition may at times be found even in a single quarry, while in other cases a limestone formation may show remarkable uniformity of composition over a wide area. Changes in Burning (8, 35). When limestones are cal- cined or "burned" to a temperature sufficiently high to drive off volatile constituents, such as carbon dioxide, water, and sulphur (in part), or, in other words, to the point of decarbonation, the rock is left in a more or less porous condition. If heated to a still higher temperature, the rock clinkers or fuses incipiently, but the temperature of clinkering depends on the amount of siliceous and clayey impurities in the rock. Lime (5, 8) . Limestone free from or containing but a small percentage of argillaceous impurities is, by decarbona- LIME AND CALCAREOUS CEMENTS 111 tion, changed to quicklime, a substance which has a high affinity for water, and which, when mixed with water, "slakes," forming a hydrate of lime. This change is accompanied by the evolution of heat and by swelling, and this action becomes the more marked the higher the percentage of lime carbonate in the rock, for the slaking activity is retarded by the presence of magnesium carbon- ate, and especially by argillaceous impurities. Limes have, therefore, been divided into "fat" limes and "meager" limes, depending on the rapidity with which they slake and the amount of heat they develop in doing so (5). Hydraulic Cements. With an increase in clayey and siliceous impurities, the burned rock shows a decrease in slaking qualities, and develops hydraulic properties, or sets when mixed with water, and even under the same. Products of this type are termed cements, and owe their hydraulic properties to the formation during burning of silicates and aluminates of lime. On mixing the burned ground rock with water, these take up the latter and crystallize, thereby producing the set of the cement. Hydraulic cements can be divided into the following classes : Pozzuolano cements, hydraulic limes, natural ce- ments, and Portland cements. Pozzuolano Cements (2,9,41). These are produced from an uncalcined mixture of slaked lime and a silico-aluminous material, such as volcanic ash or blast-furnace slag. This process was known to the ancients, and is named from its early use around Pozzuolano, Italy. The composi- tion of an Italian Pozzuolano earth may vary between the following limits (9): SiO 2 , 52-60; A1 2 O 3 , 9-21; Fe 2 O 3 , 112 ECONOMIC GEOLOGY OF THE UNITED STATES 5-22; CaO, 2-10; MgO, up to 2; alkalies, 3-16; H 2 O, up to 12. The manufacture of slag cement is now carried on at several localities in the United States, and is a growing industry (2). Hydraulic Limes (9) are formed by burning a siliceous limestone to a temperature not much above that of decar- bonation. Owing to the high percentage of lime carbon- ate, considerable free lime appears in the finished product. Hydraulic limes generally have a yellow color, and a gravity of about 2.9. They slake and set slowly, and have little strength unless mixed with sand. This class is of little im- portance in the United States, but much more so in Europe. Natural Cements (1, 8, 9, 41). These, known also as Roman cement, quick-setting cement, and Rosendale cement, are made by burning a silico-aluminous limestone (containing from 15 to 40 per cent clayey impurities) at a temperature between decarbonation and clinkering. The product shows little or no free lime. The following analyses will give some idea of the range in composition of natural cement rocks quarried in the United States : ANALYSES OF CERTAIN AMERICAN CEMENT ROCKS CaCOg MgC0 3 Si0 2 + INSOL. Fe 2 8 A1 2 8 ALKA- LIES H 2 O UN- DET. Rosendale, N.Y. 45.91 26.14 15.37 11. 38 1. 20 Utica, 111. . . . 42.25 31.98 21.12 1. 12 1.07 2.46 Milwaukee, Wis. 45.54 32.46 17.56 3.03 1.41 Fort Scott, Kas. 65.21 10.65 15.21 4.56 4.37 Cement, Ga. . . 43.50 22.00 22.10 1.80 5.45 .22 4.95 Coplay, Pa. . . 67.14 2.90 18.34 7. 49 .19 3.94 v c; rvoi i or LIME AND CALCAREOUS CEMENTS 113 Natural cements differ from lime in possessing hydraulic properties, and refusal to slake unless ground very fine. They differ from Portland cements in lighter weight, lower temperature of burning, quicker set, lower ultimate strength, and greater latitude of composition. Magnesia is not re- garded as a detrimental impurity in natural cements as it is in Portland cement. The following are some analyses of the burned material : ANALYSES OF SOME NATURAL ROCK CEMENTS CaO MgO Si0 2 A1 2 8 Fe 2 8 Na 2 0,K 2 O IGNITION Natural rock cement, Rosendale, N.Y. . 34.38 18 30.5 6.84 2.42 3.98 3.78 Natural rock cement, Akron, N.Y. . . 40.68 22 22.62 7.44 1.40 2.23 3.63 Natural rock cement, Cumberland, Md. . 43.97 2.21 22.38 11.71 2.29 9. 2.44 Roman cement, Rii- dersdorf, Germany . 56.45 4.84 27.88 6.19 4.64 Portland Cement (4, 6, 7, 10, 41). This term is applied to artificial mixtures of clay and lime rock, which are burned to a temperature of clinkering. Portland cement was first made by Joseph Apsdin, of Leeds, England, who desired to make an artificial cement that would replace natural hydraulic cements. It received its name because it hard- ened under water to a mass resembling the Portland stone of England. The three essentials for Portland cement are lime, silica, and alumina, and it is consequently necessary to use raw materials supplying these three substances in the proper quantities. This is in all cases done by artificial mixture, 114 ECONOMIC GEOLOGY OF THE UNITED STATES and many of the so-called "natural" Portland cements used in the United States are not strictly such. The fol- lowing six combinations of materials are at present used in the manufacture of true Portland cement in the United States: marl and clay; limestone and day, or shale; 1 chalk and clay; .pure limestone and argillaceous limestone; alkali waste and clay; limestone and slag. In the first four of these combinations it is evident that the sub- stances first named supply the lime and the second the silica and alumina. In the fourth the argillaceous limestone supplies some lime, as well as the silica and alumina. The nature of the raw materials chosen depends to a large degree on the location of the plant, whether in a limestone or a marl producing region. Where both of these raw materials are available, as in parts of New York, questions of manipu- lation in the process of manufacture govern the selection of one or the other. Marls, for example, though easier to excavate and reduce than lime- stones, contain so much more organic matter and water than limestones that they are more expensive to handle and prepare. Marl beds are likewise apt to be of limited extent and irregular, while limestone beds are, so far as the needs of a manufacturing plant are concerned, practically limitless. Comparing clay and shale, the former is often easier to excavate, but, on account of the water it contains, has to be dried before it can be ground and mixed. The fossils in shales are sometimes an impor- tant source of calcium carbonate, and then careful grinding and mixing is necessary to bring about a uniform distribution of the lime through the mass. Shale is, however, used by only a few works. Argillaceous limestone, mixed with a much smaller quantity of purer limestone, as in Pennsylvania and New Jersey, is superior to a lime- stone and clay mixture, because less thorough mixing and fine grinding are required. In such cements, even when grinding and mixing are 1 It is probable that the refuse of many slate quarries could also be used in place of shale. LIME AND CALCAREOUS CEMENTS 115 incompletely done, the particles of argillaceous limestone so closely resemble the proper mixture in chemical composition as to affect the result but little. The following table gives the analyses of some of the raw materials used in manufacture of Portland cement: ANALYSES OF RAW MATERIALS USED FOR PORTLAND CEMENT LOCALITY MATERIAL SiO 2 A1 2 8 Fe 2 O 3 CaCO 3 MgC0 3 H 2 + ORG. MATTER MlSCEL. ' Calc. shale Lehigh or CaS0 4 Valley, cement rock 15.40 4.26 1.38 74.66 2.66 1.88 .86 Penn. Limestone 5.87 1.59 88.00 4.00 [ Mixture 13.97 5.07| 1.88 74.1 2.04 1.82 Glens CaO MgO S0 3 Limestone 3.3 1.3 52.15 1.58 .3 Falls N.Y. CaO MgO S0 3 -Clay 55.27 28.15 5.84 2.25 8.37 .12 Warners, J Marl .26 .10 94.39 .38 4.64 N.Y. I Clay 40.48 20.95 25.80 .99 8.50 Insol. CaS0 4 Sandusky, Marl 1.28 1.72 92.70 .50 1.13 2.06 Ohio CaO MgO Clay 64.70 11.9 9.9 .90 .70 11.9 White ( Chalk 41.20 2.21 1.03 95.29 Cliffs, CaO MgO Ark. I Clay 53.3 23.29 9.52 .36 1.49 5.16 In the selection of raw materials the aim of the manu- facturers is to produce a raw mixture which runs approx- imately 70 to 75 per cent lime carbonate and the balance clay (U. S. Geol. Surv., 21st Ann. Kept., VI : 404, 1900). The proportions of clay and lime rock used at each factory are not always disclosed, and the mixture of the two in- 116 ECONOMIC GEOLOGY OF THE UNITED STATES gradients is kept under careful control by frequent chemical analysis, since slight variations from the proper composi- tion may injure the cement. The following analyses will serve to illustrate the composition of some American Port- land cements : f ANALYSES OF CEMENTS SiO 2 A1 2 3 Fe 2 O 3 CaO MgO SO 3 Empire brand . . San dusky .... Alpha . ... 22.04 23.08 22.62 6.45 6.16 8.76 3.41 2.90 2.66 60.92 62.38 61.46 3.53 1.21 2.92 2.73 1.66 1.53 Distribution of Lime and Cement Materials in the United States. Limestone for Lime. Limestones of suitable com- position for burning lime are so widely distributed that no particular regions or states require special mention. 1 In the New England states, crystalline limestones are the chief source of supply. In the Appalachian states, from New York to Alabama, there are many Paleozoic limestones of high purity, notably the Trenton, Lower Helderberg, and Carboniferous limestones (see state references). The same series of rocks are also of importance in the Mississippi Valley states from Tennessee to Michigan (27). Lime of excellent quality is obtained from the Subcarboniferous in Iowa (41), Kansas (21), and Missouri (41), and from the Cretaceous in Texas (41). Limestones suitable for lime manufacture are also found in numerous localities in the Pacific coast states (41). 1 Analyses and detailed descriptions will be found in the areal reports, mentioned in the list of References. PLATE X FIG. 1. -Quarry of natural cement rock, Cumberland, Md. Photo, by H. Ries. FIQ. 2. -Marl pit at Warners, N.Y. The dark streaks are peat, and the marl is underlain by clay. Photo, by H. Ries. LIME AND CALCAREOUS CEMENTS 117 Hydraulic Limes. Largely because of the great abun- dance of natural rock cements, which are of superior value, these materials, though much ased abroad, are of no im- portance in the United States. Natural Rock Cements (1, 41). Calcareous rocks of this class are found at a number of points, mainly in the Paleozoic formations. In 1903 they were worked in sixteen different states, eleven of which are east of the Mississippi. These are found at a number of points in the Appalachian region, .but, owing to the folded character of the beds (PL X, Fig. 1), their extraction is often difficult. The most important natural rook cement region of the United States is that of Rosendale, New York (32, 35), where the cement rocks are found in the Water Lime beds at the base of the Lower Helderberg, being obtained from underground workings. There are two beds, separated by a few feet of limestone, and often dipping at a high angle. Their thickness ranges from 7 to 25 feet. The great development of this region is due partly to the large supply of raw material, and partly to the proximity to New York City and the possibility of shipment by tide-water. Farther west, around Akron, New York, and Buffalo (31), the cement rock occurs at a somewhat higher horizon. In eastern Pennsylvania, especially in the vicinity of Coplay and Catasauqua (39), cement rock of Trenton age occurs in a region of marked folding. This region, though an im- portant producer of cement rock, is even more important as a producer of Portland cement (41). The Water Lime beds again form an important source of cement rock in the vicinity of Cumberland, Maryland (24) (PI. X, Fig. 1), where there are four beds of economic 118 ECONOMIC GEOLOGY OF THE UNITED STATES value, ranging from 6 to 17 feet in thickness, and separated by calcareous shales. The entire series is highly folded, the dip sometimes being as much as 90. Cement rock is also obtained in southeastern Ohio (36); at Louisville, Kentucky (23), probably the second most im- portant center in the United States ; in the Hamilton rocks at Milwaukee, Wisconsin (44); and at Utica and La Salle, Illinois (17), where it is found in the Calciferous formation in a bed from 6 to 8 feet thick. Portland Cements. Clay and limestone, in one form or another, are so widely distributed throughout the United States, that it is possible to manufacture Portland cement at many localities, and the geologic age of the materials used ranges from Ordovician to Pleistocene (41). Nine- teen states were making this cement in 1903, the factories being spread over the country from the Atlantic to the Pacific (41). By far the most important district is the Lehigh Valley in Pennsylvania, which supplies about 70 per cent of the domestic product. Here the raw materials consist of beds of argillaceous limestone and nearly pure limestone, this being one of the few localities where such a mixture is obtainable. The same beds are found in the adjacent terri- tory of New Jersey (30). In the eastern half of New York (35) the Ordovician and Silurian limestones form an inexhaustible supply of material to mix with Pleistocene surface clays. In the south central part of New York the Tully limestone and Hamilton shales are employed, while in the central and southwestern portion, beds of marl (PI. X, Fig. 2), associated with surface clays, are utilized. LIME AND CALCAREOUS CEMENTS 119 Ohio (36, 41), Indiana (18), and Michigan (26, 28) are important Portland cement producing states. The abun- dance of marl and Pleistocene clays makes them the favorite materials, notwithstanding the fact that beds of Paleozoic limestones occur in each of the states. Marl, although espe- cially abundant in Michigan, is found in many states lying east of the Mississippi and north of the terminal moraine. It is precipitated from the waters of ponds through the agency of minute plants, especially CJiara (26). In Kansas Carboniferous shales and limestones are used for making Portland cement (21, 22), and in Texas and Arkansas the Cretaceous shales and chalky limestones are employed (13, 14) ; Alabama has a Tertiary limestone of such composition that very little pure limestone has to be added to it (12). Portland cement is also manufactured in North Dakota (41), South Dakota (41), Utah (41), Colorado (41), and California (15). Uses of Lime. The most important single use of lime is for mixing with sand to form mortar, and many thousands of tons are used annually for this purpose. In addition to this use, lime is employed for a great variety of pur- poses, of which the following are the most important: as a purifier in basic steel manufacture; in the manufacture of refractory bricks, ammonium sulphate, soap, bone ash, gas, potassium -dichromate, paper, pottery glazes, and cal- cium carbide ; as a disinfectant ; as a fertilizer ; as a polish- ing material ; for dehydrating alcohol, preserving ^ < 05 "< 5 j g 02 ^ ^ > ^ O K H aQ 3 CB 5^2 K ^ 3 O 02 ;a oo ^ O W EH W <1 ^ 4 M < gr. per gr. per gr. per gr. per gr. per gr. per gr. per gal. gal. gal. gal. gal. gal. gal. Sodium carbonate .... 5.00 Sodium bicarbonate . . . 10.77 8.75 .49 1.26 Sodium sulphate .... 16.27 .54 Calcium carbonate .... 5.22 ) Magnesium carbonate . . | 3.17 11.41 Calcium bicarbonate . . . 143.40 41.32 12.66 12.93 17.02 Magnesium bicarbonate . 121.76 29.34 .69 12.39 Lithium bicarbonate . . . 4.76 Trace Iron bicarbonate .... .34 3.00 2.17 .04 Magnesium sulphate . . . 2.15 18.96 Potassium sulphate . . . .89 1.38 Sodium chloride .... 400.44 166.81 .33 27.34 .46 Potassium chloride . . . 8.05 1.16 Potassium bromide . . . 1.57 Sodium bromide .... 8.56 Sodium iodide . . .14 4.67 Silica .84 .53 1.72 .38 .45 2.51 .74 Calcium sulphate .... 14.53 2.54 96.64 Production of Mineral Waters. The production of mineral waters in the United States for the last three years was as follows: MINERAL WATERS 207 PRODUCTION OF MINERAL WATERS IN UNITED STATES FROM 1901 TO 1903 YEAR QUANTITY GALLONS VALUE 1901 55,771,188 $7,586,962 1902 64,859,451 8,793,761 1903 51,242,757 9,041,078 The production of the more important states in 1903 was as follows : PRODUCTION OF MINERAL WATERS IN SEVERAL STATES IN 1903 STATE QUANTITY GALLONS VALUE New York 1 827 408 $1 432 801 "VViscon sin . 1 993 777 1 058 954 California 1 862 855 706 372 Virginia 2,561,502 477,410 Pennsylvania 1,522 860 357 579 REFERENCES ON MINERAL WATERS 1. Bailey, Kas. Geol. Surv., VII, 1902. (Kas.) 2. Branner, Ark. Geol. Surv., Kept, for 1901. (Ark.) 3. Crook, Mineral Waters of United States and their Therapeutic Value. (Phila., 1899.) 4. Lane, U. S. Geol. Surv., Water Supply Bull. XXXI, 1899. 5. Peale, U. S. Geol. Surv., 19th Ann. Kept., 1898. (U. S.) 6. Schweitzer, Mo. Geol. Surv., Ill, 1892. (Mo., also general.) UNDERGROUND WATERS While much of the water used for supplying towns and cities, for irrigation purposes, etc., is obtained from below the surface, all of it originates in rainfall. The rain water falling on the surface is disposed of in part by evaporation and surface run-off, but a variable and sometimes large per- centage seeps into the ground. 208 ECONOMIC GEOLOGY OF THE UNITED STATES Ground Water (22). Of this portion soaking into the ground, a small part is retained by capillarity in the surface soil, to be returned again to the atmosphere either by direct evaporation or through plants, but most of it finds its way into the deeper layers of the soil, which it completely saturates. The water in this saturated zone, which is termed the ground water, forms a great reservoir of supply for lakes, springs, and wells, and its upper surface, known as the water table, agrees somewhat closely with that of the land surface, but is nearer FIG. 34. Ideal section across a river valley, showing the position of ground water and the undulations of the water table with reference to the surface of the ground and bed rock. After Schlichter, U. S. Geol. Surv., Water Supply Bull. 67 : 1. to it under valleys, and farther from it under hills (Fig. 34). The depth of the water table is quite variable, being but a few feet below the surface in moist climates, while in arid regions it may be 100 feet or more. In any area, however, the water table may show periodical fluctuations. In all ground water there is a slow but constant movement from higher to lower levels, just as in the case of surface waters, so that the ground water flows towards the valleys. There it may discharge into the streams, but in some instances it follows the valley bottom below the river bed, separated from the river water by a more or less impervious layer (22). The composition of the ground water also shows a somewhat close relation to the rocks or soils in which it accumulates. MINERAL WATERS 209 Artesian Water. In some areas much of the water which percolates through the soil is caught up by porous beds of sandstone, gravel, or in rarer instances limestone, and where these are between impervious beds such as shale, the absorbed water may follow them for some distance, especially if the porous stratum is inclined. Water thus confined is under pressure, and tends to rise towards the surface along any path of escape open to it, such as joint or fault planes, or where the water-bearing bed is cut into by a stream. A drill hole bored to tap the water-bearing bed serves the same pur- pose ; and when the pressure is sufficient to force the water upward so that it flows from the tube, it is called an arte- sian well. The term is however rather loosely used now and applied to many deep wells which are not flowing. The requisite conditions (1) for a supply of artesian water are : (1) a porous stratum ; (2) an impervious bed below and above the water-bearing bed ; (3) inclined beds, so that the point of intake or fountain head can be higher than the well ; (4) a sufficient area of outcrop or collecting area to obtain a large enough supply this may be many miles from the well; (5) adequate rainfall; (6) absence of escape for the water at a lower level than the surface at the well. Artesian water was formerly looked for only in synclinal basins, but it is now known that sedimentary beds may be water bear- ing in areas of monoclinal dip. Artesian wells vary greatly in their capacity and depth. Some are not more than 100 feet deep, while others are 2000 or more feet deep. Though the most productive artesian wells are found in pre-Pleistocene sedimentary rocks of regular structure (Fig. 35), still, flowing artesian wells even of large capacity are 210 ECONOMIC GEOLOGY OF THE UNITED STATES at times found in the glacial drift where water-bearing lenses of sand or gravel are overlain or surrounded by clay. Even in areas of igneous and metamorphic rocks the water seeps in along joint planes, and collects at times in sufficient quantities to serve as a source of supply which may even be under pressure (6, paper by G. O. Smith). FIG. 35. Geologic section of Atlantic Coastal Plain, showing water-bearing horizons. After Darton, Amer. Inst. Min. Engrs., Trans. XXIV: 375. Artesian wells are to be distinguished from ground water wells by their greater constancy, absence of relation to sur- rounding climatic conditions, and, in moist climates at least, of a high constituent of mineral matter. There are many areas in the United States in which the conditions are favorable to an artesian water supply, as the various state and government reports will show. A few of the more important may be briefly referred to. Along the Atlantic and Gulf Coastal Plain an abundant supply of artesian water is obtained from the Cretaceous and Tertiary beds, at depths varying from 50 feet along MINERAL WATERS 211 the inland border, to 1000 feet and over along the coast (4) (Fig. 35). A second area is that of the upper Mississippi Valley (19), in which an abundant supply of potable water is obtained from the St. Croix and St. Peters sandstone, whose outcrop in Minnesota and Wisconsin covers some 14,000 square miles. In the Great Plains (2) region water is obtained from the Dakota sandstone, whose collecting area is around the border of the Black Hills (Fig. 36). This source is available in FIG. 36. Section from Black Hills across South Dakota, showing artesian well conditions. After Darton. South Dakota and eastern Nebraska and Kansas. The chief use of the water in this region is for irrigation. For the arid regions of the West this source of supply has been of inestimable value, and has been the means of reclaim- ing many an area of hitherto useless land. REFERENCES ON UNDERGROUND WATER 1. Chamberlin, U. S. Geol. Surv., 5th Ann. Kept. : 125, 1885. (Artesian water supply.) 2. Darton, U. S. Geol. Surv., Prof. Paper 32, 1905. (Central Great Plains.) 3. Darton, U. S. Geol. Surv., Water Supply Bulls. 57 and 161. (List of deep borings in United States.) 4. Darton, U. S. Geol. Surv., Bull. 138, 1896. (Atlantic Coastal Plain.) 5. El- dridge, U. S. Geol. Surv., Mon. 27. (Denver basin.) 6. Fuller and others, U. S. Geol. Surv., Water Supply Bull. 114, 1905. (Under- ground waters, E. United States.) 7. Fuller, U. S. Geol. Surv., Water Supply Bull. 100, 1905. (Hydrography E. United States.) 8. Gilbert, U.S. Geol. Surv., 17th Ann. Kept., II: 557, 1896. (Arkansas 212 ECONOMIC GEOLOGY OF THE UNITED STATES Valley, Col.) 9. Hall, Ala. Geol. Surv., Bull. 7. (Ala.) 10. Hill, U.S. Geol. Surv., 21st Ann. Kept., VII : 666, 1901. (Tex.) 11. Holmes, Amer. Inst. Min. Engrs., Trans. XXV: 936, 1896. (Piedmont plateau.) 12. King, U. S. Geol. Surv., 19th Ann. Kept., II : 59, 1899. (Under- ground water circulation.) 13. Knight, Wyo. Univ. Exp. Sta., Bull. 45, 1900. (Wyo.) 13 a. Lane, U. S. Geol. Surv., Water Supply Bulls. 30 and 31, 1899 (Mich.) 14. Leverett, U. S. Geol. Surv., 17th Ann. Kept, II: 155, 1896. (111.) 15. Leverett, U. S. Geol. Surv., Water Supply Bulls. 26 and 21. (Ind.) 16. Singley, Texas Geol. Surv., 4th Ann. Kept. : 87. (Galveston well.) 17. McCaliie, Ga. Geol. Surv., Bull. 7, 1899. (Ga.) 18. McGee, U. S. Geol. Surv., 14th Ann. Kept, II: 1. (E. United States.) 19. Norton, la. Geol. Surv., VI: 115, 1897. (Iowa.) 20. Orton, U.S. Geol. Surv., 19th Ann. Kept., IV: 640, 1899. (Ohio rock waters.) 21. Ruddy, Wash. Geol. Surv., 1 : 296, 1901. (Wash.) 22. Slichter, U. S. Geol. Surv., Water Supply Paper No. 67, 1902. (General on underground waters.) 23. Woolman, see various annual reports N. J. Geol. Surv. Many other papers in Water Supply and Irrigation bulletins issued by U. S. Geol. Surv. CHAPTER XII SOILS THE term soil is applied to the upper few inches of the mantle of unconsolidated material (regolith) which covers the earth's surface, and which is composed of a mixture of rock, sand, and clay fragments in all stages of decay ; with it there is usually mixed a variable amount of decayed and decaying organic matter (humus). Origin. Soils are classed, according to their mode of origin, as residual and transported. Residual Soils are those formed by rock weathering (see Residual Clay, under Clay, Chapter IV), and are found resting on the parent rock from whose decay they have originated ; they consequently, in most instances, show a gradual transition from the surface soil to the solid rock beneath. Such soils are often of great extent in the unglaciated areas of the South, and their clayey character and brilliant coloring is a marked feature. With this class there is sometimes grouped the humus, or peaty soil, formed by the accumulation of vegetable matter in bogs or swamps (see Peat, under Coal, Chapter I). Transported Soils. The materials of residual areas are frequently carried away by the agency of water, ice, or wind and deposited elsewhere, commonly at lower levels, giving rise to transported soils. These are classified either accord- ing to their mode of origin or texture. 213 214 ECONOMIC GEOLOGY OF THE UNITED STATES The former grouping recognizes : Alluvial soils, deposited by water on the lowlands bordering rivers or on their deltas ; these form one of the most important soil types, and the fertile soils of the Nile Valley and the Mississippi bottoms are of this character. Their continued high fertility is due to the fact that the soil layer is added to annually or oftener during periods of flood. Glacial drift soils, representing the debris of decayed rocks of various kinds brought down from the north during the glacial period. They are made up of a mixture of many different rock types in all stages of decay; the continual decomposition of their component min- eral grains gives them a more or less permanent fertility. sEoliari soils, or those formed by wind action, include : (1) Sand dunes heaped up by the action of wind along the shores of many oceans or inland seas. When anchored by systematic planting, they develop an abundant plant growth. (2) Ash soils, representing the accumulations of ash thrown out over a region during outbursts of volcanic activity ; these are some- times of high productivity, for although at first barren and sandy they rapidly decompose to a good soil. Properties of Soils. The productivity of a soil depends largely on its chemical and physical properties, and to a lesser extent on climatic conditions. Chemical Properties. The chemical analysis of a soil shows a variable percentage of nitrogen, silica, phosphoric acid, chlorine, alumina, lime, magnesia, iron oxide, potash, and soda, all of which, with the exception of the first, are derivable from mineral grains present in the soil. When there is a deficiency of any one of these, it is commonly remedied by adding fertilizers to the soil; but the value of the latter for plant maintenance depends not so much on the total quantity of each of these present, but upon the amount existing in soluble form. While soils vary in their composi- tion from place to place, there is a most marked difference between the soils of humid and arid regions, those of the latter showing a much larger proportion of fertilizing con- SOILS 215 stituents because they have been subjected to less leaching action by rain water. Soils in arid regions are often covered by a whitish crust termed " alkali" which is composed chiefly of sulphates and carbonates of soda, and is formed by the soil water bringing these to the surface, where it escapes by evaporation. An excess of alkali is injurious to plants. Physical Properties, which are of equal importance to the chemical ones, include texture, structure, color, weight, and temperature ; a proper physical condition may often make up for a deficiency in plant food. The physical characters of a soil are produced to a large extent by natural processes, and can be modified but slightly by man. The texture of a soil refers to the size of its grains, those recognized being clay, silt, sand, and gravel ; depending on the amount of each of these present, we have clay soils, silt soils, loams, sandy soils, and gravelly soils. Texture is of importance because it affects the retentive power of the soil for moisture and gases. Clay soils hold much water and hence are wet and cold, whereas sandy soils, on account of the coarseness of their particles, have large pores and hold little water, and warm up easily. Loamy soils stand inter- mediate between these. The structure of the soil refers to the arrangement of the particles. If compacted, the pores are small and the soil holds more water, while if loose the soil behaves like sand, retaining little moisture. A puddled soil is one in which the grains are single, while in a flocculated soil the particles are bunched together, forming compound grains, and all good soils show this structure ; it increases the pore space and hence facilitates the circulation of air and water through the mass. Lime encourages flocculation. 216 .ECONOMIC GEOLOGY OF THE UNITED STATES The temperature of soils depends on their color and position with relation to the sun's rays. In moist climates the clay particles are washed out of the upper layers of the soil and settle in the lower ones, produc- ing a differentiation known as soil and subsoil. This is not found in arid regions. Distribution of Soils in the United States. So varied are the soils of the United States that it would require many pages to describe them even partially ; nevertheless, there are a few well-marked types underlying extensive areas which may be briefly referred to. The residual soils occupy a large area throughout the southern states, and in the Appalachian belt are especially prominent, being easily recog- nized by their clayey character and bright colors. Glacial soils are prominent in the northern United States, and their high fertility has been noted by various writers. The alluvial soils are prominent in all parts of the country. In the cen- tral states the prairie soil is a peculiar silty type, heavily impregnated with humus. The loess is a silty soil, low in organic matter, covering many square miles of the Great Plains, and needs but irrigation to make it blossom with har- vests. Marsh soils and dune soils both cover many thousands of acres along the Atlantic coast ; and the latter are also ex- tensive around the Great Lakes as well as along the Pacific coast. Although reclaimable they are rarely cultivated. REFERENCES ON SOILS Hilgard, U. S. Dept. Agric., Weather Bur., Bull. 3, 1892 (Relations of Soil to Climate) ; King, The Soil, Wiley & Sons (New York, 1898) ; Merrill, Rocks, Rock Weathering, and Soils, Wiley & Sons (New York, 1897) ; Ramann, Forstliche Boden-kunde und Standortslehre SOILS 217 (Berlin, 1897) ; Shaler, U. S. Geol. Surv., 12th Ann. Kept., 1 : 213, 1891 (Origin and Nature) ; Warrington, Physical Properties of Soils (Oxford, Eng., 1900). See also bulletins U. S. Dept. Agric., Bur. of Soils, especially Nos. 4, 10, 15, 17, 18, 19, 22, and the Reports on Field Operations published annually. ROAD MATERIALS Under this term are included clay, sand, gravel, and differ- ent kinds of consolidated rock, used for covering the surface of a highway. In former years but little consideration was given to the proper selection of these materials, but now the subject is receiving an increasing amount of attention from engineers, with the results that certain required standards have been set up, and in many localities carefully adhered to. Such standards can however be applied only to consolidated materials. In many parts of the United States the roads have natural beds, whose character depends on that of the local formations. The road, therefore, may consist of clay, sand, loam, gravel, or bare rock, and such a road surface is unfortunately used even when better materials are at hand, but are overlooked through indifference or ignorance. Clay makes a hard road in dry weather, but becomes very sticky in wet, or even dusty after prolonged drought. Sand packs well if wet, but makes hard pulling when dry. Gravel, if ferruginous, will often cement to a good road surface, which wears well under light traffic. Shale will also make a good road. Natural road beds are, however, unsatisfactory at best, and artificial ones of crushed stone (macadam roads) are rapidly superseding them. For this purpose a number of different kinds of rock are 218 ECONOMIC GEOLOGY OF THE UNITED STATES employed, including trap, granite, limestone, dolomite, and sandstone. The essential qualities of a stone for macadamizing are : (1) Hardness to resist crushing under traffic. (2) Sufficient abrasion to permit the formation of some dust which when moistened will form a cement to bind the particles together. (3) Freshness of the mineral grains. (4) Cheapness. Great variation is found to exist among the different stones with respect to these requirements, and even stones of the same kind lack uniformity. While the most practical test for road material is actual use, this is not always a cheap or rapid method, and conse- quently a series of physical tests has been adopted, which is in use in most highway laboratories. The two important tests are the abrasive test and impact test. In the former the abrasive resistance of the stone is determined, in the latter the cementing power of the powdered stone is meas- ured, by forming it into briquettes, which are broken by a series of blows. The same powder is remolded and again broken to determine its recementing power. Stones with a small amount of argillaceous and calcareous impurities often appear to have good cementing power ; but in every case the qualities of each stone have to be determined separately. Since, however, stone for road building will not bear the cost of long transportation, it becomes necessary to make a careful selection of the best that the vicinity affords. Trap rock and hard argillaceous limestone are perhaps more used than any other materials. Good stones for road building are more or less widely distributed in most parts of the United States, so that any detailed mention of localities is not needed. SOILS 219 REFERENCES ON ROAD MATERIALS Merrill, N. Y. State Museum, Bull. 17, 1897 (N. Y.) ; Reid and Johnson, Md. Geol. Surv., I and IV; Shaler, U. S. Geol. Surv., 16th Ann. Kept., IT : 227, 1895 (Mass.). See also bulletins issued by Highway Division of Dept. of Agric., Wash., and Reports of Massachusetts Highway Commission. PART II METALLIC MINEKALS CHAPTER XIII ORE DEPOSITS Definition. The term ore deposits is applied to concen- trations of economically valuable metalliferous minerals found in the earth's crust, while under the term ore are included those portions of the ore body of which the metallic minerals form a sufficiently large proportion to make their extraction profitable. A metalliferous mineral or rock might therefore not be an ore at the present day, but become so at a later date, because improved methods of treatment or other conditions rendered the extraction of its metallic contents profitable. A few metallic minerals serving as ores, such as gold, copper, platinum, or mercury, sometimes occur in a native condition; but in most cases the metal is combined with other elements, forming sulphides, hydrous oxides, carbon- ates, sulphates, silicates, chlorides, phosphates, or rarer compounds, the first five of these being the most numer- ous. A deposit may contain the ores of one or several metals, and there may also be several compounds of the same metal present. Gangue Minerals. Associated with the metallic minerals there are usually certain common non-metallic ones which carry no values worth extracting. These are termed the gangue minerals. They often form masses in the ore deposit 224 ECONOMIC GEOLOGY OF THE UNITED STATES which can be avoided or thrown out in mining, but at other times they are so intermixed with the valuable metalliferous minerals that the ore is crushed and the two separated by special methods. Quartz is the most abundant gangue mineral, but calcite, barite, fluorite, and siderite are also common, while dolo- mite, hornblende, pyroxene, feldspar, rhodochrosite, etc., are found in some ore bodies. Origin of Ore Bodies. The fact that ores form masses of greater or less concentration is explainable in two ways : either they have been formed contemporaneously with the inclosing rock; or else they have been formed by a process of concentration at a later date. The first theory is found to be applicable to some ores in igneous rocks, and probably some sedimentary ones, while the second applies to most ore deposits regardless of the character of the inclosing rock. Ores of Contemporaneous Origin. If the ore in an igneous rock were formed at the same time as the rock, it would indicate a crystallization of metallic minerals from the igneous magma during cooling ; and this, in some cases, is true, it being found that the metallic elements in many basic rocks tend to segregate during cooling, sometimes forming masses of considerable size and of high purity. This mode of origin, termed magmatic segregation (18, 34, 35, 36), was shown by Vogt to apply to the titaniferous ores of Scandinavia; and although the importance of the theory was not at first generally appreciated in America, where deposits of this type are rare, still it is now generally accepted. The best-known American examples of this class are the titaniferous magnetites and the chromite ores. ORE DEPOSITS 225 Spurr has suggested (34) that certain ores found in acid rocks, such as quartz veins, have also been formed by mag- matic segregation. He believes that siliceous rocks, such as granites, may originate by differentiation from a more basic magma. A further development of this process yields quartz-feldspar rocks, and after the minerals of these have crystallized out, only pure silica is left, which forms quartz veins. Examples of this type have been noted by Spurr from Alaska, and by Turner from Silver Peak, Nevada. If ores in sedimentary rocks are of contemporaneous origin, then the deposit must be a bedded one conforming to the stratification of the rock, and this explanation more- over requires the presence of metalliferous minerals in and their deposition from sea water. While certain metallic elements are found in the waters of the ocean, their quan- tity is extremely small and not to be compared with what may be found in disseminated or concentrated form in sedimentary and igneous rocks. It has been shown, how- ever, that some metallic minerals, such as limonite, pyrite, or manganese, are occasionally precipitated on the ocean floor. While economic geologists have assigned a contem- poraneous origin to certain .ores found in sedimentary strata, and in certain instances their theories have been quite generally regarded as correct (iron ores, ref. 36), still the majority at the present day believe that most ore deposits are of later date than the inclosing rock, and must have been formed by a process of concentration, aided in the majority of cases by circulating water. Concentration of Ores in Rocks. In order to demonstrate this, it is necessary to show: (1) the presence of disseminated 226 ECONOMIC GEOLOGY OF THE UNITED STATES minerals in the earth's crust ; (2) the existence of a solvent or carrier; and (3) the presence in most cases of cavities in which the precipitation of the ore can occur. It is well known that metallic minerals in small quanti- ties are widely distributed, in both igneous and sedimentary rocks. Sandberger (31), for example, has shown by analyses the presence of nickel, copper, lead, tin, and cobalt in such minerals as hornblende, olivine, and mica ; and Curtis has found traces of silver, gold, and lead in the quartz-porphy- ries at Eureka, Nevada (U. S. Geol. Surv., Mon. VII : 80), and silver, arsenic, lead, copper, gold, and silver in the granite at Steamboat Springs, Nevada (U. S. Geol. Surv., Mon. XIII : 350). Winslow has pointed out the presence of small quantities of lead and zinc in the limestones of Missouri and Wisconsin (lead and zinc, ref. 17), and Wagoner has made similar tests on California sediments (42). Since, however, the sediments were originally derived from the igneous rocks, it follows that the latter must be the original source of the minerals. It is interesting to note that even in the igneous rocks the metals are not impartially distributed, but that certain metals seem to favor certain rocks (De Launay, Ann. d. Min., August, 1897, and ref. 34). Tin seems to favor granite, and chro- mite, peridotite. As regards the second point, it is now generally admitted that water is an important agent in the concentration of many ores. While cold water, free from impurities, has comparatively little solvent power, the presence of acids or alkalies materially increases its capacity for solution, and heat and pressure have also a great influence. Analyses of mine, spring, and surface waters have shown the presence ORE DEPOSITS 227 of many dissolved alkalies and other salts (24), and occa- sionally small quantities of metals. The following two analyses, which will serve as examples, give the calculated composition of (1) vadose, or shallow water, from the 500-foot level of the Geyser silver mine, Silver Cliff, Colorado, and (2) deep water from the 2000- foot level of the same mine. The ore occurs in rhyolite. The figures are grams per 1000 liters : 1 2 SiO 9 25.90 24.42 Al O 1.06 ALOo, P <) .80 FeCO 1.50 7.25 MnCO 1.70 1.19 CaCO 3 93.50 366.03 Ca Q Po() Q . Tr O , O CaF 9 . . Tr SrC(X 3.29 MeCOo 42.85 621.84 K SO 4.20 19.18 JV 2 OV7 4 KCL 16.60 361.34 KBr, KI . . . Tr Xa 9 CO q . 38.70 1489.67 Na 2 SO 4 60.50 223.53 NaNO 3 2.19 Xa B O .... o ... Tr LiCl __ 17.30 CO 2 37.20 1418.61 PbCO 3 Tr 1.74 CuCO 3 Tr .04 ZnCO 3 .40 .66 The higher percentage of dissolved substances in the deep water is quite marked. While the importance of hot waters as an agent in the 228 ECONOMIC GEOLOGY OF THE UNITED STATES formation of ore deposits is clearly recognized by many, and traces of metals in solution are sometimes found, still ex- amples of such deposits now forming are rare. Weed has described a hot spring near Boulder, Montana (49), which is depositing auriferous quartz, and the deposit is pointed out by him to be identical with silver and gold bearing quartz veins of the region between Butte and Helena, Montana. At Steamboat Springs, Nevada, it has been found that the allu- vial gravels underlying the hot spring sinters are cemented by stibnite and pyrite (Lindgren, Amer. Inst. Min. Eng., Trans. 1905: 275). Of still more interest is the collection by evaporation of copper from certain Javan hot springs, in which the metal occurs as iodide of copper (Stevens, Copper Handbook, IV : 156, 1904). Water is known to be widely (11, 39) but not uniformly distributed in the rocks of the earth's crust, and much of it is in slow but constant circulation. While it is admitted by most geologists that this water has been an important ore carrier, collecting the disseminated metals in the rocks and concentrating them in localities favorable to deposition, still, there exists a difference of opinion regarding its source, one class maintaining that it is largely of meteoric origin, the other that it is derived chiefly from igneous intrusions. The chief exponent of the former theory is Van Hise, who points out that the earth's crust may be divided into three zones : (1) an upper zone of fracture, beginning at the sur- face ; (2)- a zone of combined fracture and flowage ; and (3) a zone of rock flowage, or of no fracture. In the zone of no fracture the pressure is so great that any dynamic disturbances will cause flowage instead of fracturing, and no ORE DEPOSITS 229 cavities of appreciable size can exist. The depth of this zone will depend on the kind of rock, Van Hise having figured that cavities probably cannot exist in soft shales at depths below 1625 feet (500 meters), and in firm granites below 32,500 ft. (10,000 meters). Into this zone of no fracture, water from the surface can- not penetrate, but above it there may be active percolation by water. It is well known that rain water, falling on the earth's surface, seeps through the soil into the underlying rocks, permeating them to a variable depth, and forming a more or less saturated zone, whose upper limit, lying at a variable depth, is known as the ground- water level. In this zone of more or less complete saturation there is a slow but continual circulation, from areas of high to areas of low pressure, along irregular winding routes, often leading back to the surface and giving rise to springs. According to Van "Hise this percolating meteoric water obtains its load of metallic elements from the rocks, which it traverses in its passage through the zone of fracture, depositing some of it in the trunk channels, but being incapable of entering the zone of no fracture. The opponents (6, 18, 20, 21) of Van Rise's theory point to the following facts as evidence that waters of igneous origin are more important as ore carriers, and are the ones involved in deep circulation. Meteoric waters do not reach great depths, in fact probably not more than 2000 feet or sometimes less from the surface, and when they (Jo penetrate to a greater distance from it, it is be- cause they have followed some fissure. The lower levels of many deep mines are so dry as to be dusty. Ores have been concentrated at a much greater depth than that reached 230 ECONOMIC GEOLOGY OF THE UNITED STATES by surface waters. It is perfectly reasonable to regard igneous rocks as an important source of water, and the experiments of Daubree have shown that a molten granite contains a large amount of water vapor which it retains while at great depths, but gives off on approaching the surface and cooling. While the temperature and pressure are still high this water escapes as vapor, and later, with decrease in temperature and pressure, as a liquid. Under favorable conditions this water may force itself upwards and finally mingle with meteoric waters, carrying metals obtained both from the liberated waters and, to a less extent, from the leaching of cooled igneous rock. It is an undeniable fact that most metalliferous veins are found in areas of igneous rocks, and Lindgren (see refer- ences on gold, 79) has shown that in the case of the gold de- posits of North America the periods of vein formation agreed closely with those of igneous activity. It is also a noteworthy fact that, with the exception of the deposits of commoner metals, such as iron, and some copper, lead, and zinc, ores are found in close association with igneous intrusions, which seems to postulate a close connection between igneous rocks and ore deposits, as advocated by such authorities as Weed, Kemp, Lindgren, and Emmons; and although opposed by Van Hise, it is now held by many economic geologists that most metalliferous deposits, aside from ores of iron, have resulted b}^ deposition from ascending waters in regions of igneous intrusions, the waters being probably in large part at least of igneous origin. This much should be said. The metalliferous minerals as originally deposited have not always been sufficiently concentrated to serve as ores, but they have become concentrated at a later date by meteoric ORE DEPOSITS 231 waters, as at Bisbee, Arizona. (See Ransome, under copper references.) Posepny (24), in his work on the Genesis of Ore Deposits, distinguishes between descending surface waters, or vadose circulations, and ascending waters from great depths. It is the former that have been active in the secondary concentration of ores. Formation of Cavities. The deposition of ores in the rocks is greatly facilitated by the presence of cavities along which the ore-bearing solutions freely pass, and consequently a great many ore deposits occur in such spaces. There are a number of different ways in which cavities may be formed in rocks. The percolation of surface water through certain ones, such as limestones, often results in the formation of solution cavities, these in many instances attaining the size of veritable caverns ; a soluble rock may contain more or less insoluble material, such as clay or chert, which collapses when the surrounding rock is dissolved, and partly fills the cave thus formed. At times the more resistant parts are so bound together that they remain in their original position, forming a porous mass, in the cavities of which mineral matter is later deposited. Dynamic disturbances produce cavities of variable extent in many different rocks. These range from microscopic cracks, like the rift planes of granite, to enormous faults of great depth and linear extent, and include the joint planes so common in the rocks of almost all regions. Fault fissures form one of the most important types of passage- ways for ore-bearing solutions. They are often irregular, branching, and partly filled by fault breccia, caused by the breaking of the rock during the movement along the fault plane. A third important group of cavities in the rocks are 232 ECONOMIC GEOLOGY OF THE UNITED STATES those resulting from shrinkage of the mass, which may be due to (1) shrinkage during cooling, as in igneous rocks ; (2) shrinkage during certain forms of replacement. For example, the change of carbonate of lime to dolomite is accompanied by a shrinkage of the mass, which renders the dolomite more porous than the original rock; and in the alteration of siderite to limonite there is a shrinkage of fully 20 per cent (25). A fourth type of channel way for the passage of underground water is the contact plane between two quite different kinds of rock, one of them fairly dense and impervious ; for example, the contact plane between a granite mass and a series of sedimentary strata. Precipitation of Metals from Solution. The conditions which increase the solvent power of water have already been referred to. To this should be added the statement that solution generally takes place out of contact with the air. When the ore-bearing solutions approach the surface or enter a cavity, the load of dissolved minerals is deposited wholly or in part, due to cooling of the solution, release of pressure, or by oxidation, which converts certain soluble salts into an insoluble form. Chemical reactions between two different solutions meeting in a cavity or at the inter- section of fissures may also cause precipitation. Iron com- pounds, for example, may go into solution in the form of carbonate, but on exposure to the air the latter is rapidly changed to limonite, which is insoluble. While the deposition of the ore often takes place in cavi- ties below the surface, there are cases in which it is not precipitated until it reaches the surface, as in a pond or in the soil. Certain special conditions of deposition should also be noted. ORE DEPOSITS 233 Replacement or Metasomatism (22). It is a well-known fact that under favorable conditions mineral-bearing solu- tions may attack the minerals of the rocks which they pene- trate, dissolving them wholly or in part, and depositing some of the original burden in place of the material re- moved. This replacement, termed "metasomatism," is an important factor in the formation of many ore deposits, and may involve a total or partial loss of certain constituents of the rock attacked and a gain of others, even to the extent of introduction of entirely new compounds and elements. The change takes place molecule by molecule, a grain of vein material being deposited for each grain of replaced rock dissolved. The ore-bearing solutions penetrate the rock first along the smallest cracks, and then work their way into the individual mineral grains along their cleavage planes, until they finally permeate the entire mass. Metasomatic processes sho'w great variety, and are not confined to one kind of rock or mineral. In its simplest form the result of metasomatism may often be seen in fossil- iferous rocks, where organic remains have been replaced by common mineral compounds, as in the replacement of the lime carbonate of corals by quartz, or the replacement of molluscan shells by pyrite. From such simple conditions there is every gradation to the complete replacement of extensive areas of rock by ore, or to the extensive operation of metasomatism along the walls of fissure veins. In most cases the changes are believed to be due to the action of underground water ; but in some instances it seems probable that the processes of pneumatolysis (see below) were in- volved. Moreover, high temperature, pressure, and concen- tration seem to have been present in replacement, especially 234 ECONOMIC GEOLOGY OF THE UNITED STATES in the case of ore deposits in fissure veins. It is rarely possible, without examination of a thin section with the microscope, to decide whether minerals present are due to replacement or to simple interstitial filling. Fig. 37 shows a replacement vein in syenite. Some minerals are more easily replaceable than others, consequently the rocks in which such predominate might be more widely affected than others. (See Butte, Mon- tana, and Clifton, Arizona, under Copper.) The theory of metasoma- tism was first applied in America by Pumpelly in 1871, in explanation of the copper deposits of Michigan; but the ore bodies of Lead- ville, Colorado, and Eureka, Nevada, were the first large deposits whose origin was explained by it. Since then the great importance of metasomatism has been widely recognized, and it has become evident that preexisting cavities are not necessary to the formation of ore bodies. Concentration by Eruptive After-action (45) {Pneumatolysis). The term pneumatolysis was first used by Bunsen to describe the combined action of gases and water. This assumes that during cooling many magmas give off watery vapor, heated above its critical temperature (365 C.) and under high pressure. With this there are also mineralizing FIG. 37. Replacement vein in Syenite Rock, War Eagle Mine, Rossland, B. C. (a) granular orthoclase with a little sericite ; (&) secondary biotite ; (q) secondary quartz ; (c) chlorite ; black, secondary pyrrhotite. After Lindgren, Amer. Inst. Min. Eng., Trans. XXX: 62. ORE DEPOSITS 235 vapors and metals, combined to form volatile compounds. These materials, together with any other elements given off, may then be deposited either at the contact between the intrusive and the surrounding rocks, forming a true contact deposit, or, as in the case of the tin veins of Cornwall, Eng- land, in fissures formed in the surrounding rocks by the intrusions. Though the great importance of this class of ore deposits has been but recently recognized, it is now being found that a number of known deposits are of this origin. They are usually found in calcareous rocks at or near the contact with granitic intrusions. The ore minerals are specularite, magnetite, bornite, chalcopyrite, pyrite, pyr- rhotite, and more rarely galena and blende; while asso- ciated with them are characteristic contact minerals, such as epidote, wollastonite, garnet, vesuvianite, and hematite. The sulphides sometimes carry gold and silver, but tellu- rides are unknown. A characteristic feature, however, is the association of iron oxides and sulphides, an almost unknown thing in fissure veins. Since these minerals are sometimes found in limestones of great purity, it is consid- ered as quite evident that in such cases, at least, most of the foreign matter has been derived from the igneous mass. Examples of contact deposits are South Mountain, Idaho, Seven Devils District, Idaho, and Clifton, Arizona (in part). Other Causes of Precipitation. Some fifty years ago not a few geologists, prominent among them De la Beche, advo- cated the theory of ore precipitation by galvanic action (1, 9), and a number of experiments were made attempting to prove the existence of such action ; now little weight is attached to this theory. More recently Gillette (13) has expressed the view that 236 ECONOMIC GEOLOGY OF THE UNITED STATES osmotic pressure is an important factor in ore deposition, aiding to spread the dissolved metals through the water in the rocks, toward centers of crystallization. Forms of Ore Bodies. Ore bodies vary greatly in their form, and this character has at times been used as a basis of classification by some writers ; but the more modern tend- ency is to use genetic characters instead, making form of secondary importance in the grouping. Certain forms of ore bodies are so numerous as to deserve special mention. Fissure Veins (8, 12, 16, 29, 47). A fissure vein may be defined (22) as a tabular mineral mass occupying or closely associated with a fracture or set of fractures in the inclosing rock, and formed either by filling of the fissures as well as pores in the wall rock, or by replacement of the latter (meta- somatism). When the vein is simply the result of fissure filling, the ore and gangue minerals are often deposited in successive layers on the walls of the fissure (Rico, Colorado), the width of the vein depending .on the width of the fissure and the boundaries of the ore mass being sharp. In most cases, however, the ore-bearing solutions have entered the wall rock and either filled its pores or replaced it to some extent, thus giving the vein an indefinite boundary. There- fore the width of the fissures does not necessarily stand in any direct relation to the width of the vein (47) (Butte, Montana). Veins formed by the simple filling of a fissure often show a banded structure of varying regularity termed crustification by Posepny (Fig. 38), which may sometimes be brecciated by later movements along the fissure. Secondary bands may be formed after reopening of the fissures (Fig. 38), and such a movement may cause brecciation of the vein ORE DEPOSITS 237 material, or allow the ingress of the weathering agents which decompose the wall rock, giving rise to a layer of clay known as selvage. Where the fissure has not been com- pletely filled, thus leaving a central space into which the crystals of gangue project, a comb structure is formed. The bands in a filled fissure may consist of gangue and ore alternat- ing, or of different ores. Among the commonest ores seen in these fis- sure veins are py- rite, chalcopyrite, galena, blende, and sulphides of silver. Some regions af- ford especially fine examples of banded veins, notably those FIG. 38. Section of vein in Enterprise mine, Rico, Colo. The right side shows later banding due to reopening of the fissure. After Ransome, U. S. Geol. Surv., 22d Ann. Kept., II : 262. of Grass Valley, California, and Rico, Colorado. Abroad the mines of Freiberg, Saxony, and Clausthal, Prussia, also often yield magnificent specimens. Even in a single vein the ore may follow certain streaks which are termed shutes, or again it may be restricted to pockets of great richness, which are known as bonanzas. Fissure veins in which metasomatic action has predom- inated show great irregularity of width and an absence of 238 ECONOMIC GEOLOGY OF THE UNITED STATES well-defined boundaries ; they also lack as a rule the sym- metrical banding and the breccias cemented by vein material. There are all gradations between these two types of fissure veins; and even in a single vein, simple filling may occur in one part and replacement in another. Veins often split (PL XX, Fig. 2), or intersect, and at the point of intersection or splitting the ore is apt to be richer. There are other reasons for variations in richness, among the most important being the character of the wall rocks, some kinds being more easily replaceable or more porous than others. Their physical character will moreover exer- cise considerable influence on the shape and size of the fissure. Hard rocks like quartzite, for example, give a clean- cut fissure, while in soft rocks the fissure is apt to split fre- quently, and therefore a vein may be workable in one kind of rock, but becomes worth- less when passing to another, since the profuse branching interferes with economical mining (Fig. 39). A dike may also cause local irregu- larities, and in a given region the fissures not uncommonly show great variation in their direction. Thus at Butte, Montana, east- west veins predominate (Fig. 53), while in the Silverton district of Colorado they cut the rocks in all directions, but the majority show a north of east trend. In the Monte Cristo, Washington, district the veins with north- east trend are predominant (Fig. 40). Fissure veins vary considerably in their width, swelling FIG. 39. Section showing change in character of vein passing from gneiss (g) to soft shale (p). After Beck, Lehre von der Erzlagerstdt- ten : 13, 1901. ORE DEPOSITS 239 at some points and pinching or narrowing at others. They also at times show lateral enrichment ; for instance, where the ore cuts through stratified beds, into which the ore- bearing solutions have spread out laterally along the planes of stratification or other planes. It has been noticed in some veins, especially those formed by replacement, that the filling varies with the wall rock, at times w changing suddenly ; but where the vein is formed wholly by the filling of an open fis- sure, the rock exerts no influence on the character of the FIG. 40. Tabulation of strikes of principal veins in Monte Cristo, Wash., district. After Spurr, U. S. Geol. Surv., 22d Ann. Kept., II : 810, 1902. ore (47). If the vein is inclined, the lower wall is spoken of as the foot watt and the upper one as the hanging wall. Parallel fissures are not uncommon, but the several veins do not necessarily show an equal degree of richness. Where the vein is of composite character, that is, consisting of closely spaced parallel fissures accompanied sometimes by a mineralization' of the intervening rock, it is termed a lode. The outcrop of the vein is called the apex, and is occasionally traceable for a long distance. Linked veins represent a type in which the parallel fissures are connected by diagonal ones (Fig. 41), giving a series resembling the links of a chain. 240 ECONOMIC GEOLOGY OF THE UNITED STATES FIG. 41. Linked veins. After Ordonez. Crash veins are a special type of fissure vein, formed by the enlargement of joint planes and sometimes bedding planes. They are characteris- tic of the up- per Mississippi Valley lead and zinc region, but are usually of limited extent and local impor- tance. In the simplest form they are a vertical fissure, but develop into types shown in Fig. 42. Filling of Fissure Veins (16). The manner in which fissure veins have been filled, and the source of the metals which they contain, formed a most fruitful subject of dis- cussion among the earlier geologists. Four general theories were advanced at an early date (2). They are : (1) Con- temporaneous formation, a theory no longer advocated by any one. (2) Descension, which likewise no longer has any adherents. (3) Lateral secretion, in which the vein contents are supposed to have been leached from the wall rock, usually in the immediate vicinity of the fissure, but at variable depths below the surface ; some geologists hold- ing this view believe that the area leached was very exten- i FIG. 42. Gash vein with associated "flats" (a) and "pitches". (6). Wisconsin zinc region. After Grant, Wis. Geol. and Nat. Hist. Surv., Bull. IX : 62. ORE DEPOSITS 241 sive and not confined to the immediate vicinity of the walls. (4) Ascension, the material being deposited by infil- tration, sublimation with steam, sublimation as gas, or igneous injection. The several arguments for or against these theories are well set forth in Kemp's paper (ref. 16), and it will suffice here to state that of the various ones those of lateral secretion and ascension by infiltration are the most rational. It is probable that the majority of geol- ogists now believe in a modified theory of lateral secretion, in which the area of supply extends beyond the immediate walls of the fissure, and that the ore-bearing solutions have either ascended the fissure or entered through the walls. FIG. 43. Section at Bonne Terre, Mo., showing ore disseminated through limestone. Other Forms of Ore Deposits. Impregnations represent deposits in which the ore has been deposited in the pores of the rock, or the crevices of a breccia (Keweenaw Point, Michigan). Fahlband is a belt of schist impregnated with sulphides. Ore channels include those ore bodies formed along some path which the mineral solutions could easily follow, as the boundary between two different kinds of rock (Leadville, Colorado, Mercur, Utah). Bedded deposits, found parallel with the stratification of sedimentary rocks, and sometimes of contemporaneous origin (Clinton iron ore). Contact deposits, as now understood, represent ore bodies formed along the contact of a mass of igneous and sedimen- tary rock (usually calcareous), the ore having been derived 242 ECONOMIC GEOLOGY OF THE UNITED STATES wholly or in part from the intrusive mass (Clifton, Arizona, in part). Chamber deposits, whose ore has been deposited in caves of solution (Missouri lead and zinc ores). Dissemina- tions, deposits in which the ore is disseminated through the rock (Southeastern Missouri lead ores). Secondary Changes in Ore Deposits. Ore deposits may be changed in their upper parts by weathering agents, while the lower-lying portions, below the ground water level, are often enriched by secondary processes. Weathering or Superficial Alteration (25) . This involves both chemical and physical changes similar to the decay and disintegration of common rocks, but the great number of mineral compounds involved, including many with metallic base, give rise to a large number of intricate chemical reac- tions. Since many of the minerals in ore deposits are more easily decomposed than the common rock-forming minerals, the alteration is quite rapid and extends to a greater depth than in the country rock. There is, however, marked varia- tion in the rate at which the different ore-forming minerals decay, and this variation exists even in a single group, like the sulphides in which the order or rate of decomposition is arsenopyrite, pyrite, chalcopyrite, blende, galena, chalcocite, and tetrahedrite (41). The altered portion of the ore deposit is known as the gossan, or iron hat (French, chapeau-de-fer ; German, eisener Hut), because the deposit is usually stained by iron minerals, such as limonite, which may sometimes completely mask the true nature of the ore. The first chemical changes are oxidation or hydration, or both, and these, together with other changes, produce many ORE DEPOSITS 243 soluble compounds, which can be, and often are, leached out of the gossan by percolating waters. An example of oxida- tion is the alteration of pyrite to ferrous and ferric sulphate, and by hydration and further oxidation to limonite. Chal- copyrite oxidizes to copper sulphate, and by hydration and further oxidation to copper carbonate, silicate, or oxide. We see therefore that the first change in each of the above cases is the same, sulphates being formed from sulphides, but the later changes are different, the iron sulphate changing to hydrous oxide, while the copper forms a different set of com- *#%z% 050100 200 300 400 500^ '^ 'A FIG. 44. Section through. Copper Queen Mine, Bishee, Ariz., showing variable depth of weathering. After Douglas, Amer. Inst. Min. Engrs., Trans. XXIX., 1900. pounds. Reduction may, however, occur, as when, for ex- ample, two partly oxidized salts of iron and copper react with each other, giving ferric salts and metallic copper, owing to the stronger affinity of iron for oxygen. The porosity of the gossan is sometimes due to leaching, sometimes to shrinkage, as when siderite or pyrite change to limonite. Hydration, on the contrary, causes expansion. The depth of weathering depends on topographic condi- tions, chemical nature and porosity of the deposits, and climate ; but in any event it is liable to vary in the same deposit, owing to variation in the permeability of different parts of the mass (Fig. 44). In Arizona many copper de- 244 ECONOMIC GEOLOGY OF THE UNITED STATES posits have been changed from sulphides to carbonates, to a depth ranging from 100 to 700 feet; the oxidized ores of the Appalachian region average about 100 feet in depth; while those of the Rocky Mountain area range from 50 to 700 in depth. The ferric sulphate produced by the weathering of pyrite is a most important factor in the alteration of ore deposits. When formed it attacks pyrite and other sulphides, convert- ing them into sulphates, at the same time being itself reduced to ferrous sulphate, which is in part changed to limonite and sulphuric acid. That portion remaining unreduced begins anew the scale of change. Ferric sulphate is thus the main agent by which the sulphides are dissolved. Moreover it also acts as a solvent of free gold. All the metallic contents are not, however, leached from the gossan, for some minerals are either difficult to dissolve or remain unattacked. Thus in some cases the leaching produces an enrichment by the removal of worthless con- stituents and a consequent increase per ton of valuable minerals. The soluble compounds produced by weathering are often carried downward by percolating water and de- posited in an irregular zone between the gossan and the unweathered ore below. In many copper deposits there is found a rich zone of black copper between the gossan and unaltered sulphides. Secondary Deposition below Ground Water Level (4, 41). If the body of unaltered sulphides below is broken by fissures, the solutions containing the various metallic sul- phides and sulphuric acid will enter them, penetrating at times to considerable depths. If pyrite or pyrrhotite are present at these depths, a reac- ORE DEPOSITS 245 tion occurs between the ferric sulphate, the dissolved metallic sulphides, and the pyrite. This may result in the precipita- tion of new sulphides on the walls of the fracture, forming rich patches of ore or bonanzas (28) . The association of these fractures formed after the primary sulphides is an important character of value to the mining engineer, and from what has been said above, it can be seen that ore bodies lacking in iron pyrite will not show this secondary enrichment. It has been noticed, however, that pyrite is not the only reducing and pre- cipitating agent in ore deposits. Carbon is a strong reducer, and other minerals also exert a variable influence (14). (See deposition of lead and zinc in Wisconsin and Ozark region, Chap. XVII.) Value of Ores. The terms rich and poor, as applied to ores, are used with great frequency, although most indefinite and often meaningless. Under very favorable conditions it is possible to profitably work an ore of given value at one locality, while if found under other less favorable conditions at another point it might be almost worthless. Those who have not given special study to ore deposits often fail to realize that in the majority of ores the per- centage of metal contained in the ore falls considerably below the theoretic percentage of the metallic contents in the ore-bearing minerals, due of course to the presence of a greater or less quantity of gangue minerals which tend to dilute the metallic values of the vein. Lake Superior copper ores contain as little as .65 per cent native copper ; and many sulphide ores running as low as 5 or 6 per cent metallic copper or even less are successfully worked. Many low- grade lead ores are profitably mined because their gold and 246 ECONOMIC GEOLOGY OF THE UNITED STATES silver contents more than pay the cost of metallurgical treat- ment. Gold ores alone, running as low as $2 or $3 per ton, can likewise be successfully worked at times. In many cases the metallic contents of the ore is increased by mechanical concentration or by roasting (in the case of sulphides), or both, before the ore is smelted. Classification of Ore Deposits. Many attempts have been made to develop a suitable classification of ore deposits, and many schemes have been suggested (17). These are usually based either on form, mineral contents, or inode of origin. The first is perhaps the most practical from the miner's standpoint, the second is undesirable because several kinds of ore may often be found in the same ore body, while the third is the most scientific, and is of value to the mining geologist and engineer. Those desiring to look into this phase of the subject in more detail are referred to the bibliography at the end of this chapter, especially the papers by Kemp (17), Posepny (24), and Van Hise (40). Only one classification is given here, viz. that of W. H. Weed, not because it is considered entirely .satisfactory or especially simple, but because it embodies the results of the more modern studies of ore deposits and their genetic character. CLASSIFICATION OF ORE DEPOSITS (AFTER WEED) A. Igneous, magmatic segregation, (a) Siliceous. 1. Masses, Aplitic masses. Ehrenberg, Shartash. 2. Dikes, Beresite or Aplite. Berezovsk. 3. Quartz veins. Alaska, Randsburg, Black Hills. ORE DEPOSITS 247 (6) Basic. 1. Peripheral masses. Copper, iron, nickel. 2. Dikes, titaniferous iron. Adirondacks, Wyoming. B. Igneous emanations. Deposits formed by gases above or near the critical point, e.g. 365 C. and 200 atmospheres for H 2 0. (a) Contact metamorphic deposits. 1. Deposits confined to contact. Magnetite deposits, chalcopy- rite deposits, Kristiania type, gold ores, Bannock type. 2. Deposits impregnating and replacing beds of contact zone. Chalcopyrite deposits, pyrrhotite ores, magnetite ores, Can- anea type, Gold tellurium ores, Elkhorn type, Arsenopyrite ores, Similkameeii type. (&) Veins closely allied to magrnatic veins and to Division D. 1. Cassiterite. Cornwall. 2. Tourmaline copper. Sonora. 3. Tourmaline gold. Helena, Mont., Minas Geraes, etc. 4. Augite copper, etc. Tuscany. C. Fumarolic deposits. (a) Metallic oxides, etc., in clefts in lava. No commercial impor- tance. Copper, iron, etc. D. Gas-aqueous or pneumato-hydato-genetic deposits, igneous emana- tions, or primitive water mingled with ground water, (a) Filling deposits. 1. Fissure veins. 2. Impregnation of porous rock. 3. Cementation deposits of breccia. (&) Replacement deposits. 1. Propylitic. Comstock. 2. Sericitic kaolinic, calcitic, Copper silver, Silver lead. Clausthal. 3. Silicic dolomitic, silver lead, aspen. 4. Silicic calcitic, cinnabar. 5. Sideritic silver lead. Cceur d'Alene, Slocan, Wood River. 6. Biotitic gold copper. Rossland. 7. Fluoric gold tellurium. Cripple Creek. 8. Zeolitic. 248 ECONOMIC GEOLOGY OF THE UNITED STATES Structure Types of Above Fissure veins. Volcanic stocks, Nagyag. Cripple Creek. Contact chimneys. Judith. Dike replacements and impregnations. Bedding or contact planes. Leadville, Mercur. Axes of folds, synclinal basins, anticlinal saddles. Bendigo, Elkhorn. E. Meteoric waters. Surface derived, (a) Underground. 1. Veins. 2. Replacements. Iron ores, Michigan ; copper ores, Michigan ; lead, zinc. 3. Residual. Gossan iron ores, manganese deposits, (ft) Surficial. 1. Chemical. Bog iron ores, copper ores, sinters. 2. Mechanical. Gold and tin placers. Sedimentary beds, iron ores, etc. F. Metamorphic deposits. Ores concentrated from older rocks by metamorphism, dynamo or regional. Igneous ore deposits, forming the first division, are those in which the metallic minerals have crystallized directly from the igneous magma during cooling. The pneumatolytic deposits include those formed along igneous contacts, the material being supplied by the in- trusive, as explained on an earlier page. The gas-aqueous deposits include those which have been deposited from a mixture of water and steam, probably under pressure and at high temperature. They may either fill true fissures or porous deposits, or replace the wall rock lining a narrow fissure. It will be seen that the types mentioned under B and C might pass into each other. The same igneous mass could at great depths give off metallic min- ORE DEPOSITS 249 erals under conditions mentioned under B, while higher up the emission from it would yield a deposit, classifiable under C. Fumarolic deposits include those in which metallic com- pounds are deposited from volcanic vapors or gases in clefts in lavas. They are of no commercial importance. The last class is the result of meteoric circulation, the waters having collected the ore particles from the rocks through which they moved, and deposited them under favor- able conditions, either on the surface or below it. REFERENCES ON ORE DEPOSITS GENERAL. 1. Barus, Amer. Inst. Min. Engrs., Trans. XIII : 417, 1885. (Electrical activity in ore bodies.) 2. von Cotta-Prime, Ore De- posits (English translation by Prime, N. Y., 1870). 3. Don, Amer. Inst. Min. Engrs., Trans. XXVII : 564, 1898. (Genesis of gold.) 4. Emmons, Amer. Inst. Min. Engrs., Trans. XXX : 177, 1901. (Sec- ondary enrichment ore deposits.) 5. Emmons, Amer. Inst. Min. Engrs., Trans. XXII : 53, 1894. (Geol. distribution useful metals.) 6. Emmons, Geol. Soc. Amer., Bull. XV : 1, 1904. (Theories of ore deposition.) 7. Emmons, Amer. Inst. Min. Engrs., Trans. XVI : 804, 1888. (Structural relations of ore deposits.) 8. Emmons, Colo. Sci. Soc., Proc. II : 189, 1885-7. (Origin of fissure veins.) 9. Fox, Amer. Jour. Sci. i, XXXVII : 199, 1839. (Vein formation by gal- vanic agency.) 10. Fuchs et De Launay, Traite des Gites Mineraux et Metallif eres, Paris, 1893. 11. Finch, Colo. Sci. Soc., Proc. VII : 193, 1904. (Underground waters and ore deposition.) 12. Glenn, Amer. Inst. Min. Engrs., Trans. XXV : 499, 1896. (Fissure walls.) 13. Gil- lette, Amer. Inst. Min. Engrs., Trans. XXIII, 1903. (Osmosis theory.) 14. Jenney, Amer. Inst. Min. Engrs., Trans. XXXII: 445, 1902. (Chemistry of ore deposition.) 15. Kemp, S. of M. Quart., X: 54,116, 326, 1889; XI: 359,1890; XII: 218, 1891. (Literature on ore deposits.) 16. Kemp, S. of M. Quart., XIII : 20, 1892. (Fill- ing of veins.) 17. Kemp, S. of M. Quart., XIV : 8, 1893. (Classifi- cation of ore deposits.) 18. Kemp, Min. Indus., IV : 755, 1896. (Theories of origin of ores.) 19. Kemp, Ore Deposits of United States and Canada, N. Y., 1903. 20. Kemp, Amer. Inst. Min. Engrs., Trans. XXXIII : 699, 1903. (Relation of igneous rocks to ore deposition.) 21. Kemp, Amer. Inst. Min. Engrs., Trans. XXXI : 169, 250 ECONOMIC GEOLOGY OF THE UNITED STATES 1901. (Igneous rock and vein formation.) 22. Lindgren, Amer. Inst. Min. Engrs., Trans. XXX : 578, 1901. (Metasomatic processes in fissure veins.) 23. Lindgren, Amer. Jour. Sci. iv, V: 418, 1898. (Orthoclase gangue.) 24. Posepny, Amer. Inst. Min. Engrs., Trans. XXIII: 197, 1894. (Genesis of ore deposits.) 25. Penrose, Jour. Geol., II : 288, 1894. (Weathering of ore deposits.) 26. Phillips, Treatise on Ore Deposits, London, 1884. 27. Rickard, Eng. and Min. Jour., LXXIII : 106, 1902. (Recent advances in study of ore deposits.) 28. Rickard, Amer. Inst. Min. Engrs., Trans. XXXI : 198, 1901. (Bonanzas in gold veins.) 29. Rickard, Amer. Inst. Min, Engrs., Trans. XXVI : 193, 1897. (Vein walls.) 30. Rickard, Eng. and Min. Jour., LXV : 494, 1898. (Minerals accompanying gold.) 31. Sandberger, Untersuchungen iiber Erzgange, Wiesbaden, 1882. 32. Suess, Eng. and Min. Jour., LXXVI : 52, 1903. (Hot springs.) 33. Spurr, Eng. and Min. Jour., LXXVI : 54, 1903. (Relation of rock segregation to ore deposition.) 34. Spurr, Amer. Inst. Min. Engrs.. Trans. XXXIII : 288, 1903. (Magmatic segregation of rocks and ores.) 35. Vogt, Zeitsch. f. Prak. Geol., 1 : 4, 125, 257, 1893. (Magmatic segregation of ores.) 36. Vogt, Min. Indus., IV : 743, 1896. (Formation of eruptive ore deposits.) 37. Vogt, Zeitsch. f. Prak. Geol., VI : 225, 314, 377, 413, 1898 ; VII : 10, 1899. (Dis- tribution of elements and concentration of metals in ore bodies). 38. Vogt, Amer. Inst. Min. Engrs., Trans. XXXI : 125, 1901. (Prob- lems in geology of ore deposits.) 39. Van Hise, Amer. Inst. Min. Engrs., Trans. XXX : 27,1901. (Deposition of ores.) 40. Van Hise, U. S. Geol. Surv., Mon. XLVIL 1905. (Metamorphism.) 41. Weed, Amer. Inst. Min. Engrs., -Trans. XXX : 424, 1901. (Enrichment, gold and silver veins.) 42. Wagoner, Amer. Inst. Min. Engrs., Trans. XXX : 798, 1899. (Gold and silver in sedimentary rocks.) 43. Weed, Eng. and Min. Jour., LXXVI : 193, 1903. (Cross vein ore shoots.) 44. Weed, Eng. and Min. Jour., LXXIV : 545, 1902. (Vein en- richment by ascending alkaline waters.) 45. Weed, Eng. and Min. Jour., LXXIV : 513, 1902. (Contact deposits.) Also Lindgren. 46. Weed, Amer. Inst. Min. Engrs., Trans. XXXIII : 747, 1903. (Vein enrichment by ascending hot waters.) 47. Weed, Amer. Inst. Min. Engrs., Trans. XXXI : 634, 1901. (Influence of wall rock on mineral veins.) 48. Weed. U. S. Geol. Surv., Bull. 260, 1905. (Hot spring deposits.) 49. Weed, U. S. Geol. Surv., 22d Ann. Kept., II : 227, 1900. (Hot springs depositing gold.) 50. Whitney, Metallic wealth of U. S., Phil., 1854. CHAPTER XIV IRON ORES IRON is an abundant constituent of the earth's crust, and yet few minerals are capable of serving as ores of this metal, because they do not contain it in the right combination or in sufficient quantity to make its extraction possible or profitable. The iron ores having the greatest commercial value at the present day are usually those which are favorably located, of high quality, in/considerable quantity, and /possessing a structure such as to render their extraction easy. These four requirements have been met to such an eminent degree by the deposits located in the Lake Superior district that they now form the main source of supply for furnaces in the Eastern and Central states, many of the iron mines in the eastern part of the United States having been forced to shut down, although it is true that a number of small deposits are worked to supply local demand, owing to their proximity to furnace, flux, and coal, or because they possess certain desirable characteristics. Ores of Iron. The ores of iron, together with their com- position and theoretic percentage of metallic iron, are : MAGNETITE. Magnetic iron ore. Fe 3 O 4 ..... 72.4 per cent. HEMATITE. Specular iron ore, red hematite, fossil ore, clinton ore. Fe 2 O 3 70 per cent. 251 252 ECONOMIC GEOLOGY OF THE UNITED STATES LIMONITE. Brown hematite, bog iron ore, ocher. 2 Fe 2 O 3 , 3 H 2 O ........ 59.89 per cent. SIDERITE. Spathic ore, blackband, clay ironstone, kidney ore. FeCO 3 48.27 per cent. PYRITE. FeS 2 46 - 7 percent. Of these hematite is the most valuable by far, because the known important deposits of it approach more closely to the theoretical composition than the other ores do. The deficiency in iron contents shown by many ores is due to the presence of common rock-forming minerals in the gangue, the impurities yielded by them being: alumina, lime, magnesia, silica, titanium, arsenic, copper, phosphorus, and sulphur. The effect of the last six is to weaken the iron in general. While silica in high amounts is not desirable, still some fur- naces turn out iron for foundry purposes containing 10 or more per cent. Pyrite is the source of the sulphur, and apatite of the phosphorus. Titanium, a common but injuri- ous ingredient, is found in many magnetite deposits (see Titaniferous magnetites ; also refs. 20, 21), and up to the present time has rendered them practically useless, not because it interferes with the quality of the iron, but because it makes the ore highly refractory, and drives much of the iron into the slag. Experiments have been undertaken looking towards the utilization of these titan- iferous magnetites for the manufacture of ferro-titanium. Manganese, when present, is found mostly in the limonite ores, and for certain purposes is desirable. It is also promi- nent in some of the Lake Superior hematites. As phosphorus cannot be eliminated in either the blast furnace or the acid converter used in making Bessemer steel, and as the allowable limit IRON ORES 253 of phosphorus in pig iron used for this purpose is T V percent, a distinction is usually made between Bessemer and non-Bessemer ores, the maximum amount of phosphorus permissible in iron ore to be used for this purpose being jtfW ^ the percentage of metallic iron contents of the ore. The phosphorus content of many high-grade ores, however, falls considerably below the allowable limit. With the exception of iron ores formed by magmatic segregation, gas-aqueous action, and some deposits of sedi- FIG. 45. Map showing distribution of iron ores in the United States. Adapted from Ransome, Min. Mag., X: 1. mentary character, most iron ores owe their concentra- tion to the action of circulating meteoric waters, which have leached the iron out of the rocks and deposited it under favorable conditions either in cavities or by replace- ment. The ore most commonly formed in this manner is limonite, arid the deposits are of surficial character, but hematite bodies of similar origin are known. Deposits of siderite formed 254 ECONOMIC GEOLOGY OF THE UNITED STATES by replacement are frequently changed to limonite by weathering. Iron-ore bodies may show a variety of form, but most of those known in this country are lens-shaped or basin-shaped in outline. The iron ores found in the United States are widely dis- tributed (Fig. 45), and their age ranges from pre-Cambrian to recent. The occurrence and distribution of the different kinds of ore are best discussed separately. MAGNETITE Magnetite occurs in the United States, (1) as lenticular masses commonly in metamorphic rocks; (2) as more or less lens-shaped bodies in igneous rocks; (3) as sands on the shores of lakes and seas; and (4) as contact deposits. The first class includes the most important deposits now worked in this country. The second and third groups run too high in titanium to have any commercial value at the present time, but the second may become of importance in the future, and moreover some of the deposits of this group are of large size. Undoubted representatives of the fourth class of commercial value are not worked. There are some, it is true, which occur along the contact of an intrusive and sedimentary rock, but their origin is ascribed to meteoric circulations. Distribution of Magnetites in the United States. Nbn- Titaniferous Magnetites. These are usually found in the form of lenticular deposits in metamorphic rocks. The most important series of occurrences is found in the crys- talline belt of rocks extending from New York into Alabama, deposits being known in New York, New Jersey, Pennsyl- vania, Virginia, and North Carolina. PLATE XIV FIG. 1. View of open cut in magnetite deposit, Mineville, N.Y. The pillars are ore left to support the gneiss hanging wall. After Witherbee, Iron Age, Dec. 17, 1903. FIG. 2. General view of magnetic separating plants and shaft houses, Mineville, N.Y. After Witherbee, Iron Age, Dec. 17, 1903. IRON ORES 255 The lenses, which are interbedded with the gneisses of either acid or basic character and often conform with the latter in dip and strike, are of variable size, and may occur either singly or in series, the ore body commonly showing pinching and swelling, or even faulting. Well- defined boundaries are sometimes wanting. Feldspar, hornblende, and quartz are common garigue minerals, while apatite is prominent in some. Although the ore as mined is frequently of sufficient purity to be shipped direct to the blast furnace, in some instances it is so lean as to require concentration by magnetic methods. This same plan has been adopted at Mineville, New York, to treat the high phosphorus magnetite, thereby yielding a rich con- centrate (68 per cent Fe) for iron manufacture, a fairly pure apatite used in making fertilizers, and a hornblende tailings or waste product. The magnetites have been extensively worked on the northern and eastern side of the Adirondacks, notably at Mineville (19), where one lens has been traced for a distance of 2000 feet. Many ore bodies have also been mined in New Jersey, where they are disposed in more or less parallel belts. The origin of these magnetites has been a subject of niuch discussion, but their interfoliation with the gneisses is thought by some to indicate that the ores and rock had a common origin. Those believing the gneisses to be meta- morphosed sediments thought the magnetites were originally limonite, but if the gneisses are metamorphosed igneous rocks, then the ore may represent magmatic segregations. The North Carolina magnetites have been suggested by Keith (18 a) to be replacement deposits, while Kemp be- 256 ECONOMIC GEOLOGY OF THE UNITED STATES lieves that the ore bodies at Mineville (19) have been formed by iron-bearing magmatic waters, which were given off from the neighboring gabbros and penetrated the gneisses, while the latter were probably still at great depths and before their metamorphism was complete. The presence of apatite and fluorite shows that mineralizing vapors also played a part. A similar origin has recently been suggested by Spencer (23) to explain some of the New Jersey magnetites. Other theories advanced are that the magnetite deposits were formed as beach sands or even river bars, but such an as- sumption would require the gneisses to be metamorphosed sediments. A somewhat unique deposit and one of the largest ever worked occurs at Cornwall (17), Pennsylvania, where a bed of soft magnetite with some pyrite is found between Cam- brian limestone and Triassic shales, and against igneous dikes. Their age has been placed as both Cambro-Silurian and also Triassic, and whether they represent metamor- phosed pyritiferous shale or limonites is also unsettled. The ore runs from 40 to 55 per cent Fe and usually under .02 P, but is rather high in S and SiO 2 . Other Occurrences. Magnetite occurs sparingly in the Marquette range of Michigan, where it is found in the schists. Other western occurrences include Colorado (6), Utah (32), Wyoming (la), New Mexico (la), and California. In the table given below there will be found the analyses of a number of magnetite samples from eastern mines. These it will be seen show considerable variation in their metallic iron contents, and are not all to be regarded as a strict average of the region which they represent. IKON ORES 257 ANALYSES OF MAGNETITES Fe SiO 2 P Mn A1 2 8 CaO MgO 8 TiO 2 Tr Alk H 2 Fe3 2 Belvidere, N.J. . Little Mine, N.J. . 51.42 67.54 8.85 1.20 1.048 .02 .17 .90 3.86 .74 1.68 .31 .18 .51 .08 McKnightstown , Adams Co., Pa. . 46.90 17.054 P 2 5 .128 MnO .896 4.424 1.868 4.198 .953 5.00 .05 Dillsburg, York Co. Pa . ... 45.00 20.33 P 2 6 .107 P MnO .036 3.775 5.604 4.129 S0 3 1.105 1.14 1.605 Cornwall, Pa. . . 42.70 .135 3.411 .62 Mineville, N.Y. P (Mine 21) . . . 62.10 1.198 Titaniferous Magnetites. These form a peculiar class by themselves, and with only one or two exceptions are found always associated with rocks of the gabbro family. The ore bodies occur in the midst of igneous intrusions, and according to Kemp (19, 20, 21), seem to have been formed by the segregation of fairly pure titaniferous iron oxide, either before or during the process of cooling and con- solidation. Mineralogically they may contain both ilmenite, FeO, TiO 2 (FeO, 46.75; TiO 2 , 53.25), and titaniferous magnetite, which is of variable composition. The gangue minerals may be pyroxene, brown hornblende, hypersthene, enstatite, olivine, spinel, garnet, and plagioclase. The ores are usu- ally low in phosphorus and sulphur, but Va, Cr, Ni, and Co are almost always present. In the United States they are found in New York, New Jersey, Colorado, Minnesota, and several other states, but are not worked. The following analyses illustrate their composition : 258 ECONOMIC GEOLOGY OF THE UNITED STATES ANALYSES OF TITANIFEROUS MAGNETITES 1 2 3 4 FeO . . ] f 27.95 1 Fe O, 70.50 J 80.78 1 15.85 f 79.78 * C 2^3 TiO 2 .... 14.00 12.09 15.66 12.08 SiO 2 8.60 2.02 17.90 .75 AloO. . 4.00 2.58 10.23 4.62 ^"2^3 ' Cr 2 3 V 2 5 MnO 2.40 .51 .55 Tr .32 Tr .28 CaO 1.60 2.86 .13 MgO ... 2.30 6.04 2.04 H 2 O .04 pn .03 .14 101.00 99.90 99.05 100.00 1. Grape Creek, Colo. 2. Mayhew Range, Minn. 3. Split Rock, N.Y. 4. Greensboro, N.C. Magnetite Sands. These are found in those regions where the beach sands are composed of weathering products of metamorphic and igneous rocks. The sorting action of the waves serves to carry the heavy mineral grains high up on the beaches, where they form black streaks, composed mostly of magnetite (usually titanifer- ous), mixed with monazite, apatite, and other heavy min- erals. Deposits are known in this country on the shores of Lake Champlain, Long Island, etc., but they are of small extent as well as lacking in quality. New Zealand and Brazil are said to possess magnetite JL O sands of commercial value. IRON ORES 259 HEMATITE This is by far the most important ore of iron in the United States, having in 1903 formed 86.6 per cent of the total production. Its distribution, however, is rather restricted, and about five sixths of the total quantity mined came from the Lake Superior region. The varieties mined in the United States include the earthy, specular, oolitic, and fossiliferous. Most of the deposits belong to the replacement type and are basin-shaped, while bedded and contact deposits are also known, but the last are not worked. FIG. 46. Map of Lake Superior iron regions, shipping ports, and transportation lines. After Grant, Min. Mag., X: 175. Distribution of Hematite Ores in the United States. At the present day there are but two very important hematite producing regions, viz. the Lake Superior region and the Birmingham, Alabama, area. Lake Superior Region. Under this head are included a great series of deposits lying in the region surrounding the south and west sides of Lake Superior (13). The rocks are of remote geological age, as can be seen from the following section : 260 ECONOMIC GEOLOGY OF THE UNITED STATES Cambrian. Keweenawan. Upper Huronian. Lake Superior sandstone. [Upper sedimentary, or copper series. | Lower igneous, with interstratified sediments, f Sedimentaries with local volcanics, and cut by Upper Huronian and Keweenawan intrusions. Lower Huronian. Sediments with some volcanics, cut by intrusives. Archaean or Basement com- plex. Mainly ancient igneous rocks and some sediments. These igneous intrusions pierced by many others of later date. Each of the above series is separated from its neighbor by a great unconformity, due to intervals of elevation above the sea level and periods of erosion. The rocks of the iron- bearing formations are cherty iron carbonates; ferrous silicate rocks ; pyritic quartz rocks (Archsean); ferrugin- ous slates ; ferruginous cherts; jaspilites; am- phibolites and magne- tite schists; iron ore deposits; detrital fer- ruginous rocks from foregoing. Since their formation they have been folded, faulted, FIG. 47. Sections of iron-ore deposits in Mar- quette range. After Van Hise. and sometimes brec- ciated, and it is in the troughs formed by folding that the ore usually occurs (Fig. 47). PLATE XV FIG. 1. Iron mine, Soudan, Minn. Shows old open pit with jasper horse in middle. FIG. 2. Out ?rop of Clinton iron ore, Red Mountain, near Birmingham, Ala. Photo, from Tennessee Coal and Iron Company. IRON OKES 261 The Archaean, Lower Huronian, and Upper Huronian are the most productive iron-bearing formations, the last men- tioned containing the ore at two horizons, viz. near its base and in its central portion. Six districts, or ranges, are recognizable in the Lake Superior region, viz. Marquette (13) and Crystal Falls (27) in Michigan ; Menominee (25) in Wisconsin ; Penokee- Gogebic (37) on the Michigan- Wisconsin boundary; Mesabi FIG. 48. Generalized vertical section through Penokee-Gogebic ore deposit and adjacent rocks ; Colby mine, Bessemer, Mich. After Leith. (31) and Vermilion (28) in Minnesota. The general mode of occurrence of the ore in several of these is shown in Figs. 47, 48, and 49. The ore is not found at the same horizons in all the districts, the Marquette being the only one where all the iron-bearing formations of the series are found. Of these, the Archaean iron-bearing forma- tions are unproductive, the chief ore bodies lying within the Lower Huronian and at the base of the Upper Huronian. In the Crystal Falls district, the iron-bearing horizon of the Lower Huronian carries the ore as well as the horizon within the Upper Huronian. In both the 262 ECONOMIC GEOLOGY OF THE UNITED STATES Penokee and Mesabi districts the conditions are similar to those in the western part of the Crystal Falls district, the ore being found in a single formation in the Upper Huronian, while the same one in the Marquette region is thin and of little consequence. The smaller deposits are associated with plications, folding, brecci- ations, etc., but the larger masses of ore occur at the contact of the iron-bearing formations with others or between different members of the iron-bearing formations. These contacts were favorable for con- centration of ore, because they are planes or horizons of slipping, and the effect of this movement would be to loosen the rock, thus making channels for the percolating water. Underlying the deposits of first FIG. 49. Generalized vertical section through Mesabi ore deposit and adjacent rocks. After Leith. magnitude there occur impervious formations which are bent into troughs. Slate, quartzite, limestone, or igneous rock may all serve as floors, or two may combine, as in the Penokee-Gogebic district, where the trough is formed by the intersection of quartzite and dikes. The ore bodies are often U-shaped in section, being thickest at the bottom. The origin of these ores has for years been a puzzling problem to geologists (37). Foster and Whitney considered them eruptive, while Brooks and Pumpelly looked upon them as altered limonite beds. In recent years the studies of Irving and Van Hise (37), aided by others, have demon- strated that the ores owe their origin partly to a replace- ment of the chert. The trough-shaped location shows that IRON OEES 263 the deposits were formed after the rocks had been folded, and it is also noticed that these troughs are even still the lines of underground waters. That they have been produced by descending waters is shown by the fact that they are on the upper side of the impervious bed, and because the ores are oxidized ones, viz., hematite and limonite. The chemistry of the process is thought to be as follows : Part of the ferric oxide was deposited as an original sediment containing silica and other impurities, or in some cases as sulphides or carbonates. This was later enriched by the addition of iron carbonate. These were originally contained in the rocks near the surface, and became oxidized by perco- lating waters, which took up the carbon dioxide liberated, and were thus able to dissolve iron carbonates or silicates, which they came in contact with in their downward course toward the troughs in which the ore is found. The precipitation of the ore was then caused by these solutions meeting with others which had filtered in by a more open and direct path from the surface, and hence contained some free oxygen, which converted the dissolved iron compounds into oxides. The same solutions, carrying carbon dioxide, dissolved the alkalies out of the basic igneous rocks and these waters were then able to dis- solve silica. In some cases the solution of silica proceeded faster than the deposition of the iron ore, and made the rock quite porous. The general result was therefore a concentration of the iron and removal of silica. The ores of the Lake Superior region vary from hard blue ores to soft earthy ones. They are mostly hematite, with small quantities of limonite, but some magnetite is known in the Marquette district. The following table taken from Birkenbine's report gives a number of typical analyses (la). Many additional ones can be found in the reports on Mineral Resources issued annually by the United States Geological Survey. 264 ECONOMIC GEOLOGY OF THE UNITED STATES TYPICAL ANALYSES OF LAKE SUPERIOR IRON ORES CONTENT MABQUETTE KANGE MENOMINEE RANGE GOGEBIC RANGE VERMILION RANGE MESABI RANGE Iron 565 55.2423 56.308 61.36 56 0996 Phosphorus . . . Silica .0353 4.584 .0594 6.7693 .0338 3.3961 .0373 4.2545 .0365 3 4867 Sulphur .... Moisture .... .0089 11.85 6.525 10.828 4.5649 12.3158 ANALYSES OF SILICEOUS ORES CONTENT MARQUETTE RANGE MENOMINEE RANGE VERMILION RANGE Iron . 4927 49 129 PJ1 1Q'4ft Phosphorus 0316 0044 04Q8 Silica 35834 34 141 oo Qfi4O Sulphur .... 0099 Moisture .... 1 23 2 2 Q 91 Most of the rich ores are found above the 1000-foot level, except in the Mesabi district where the deposits are shallow, as compared with their horizontal extent, some, however, being over 400 feet deep. In the early period of mining many of the Lake Superior bodies were worked as open cuts, but with depth underground working has been resorted to. There are many deposits in the Mesabi district which are worked as open pits from which the granular ore is dug with a steam shovel and loaded directly on to the ore cars, which are run along the working face (PI. XVI). The development of the Lake Superior region has ad- PLATE XVI IRON OKES 265 vanced with phenomenal strides. The Marquette range was developed as early as 1849, and the Mesabi as late as 1892. The total yield of the Lake Superior region from 1850 to 1902 was 246,558,896 long tons. Between 1891 and 1903 it was 191,646,959 long tons, or 77.75 per cent of the total amount mined. Van Hise, in estimating the available quan- tity of high-grade ore still in the ground, believes that even if it approached 1,000,000,000 long tons, mining at the rate of 20,000,000 tons per year would exhaust the supply in the first half of the twentieth century. Indeed, it will not be many years before lower grades of ore, hitherto thrown aside, will be shipped to market. Already ore carrying 40 per cent iron, but low in phosphorus and high in silica, has been sold for mixing in with high- grade Mesabi ores, and Van Hise believes that ores below 40 per cent in iron will be marketed before another generation. The market value of the ores is based on the iron contents, percentage of water, and amount of phosphorus, and at times the manganese contents is taken into consideration. Some objection has been raised in the last few years to the fine character of the Mesabi ore and its tendency to clog the blast furnace, therefore requiring the admixture of lump ore from the other ranges ; but this objection is rapidly disappearing, and some furnaces now use 75 per cent of Mesabi ore in their charge. The Lake Superior iron ore region is not only the most important in the world, but the production of some of the individual mines is star- tling. This enormous output can, perhaps, be best appreciated by some comparative figures. Thus, for example, the production of 15,371,396 long tons of ore mined in Minnesota in 1903 is about three quarters of the total amount extracted from the famous magnetite deposits of Cornwall, Pennsylvania, since they were opened in 1740, or of the total 266 ECONOMIC GEOLOGY OF THE UNITED quantity of New Jersey magnetites mined since they were first worked in 1710. The production even of single mines is often great, six mines in 1903 producing over 1,000,000 long tons of ore each (1 a). Clinton Ore (35, 36, 30). This ore, which is also called fossil, pea, or dyestone ore, was given the first name on account of the ore bed having been originally discovered at Clinton, New York. It is one of the most persistent iron- ore deposits that is known, for it occurs wherever rocks belonging to the Clinton stage of the Silurian are found, f e, FIG. 50. Section Clinton ore beds, Oxmoor, Ala. a, red sandstone, 5'; 6, yellow sandstone, 6'; c, red sandstone, 15'; d, ore, 22', upper 2' soft; e, shale, 6' : /, rich ore, 2' t>". After Smyth, Amer. Jour. Sci., June, 1892. including many localities, therefore, along the line of the Appalachians from New York to Alabama, as well as in Ohio and Wisconsin. In Pennsylvania there are several belts of the ore, owing to the presence of many eroded folds carrying the Clinton rocks. The ore is interstratified with sandstones and shales, varies in thickness from a few inches to ten or twenty feet, is at times oolitic in its structure, and at others is made up of a mass of small fossils. At Birmingham, where the greatest development has occurred, the ore occurs in a ridge known as Red Mountain, the bed having a shale roof and sandstone IRON ORES 267 floor, while the thickness of the main bed varies from twelve to twenty feet. The beds dip gently to the east, and the iron ore is worked by means of slopes, although the early workings at some of the mines were open cuts, on account of the thin overburden. The prominence of this locality is due to peculiar conditions, the ore being bordered on the west by Cambrian limestone which forms the valley floor, while on the western side of the valley the coals of the Warrior Field outcrop. Thus the three essential elements for iron manufacture are brought in close contact by folding and faulting. East of the iron range are two additional coal basins. The great development of this ore in Alabama is due partly to favorable local conditions and partly to its re- moteness from the Lake Superior region. The origin of these ore bodies has been argued from different standpoints, some holding that they represent altered limestone beds (35 a), because of the presence of fossils in them, while the concentric nature of the oolites, with a nucleus of worn quartz grains, has led others, espe- cially Smyth, to ascribe a concretionary origin (36) to them. The former theory is strengthened by finding at many places an increase of the lime contents of the ore with the depth. Thus at Attalla, Alabama, the Clinton limestone at 250 feet from the surface carries only 7.75 per cent of iron, while at the outcrop it has 57 per cent of iron. The Clinton iron ores usually run high in phosphorus and also silica. Of the two following analyses, No. 1 is hard ore and No. 2 soft ore. The latter runs higher in lime. A difference also appears to exist between the composition of the fossil or upper ore bed and the oolitic or lower ore bed, as represented by analyses 3 and 4 (30) of the following table: 268 ECONOMIC GEOLOGY OF THE UNITED STATES 1 2 3 4 Fe 52.87 37.00 Fe O 30.24 46.04 P ... .43 .37 P O .75 1.29 s .11 .07 SOo . .15 .20 SiO . 13.66 13.44 8.71 16.82 Al O 6.13 3.18 3.67 3.54 CaO 1.26 16.20 20.64 9.96 MffO .37 7.84 3.41 MnO .30 H 2 O 1.62 .50 CO 2 .08 12.24 24.78 13.62 Other Occurrences. Extensive deposits of hematite in Carboniferous limestone are found in Laramie County, Wyo- ming (1). The ore carries 60 to 67 per cent iron, 2J to 5 per cent silica, and is low in phosphorus. In New Mexico, near Hanover, a deposit carrying about one quarter hematite and three quarters magnetite, along the contact of granite and limestone, is also extensively worked. Deposits of hematite in brecciated Carboniferous limestones, and formed proba- bly by replacement, are known in Iron and Washington counties of southwestern Utah, and are probably the largest iron-ore deposits in the West. Other deposits are found in the Wasatch Mountains, along the contact of andes- ite and limestone. The ore here consists of hard black crystallized hematite and magnetite, associated with chal- cedony and crystalline quartz. Leith (32) considers it to be a replacement deposit. While much of the ore is of good quality, it is mostly non-Bessemer. The Utah deposits are IRON ORES 269 at present too far from the railroad to be of much value, but are to be looked on as an important future source of supply. Specular hematites also occur at Pilot Knob, Mis- souri, interstratified with breccias and porphyry sheets, and were formerly much worked. LIMONITE Limonite (41-52) or brown hematite is, like magnetite, of comparatively little importance in the United States as compared with hematite, having yielded an average of but 12.2 per cent of the total iron production of the United States in the last fifteen years, and but 8.8 per cent of the total domestic iron ore production in 1903. Although deposits of limonite are widely scattered over the United States, about nine tenths of the total quantity comes from the deposits located in western New England and the Appalachian belt. Owing to their mode of origin, limonites are rarely of high purity, being commonly associated with more or less ferruginous clay, which has to be separated from the ore by washing. Limonite may occur under a variety of conditions and associated with different kinds of rocks, but two impor- tant types are recognized, viz. bog ores, and residual limonites. Bog Ores. The bog ores are formed by the precipitation of limonite in swamps, ponds, or lakes. The iron is dissolved from the rocks or soil by percolating waters charged with carbon dioxide or organic acids, either in the form of ferrous carbonate or ferrous sulphate. As these iron-bearing waters 270 ECONOMIC GEOLOGY OF THE UNITED STATES discharge into the ponds the iron compounds are oxidized to hydrous ferric oxide or limonite, which settles on the bottom. Such ores are usually impure from an admixture of sand or clay which has been deposited at the same time, and are rarely of any thickness. They are of no commercial value in the United States, but in foreign countries are worked in Sweden, in which kingdom they have been known to accumulate in ponds to the depth of 18 inches or more every 15 to 30 years. The ore is collected periodically by dredging. Residual limonites. The residual limonites are a much more important class, and form (1) by the weathering of FIG. 51. Section illustrating formation of residual limouite in limestone. After Hopkins, Geol. Soc. Amer., Bull. XI : 485. pyritiferous veins (see gossan, Chapter XIII), or (2) more often from the weathering of ferruginous rocks. The sec- ond process results in the formation of deposits of iron- stained clay scattered through which are nodules and irregularly shaped masses of limonite, these making up from 5-10 per cent of the entire mass. The limonite may accumulate first by deposition in the cracks of the rock, or by impregnation or replacement, and prior to the breaking down of the rock to a mass of residual clay. Since these deposits often represent the concentra- tion of iron from a great thickness of rock, it is not PLATE XVII FIG. 1. Pit of residual limonite, Shelby, Ala. After McCalley, Ala. Geol. Surv. Report on Valley Regions, Pt. II: 77, 1897. FIG. 2. Old limonite pit, Ivauhoe, Va., showing pinnacled surface of limestone which underlies the ore-bearing clay. The level of surface before mining began is seen on either side of excavation. H. Ries, photo. IRON ORES 271 necessary that the parent material contain a high percentage of iron. An important belt of residual limonites of Cambro-Silurian age, and associated with slates, schists, or limestone, is found extending from Vermont to Alabama, along the Great Valley, and consisting of beds of residual clay carrying limonite nodules (42, 44-48 ). This type of deposits is worked from Vermont to Alabama, and some of the larger mines in the latter state have an annual production of over 100,000 tons. Those found in Georgia are associated with manganese. Plate XVII, Fig. 2, shows the irregular surface of the Cambro-Silurian limestone in one of the Virginia pits. In addition to these, important deposits are found in Vir- ginia, representing the weathered portion of a great belt of pyrite bodies. This extends for over 20 miles and is known as the " Great Gossan Lead," its contents averaging from 40 to 41 per cent metallic iron (48 6, see also Copper, Duck- town, Tennessee). The Oriskany formation also carries large deposits of limonite to the westward of the Cambro-Silurian belt, and these are actively worked in Virginia (49). Other Occurrences. Limonites of more or less distinctly bedded character are found in the Tertiary of northeastern Texas (50, 52), where they occur as thin beds capping the hills and are mined for local use (50). Others are found at the same horizon in Arkansas but promise to be of little commercial value. In the former case they are closely associated with greensands, and may have formed by weathering either from these or from pyrite grains. Small deposits are known In Iowa (41), Wisconsin, Minnesota, and Oregon (3 a). Much limonite, at times manganiferous and containing even small 272 ECONOMIC GEOLOGY OF THE UNITED STATES quantities of silver, is obtained from the gossan of the Lead- ville ore bodies. Its chief use is as a flux. The following analyses give the composition of limonites from several localities. ANALYSES OF LIMONITES Fe P s SiOj Ah0 3 CaO MgO H 2 O Moist. MnO a Average composition Alabama 48.64 .88 .09 11.22 8.61 84 6.00 7.00 Average of 29 commercial P 8 B analyses, Pa., Cambro-Silurian 48.47 1.10 .06 18.97 2.89 .48 .42 11.62 2.85 8O 3 Rusk, Cherokee Co., Texas . . 44.68 .09 .20 18.90 5.76 .18 Tr 11.08 Allamakee County, la. ... 54.32 1.8 Those of the Appalachian belt are much used by pig-iron manufacturers because, owing to their siliceous character, they can be mixed in with high-grade Lake Superior ores which are deficient in silica. They are also cheaper, and their mixture with other ores seems to facilitate the reduc- tion of the iron in the furnace. SIDERITE Siderite (53-58) is the least important of all the ores of iron mined in the United States, both on account of the small quantity and its low iron contents. When of con- cretionary structure, with clayey impurities, it is termed clay ironstone, and these concretions are common in many shales and clays. In some districts siderite forms beds, often several feet in thickness, but containing much bitumi- nous and argillaceous matter, and known as blackband ore. This is found in many Carboniferous shales. IRON OEES 273 Eastern Ohio (54) and Kentucky (53) and western Penn- sylvania (55) are the most important producing states. The ore is obtained chiefly from the Lower Coal measures, although known in the other stages of the Pennsylvania series. Another important occurrence is at the Burden Mines, near Hudson, New York (56), where lens-shaped beds of clay ironstone are found in the Hudson River shales and sandstones. The beds have been folded and faulted, so that the ore bodies lie in basins. The ores are rather magnesian, and on this account it has been suggested by Kimball that they have been formed in shore waters receiving drainage from the Archaean Highlands ; they are also high in phosphorus. Siderite is of far greater importance in foreign countries, and large quantities are shipped to the United States from Spain. It is roasted for use, thereby expelling the carbonic acid and raising the iron contents. Production of Iron Ores. The iron ore mining industry in the United States has progressed with phenomenal strides, and this country now leads the world in the pro- duction of iron ore. Indeed, so great has the production become that in 1903 it was equal to the combined output of Germany and Luxemburg and the British Empire for 1902. Moreover, the average iron content of the ore mined in the United States is higher than that mined in foreign countries, thereby resulting in the production of a greater amount of pig iron from a given quantity of ore. The Lake Superior region is now producing at least three quarters of the iron ore used in the United States, and it 274 ECONOMIC GEOLOGY OF THE UNITED STATES has much the largest reserves of high-grade ores, but even these may be exhausted in fifty years or less at the present rate of consumption. The low-grade ores of this region and others will, however, be available for a much longer time. While there is not danger of the present supply of ore soon becoming exhausted, still with the present con- sumption it is well to consider possible sources of the future. In the United States the Utah and some other western deposits will no doubt be drawn upon, and many ores now looked upon as too low grade to work will also be con- sidered. Aside from domestic sources of supply there are foreign ones which may perhaps be eventually turned to, such as those from Canada, Newfoundland, and Brazil on this side of the Atlantic, or even those of Scandinavia on the European side. In the last-mentioned country especially attention has been drawn in the last few years to mag- netite deposits located well within the Polar circle and of stupendous size. The production of iron ores in the United States from 1889 to 1903 was as follows : TOTAL PRODUCTION OF IRON ORES IN THE UNITED STATES YEAR LONG TONS YEAR LONG TONS 1889 14,518,041 1895 15,957,614 1890 16,036,043 1896 16,005,449 1891 14,591,178 1897 17,518,046 1892 16,296,666 1898 19,433,716 1893 11,587,629 1899 24,683,173 1894 11,879,679 1900 27,553,161 IRON ORES 275 PRODUCTION OF IRON ORE IN THE MORE IMPORTANT STATES FROM 1901 TO 1903 1901 LONG TONS 1902 LONG TONS 1903 LONG TONS 11,109,537 15,137,650 15,371,396 Michigan ... 9,654,067 11,135,215 10,600,330 Alabama 2,801,732 3,574,474 3,684,960 T6I11)6SS66 . 789,494 874,542 852,704 Virginia and West Virginia . . \Visconsin 925,394 738,868 987,958 783,996 801,161 675,053 1,040,684 822,932 644,599 New York 420,218 555,321 540,460 401,989 441,879 484,796 215,599! 364,890 2 443,452 Other states 789,897 875,278 920,397 Total 28,887,479 35,554,135 35,019,308 PRODUCTION OF LAKE SUPERIOR IRON ORES BY RANGES RANGE 1901 LONG TONS 1902 LONG TONS 1903 LONG TONS Go^ebic . 3 041 869 3,683 792 3 3,422,341 JVIarouette 3,597,089 3,734,712 3,686,214 Mepominee . 3 697 408 4 421 50 3 4 093 320 Alesabi .... 9 303 541 13080 118 13,452,812 3 Vermilion 1,805,996 2,057,532 3 1,918,584 PRODUCTION OF MOST IMPORTANT IRON-ORE PRODUCING COUNTRIES COUNTRY YEAR QUANTITY LONG TONS PERCENTAGE WORLD'S PRODUCTION United States 1903 35 019 308 3471 Germany and Luxemburg . Great Britain 1903 1903 21,230,639 13 715645 21.04 13.59 Spain 1903 8 478 600 8.40 Russia and Finland. . . France ' . 1902 1902 5,648,227 5 003 782 5.60 4.96 Sweden 1903 3,677 841 3.65 Austria-Hungary .... 1902 3,329,128 3.30 1 Includes North and South Carolina. 3 Maxima. 2 Includes North Carolina. 276 ECONOMIC GEOLOGY OF THE UNITED STATES The exports of iron ore from the United States in 1903 amounted to 80,611 long tons, valued at 1255,728. REFERENCES ON IRON ORES GENERAL. 1. Birkenbine, Chapters on Iron Ores in Mineral Resources of United States, published annually by U. S. Geol. Survey ; 1 a. Mining Census, 1902, Mines and Quarries. 2. Kimball, Amer. Geol., XXI : 155, 1898. (Concentration by weathering.) 3. Penrose, Jour. Geol., 1 : 356, 1893. (Chemical relations of iron and manganese.) 3 a. Putnam, Tenth Census, XV. 4. Swank, Eng. and Min. Jour., LXXIII: 347, 1902. (U. S. iron and steel works.) 5. Winchell, Ainer. Geol., X : 277, 1892. (Theories of origin.) STATE REPORTS. 6. Chauvenet, Amer. Inst. Min. Engrs., Trans. XVIII : 266, 1890. (Colo.) 7. Nason, Mo. Geol. Surv., II, 1892. (Mo.) 8. Nitze, N. Ca. Geol. Surv., Bull. I, 1893. (N. Ca.) 9. Orton, Ohio Geol. Surv., V: 371, 1884. (Ohio.) 10. Putnam, 10th Census, XV: 467. (U.S.) 11. Shaler, Ky. Geol. Surv., New Series, III : 163, 1877. 12. Smock, N. Y. State Museum, Bull. 7, 1889. (N.Y.) 13. Van Hise, U. S. Geol. Surv., 21st Ann. Kept., Ill : 305, 1901. (Lake Superior region.) 14. Winchell, Minn. Geol. Surv., Bull. 6, 1891. (Minn.). SPECIAL PAPERS. Magnetite. 15. D'Invilliers, Second Pa. Geol. Surv., D3, II, pt. 1 : 227, 1883. (Berks Co.) 16. Prime, Ibid. 1 : 190, 1883. (Lehigh Co.) 17. D'Invilliers, Amer. Inst. Min. Engrs., Trans. XIV: 873, 1886. (Cornwall.) 18. Hulst, Eng. and Min. Jour., LXXVIII : 350,1904. (Titaniferous ores.) 18 a. Keith, U. S. Geol. Surv., Bull. 213 : 243, 1903. (N. Ca.) 19. Kemp, Amer. Inst. Min. Engrs., Trans. XXVII : 146, 1898. (Mineville, N. Y.) 20. Kemp, U.S. Geol. Surv., 19th Ann. Kept., Ill: 377, 1899. (Adirondack titaniferous ores.) 21. Kemp, S. of M. Quart., XX : 323, 1899. (Titaniferous magnetites.) 22. Nason, Amer. Inst. Min. Engrs., Trans. XXIV : 505, 1895. (N. J.) 23. Spencer, Min. Mag., X: 377, 1904. (N.J.) 24. Wolff, N. J. Geol. Surv;, Ann. Kept, for 1893: 359,1894. (N.J.) Hematite. 25. Bayley, U. S. Geol. Surv., Mon. XL VI, 1904. (Menomi- nee range.) 26. Boutwell, U. S. Geol. Surv., Bull. 225: 221, 1904. (Uinta Mts., Utah.) 27. Clements, Smythe, Bayley, and Van Hise, U. S. Geol. Surv., 19th Ann. Kept., Ill: 1, 1899. (Crystal Falls district.) 28. Clements, U. S. Geol. Surv., Mon. XLV, 1903. (Ver- milion range.) 29. Dewees, Second Pa. Geol. Surv., Kept. F, 1878. (Pa.) 30. Eckel, Eng. and Min. Jour., LXXIX: 897, 1905. 31. Leith, IRON ORES 277 U. S. Geol. Surv., Mon. XLIII, 1903. (Mesabi range.) 32. Leith, U. S. Geol. Surv., Bull. 225 : 229, 1904. (S. Utah.) 33. McCreath, Second Pa. Geol. Surv., MM : 229, 1879. (Many analyses.) 34. Pechin, Amer. Inst. Min. Engrs., Trans. XIX : 1016, 1891. (Va.) 35. Porter, Amer. Inst. Min. Engrs., Trans. XV : 170, 1887. (Tenn., Ala., Ga.) 35 a. Russell, U.S. Geol. Surv., Bull. 57: 22, 1889. (Clinton ore.) 36. Smyth, Amer. Jour. Sci., XLIII : 487, 1892 (Clinton ore) ; and N. Y. State Geologist, 22d Ann. Kept, 1902 : 116, 1904. 37. Van Hise, U. S. Geol. Surv., 21st Ann. Kept., Ill: 305, 1901. (Lake Superior region.) 37 a. Van Hise, Bayley and Smyth, U. S. Geol. Surv., Mon. XXVIII, 1897. (Marquette.) 38. Van Hise and Irving, U. S. Geol. Surv., Mon. XIX, 1892. (Penokee-Gogebic range.) 39. Weidman, Wis. Geol. and Nat. Hist. Surv., Bull. 13, 1904. (Baraboo district, Wis.) 40. Woodbridge, Series of articles on Mesabi range, Eng. and Min. Jour., 1905. Limonite. 41. Calvin, la. Geol. Surv., IV: 101, 1895. (la.) 42. Cat- lett, Amer. Inst. Min. Engrs., Trans. XXIX : 308, 1900. (Va.) 43. Diller, U. S. Geol. Surv., Bull. 213 : 219, 1903. (Redding quad- rangle, Calif.) 44. Eckel, Eng. and Min. Jour., LXXVIII : 432, 1904. (E. N. Y. and W. New Eng.) 45. Garrison, Eng. and Min. Jour., LXXIII : 258, 1904. (Chemical characteristics.) 46. Hayes, Amer. Jnst. Min. Engrs., Trans. XXX: 403, 1901. (Ga.) 47. Hayes and Eckel, U. S. Geol. Surv., Bull. 213 : 233, 1903. (Cartersville, Ga.) 48. Hopkins, Geol. Soc. Amer., Bull. XI : 475, 1900. (Pa.) 48 a. Mc- Calley, Ala. Geol. Surv., Report on Valley Region, II, 1897. (Ala.) 485. Moxham, Amer. Inst. Min. Eng., Trans. XXI: 133. (Great Gossan Lead.) 49. Pechin, Eng. and Min. Jour., LIV : 150, 1892. (Va. Oriskany ores.) 50. Penrose, Geol. Soc. Amer., Bull. Ill : 44, 1892 (Ark. and Tex. Tertiary ores); also Ark. Geol. Surv., Rep. 1892, vol. 1, 1892. 51. Phillips, Eng. and Min. Jour., LXV: 489, 1898. (Ala.) 52. Walker, Tex. Geol. Surv., 2d Ann. Kept., 291, 1891. (Cherokee Co., Texas.) Siderite. 53. Moore, Ky. Geol. Surv., 2d Ser., I, pt. 3 : 63, 1875. (Ky.) 54. Orton, Ohio Geol. Surv., V : 378, 1884. (Ohio.) 55. Second Pa. Geol. Surv., K: 386, and MM: 159, 1879. (Pa.) 56. Raymond, Amer. Inst. Min. Engrs., Trans. IV : 339, 1875. (N. Y.) 57. Smock, N. Y. State Museum, Bull. 7 : 62, 1889. (N.Y.) CHAPTER XV COPPER Ores of Copper. Copper-bearing minerals are not only numerous, but widely although irregularly distributed. More than this, copper is found associated with nearly every variety of ore or ore deposit. Nevertheless but few minerals serve as ores of copper, and the same may be said regarding the number of important producing districts in the United States. The ores of copper together with their theoretic composi- tion are as follows : ORE COMPOSITION Cu S Fe Native copper . . . . . Cu CuoS 100 79.8 20.2 ^"2^ CuFeS 2 34.5 35.0 305 (Copper pyrite) CuoFeSo 55.5 28.1 164 (Horseflesh ore) Tetrahedrite .; mmmmr Sj Pal - ALLUVIUM AND WASH PLEISTOCENE ffi& NH - INTRUSIVE RHYOLITE NEOCENE 1 ap- APLITE / " .r^j f POST CARBON|!>ER ous v^J 9/"- ORANITE SILVER VEINS COPPER VEINS FIG. 53. Map of Butte, Mont., district showing distribution of veins and geology. After Weed, U.S. Geol. Surv., Atlas Folio. 284 ECONOMIC GEOLOGY OF THE UNITED STATES rhyolite flows and ash beds, and dikes of the same rock also cut the silver veins of the region. The Butte district contains both silver and copper veins. The latter are found in an area about a mile long and one half mile wide, in the south- eastern part of the district, while the silver veins sur- rounding it are of much less importance. The granites are traversed by several systems of joints and shear planes, and the ore has not only been deposited in them, but has replaced the wall rock as well. The veins are of varying age, the larger and richer ones hav- ing been broken, reopened, and even displaced by fault- ing, and a careful study of the district has shown four separate periods of fracture, in three of which ores have been formed. 0. OXIDIZED ZONE 6. CHALCOCITE C. ENARGITE d. PYRITE e. QUARTZ /. BORNITE g. CHALCOCITE FIG. 54. Section at Butte, Mont., show- ing mode of occurrence of ore. After Winchell, Eng. and Min. Jour., L XX VII: 782. :$} QUARTZ PORPHYRY | FAULT In the earliest, the vein filling, which was the result of replacement in sheeted granite, is quartz and pyrite with some copper. Later fracturing produced large masses of crushed granite, clay, etc., with boulders of ore, and this was sometimes added to by the deposition of enargite by later ascending solutions. The richest masses or bonanzas PLATE XVIII COPPER 285 of glance found in some of the mines are of secondary origin. While the veins exhibit a curious uniformity of direction, most of them striking nearly east and west, and few of them departing more than 15 to 20 from the vertical, still they show considerable variation in width, ranging from a few feet to 50, or even 150 where the altered country rock is impregnated with glance. Unfortunately, the complexity of the veins and uncertainty of boundaries has given rise to much costly litigation in the district. The common vein minerals are pyrite, chalcocite, enar- gite, and bornite, with small amounts of chalcopyrite and covellite, in a quartzose gangue. Others existing in sub- ordinate quantities are tetrahedrite, tennantite, and argen- tite. The chalcocite is always of secondary character. The average composition of first-class ore in Butte in 1902 was: Cu, 11.4 per cent; Fe, 16.6 per cent; Zn, .3 per cent; S, 22.6 per cent; As and Sb, 1.4 per cent; A1 2 O 3 , 7.9 per cent; insoluble, 44.7 per cent; SiO 2 , 38.2 per cent; Ag, oz. 5.2; Au, oz. .04. Second-class ore averages: Cu, 5.2 per cent ; Fe, 16 per cent ; S, 19.8 per cent ; insoluble, 56 per cent; Ag, 3 oz. Gold is quite universally distributed through the ores, though in very small amounts, forming 3 per cent of the values in the copper bullion. Small amounts of arsenic, anti- mony, bismuth, tellurium, selenium, and nickel have been found, and manganese is widespread in the silver veins, though wanting in copper-bearing ones. Zinc is not limited in distribution, but is more abundant in the silver veins. The deposition of the ores is considered by Weed to be due to aqueous alkaline solutions, which have probably 286 ECONOMIC GEOLOGY OF THE UNITED STATES leached the metals from the granite at considerable depths. These solutions, which came up in the fissures, were hot, but not necessarily under pressure. Where the fissures were open they were filled with ore, and where narrow, replacement of the walls occurred, so that the vein matter shades off into the country rock. Since their formation faulting has occurred, usually parallel to the vein. The entrance of meteoric waters into the vein has carried much ore downward, resulting in a richer zone below even the zone of oxidation, and showing bornite, chalcocite, and covellite as a result of this; some of these have been derived from the breaking up of the pyrite. It has been found that these bonanza bodies of secondary origin pass downward into lower-grade ores. Most of the ores are put through a process of mechanical concentration before being sent to the smelter. The vertical limits of the ore have not yet been determined, but certain silver mines have reached a depth of 1450 to 1500 feet, while most of the copper mines have gone to 1000 or 1500 feet. The history of this mining camp is full of interest. Butte in 1864 was a gold camp, but difficulties in working the gravels directed atten- tion to the mineral-vein outcrops, and unsuccessful attempts were made to work their copper and silver contents, so that it was not until 1875, following a period of quiescence, that the discovery of rich silver ore in. the Travona lode revived the mining industry of Butte. In 1877 several silver mines were opened, followed by others ; but this did not last many years, for with the drop in the price of silver many mines closed, although one, the Bluebird, had produced 2,000,000 ounces of silver from 1885 to 1892. The copper mines were worked to only a limited extent at first, and the industry did not assume permanence until 1879-1880, when matte smelting was introduced. In 1881 the Anaconda mine, which COPPER 287 was first worked for silver, began to show rich bodies of copper ore, and since then the output of copper has steadily increased, there being a number of large smelting plants distributed between Butte, Ana- conda, and Great Falls. Up to the end of 1896 the commercial value of the copper pro- duced was about $330,000,000. This greatly exceeds the total output of Leadville, and nearly equals the famous Comstock lode. W. H. Weed has estimated that up to January 1, 1897, the district had yielded 500,000 ounces of gold, 100,000,000 ounces of silver, and 1,600,000,000 pounds of copper. In 1887 Butte passed the Lake Superior District in the production of copper, and has kept ahead of it ever since, having in 1903 produced 38.9 per cent of the United States produc- tion. AND AMYGDALOID LAYERS ^^^^^ COPPER LODES IN CONGLOMERATE NO AMYGOALOIO LAYERS OR CLIFF t Lake Superior GEOLOGICAL CROSS-SECTION OF THE COPPER MINING REGION FIG. 55. Section across Keweenaw Point. After Rickard. Michigan (2,24-26). This region, which was discovered in 1830 by Douglas Houghton, a mining engineer, has become one of the most famous, and for some years one of the leading, copper-producing districts of the world. The' rocks of the region, known as the Keweenaw series, consist of steeply northwesterly dipping, interbedded lava flows, sandstones, and conglomerates. These form a belt from 2 to 6 miles wide, which extends from Houghton to the end of the Keweenaw peninsula, and rises as a ridge from 400 to 800 feet above the lake, being flanked on either side by Potsdam sandstone (Fig. 55). .The ore, which is native copper, and is occasionally asso- ciated with native silver, occurs (1) as a cement in the 288 ECONOMIC GEOLOGY OF THE UNITED STATES conglomerate of porphyry pebbles or replacing the latter; (2) as a filling in the amygdules of the lava beds ; (3) as masses of irregular and often large size, in veins with calcitic and zeolitic gangue. The veins, which cut both the igneous and sedimentary rocks, have yielded much copper in former years, and the large masses obtained from them have made the region famous; but at the present time about 75 per cent of the production comes from the Calumet conglomerate, while FIG. 56. Section showing occurrence of amygdaloidal copper, Quincy mine, Mich. After RicTcard, Eng. and Min. Jour., LXXVIII: 626, 1904. the balance comes from two other copper-bearing conglom- erates known as the Albany and the Allouez, and from the ash-beds and amygdaloids, whose gas cavities are filled with a mixture of native copper, calcite, and zeolites. A curious and hitherto unexplained feature is the irregu- lar distribution of the copper in the different beds. Thus the Calumet conglomerate carries practically no ore outside of the Calumet and Hecla ore shoot which is three miles long, 12-15 feet thick, and has been mined to a depth of 5000 feet. Various theories have been brought forward to account for the origin of the copper ores in this region. COPPER 289 That it is not a true contact deposit is shown by the fact that the amygdules in the diabase, the fissure veins, and the crevices in the broken pebbles are filled with copper, show- ing a subsequent deposition. The diabase was looked upon by Pumpelly (25 &) as a possible source of the ore, and since its extensive alteration was no doubt accompanied by the oxidation of protoxides, this might account for the reduc- tion of copper mineral to the native or metallic condition, it being known that ferrous salts may precipitate metallic copper (1). More recently Lane (25 a) has suggested that the ores were deposited chiefly by descending meteoric waters, because the more productive mines seem to be situated under the highest portions of the point, and hence were in the path of the descending waters. Such a theory, however, requires the topography to have been the same when the copper was deposited as it is now. Although these deposits have been worked in prehistoric times, as evidenced by copper implements and ornaments found in the mines, the famous Calumet and Hecla Mine was not opened up until 1846. In 1847 Michigan pro- duced 213 long tons of the total United States production of 300 tons of copper. Since 1863 the annual output has exceeded 1000 tons and has gradually and steadily increased, reaching 85,893 long tons in 1903, having a market value of $20,269,000. The ores from this district, which are known as Lake ores, are all of low grade, some running as low as .55 per cent native copper. Owing, however, to the brittle character of the gangue and the malleability of the ore, as well as their difference in specific gravity, it is possible to separate the two quite thoroughly by crushing in stamps and concentrat- 290 ECONOMIC GEOLOGY OF THE UNITED STATES ing by jigs, tables, etc. This concentrated material is then refined electrolyffcally. Arizona (8-16). This territory ranks third as a producer of copper ores in the United States, and differs from most other copper-producing localities in supplying chiefly ores of oxidized character ; in fact, from 1880 to 1895 Arizona was the only copper area in the world whose ores were exclusively oxidized. The territory contains four important districts, all lying within the mountain region, and which in the order of their importance are, (1) Bisbee or Warren, (3) Jerome or Black Range, (3) Clifton, Morenci, or Copper Mountain, and (4) Globe. In all except the second the modes of the ore occur- rences possess certain similarities. Bisbee or Warren District. This district (11,15), which contains the famous Copper Queen Mine, lies on the eastern slope of the Mule Pass Mountains, but a short distance from the Mexican boundary. The section at that locality involves strata from pre-Cambrian to Cretaceous age, with an im- portant unconformity between the Carboniferous and Cre- taceous (Fig. 57). Prior to the deposition of the latter the rocks had been broken by numerous faults, one of these, the Dividend fault, being specially prominent in forming one boundary of the ore-bearing area. This was followed by intrusions of a granitic magma forming dikes, sills, or irregular stocks, which have metamorphosed the Carbon- iferous limestones, with the production of characteristic contact minerals. The ore bodies, which are generally developed in the zone of metamorphic silicates surrounding the porphyry, as well as sometimes outside of it, form large, irregularly distributed, COPPER 291 but rudely tabular masses, which are generally parallel to the limestone bedding. As now found they consist of oxi- dized ores, such as malachite, azurite, and cuprite, above, which pass at variable depths into unaltered sulphides ; but between the two, or at least never far from the effects of GENERALIZED COLUMNAR SECTION OF THE ROCKS OF THE BISBEE QUADRANGLE. FIG. 57. Geological section at Bisbee, Ariz. After Ransome. U. S, Geol. Surv., Prof. Pap. 21. oxidation, masses of massive or sooty chalcocite are fre- quently found. The ore-bearing solutions are believed to have been stimu- lated by the porphyry and to have risen from an unknown source, but although they may have followed some of the 292 ECONOMIC GEOLOGY OF THE UNITED STATES GRANITE MINERALIZED CHALCOCITE OXIDIZED MINERALIZED CARBONIFEROUS PORPHYRY GRANITE COPPER LIMESTONE LIMESTONE PORPHYRY ORES fault fissures, the ore, which originally consisted of pyrite, chalcopyrite, and occasionally sphalerite, owes its deposition to metasomatic replacement in the limestone. As originally formed, the deposits contained too little copper to make them of commer- cial value, but they have been subse- quently enriched by concentration due to weather- ing in the upper pg part, and second- ary deposition of FIG. 58. Generalized section of ore bodies at Bisbee, chalcocite in the Ariz. After Ransome. underlying zone. Indeed it is said that nearly all the bodies of workable sulphides owe their value to its presence. The gossan of some of the ore bodies forms prominent ferruginous ledges, and while these rarely show surface in- dications of copper, still experience has shown that they are connected with underlying ore bodies; however, many of the latter have no outcrops. Although always important, this region assumed great prominence in 1903, due to the opening and extensive de- velopment of new ore bodies of great extent. Jerome District. This was the leading copper-producing district of Arizona for 1897 to 1900 inclusive, but then dropped to second place. The mode of occurrence of the ore differs markedly from that noted in other areas. It is bornite and chalcopyrite, which is associated with a sheared dike and fills fissures and impregnates the slate rock. PLATE XIX FIG. 1. Smelter of Arizona Copper Co., Clifton, Ariz. After Church, Min. Mag., X: 2, 1904. FIG. 2. View of Binghara Canon, Utah. After Boutwell, U. S. Geol. Surv., Prof. Paper 38, 1905. COPPER 293 Olifton District. In this district (12, 13), which ranks third among the Arizona copper districts, the conditions are in part similar to the Bisbee district in so far as the geologic section and the intrusion of porphyry and granite into the Palaeozoic sediments is concerned. They have likewise been broken by extensive fracturing and faulting, the faults sometimes having a throw of 1000 to 1500 feet, and there was also an extensive flow of Tertiary eruptives. The ore bodies differ from the Bisbee ones, however, in point of origin, being true contact deposits, the porphyry by contact influence having produced great masses of garnet Copper Mt Dike FIG. 59. Section of Morenci district. P, porphyry; S, unaltered sediments; F, fissure veins ; M , metamorphosed limestone and shale ; 0, contact meta- morphic ores ; R, disseminated chalcocite. After Lindgren, Eng. and Min. Jour., LX XVIII: 987, 1904. and epidote in the Carboniferous limestones ; and wherever alteration has not masked the phenomena, the metallic minerals, magnetite, pyrite, chalcopyrite, and sphalerite, are found accompanying the contact silicates, and often inter- grown with them in such a manner as to leave no doubt concerning the contact origin of the ores and the porphyry as their source. The concentration and commercial value of the ores is due, however, to later processes intimately connected with weathering. This has produced malachite and azurite in the gossan, but some of the copper has been carried to lower levels and precipitated as chalcocite. The sphalerite has been removed in solution as zinc sulphate, and the magnetite and garnet have yielded silica and limonite. 294 ECONOMIC GEOLOGY OF THE UNITED STATES The ore deposits in the limestone are irregular or tabular, due to the accumulation of the minerals along bedding planes, but in addition, fissure veins, cutting through many of the rocks, and of later age than the porphyry, are found. G-lobe District (14). While the most important deposits here occur in limestone, near the contact with granite and trachyte, still others are found as fissure, veins in sand- stone (Old Dominion Mine), or in slate and gneiss, or even veinlets in gneiss ; the ores are largely oxidized. The output of this district, which has been the least actively worked of any, though small for several years, increased greatly in 1901. Appalachian Region (42, 43) . The existence of copper in the Appalachian belt has been known for a number of years, but the copper-mining industry has not been active. The early attempts to work the deposits were chiefly to obtain both gold and copper, and resulted in failure, due chiefly to the low market values of copper ; hence for many years the deposits, with few exceptions, have been but little worked, and it is only recently that a demand for the metal and cheaper metallurgical treatment have revived copper mining. The deposits in many cases occur in metamorphic rocks scattered over a wide belt, but five important types are recognizable (42) : 1. True fissure veins, filled with quartz and copper, the vein crossing or conforming to the banding of the schists, and replacement of the wall rock being rare. The ores are bornite, with a little chalcopyrite and iron pyrite. The deposits at Virgilina, Virginia, belong in this group. 2. True fissure veins with auriferous quartz, chalcopyrite, COPPER 295 and pyrite formed chiefly by replacement. The fissures are usually found along sheeting planes, and the deposits at Gold Hill, North Carolina, are taken as a type of this group. 3. Pyrrhotite veins of the Ducktown type (36-38), filling true fissures, and consisting chiefly of pyrrhotite and pyrite with a little quartz. The ore has been formed by the replacement of a zone of sheeted rock, which was com- posed chiefly of metamorphic minerals, such as garnet, actinolite, epidote, pyroxene, etc., these latter being the products of alteration of a calcareous shale. The Duck- town ore body represents a type forming a belt extending all the way from Vermont to Alabama. They all show a gossan which can be mined for iron ore, while under this there is a zone of black copper, the result of local enrich- ment, which passes into the sulphide ore below. The copper is richest in those portions where the pyrrhotite predominates. The Ducktown ore, which has been worked for a number of years, averages 3.5 per cent copper as it comes from the mine. Some of the chambers are from 50 to 150 feet across, and from 25 to 150 feet high without timbering. The great gossan lead of Virginia and the copper de- posits of Ore Knob, North Carolina, also belong to this type. 4. The Catoctin type, representing segregations of native copper, copper oxides, and carbonates along shear zones in altered igneous rocks of Algonkian age, the ores extend- ing below ground water level. They are found at a num- ber of localities in the Appalachian and Piedmont plateau districts, usually in the Catoctin schist. The ore shows 296 ECONOMIC GEOLOGY OF THE UNITED STATES on the outcrop, but does not extend usually more than 50 to 60 feet below the surface. It is supposed to have been leached out of the vein walls. Occurrences of this type occur in Green County, Virginia. 5. Deposits of native copper along the contact of diabase and sandstone. These have been found in New Jersey (32, 33), but are unimportant, although the mines have been worked from time to time. Similar occurrences have been reported from Pennsylvania (34, 35) and Connecticut. Utah. This state ranks fourth among the copper-produc- ing regions of the United States. The most important dis- trict is that of Bingham Canon (44), in the Oquirrh range, southwest of Salt Lake City, and is unique in that it includes the oldest mining claim in the state. It moreover differs from the other important copper mining localities in the country, in having a considerable quantity of gold, silver, and lead associated with the copper. The rocks of this district include: (1) a great thickness of sedimentaries of Carboniferous age and divisible into a lower member consisting of massive quartzite with several interbedded limestones which carry most of the ore bodies in the camp, and an upper member of quartzite with black calcareous shales, sandstones, and impure limestones; (2) igneous rocks, which have pierced the entire series of sedimentaries, forming dikes, sills, or laccoliths, and consist- ing either of a type between diorite porphyrite and mon- zonite, which is closely associated with the ore bodies, or an andesite, having no relation to the ores. Folding, fracturing, and faulting have greatly complicated the structural relations of this region. The ores form lenses in the limestone, which lie roughly COPPER 297 parallel to its bedding, or occupy fractures or fissure zones. Copper, lead, silver, and gold may occur in either, but the copper rather favors the lenses, and the lead and silver the fissures. The mining operations have been based in turn on the oxidized gold ores, carbonate ores of lead and copper, sul- phides of lead, and finally sulphides of copper, which now constitute the mainstay of the district. These copper sul- phides are cupriferous pyrite, chalcopyrite, black sulphides (probably tetrahedrite), and chalcocite with a little galena, zinc, and siliceous gangue. The pyrite, which is widespread in the district, forms immense replacement bodies in the limestone, but is of secondary importance in the fissure zones. The Bingham ores are of low value, and bonanzas are rare ; indeed, the copper ores can often only be profitably worked because of their gold, lead, and silver contents. California. California (17, 18, 2) in 1903 was fifth in the list of copper-producing states, and owes its position to the output from Shasta County in the northern part of the state. This region lies at the northern end of the Sacramento Valley, and contains a series of sedimentary rocks, ranging from Devonian to Miocene and pierced by igneous intrusions. Folding, faulting, and shearing are common. The ore is found either : (1) as sulphide deposits in contact zones, between diabase dikes and Carboniferous limestones; or (2) as bodies of sulphides, in shear zones, the latter having been mineralized with the development of irregular ore bodies of variable size. The ores are rare generally in the metamor- phosed igneous rocks. Superficial alteration has produced a gossan which may show a thickness of as much as 100 feet at some localities (Iron Mountain). 298 ECONOMIC GEOLOGY OF THE UNITED STATES The important districts are the Iron Mountain and Bully Hill. In both, the ores are chalcopyrite and pyrite, but that from the latter district also contains some bornite and chalcocite. An analysis of the Iron Mountain ore gave, Cu, 7.45 per cent; S, 45.60 per cent; Fe, 36.97 per cent; Zn, 3.41 per cent ; SiO 2 , 5. 62 per cent ; A1 2 O 3 , 1.57 per cent; Moisture, 0.88 per cent. This is probably higher than the average in cop- per. Copper deposits are also known in other parts of California (17). Other Occurrences. Colorado has few copper mines proper, but many of the ores mined in the state carry copper, and it is util- ized by lead smelters as a carrier in the extraction of other metals. Copper is mined in New Mexico and Idaho, the Seven Devils Dis- trict of the latter state being well known (23). The Grand Encampment district of southern Wyoming (50) has also supplied more or less ore, and a small amount is mined in Missouri (28). Copper has been found at several localities in Alaska (4-7), but no shipments were made prior to 1903. Uses of Copper. Since prehistoric times copper alloyed with tin has been used in various parts, of the world for the manufacture of bronze. Thus it was used for this purpose in Homeric times, and it is found in the lake dwellings of OXIDIZED ORES (ENRICHED SULPHIDES \/'\ GOSSAN FIG. 60. Section of ore body at Bully Hill, Calif. After Diller. COPPER 299 Switzerland. The bronze found in Troy contains a very little tin, and since this metal is not found in the excavations in the West, it seems probable that the bronze was made in Asia, perhaps in China or India, by some secret process and imported to the western countries. By an alloy of copper and tin, although both metals are soft, a comparatively hard metal is produced. The properties of this alloy, bronze, vary greatly according to the proportions of the two metallic constituents, and these vary with the use for which the alloy is intended. United States ordnance is 90 per cent copper and 10 per ceat tin, while ordinary bell metal is about 80 per cent copper, though the percentage varies with the tone re- quired. Statuary bronze is generally an alloy of copper, tin, and zinc ; and, in these various bronzes, the color varies from copper-red to tin-white, passing through an orange-yellow. An alloy of copper and zinc produces brass, which is found of so much value for small articles used in building and for ornamental purposes in machinery. Copper is also used in roofing and plumbing. A large supply of this metal is made into copper wire, and the most important present use of copper is in electricity, for which its high conductivity especially fits it for the transmission of electric currents. Production of Copper. The production of copper in the United States has increased steadily and rapidly in the last fifty years, placing the United States in the lead of the world's copper producers. This increase can be seen from the table given below : 300 ECONOMIC GEOLOGY OF THE UNITED STATES PRODUCTION OF COPPER IN UNITED STATES FROM 1845 TO 1903 YEAR PRODUCTION LONG TONS YEAR PRODUCTION LONG TONS 1845 100 1885 74,052 1850 650 1890 115,996 1855 3,000 1895 169,917 1860 7,200 1900 270,588 1865 8,500 1901 268,782 1870 12,600 1902 294,423 1875 18,000 1903 311,627 1880 27,000 PRODUCTION OF COPPER IN THE UNITED STATES BY STATES (In pounds) SOURCE 1901 1902 1903 130,778,511 119,944,944 147 648 971 California 33,667,456 25,038 724 17 776 756 Colorado 1 9,801,783 8 422 030 4 158 368 156,289 481 170 609 228 192 400 577 Montana . 229 870 415 288 903 820 272 555 854 New Mexico 9 629 884 6 614 961 7 300 83 9 Utah 20 116 979 23 939 901 38 30 60 Eastern Atlantic States . . 1 All others 6,860,039 4 526 341 13,599,047 1 935 989 13,855,612 3 546 645 Of the several producing states Montana has for some years been the first, with Michigan second and Arizona third. The marked decrease of Montana in 1903 was due to litigation and labor troubles. 1 Including copper smelters purchasing copper ore and mattes in the open market, sources not known. COPPER 301 WORLD'S PRODUCTION OF COPPER IN LONG TONS COUNTRY 1903 Chile 30,930 Germany 21,205 Japan 31,360 Mexico 50,480 Spain and Portugal 49,740 United States 311,627 All others : 89,739 The total value of the imports of copper (including ore, matte, and manufactured copper) in 1903 was 20,441,977, while the total value of the exports covering the same class of materials was $44,365,155. REFERENCES ON COPPER GENERAL. 1. Biddle, Jour. Geol., IX: 430, 1901. (Origin.) 2. Weed, Miu. Mag., X:185, 1904. (United States.) 3. Winchell, Geol. Soc. Amer., Bull. XIV: 269, 1903. (Origin.). Alaska : 4. Brooks, Eng. and Min. Jour., LXXIV : 13. (Tanana and Copper River regions.) 5. Mendenhall and Schrader, U. S. Geol. Surv., Bull. 213 : 141, 1903. (Mt. Wrangell region.) 6. Rohn, U. S. Geol. Surv., 21st Ann. Rept., 11:893, 1900. (Chitina River and Skolar Mts.) 7. Schrader, U. S. Geol. Surv., 20th Ann. Rept., VII: 341, 1900. (Prince William Sound and Copper River district.) Arizona : 8. Blandy, Eng. and Min. Jour., LXIV : 97, 1897. (Ariz.) 9. Church, Amer. Inst. Min. Engrs., Trans. XXXIII : 13, 1903. (Tombstone district.) 10. Douglas, Min. Indus., VI : 227, 1898. 11. Douglas, Amer. Inst. Min. Engrs., Trans. XXIX : 511, 1900. (Copper Queen Mine). 12. Lindgren, U. S. Geol. Surv., Bull. 213 : 133, 1903. (Clif- ton district.) 13. Lindgren, Amer. Inst. Min. Engrs., Trans. XXXV, 1905. (Clifton district.) 14. Ransome, U. S. Geol. Surv., Prof. Paper 12, 1903. (Globe district.) 15. Ransome, U. S. Geol. Surv., Prof. Paper 21, 1904. (Bisbee district.) 16. Wendt, Amer. Inst. Min. Engrs., Trans. XV: 25, 1887. California : 17. Aubury, Calif. State Mining Bureau, Bull. 23, 1902. 18. Diller, Eng. and Min. Jour., LXXIII:857, 1902. (N. Calif.) Colorado: 19. Emmons, Tenth Census, XIII : 68, 1880. (Gilpin Co.) 20. Spencer, U. S. Geol. Surv., Bull. 213:163, 1903. (Pearl, Colo.) 21. Emmons, U. S. Geol. Surv., Bull. 260:221, 1905. (Red Beds, Colo, plateau.) 302 ECONOMIC GEOLOGY OF THE UNITED STATES Georgia: 22. Weed, U. S. Geol. Surv., Bull. 225:180, 1904. Idaho: 23. Lindgren, Min. and Sci. Pr., LXXVIII:125, 1899. (Seven Devils district.) Michigan : 24. Irving, U. S. Geol. Surv., Mon. V, 1883, also 3d Ann. Kept. : 89, 1883. 25. Lane, Amer. Geol., XXII : 251, 1898. (Magmatic differentiation in copper rocks.) 25 a. Lane, Mich. Miner, Jan.-Feb., 1904. 256. Pumpe]ly, Mich. Geol. Surv., I, pt. 2 : 14. 26. Rickard, Eng. and Min. Jour., LXXVIII:585, 625, 665, 745, 785, 865, 905, 1025, 1904. Missouri : 27. Nicholson, Arner. Inst. Min. Engrs., X : 444, 1881. (St. Genevieve district.) 28. Bain and Ulrich, U. S. Geol. Surv., Bull. 260 : 233, 1905. (General.) Montana: 29. Weed, U. S. Geol. Surv., Bull. 213:170, 1903. (Butte.) 30. Winchell, Eng. and Min. Jour., LXXVII : 782, 1904. 31. Winchell, Geol. Soc. Amer., Bull. XIV: 269, 1903. New Jersey: 32. Kiimmel, N. J. Geol. Surv., Ann. Kept., 1899 : 171, 1900. 33. Weed, U. S. Geol. Surv., Bull. 225 : 187, 1904. (Griggstown.) - Pennsylvania : 34. Bailey, Eng. and Min. Jour., XXXV : 88, 1883. (Adams County.) 35. Lyman, Jour. Franklin Inst., CXLVI:416, 1898. (Bucks and Montgomery counties.) Tennessee: 36. Hen- rich, Amer. Inst. Min. Engrs., Trans. XXV : 173, 1896. (Ducktown.) 37. Kemp, Amer. Inst. Min. Engrs., Trans. XXXI : 244, 1902. (Ducktown.) 38. Weed, Amer. Inst. Min. Engrs., Trans. XXX: 449,1901. (Southern Appalachians.) Texas: 39. Schmitz, Amer. Inst. Min. Engrs., Trans. XXVI : 97, 1897. (Permian ores.) United States: 40. Douglas, Amer. Inst. Min. Engrs., Trans. XIX: 678, 1891. 41. Stevens, Copper Handbook, published an- nually at Houghton, Michigan, by the author, $5. 42. Weed, U. S. Geol. Surv., Bull. 213 : 181, 1903 (Appalachians) ; and Bull. 260 : 217, 1905. (E. U. S.) 43. Weed, U. S. Geol. Surv., Bull. 260 : 211, 1905. (U. S. localities and industry.) Utah : 44. Boutwell, U. S. Geol. Surv., Bull. 213 : 105, 1903. (Bingham.) Also U. S. Geol. Surv., Prof. Paper 38, 1905. Vermont: 45. Weed, U. S. Geol. Surv., Bull. 225: 190, 1904. 46. Smyth and Smith, Eng. and Min. Jour., April 28, 1904. Virginia: 47. Watson, Geol. Soc. Amer., Bull. XIII: 353, 1902. (Virgilina district.) Wisconsin : 48. Grant, Wisconsin Geol. and Nat. Hist. Surv., Bull. No. 6, 1901. (Douglas Co.) Wyoming : 49. Kennedy, Eng. and Min. Jour., LXVI : 640, 1898. 50. Spencer, U. S. Geol. Surv., Bull. 213 : 158, 1903. (Encampment region.) CHAPTER XVI LEAD AND ZINC THESE two ores can hardly be treated separately for the reason that they occur so often associated with each other ; the combination of lead and silver, of importance in the Rocky Mountain region, is treated under a separate head. Ores of Lead. The ores of lead, together with their com- position and the percentage of lead which they contain, are : Galena, PbS, 86.4; Cerussite, PbCO 3 , 77.5; Anglesite, PbSO 4 , 68.3; Pyromorphite, Pb 3 P 2 O 8 + J PbCl 2 , 76.36. Of these, galena is the commonest, while the other two are usually found in those localities where superficial oxidation of the ore deposit has taken place. The lead obtained from argentiferous ore is commonly spoken of as desilverized or hard lead, while that from non-argentiferous ones, such as those of the Mississippi Valley areas, is known as soft lead. Ores of Zinc. The ores of zinc, together with the per- centage of zinc they contain, are : Sphalerite, ZnS, 67 ; Smithsonite, ZnCO 3 , 51.96 ; Calamine, H 2 Zn 2 SiO 5 , 54.2; Zincite, ZnO, 80.3; Willemite, Zn 2 SiO 4 , 58.5; Franklinite (FeZnMn)O(FeMn) 2 O 3 , composition vari- able but containing about 51.8 Fe and 7.5 Mn. 304 ECONOMIC GEOLOGY OF THE UNITED STATES Of these ores, sphalerite (also known as blende, jack, or black-jack) is by far the most important, except in northern New Jersey, where it is practically lacking and franklinite and willemite abound. With few exceptions, zinc is con- stantly associated with lead, and at times, as in portions of the Cordilleran region, carries silver or even gold. Calcite, dolomite, and pyrite are common gangue minerals of non-argentiferous lead, and zinc ores, and others may occur at certain localities. In the argentiferous ores, quartz is probably the commonest gangue mineral, but there may be other less important ones. Iron, lead, and manganese are not uncommon impurities in zinc ores, and those of Missouri contain small amounts of cadmium, but this is not injurious, as it is more volatile than the zinc and easily driven off by heat. Argentiferous lead ores sometimes contain antimony, arsenic, and iron as impurities. Those of the Appala- chians, which are practically non-argentiferous, are free from most of these. Neither lead or zinc ores are restricted to any one forma- tion, but the majority of economically valuable deposits of these metals, without silver, gold, or copper, are found in the Paleozoic formations, although a few are known in pre- Cambrian rocks. They exist as disseminations, chamber deposits, as filling in brecciated zones, in gash veins and replacements. While the metallic contents of the ore as mined is often low, still, owing to the great difference in gravity between ore and gangue (excepting pyrite), it is often possible to separate them by mechanical concentration ; and for the zinc ores magnetic separation has been success- fully tried. LEAD AND ZINC 305 Superficial Alteration of Lead and Zinc Ores. Galena is often altered near the surface to anglesite or cerussite. The former, however, is unstable in the presence of carbonated waters and changes readily to carbonate. Phosphates are developed in rare instances. Sphalerite, the common ore of zinc, is often changed super- ficially to smithsonite, hydrozincite, or calamine. Such oxi- dized ores are of greater value than unoxidized ones, because FIG. 61. Map showing distribution of lead and zinc ores in United States. Adapted from Ransome, Min. Mag., X: 1. although carrying a lower percentage of zinc, they occur in a more concentrated form and yield more easily to metal- lurgical treatment. Distribution of Lead and Zinc Ores in the United States. The occurrence of lead or zinc with gold, silver, and copper is confined chiefly to the Cordilleran region, and shows a most varied mode of occurrence; but commercially valuable deposits of lead alone, or lead and zinc, are confined to the 306 ECONOMIC GEOLOGY OF THE UNITED STATES Mississippi Valley, while those of zinc alone or with little lead are restricted to the Appalachian region as seen below. Lead Alone. Appalachian Belt (11, 25, 29). Lead (some- times argentiferous) occurs at a number of localities from Maine to Georgia, filling small veins in metamorphic rocks, and the deposits have at various times aroused temporary interest. There is no likelihood of their ever becoming im- portant producers, although exciting rumors regarding them are occasionally circulated. Southeastern Missouri (12, 18, 19).- This area forms a subdistrict of the Ozark lead and zinc region, to be mentioned later. The galena is found in Lower Silurian lime- stones, the larger lead deposits oc- curring in mas- pncAMBR.AN Fas!" MOTTE PIERRE rnm POTO8) ma r WHWH " sive strata near l> IGRANIT JT HE ORE OCCURS FIG. 62. Generalized section of Southeastern Missouri the base, Called lead region. After Bain. ^ J()gepll stone, while others with a little zinc are in the cherty Potosi limestone near the summit ; the sandstone layers are barren. The ore forms great impregnations, but cavern or vein de- posits so common in other parts of Missouri are wanting in this region; while many small faults occur, the ore sel- dom favors, them. The origin of these ores is treated under lead and zinc. The average ore runs from 6 to 8 per cent galena; when roughly handpicked, 10 to 12; and subse- LEAD AND ZINO 307 quent jigging of the crushed ore brings the galena contents up to 60 or 70 per cent. The Missouri lead mines were worked at a very early date for making bullets, and their product is said to have been used during the Revolution. Desilverized Lead. The important localities supplying this type of lead are described under lead-silver ores, but brief reference may be made to them here. Idaho is the most important producer, more than 96 per cent coming from the Coeur d'Alene district. In Utah much is ob- tained from the Park City district of Summit County, the Bingham Canon and Cotton wood districts of Salt Lake County, and the Tintic district of Juab County. Colorado's main supply is yielded by the Leadville mines in Lake County and 'the Aspen mines of Pitkin County, while smaller amounts are obtained from Creede, Lake City, Ouray, and Rico. (See Lead-Silver references, also map, Fig. 73.) (28.) Comparatively little lead is produced in the western states, except in the three mentioned above. As pointed out by Bain, the important lead ores of this region are closely associated with both igneous and sedi- mentary rocks. At Leadville, Aspen, and Park City the sediments are dolomites and limestones, and at Coeur d'Alene they are shales and quartzites. While the ores seem to favor igneous associations, still the larger bodies are found where both classes of rocks occur. Zinc Ores. The zinc-producing regions of the United States are the eastern and southern states, the Mississippi Valley, and the Rocky Mountain region. 308 ECONOMIC GEOLOGY OF THE UNITED STATES The ore from the different districts varies in grade, associa- tions and mode of occurrence. In tonnage terms, the main zinc-producing districts are the Joplin, Missouri, Sussex County, New Jersey, and Colorado. The Joplin ores are the main source of supply of the Kansas, Missouri, and Illinois smelters, but Colorado and even British Columbia ore is shipped to Kansas. Most of the New Jersey ore is used for zinc oxide, but smaller amounts are exported or used for spelter. Eastern and Southern States. The localities where zinc alone occurs are Sussex County, New Jersey ; Saucon Valley, Pennsylvania ; and the Virginia-Tennessee belt. Of these the first is the most important, and the third yields a little lead. Sussex County, New Jersey (20-22). The output of these mines is second in importance to those of the Mississippi Valley region. The district includes two general mining areas situated close together, the one called Mine Hill, at Franklin, and the other called Sterling Hill, at Ogdens- burg, two miles farther south, but not now worked. The ore-bearing minerals, which represent a unique type of OQCurrence, consist of franklinite, zincite, willemite, and calamine, the typical ore being a granular mixture of frank- linite and calcite, with zincite and willemite scattered through it. /Manganese minerals are klso present, thus giv- ing a combination of three common elements, viz., man- ganese, zinc, and iron. The average mineralogical composition of the Franklin Furnace ore (Ingalls) is franklinite, 51.92; willemite, 31.58 ; calcite, 12.67 ; zincite, .52 ; other silicates, 3.31 ; LEAD AND ZINC 309 while the average chemical composition is : Fe 2 O 8 , 32.06 ; MnO, 11.06 ; ZnO, 29.35; CaCO 3 , 12.67; silica and in- soluble matter, 14.57. The ore body at both localities is interbedded with a white crystalline limestone of probably pre-Cambrian age, which in turn rests on gneiss. The Ogdensburg ore deposit forms a great hook, giving two veins apparently, and the ore body seems to be an impregnated streak of limestone ; while at Mine Hill the northerly pitching ore body is also FIG. 63. Model of Franklin zinc ore body. After Nason, Amer. Inst. Min. Engrs., Trans. XXIV: 127. a synclinal fold, whose southern end in addition appears to be doubled over into an anticline. In both cases the wall rock is heavily impregnated at the bends of the fold with franklinite and other minerals, while the ore bodies are pierced by intrusive rocks. The origin of these de- posits is of unusual interest, for they not only contain in abundance a number of zinc minerals rare or unknown elsewhere, but many other mineral species as well. No sulphides of either zinc or iron have been noted, to suggest a derivation from that source, and faults which might serve as ore channels are likewise lacking, consequently their origin is difficult to explain. 310 ECONOMIC GEOLOGY OF THE UNITED STATES Kemp (20) considers that the ore was probably deposited from solutions stimulated by intrusions of granite, and sub- sequently metamorphosed, but Wolff (21) suggests that they are contemporaneous in form and structure with the in- closing limestones, and hence older than the granites. The extent to which they have been metamorphosed has served to hide their original character, and theories regarding their possible origin have been largely speculative. FIG. ()4. Section of Bertha zinc mines, Wythe Co., Va., showing irregular surface of limestone covered by residual clay bearing ore. After Case, Artier. List. Min. Engrs., Trans. XXII: 520. These ore bodies are of some historic interest, having been prospected as early as 1640 and mined in 1774. The Mine Hill deposits were worked for iron ore as early as the beginning of the last century, the zinc mining having begun about 1840. The ores are now treated by magnetic sepa- rators, which remove the franklinite and garnet from the willemite and zincite, while the calcite is taken out by jigging. The zinc ores are used for metallic zinc and zinc white, and the manganese for Bessemer steel. Virginia-Tennessee Belt (32-35, 26, 27). Zinc and some lead occur in a belt extending from southwest Virginia into Tennessee. The ores are intimately associated with Cambro-Ordovician limestone, and show two types, viz. : (1) secondary or weathered ores, including calamine, smith- LEAD AND ZINC 311 sonite, and cerussite, which are concentrated in the residual clays next to the irregular weathered surface of the lime- stone (PL. XVII, Fig. 2); and (2) primary ores, including sphalerite, galena, and some pyrite, belonging to the dis- seminated replacement breccia type, and which have been localized by ground waters along the crushed and faulted axes of the folds. The gangue minerals are chiefly calcite, dolomite, and some barite. . Fluorite is known, and quartz may occur in the form of chert. One deposit only, in Albe- marle County, is found in schist, and is closely associated with igneous rocks. Pennsylvania (25 a). The Saucon Valley deposits promised at one time to become prominent producers, but have not, owing more to geological conditions than actual scarcity of ore. Lead and Zinc Ores of the Mississippi Valley Region. This includes two important areas, viz., the Upper Missis- sippi Valley and the Ozark Region. Upper Mississippi Valley Area (36,8,9). This area em- braces southwestern Wisconsin, eastern Iowa, and north- western Illinois, but the first-named state contains the most productive territory. The section in the Wisconsin area, which may be taken as typical, involves the following formations, beginning at the top : Niagara limestone Silurian. Cincinnati (Maquoketa) shales Galena limestone 250 ft. Trenton limestone . . . . 40-100 ft. St. Peter's sandstone .... 150 ft. Lower magnesian limestone, 100-250 ft. 1 Potsdam sandstone 700-800 ft. Cambrian ' 312 ECONOMIC GEOLOGY OF THE UNITED STATES A bituminous shaly layer, known as the oil rock, occurs at the base of the Galena, and below it, or at the top of the Trenton, is a fine-grained limestone called the glass rock. While the series as a whole shows a very gentle southwest dip, there are a few low folds. The ore-bearing minerals, consisting of galena, smith- sonite, and sphalerite, associated with marcasite and some J TRENTON JLIMESTONE I GLASS ROCK 1 GALENA LIMESTONE' FIG. 65. Section showing occurrence of lead and zinc ore in Wisconsin, show- ing fissure ore in flats and pitches, and disseminated ore in oil rock. After Bain. calcite, occur as disseminations, as honeycomb masses in brecciated or porous limestone, and in crevices. The last type, which forms the most important source of the ore, consists of a vertical fissure, which at its lower end splits into two horizontal branches called flats, while these in turn pass into a steeply dipping fissure termed pitches (Figs. 42 and 65). There are at times several flats. Galena commonly predominates in the crevices, while sphalerite occurs in great abundance lower down. The main crevices extend approximately east and west, but there are other LEAD AND ZINC 313 less important intersecting fissures. The Galena limestone is the most important ore-bearing formation, but ore is also known to occur in the lower-lying limestones and sandstones, although no deposits have been worked in them. In the crevices the order of deposition is mar- casite, sphalerite, and galena. The ores, are frequently oxidized, yielding smithsonite and some calamine. A careful study of the origin of the ore bodies indicates that the metallic minerals have been gathered by circulat- ing meteoric waters from the Galena limestone ; these waters entered the limestone probably from the northeast, where the overlying shales had been eroded, and moved to the southwest. The ore was precipitated in crevices as sul- phides, either because of a reducing action exerted by bitu- minous matter present in. the rocks or hydrogen sulphide. Surface waters descending crevices have produced a sec- ondary concentration, which has resulted in a separation of the zinc and galena, accompanied by a transferal of much of the former to lower levels. Lead was discovered in the Upper Mississippi area as early as 1692, and the first mining was done in Dubuque in 1788. The early work was restricted to lead mining entirely, the zinc ores being disregarded. Owing to uncertainty regarding the size of the deposits, the mining for many years has been done in a most primitive manner, but more re- cently prospecting at lower levels and the discovery of new ore bodies has stimulated the erection of better plants. Mechanical concentration methods have also been introduced, and while the galena can be sepa- rated quite thoroughly from the sphalerite and marcasite, the last two are parted with difficulty. On account of the presence of marcasite in most of the mines, the zinc ores of this district command a lower price than those from other areas. For this same reason much of the ore cannot be used for spelter, but is employed for zinc oxide and sul- phuric acid manufacture. 314 ECONOMIC GEOLOGY OF THE UNITED STATES Louis Ozark Region (12,13,15,17). The position of the region is shown on the map, Fig. 66. The southern part of the area is underlain by Carboniferous sandstone and shales, while the northern part, forming the Ozark plateau, and containing the lead and zinc deposits, is underlain by slightly disturbed sedimentaries. In the eastern part of the plateau, or Salem Upland, they are Cambro-Silurian dol- iemphis FIG. 66.-Map of Ozark region. After Branner, omites and magne- sian limestone, while those of the western portion, or Springfield Upland, are Lower Carboniferous limestones. Within this region the following four districts are recognized : 1. Southeastern Missouri, yielding lead from dissem- inated ores. This area has been mentioned under Lead Alone. 2. Southwestern Missouri, or the Missouri-Kansas dis- trict, with Joplin as the most important mining town. It yields chiefly zinc, with some lead. The ore occurs in limestones of Subcarboniferous age, filling fissures, as a cement of brecciated patches, or more rarely parallel to the bedding. The ore bodies are sometimes hundreds of feet in diameter. In some cases the ore extends to the LEAD AND ZINC 315 surface, and is then usually surrounded by more or less residual clay. 3. Central Missouri district, containing small deposits of both lead and zinc. In this area the ore as far as exploited occurs rather in vertical crevices or chim- neys than in brec- cias. 4. The northern Arkansas district, but partly devel- oped, and with E3 ^ HI SSI 13 CAMBRO-SILURIAN DEVONO- LOWER UPPER ORE . -i LIMESTONE CARBONIFEROUS CARBONIFEROUS CARBONIFEROUS many riCil OreS, OC- SHALE LIMESTONE SHALES -,_,-.-, FIG. 67. Generalized section showing occurrence of CUrring as I lead and zinc ore in sou thwest Missouri. After deposits (dissem- Bam ' inations), veins (in faults or filling breccias), or as altera- tions. The common ores are sphalerite and galena, with a gangue of secondary chert, dolomite, calcite, and barite. Residual clays occur in some mines, and bitumen is not uncommonly found with the ores. These deposits afford an interesting example of the para- genesis of minerals, the succession seeming to be (Win- slow, Trans. Am. Inst. Min. Engrs., p. 651, 1893) dolomite, blende, galena, barite, calcite, and pyrite. The ores of this region are mechanically concentrated after mining, and the composition of an average sample of 3800 carloads of blende shipped from the Joplin district in the first part of 1904 is given by Ingalls as : Zn, 58.26 ; Cd, .304; Pb, .70; Fe, 2.23; Mn, .01; Cu, .049; CaCO 3 , 316 ECONOMIC GEOLOGY OF THE UNITED STATES 1.88; MgCOj, .85; SiO 2 , 3.95; BaSO 4 , .82; S, 30.72; total, 99.773. Origin of the Ores. Most of the theories of the origin of these ores agree in considering that their concentration has been caused by circulating meteoric waters which have collected the ore particles from the limestones, although in one instance at least they seem to be associated with FIG. 68. A typical hoisting outfit in the southwestern Missouri zinc region. Photo, by H. F. Bain. igneous intrusions (19). Analyses of the limestones show amounts of from .001 to .015 per cent of lead and zinc in the Cambro-Silurian magnesian limestones and Archaean rocks to the southeast of the region, and from .002 to .003 per cent in the Lower Carboniferous limestones. These aver- ages calculated give 87 pounds of galena per acre in a one-foot layer, and 261 pounds of blende in the same volume of rock. W. P. Jenney, who studied the deposits in some detail, has emphasized the importance of ascend- LEAD AND ZINC 317 ing waters, while Winslow has argued for their concen- tration by descending currents. The more recent studies of H. F. Bain indicate that both ascending and descending waters were active, and that the chemical reactions involved were characteristic of dilute solutions; rich ores, therefore, indicate great aqueous activity. The more important circulations have occurred in the Cambro-Silurian limestones and those of the Mississippi or Lower Carboniferous series, but the concentration pro- cess has been often repeated in many different horizons and at different depths. The chemical changes which took place in the primary concentration of the ores were the oxidation of sulphides to sulphates, the transportation of these in solution, and their reprecipitation as sulphides in favorable localities. The localization of the ore bodies has been due to the pres- ence of fissures which permitted the mixing of the ore-bear- ing solutions, but the circulation of the latter has been limited in many instances by impervious beds of shale, and organic matter has served as a reducing agent. All of the ores are found to be closely associated with lines of sub- terranean seepage, and since the open character of the brec- cias favored circulation, much ore is found in them. Where folding has occurred, the water has also sought the troughs of synclines as in the Lake Superior district. In the section presented in the Ozark region, the Devono- Carboniferous shales and the undifferentiated Carboniferous shales afforded impermeable barriers to circulation. The former, where not faulted, held down the ascending solu- tions; but where absent or fissured, the solutions from the 318 ECONOMIC GEOLOGY OF THE UNITED STATES underlying Cambro-Silurian formation were able to pass up- ward into the Mississippian and impregnate them. The Cambro-Silurian ores were first concentrated by deep circulation, and formed the disseminated ores. Later, when erosion cut away the Devono-Carboniferous capping, further concentration took place by descending solutions, giving rise to the ore bodies in crevices, breccias, and synclines. Two concentrations have occurred in the Mississippian limestones. The ore bodies are of two types, viz. : (1) those containing sulphides and clean untarnished minerals, the result of pri- mary concentration ; and (2) those due to surface concen- tration, and containing oxidized ones with red clay. The ores pass into sulphides below the water level. Where ascending solutions alone acted, the ore bodies are less rich but more reliable, however secondary enrichment of the deposits has been marked. Rocky Mountain States (28) . Although much ore is mined in this region, its resources of this rnetal are still largely undeveloped, and up to 1903 most of the ore mined was either shipped to Kansas smelters or exported. The recent construction of a zinc-smelting plant at Pueblo, Colorado, and the enlargement of the oxide plant at Canyon, Colorado, has largely stimulated the production of both that state and Utah. The zinc-producing localities of Colorado are chiefly the same as those yielding lead, Leadville being the largest pro- ducer. According to Ingalls the zinc shipments average about 25 per cent Zn, 10 Pb, 2.2 Fe, 4 SiO 2 , 39 S, and 10 oz. Ag. Much zinc ore is also supplied by the mines at LEAD AND ZINC 319 Creede (Ingalls), where it is concentrated to a product assaying 55-59 per cent Zn, 3.75-6 Pb, and 1.1-2.1 Fe, which is shipped to Kansas. The blende carries 2-3 oz. Ag per T. Blende concentrates are also produced at Mon- tezuma and Rico, Colorado. The Colorado ores are usually of lower grade than the Joplin ones, and their complex nature makes treatment difficult ; indeed until recently zinc has been a source of loss to the miners and smelters, those ores high in zinc being either neglected or thrown out. In addition to Colorado, New Mexico produces considerable ore, the deposits near Hanover yielding blende and smith- sonite (28) from Carboniferous limestone near igneous con- tacts. It was shipped to Wisconsin for treatment. Utah, Idaho, and Montana will no doubt also become important sources of supply in the future. Uses of Lead and Zinc. Both of these are important base metals, although in value of production they rank below gold, silver, copper, and iron, neither do they come into competi- tion with these, for they lack the high tenacity of iron and steel, the conductivity of copper, and the value resulting from scarcity possessed by gold and silver. They are of value, however, on account of their high malleability and the application of their compounds for pigments. Uses of Lead. Lead finds numerous uses in the arts, the most important being for white lead. Litharge, the oxide of lead, is used not only for paint, but also somewhat in the manufacture of glass, although red lead is more frequently employed instead. A further use of lead is for making pipe for water supply, sheet lead for acid chambers, and shot. 320 ECONOMIC GEOLOGY OF THE UNITED STATES Among the alloys formed by lead are type metal (lead, anti- mony, and bismuth, with copper or iron), white metal, organ pipe composition, and fusible alloys used in electric lighting. In addition to these, the acetate, carbonate, and other com- pounds are used in medicine. In smelting, lead is used to collect the gold and silver, and the bulk of the lead of com- merce is obtained as a by-product in the smelting of the precious metals. Uses of Zinc. Metallic zinc is used for a variety of purposes, partly owing to its slight alteration in air, and secondly, because it can be rolled into thin sheets. In this condition it is used extensively for roofing and also for plumb- ing, and as a coating to iron this metal is extensively called for in galvanizing. One of the most important applications is for making brass, which is ordinarily composed of from 66 to 83 parts of copper and 27 to 34 parts of zinc. The composition varies, entirely depending on the use to which it is to be put, and, with the variation in proportion, the color becomes more golden, or whiter, according as the percentage of copper is increased or decreased. With an increase in the amount of zinc, the alloy becomes more fusible, harder, and more brittle. Brass was made long before zinc, as a metal, was discovered, and Aristotle says that the people by the Euxine Sea made their copper a beautiful whitish color by mixing it with a white earth found there. Strabo also tells us that the Phrygians made brass in this way. White metal is an alloy of zinc and copper in which zinc predominates, and which is often employed for making buttons. Imitation gold is also made by alloying zinc with a predominance of copper, varying from 77 to 85 per LEAD AND ZINC 321 cent of the mass, and this is in common use as " gold foil " for gilding. Zinc is also made use of in the construction of electric batteries. German silver has 60 parts copper, 20 zinc, and 20 nickel. Its use is for mathematical and scientific instruments. Production of Lead and Zinc. The production of lead in the United States from 1825 to 1900 was as follows : YEAR SHORT TONS YEAR SHORT TONS 1895 1 500 1875 59,640 1835 13,000 1885 129,412 1845 30000 1895 .... 170 000 1855 . . . . 15 800 1900 270 824 1865 14,700 About 70 per cent of the lead produced in the United States is derived from five districts, viz. : Southeastern Mis- souri ; Joplin, Missouri ; Leadville, Colorado : Park City, Utah ; and Cceur d'Alene, Idaho. LEAD CONTENT OF ORES SMELTED IN THE UNITED STATES FROM 1901 TO 1903 1901 1902 1903 Colors, do Short tons 73265 Short tons 51 833 Short tons 45554 Idaho 79,654 84,742 99,590 Utah . 49,870 53,914 51,129 Miontana . 5791 4438 3,303 New Mexico 1,124 741 613 1,873 1,269 2,237 Arizona 4,045 599 1,493 California 381 175 55 Washington ] r 1,457 538 Oregon, Alaska, South Dakota, !- Texas J 1,029 I 2,184 1,765 Missouri, Kansas, Wisconsin, Illinois, Iowa, Virginia, Kentucky .... . 67172 79445 86597 Total . 284 204 280 797 292 874 322 ECONOMIC GEOLOGY OF THE UNITED STATES The production of spelter in the United States from 1873 to 1900 was : YEAR SHORT TONS YEAR SHORT TONS 1873 7,343 1890 63,683 1880 23,239 1895 89,686 1885 40688 1900 1 9 3 886 PRODUCTION OF SPELTER FROM 1901 TO 1903 BY STATES EASTERN ILLINOIS AND SOUTHERN AND INDIANA KANSAS MISSOURI COLORADO TOTAL STATES Short tons Short tons Short tons Short tons Short tons Short tons 1901 8,603 44,896 74,240 13,083 140,822 i 1902 12,180 47,096 86,564 11,087 1 56,927 2 1903 12,301 47,659 88,388 9,994 877 159,2198 World's Production of Lead. This in 1902 amounted to 926,895 metric tons. Of this quantity the United States produced approximately 26 per cent; Spain, 19 per cent; Germany, 15 per cent ; and Mexico, 11 per cent. Of these countries Spain and Mexico afforded the greatest surplus production, and both Germany and the United Kingdom required more lead than they mined. The figures of world's production together with imports and exports in metric tons for 1902 are given, below : 1 Including 2716 tons dross spelter. 2 Including 2675 tons dross spelter. 8 Including 3302 tons dross spelter. LEAD AND ZINC 323 PRODUC- TION IMPORTS TOTAL EXPORTS CONSUMP- TION Austria-Hungary . . Belgium 13,543 19 500 8,706 53,000 22,249 72,500 53 50,000 22,196 9 2 500 France 18817 72,730 91,547 6,454 85093 Germany 140 331 39006 179,337 23,100 156 237 Italy 26,494 7,563 34,057 5,650 28,407 Prussia 250 23,000 23,250 23,250 Spain 177,560 177,560 172,480 5,080 United Kingdom . . United States . . . 27,100 342,160 235,522 65,235 262,622 407,395 24,408 129,637 238,214 277,758 World's Production of Zinc. The production of zinc ore and spelter in metric tons for 1902 is given below : COUNTRY SPELTER ORE COUNTRY SPELTER ORE Germany . . . 174,927 702,504 Austria . . . 7,960 31,927 United States . 143,552 500,000 Spain . . . 5,569 127,618 Belgium . . . 124,780 3,852 Italy .... 485 149,965 United Kingdom 40,244 25,462 Sweden . . . 48,783 France .... 36,282 57,982 Algeria . . . 33,139 Holland . . . 20,760 Greece . . . 18,020 Russia .... -8,280 Tunis . . . 18,400 The above table indicates that the mining districts and smelting centers are not identical. Belgium and Holland have a smelting industry greatly in excess of the local min- ing interests, but in the United States they are in approxi- mate equilibrium. REFERENCES ON LEAD AND ZINC Arkansas : 1. Adams, U. S. Geol. Surv., Bull. 213 : 187, 1904. (N. Ark.) 2. Adams, U. S. Geol. Surv., Prof. Paper No. 24, 1904. 3. Branner, Ark. Geol. Surv., Kept, for 1892. (N. Ark.) Colorado : 4. Em- mons, U. S. Geol. Surv., Mon. XII, 1886. (Leadville.) 5t Ran- some, U. S. Geol, Surv., 22d Ann. Kept., II : 229, 1902. (Rico Mts.) 324 ECONOMIC GEOLOGY OF THE UNITED STATES 6. Spurr, U. S. Geol. Surv., Mon. XXXI, 1898. (Aspen.) Idaho : 7. Lindgren, U. S. Geol. Surv., 20th Ann. Kept., Ill: 190, 1900. (Wood River district.) Illinois : 8. Bain, U. S. Geol. Surv., Bull. 225: 202, 1904, and Bull. 246, 1904. Iowa: 9. Leonard, la. Geol. Surv., VI: 10, 1897. Kentucky : 10. Ulrich and Smith, U. S. Geol. Surv., Prof. Paper No. 36, 1905. Massachusetts : 11. Hubbard, Amer. Jour. Sci., IX: 167, 1825. Missouri : 12. Bain, U. S. Geol. Surv., 22d Ann. Kept., II: 23, 1901. (Ozark region.) 13. Bain, U. S. Geol. Surv., Bull. 267, 1905. (Mo.) 14. Ball and Smith, Mo. Bureau Geol. and Mines, Bull. Vol. I, 2d Series, 1903. (Central Mo.) 15. Branner, Eng. and Min. Jour., LXXIII : 475, 1902. (Ozark region.) 16. Jenney, Amer. Inst. Min. Engrs., Trans. XXII : 189, 1904. (Mo.) 17. Winslow, Mo. Geol. Surv., Vols. VI and VII, 1894. 18. Winslow, U. S. Geol. Surv., Bull. 132, 1896. (S. E. Mo.) 19. Wheeler, Eng. and Min. Jour., LXXVII: 517, 1904. (Relation of lead ore to igneous rock.) New Jersey: 20. Kemp, Trans. N. Y. Acad. Sci., XIII: 76, 1894. 21. Wolff, U. S. Geol. Surv., Bull. 213 : 214, 1903. 22. Nason, Amer. Inst. Min. Engrs., Trans. XXIV : 121, 1894. A U. S. Geol. Surv. report by Spencer is also in preparation. New Mexico: 23. Blake, Amer. Inst. Min. Engrs., Trans. XXIV: 187, 1894. (S. W. New Mexico.) 24. Keyes, Min. Mag., XI, Aug., 1905. (Magdalena Mts.) New York: 25. Ihlseng, Eng. and Min. Jour., LXXV: 630, 1903. (El- lenville.) Pennsylvania: 25 a. Clerc, U. S. Geol. Surv., Min. Res. 1882, 361. Tennessee: 26. Keith, U. S. Geol. Surv., Bull. 225: 208, 1904. 27. See also Morristown, Maynardville, and Cleveland folios, U. S. Geol. Surv. United States: 28. Bain, U. S. Geol. Surv., Bull. 260 : 251, 1905. 29. Whitney, Metallic Wealth of U. S., 1854. (Ap- palachians.) Utah: 30. Emmons, Amer. Inst. Min. Engrs., Trans. XXXI: 675, 1901. (Delamar and Hornsilver Mines.) 31. Tower and Smith, U. S. Geol. Surv., 19th Ann. Rept., Ill: 601, 1899. (Tintic.) Virginia: 32. Boyd, Resources of Southwest Virginia, 1881. 33. Case, Amer. Inst. Min. Engrs., Trans. XXII: 511, 1894. 34. Payne, Eng. and Min. Jour., LXXVIII : 544, 1904. 35. Watson, Va. Geol. Surv., Bull. 1, 1905. (Va.-Tenn.) Wisconsin : 36. Grant, Wis. Geol. and Nat. Hist. Surv,, Bull. 9, 1903. CHAPTER XVII GOLD AND SILVER GOLD and silver are obtained from a variety of ores, in some of which the gold predominates, in others silver, while in still a third class these two metals may be mixed with the baser metals, lead, copper, and zinc. Few gold ores are absolutely free from silver, and vice versa, so that a separate treatment of the two is more or less difficult ; however some lead-silver ores, although they may carry some gold, are sufficiently prominent to be discussed as a separate type, and are described as such on a later page. Ores of Gold. Gold occurs in nature chiefly as native gold, mechanically mixed with pyrite, or as a telluride such as calaverite (Au, 39.5 per cent; Ag, 3.1 per cent; Te, 57.4 per cent). 1 Ores of Silver. The minerals which may serve as ores of silver, together with the percentage of silver they con- tain, are : ORES Ag S Native silver Aff 10000 Argentite, silver glance CAffoS) 87.1 12.9 Pyrargyrite, ruby silver 3 AsToS, SboSo 59.9 17.8 Proustite light ruby silver 3 As* S \s So 65 5 194 Stephanite, brittle silver, black silver . Cerargyrite, horn silver 5Ag 2 S, Sb 2 S 3 Ae-Cl 68.5 75.3 16.3 Bromyrite AgBr 57.4 Embolite Ag(ClBr) 64.5 approx. 9 Ag 2 S, Sb S 3 75.6 1 Other tellurides are sylvanite, kalgoorlite, and krennerite. 325 326 ECONOMIC GEOLOGY OF THE UNITED STATES Mode of Occurrence. Most of the gold and silver mined in the United States is obtained from fissure veins, or closely related deposits of irregular shape (79), in which the gold and silver ores have been deposited from solution, either in fissures, or other cavities, or by replacement. Considerable gold and a little silver is obtained from gravel deposits. Some true contact deposits are known. Gold has been found to occur in rare instances as an original constituent of igneous rocks (1, 8, 11) and also metamorphic ones (12), but there are no known deposits of commercial value belonging to this type. The gold and silver-bearing fissure veins include two prominent types (79), viz. : (1) the quartz veins, and (2) the propylitic type, in which the metasomatic alteration of the wall rock is often propylitic, that is, accompanied by the for- mation of chlorite and epidote, but near the veins of sericite and kaolin. In the quartz-vein type silver is present usu- ally in but small quantities, while in the propylitic type the silver often is an important constituent. While the mode of occurrence of gold and silver is quite variable, the character of the wall rock is equally so, gold and silver ores being found in either sedimentary or igneous rocks, and along the contact between the two, showing that the kind of rock exerts little influence, except perhaps where replacement has been active. On the other hand the influ- ence of locality is much stronger, for it has been found that many gold and silver-bearing deposits are closely associated with masses of igneous rock, the most common of these being diorite, monzonite, quartz-monzonite, granodiorite, while true granites are rare as associates. A second large class of vein systems shows a close association with lavas of recent age, and the telluride ores rather favor these (6). GOLD AND SILVER 327 Weathering and Secondary Enrichment. The superficial alteration of gold ores differs somewhat from that of deposits containing ores of the other metals. In quartz veins with auriferous pyrite, the change of the latter to limonite leaves a rusty quartz with nuggets or threads of free gold, and leaching may remove most of the iron. Some of the gold may also be leached out by the ferric sulphate, formed by the oxidation of the pyrite, and carried to lower levels, where it is reprecipitated. Whether the reprecipitation of the gold is due to pyrite or carbonaceous matter, is, in some cases at least, an unsettled question (4, and Ref. on ore deposits). The silver sulphides are changed to sulphates or chlorides, part of which at least are leached out of the gossan and carried to lower levels, where they are reprecipitated by iron or even copper sulphides. Classification. The gold and silver ores are some- times grouped (80) according to their associations, as below ; this also has the advantage of bringing out more clearly their metallurgical character. 1. Placers or gravel deposits. These serve chiefly as a source of native gold, but may and often do contain a little silver, much of which is never separated from the ore in which it occurs. These gravels are derived chiefly from quartz veins of Mesozoic age in the Pacific coast region, and to a less extent from pre-Cambrian veins of the Ap- palachian region and Black Hills of South Dakota. Some are also derived from veins in Tertiary lavas, but these usually contain the metals in such a finely divided con- dition, or in such combination, that they do not readily accumulate in stream channels. 328 ECONOMIC GEOLOGY OF THE UNITED STATES 2. Quartzose or dry ores, in which the gold and some silver are found in a quartz gangue, and are either free or mixed with sulphides, commonly pyrite. They are of varying age. Those of California, Oregon, and Alaska are Mesozoic and associated chiefly with quartz monzonite, granodiorite, and diorite. Another great class of post-Miocene age, found chiefly in Colorado, Nevada, and Montana, is associated with Tertiary lavas and characterized by bonanzas. The most productive ones carry fluorite and normally also tellurides. In some, gold may predominate ; in others, silver. A third class, of pre-Cambrian age, is found in the Atlantic States, Wyoming and South Dakota, the last mentioned including the famous Homestake Mine. These are classified as dry ores, because they are not as a rule smelting ones ; they con- tain limited quantities of copper and lead, but may have some pyrite. 3. Gold and silver bearing copper ores. These are widely distributed throughout the United States, and exhibit great differences in form and age, neither do all the occurrences yield much gold or silver. The output is obtained chiefly from Colorado, Utah, and Montana. Those of the last two states, which supply most of the production, are found as replacement veins in granites or early Tertiary igneous rocks. The large copper deposits of Arizona produce but little gold or silver, with the exception of those at Jerome. This class of ores yields about one third of all the silver mined in the United States. 4. Gold and silver bearing lead ores. This class includes a variety of deposits, containing much lead, and also silver, with gold usually in subordinate amounts. They occur chiefly in Colorado, Utah, and Idaho, and furnish about one GOLD AND SILVER 329 half of the silver obtained in the United States. They are discussed separately under the head of Silver-Lead ores. A subtype of this class is represented by the veins of argentiferous galena and tetrahedrite of the Wood River district, Idaho. These are veins in slates near the contact of intrusive granite and are of late Mesozoic age. Arizona, California, Washington, and New Mexico produce small amounts of argentiferous lead ores. Geological Distribution. Gold and silver ores have been formed at a number of different periods in the geological history of the continent, notably in the pre-Cambrian, Cam- brian, Cretaceous, and Tertiary ages, but Silurian, Devonian, and Carboniferous gold deposits are not definitely known to exist in North America, although some of the Appalachian veins may be of this age (79). Silver ores show much the same geological distribution. Extraction. Since gold and silver ores vary so in their mineralogical associations and richness, the metallurgical processes involved in their extraction are varied and often complex. Those ores whose precious metal contents can be readily extracted after crushing, by amalgamation with quicksilver, are termed free-milling ores. This includes the ores which carry native gold or silver, and often represent the oxidized portions of ore bodies. Others, containing the gold as tel- luride or containing sulphides of these metals, are known as refractory ores and require more complex treatment. These, after mining, are sent direct to the smelter if sufficiently rich, but if not they are often crushed and mechanically concentrated. The smelting process is also used for mixed 330 ECONOMIC GEOLOGY OF THE UNITED STATES ores, the latter being often smelted primarily for their lead or copper contents, from which the gold or silver is then separated. While in some cases there are smelters at the mines, still there is a growing tendency towards the central- ization of the industry, and large smelters are now located at Denver, Salt Lake City, etc., which draw their ore supply from many mining districts. Low-grade ores may first be roasted, and the gold then extracted by leaching with cyanide or chlorine solutions. The introduction of the cyanide and chlorination processes, which are applied chiefly to gold ores, has permitted the working of many deposits formerly looked upon as worth- less, and in some regions even the mine dumps are now being worked over for their gold contents. It is estimated that in 1902 $8,000,000 worth of gold ores were cyanided. The chief fields are in the Cripple Creek region of Colo- rado ; the De Lamar district, Idaho ; Marysville, Montana ; Bodie, California ; and in Arizona. The most important gold-milling centers of the United States are the Mother Lode district of California, the Black Hills, South Dakota, and Douglas Island, Alaska. The value of ore and bullion is determined from a sample assay, and the smelter, in paying the miner for his ore, allows for gold in excess of $1 per ton of ore at the coin- ing rate of $20.67 per ounce, and for silver at New York market price, deducting 5 per cent in each case for smelter losses. Lead and copper are paid for in the same manner, as are also iron and manganese, if there is a sufncient quan- tity present. No allowance is, however, made for zinc, and, in fact, a deduction is made if it exceeds a certain per cent. GOLD AND SILVER 331 Distribution of Gold and Silver Ores. Gold ores are widely distributed in the Cordilleran region and Appa- lachian province, while the silver ores are found chiefly between the Great Plains and Pacific coast ranges, exclu- sive of the Colorado plateau region. This occurrence in two widely separated areas is brought out in an interest- ing manner in Fig. 69. FIG. 69. Map showing distribution of gold and silver ores in United States. Adapted from Ransome, Min. Mag., X: 1. More than a third of the United States production of gold comes from the southern half of the Rocky Moun- tains, Colorado being the main producer. In this area, however, the ores vary widely in their mineralogical asso- ciations, the gold occurring mostly in combination with silver, lead, copper, and zinc ores, but also at times free, or, in the most productive district, as a telluride. ' The Pacific belt, excluding Alaska, supplies about one fourth the total amount of gold produced, the famous Mother Lode region, mentioned later, being the most im- 332 ECONOMIC GEOLOGY OF THE UNITED STATES portant producer. Alaska yields about 10 per cent, and the Basin Range province about 14 per cent, collected from widely separated deposits in Utah, Nevada, Arizona, and New Mexico, and in which the gold is associated with copper, silver, or lead. Probably two thirds of the silver obtained in the United States comes from the Rocky Mountain region, Colorado alone yielding about one third, while Montana supplies about one third of the total amount produced, and about three fourths of this is obtained as a by-product in copper smelting. The Basin Range province furnishes about 28 per cent, two thirds of this coming from Utah, especially from the Park City mines near Salt Lake City (83). The gold and silver occurrences of the United States and Alaska can be grouped under five areas, as follows : 1. Cordilleran region. 2. Black Hills, South Dakota region. 3. Michigan region. 4. The eastern crystalline belt. 5. Alaska. Of these, the first, second, and fifth are the most impor- tant, while the third is insignificant. CORDILLERAN REGION This area contains a number of important deposits of gold and silver ores, occurring chiefly in quartz veins, and to a lesser extent in gravels. There are also some representa- tives of the propylitic type. Pacific Coast Cretaceous Gold-quartz Ores. Extending along the Pacific coast from Lower California up to the PLATE XX FIG. 1. Kennedy mine on the Mother Lode near Jackson, Calif. FIG. 2. Auriferous quartz veins in Maryland mine, Nevada City, Calif. After Lindgren, U. S. Geol. Surv., 17th Ann. Kept., III. GOLD AND SILVER 333 British Columbia boundary there is a gold belt of great importance, which throughout its extent is characterized by quartzose ores and gold-bearing sulphides. The de- posits belonging to this are especially important in Cali- fornia, but farther north, in Oregon and Idaho, the veins in many cases have been covered up by the lava flows of the Cascade Range, and those known in that region differ somewhat from the California deposits in containing many mixed silver-gold ores and also veins carrying aurif- erous sulphides without free gold. The ores of this belt are all of undoubted Mesozoic age, and are accompanied by many extensive placer deposits, which .have been derived by the weathering down of the upper parts of the quartz veins, the portions now remaining in the ground repre- senting probably but the stump of originally extensive fissure veins (79). Among the deposits of this belt two groups stand out in some prominence, namely, those of the so-called Mother Lode district and of Nevada County. Mother Lode Belt (25, 27). This includes a great series of quartz veins, beginning in Mariposa County and extending northward for a distance of 112 miles. The veins of this system break through black, steeply dipping slates and altered volcanic rocks of Carboniferous and Jurassic age, and since they are often found at a considerable distance from the granitic rocks of the Sierra Nevada, they have apparently no genetic relation with them. The veins, which occur either in the slate itself or at its contact with diabase dikes, show a remarkable extent and uniformity, due to the fact that in the tilted layers of the slates there lay planes of weakness for the mineral-bearing solution to follow. The ore is native 334 ECONOMIC GEOLOGY OF THE UNITED STATES gold or auriferous pyrite in a gangue of quartz, and the average value may be said to vary from $3 or $4 up to $50 or $60 per ton. The veins often split and some of the mines have reached a depth .of several thousand feet. Jm / ' ' ' nms t I ama j Cc II ( / Ng FIG. 70. Map and section of portion of Mother Lode district, Calif. Pgv, river gravels, usually auriferous ; Ng, auriferous river gravels. Sedimentary rocks: Jm, mariposa formation (clay, slate, sandstone, and conglomerate); Cc, calaveras formation (slaty mica schists). Igneous rocks: Nl, latite; Nat, andesite tuffs, breccia, and conglomerate; mdi, meta-diorite ; Sp, ser- pentine; ma, meta-andesite ; ams, amphibole schist. From U. S. Geol. Surv., Atlas Folio, Mother Lode sheet. Nevada County (26). In Nevada County the mines of Grass Valley and Nevada City are likewise quartz veins, but they occur along the contact between a granodiorite and diabase porphyry, as well as cutting across the igneous rock (Fig. 71). Two systems of fault fissures occur, and in these the ore is found either in native form or associated GOLD AND SILVER 335 with metallic sulphides. The width of the vein averages from 2 to 3 feet, and the lode ore generally occurs in well- defined bodies or pay shutes. The vein filling was deposited by hot solution, and while the wall rocks contain the rare metals in a disseminated condition, Lindgren (26) believes that the ores have been leached out of the rocks at a con- siderable depth. The mines at Nevada City and Grass Valley have been large producers of gold and some silver. Placer mines have furnished a small portion of the product, but at the present day these latter are of little importance. -|- r-^*< WK V \ ' x /\ //> J i -A /^ \-/^i^ '- \-\/^\^^ ~ '/X- 1 ^ 7 - - ' - \ - - \ / &^ r 'l \ I -~ ^-\ ' ,-lN'i.V^ R757] METAMORPHIC SCHIST AND DIABASE I/VA | GRANODIORITE ' fl.MERRIFIELD VEIN b. URAL VEIN C. SLATE VEIN FIG. 71. Section illustrating relations of auriferous quartz veins at Nevada City, Calif. After Lindgren, U. S. Geol. Swry., Ylth Ann. Rept., II. In Oregon, the quartz veins are worked in Baker County, which is the most important gold-producing region of the state (72,73). Gold ores with sulphides in quartz gangue are worked in the Monte Cristo district of Washington (88). Central Belt of Gold-Silver Ores. To the east of the Creta- ceous gold-quartz belt there lies a second one, in the central and eastern part of the Cordilleran region, containing many gold and silver deposits of late Cretaceous or early Ter- tiary age, although they occur in older rocks, such as Car- boniferous. 336 ECONOMIC GEOLOGY OF THE UNITED STATES Mercur, Utah. The gold-silver mines of the Mercur (85) district in Utah form perhaps the most important occurrence in this central zone. Here the Carboniferous limestones, shales, and sandstones, representing about 12,000 feet of sediments, are folded into a low anticline. Near the center of the section is the great blue limestone, carrying an upper and a lower shale bed. Quartz porphyry has intruded the limestone, and at two places especially, spread out laterally in the form of sheets, on whose under side the ore is found, the silver ores under the lower sheet, the gold ores under the EAGLE HILL PORPHYRY GREAT BLUE LIMESTONE GREAT BLUE LIMESTONE LOWER INTERCALATED SER OWER LIMESTONE FIG. 72. Section of Mercur, Utah. After Spurr, U. S. Geol. Surv., 16th Ann. Kept., II. upper one, about 100 feet above the first. The silver ore is cerargyrite and argentiferous stibnite in a silicified belt of the limestone. The gold is native and occurs in a belt of re- sidual contact clay, near northeast fissures cutting the lime- stone, being oxidized in places and accompanied by sulphides in others. The ore runs 1-19 ounces of silver per ton, and 2-3 ounces of gold, with a gangue of quartz, barite, limonite, and arsenical sulphides. The silver minerals are thought to have been deposited by heated solutions which came up along the igneous sheet some time after its intrusion, and the deposi- tion of the gold ore is believed to have taken place some time UNIVERSITY GOLD AND SILVER ^ after the silver was deposited. Some doubt exists as to the exact source of the ascending waters, but in all probability they were derived from some deep-seated cooling laccolith. The ores are especially suited to the cyanide treatment. Other Occurrences. The northward continuation of this belt of gold-bearing veins in Idaho and Montana presents somewhat different types of deposits, for there the veins are causally connected with great batholiths of Mesozoic gran- ite ; and while the veins resemble those of the Pacific Coast in the quartz filling and free gold contents, they differ from the latter in containing more silver, and often large quanti- ties of sulphides with little free gold. In fact in their geo- logic relations they are intermediate between the quartz vein and propylitic type. Of special prominence are those of Marysville, Montana, and Idaho Basin, Florence, etc., in Idaho. This difference is more marked in the Montana occurrences, in which the gold becomes subordinate and is obtained as a by-product in silver mining. Eastern Belt of Tertiary Gold-Silver Veins. Of greater importance than the preceding class are the veins of Tertiary, mostly post-Miocene, age, which, according to Lindgren, are characteristic of regions of intense volcanic activity, and cut across andesite flows, or more rarely rhyolite and basalt. The veins may be entirely within the volcanic rocks, or the fissures may continue downward into the underlying rocks, which have been covered by the extrusive masses. Most of these Tertiary deposits belong to the propylitic class, showing characteristic alterations of the wall rock. The ores are commonly quartzose, and though either gold or silver may predominate, the quantities of the two metals are 338 ECONOMIC GEOLOGY OF THE UNITED STATES apt to be equal. Bonanzas are of common occurrence, and on this account the mines may be very rich but short-lived ; still, the workable ore in many, extends to great depths, but is less rich than nearer the surface. Extensive and rich placers are rarely found in the Tertiary belt of veins, for the reason that the fine distribution of the gold is not favorable to its concentration and retention in stream FIG. 73. Map of Colorado showing location of mining regions. After Richard, Amer. Inst. Min. Eng., Trans., 1904. channels. Deposits of this type are worked in a number of states, including Colorado, Nevada, Arizona, New Mexico, and Idaho. Colorado leads in the production of gold ores, for in no state are the Tertiary deposits of the pro- pylitic type developed on such a scale. Cripple Creek (39, 45, 47). This district, which is the most important in this belt, is a producer of ores containing GOLD AND SILVER 339 gold almost exclusively, and may therefore be mentioned in some detail. The region lies about ten miles west of Pikes Peak proper, but in the foothills of this mountain mass. The most common rock of the region is the red Archaean granite of Pikes Peak, in which, however, are inclusions of still older schists. In Tertiary times, the region was one of great volcanic activity, which began with the expulsion of the breccias of phonolitic and pos- sibly in part andesitic types, and was followed by a series of phonolitic rocks, which grade into each other. Finally, there were intrusions of basaltic dikes of several types. The ore is chiefly calaverite, and to a less extent sylvanite, and probably some other gold- silver-lead tellurides. The tel- lurides are often associated with auriferous and highly argentiferous tetrahedrite, molybdenite, and even stibnite. Pyrite, though widely disseminated in both country rock and fissures, rarely carries enough gold to serve as an ore. Native gold exists only as an oxidation product of the tel- luride. The common gangue minerals are quartz, fluorite, and dolomite ; secondary orthoclase is sometimes prom- inent in the granites, while other minerals occur in small amounts. ORE ALONG SHEETE.O ZONE'- FIG. 74. Section of vein at Cripple Creek, Colo. After Rickard. 340 ECONOMIC GEOLOGY OF THE UNITED STATES Two types of ore bodies exist : 1. Fissure veins, some- times simple, but more often compound, and formed in the more or less closely spaced fractures of a sheeted zone. These may occur in any kind of rock, but favor the brec- cias. Their dip is generally steep, and the lode may vary from 1 foot to 50 or 60 feet in width. A subtype of this are composite veins in sheeted basalt dikes. 2. Irregular deposits, often of large size, formed by the replacement of granite, and usually occurring close to or within 1000 feet of its contact with the breccias. The ore is of somewhat lower grade than that found in the fissures. The two types are not always distinct, and in both the ore has been deposited in relatively small spaces, with but small quantities of gangue minerals, so that the fissures are never completely filled. The ores which show oxidation to a depth of from 200 to 400 feet often occur in shutes, but no evidence of secondary enrichment has been found by recent investigators. The principal productive zone does not seem to extend more than 1000 feet from the surface, and while ore may be looked for below this, the quantity of it will probably be less. The Cripple Creek ores as a rule run low in silver and from 1 to 10 ounces of gold per ton, with an average value of $30 to $40 per ton. Most of the ores are treated by the chlorination or cyanide process, especially the former, and about one sixth of the output is shipped directly to the smelters at Denver and Pueblo. The rapid rise of this district is well shown by the fol- lowing figures of production. A maximum was reached in 1900, since which the output has gradually declined. PLATE XXI FIG. 1. View of Independence Mine and Battle Mountain, Cripple Creek, Colo. A. J. Harlan, photo. FIG. 2. General view of region around Tonopah, Nev. /. E. Spurr, photo. GOLD AND SILVER 341 PRODUCTION IN CRIPPLE CREEK DISTRICT IN 1893-1903 YEAR VALUE YEAR VALUE 1 893 $ 9 010 367 1899 .... $15 658 254 1894 2,908,702 1900 18,073,539 1895 6 879,137 1901 17,261,579 1896 7512911 1902 16,912,783 1897 10,139,708 1903 12,967,338 1898 .... 13,507,244 Total .... 1123,831,562 San Juan Region. As an example of a more mixed type of ore of this class may be mentioned the San Juan region of southwestern Colorado, which includes the counties of San Juan, Dolores, La Plata, Hinsdale, and Ouray, and is one of the most important gold and silver producing regions of the state, being noted for its persistent vertical veins, carrying gold, silver, and lead ores in varying proportions. Those in the vicinity of Rico are mentioned under Silver- Lead. Other important mining camps are Silverton, Creede, Telluride, and Ouray. The rocks of the San Juan district consist of a series of older sedimentaries, ranging from Algonkian to Cretaceous, buried under a complex of Tertiary volcanics, of both acid and basic types. In the Silverton quadrangle (43), for ex- ample, this volcanic series is several thousand feet thick and consists of tuffs, agglomerates, and lava flows. The more or less distinctly horizontal surface volcanics have been pen- etrated by later stocks of igneous rock, ranging from gabbro nearly to granite in composition, and by many small dikes of different types. The ore deposits form lodes, stocks, or masses (locally called chimneys), and replacement deposits. The lode 342 ECONOMIC GEOLOGY OF THE UNITED STATES fissures, which form the most important class, have been formed at several different periods and show varying strikes, but are often of great length, two or three miles being not uncommon, while some of the fractures probably extend continuously for as much as six miles. The ore-bearing minerals are pyrite and sulphides of cop- per, silver, lead, or zinc, in a gangue of quartz, barite, calcite, dolomite, rhodochro- site, etc. They have probably been depos- ited from aqueous solutions either in spaces or pores of the rock, or by re- placement. The ores are mostly low grade, and require careful milling to yield profit- able returns, but some are sufficiently rich to be shipped directly to the smelter. Another remarkable development of veins is found around Telluride (42) (Fig. 75), one of which, the Smuggler vein, has been traced four miles, and cuts the Tertiary volcanics. The ores are gold and silver in a gangue of quartz, with some rhodochrosite, siderite, calcite, and barite. The ore bodies around Ouray (36) differ from those around Silver- ton and Telluride in being found in the sedimentaries of the region, and form either fissure veins or replacements ** | a | JSljSSjL FIG. 75. Geologic map of Telluride district, Colorado, showing outcrop of more important veins. After Winslow, Amer. Inst. Min. Eng., Trans. XXIX: 290. GOLD AND SILVER 343 in quartzite or limestone connected with vertical fissures. Owing to the different degrees of replaceability shown by the wall rocks, the ore bodies present a most varied form. Tonopah, Nevada. Some fine examples of replacement deposits are also known in Nevada, an excellent one being that found in the recently discovered mining district of Tonopah, Nevada (63), which, although opened up only in 1900, has during the first three years produced over $ 3,000,000 worth of gold. The district, which lies in the arid desert FIG. 76. Ideal cross section of rocks at Tonopah, Nev. After Spurr, U.S. Geol. Surv., Bull. 225: 108. region of Nevada, contains a series of Tertiary lavas and tuffs, the former including andesites, dacites, rhy elites, and basalt (Fig. 76). The earlier lavas and tuffs have been broken by a complex series of faults which have not, however, affected the older dacites and closely associated rhyolite necks. Four periods of vein formation have been discovered closely fol- lowing periods of eruption, and of these only the oldest, namely, those found in the earlier andesite, are available sources of ore. The veins, which have been formed by replacement in sheeted zones and show more or less de- 344 ECONOMIC GEOLOGY OF THE UNITED STATES velopment of ore shoots, contain quartz with orthoclase, and inclose as metallic minerals stephanite and probably polybasite. The values are about two sevenths gold and five sevenths silver. Subsequent to their formation they have been pierced and covered by later volcanic rocks, and these, together with the complex faulting, has pro- duced most puzzling structural conditions. The Tonopah ore deposits are analogous genetically to the Comstock lode deposits of Nevada (61). FIG. 77. Section of Comstock lode. D, diorite; Q, quartz; F, vein matter iu earlier diabase (Db) ; H, earlier hornblende andesite; A, augite andesite. After Becker. Comstock Lode, Nevada. This lode, which is of historic interest, occurs near Virginia City, in southwestern Ne- vada, and is a great fissure vein, about four miles long, sev- eral hundred feet broad, and branching above, following approximately the contact between eruptive rocks, and dip- ping at an angle of 35 to 45 degrees. There is abundant evidence of faulting, which in the middle portion of the vein has amounted to 3000 feet. The lode is of Tertiary age, and contains silver and gold minerals in a quartzose gangue. GOLD AND SILVER 345 One of the peculiar features of the deposit is the extreme irregularity of the ore, which occurs in great " bonanzas," some of which carried several thousand dollars to the ton. The faulting is considered to have been quite recent, and the high temperatures encountered in the lower levels of the mine indicates that there is probably a partially cooled mass of igneous rock at no great depth. In former years the enormous output of this mine caused Nevada to be one of the foremost silver producers. It was discovered as early as 1858, and increased until 1877, after which it declined. Many serious obstacles were met with in the development of the mine, such that it has never become a source of much profit in spite of its enormous output. In 1863, at a depth of 3000 feet, the mine was flooded by water of a tem- perature of 170 F., due to a break in the clay wall ; and to drain it 12,900,000 were spent in the construction of the Sutro tunnel, which was nearly four miles long, but by the time it was finished the workings were below its depth. A second difficulty was the encountering of high tem- peratures in lower workings, these in the drainage tunnel mentioned being 110 to 114 F. The mine is credited with a total production of $368,- 000,000. In recent years its output has been slowly increasing again. Other occurrences of the propylitic type are found in Gil- pin, Boulder, and Clear Creek (48) counties, Colorado. In Arizona the Commonwealth Mine of Cochise County is probably referable to this group, as is also the Congress Mine (19,20). Fissure veins associated with Tertiary eruptives are found in Owyhee County, Idaho, in the Monte Cristo dis- trict of Washington (88), and the Bohemia district of Oregon (70). The auriferous copper veins of Butte, Mon- tana, also belong in this group, but since they are more important as producers of copper, they are described under that head. 346 ECONOMIC GEOLOGY OF THE UNITED STATES Auriferous Gravels (23, 29, 30). These form an important source of supply of gold, together with a little silver, and, although widely distributed, become prominent chiefly in those areas in which auriferous quartz veins are abundant. So, while they are found in many parts of the Cordilleran region, in the Black Hills, and in the Atlantic States, their greatest development is in the Pacific coast belt from Cali- fornia up to Alaska. These auriferous gravels represent the more resistant products of weathering, such as quartz and native gold, which have been washed down from the hills on whose slopes the gold-bearing quartz veins outcrop, and were too coarse or heavy to be carried any distance, unless the grade was steep. They have consequently settled down in the stream channels, the gold, on account of its higher gravity, collecting usually in the lower part of the gravel deposit. Although the gold-bearing gravels have been derived from veins of varying age, the deposition of the gravel has rarely occurred in pre-Tertiary times, and some, indeed, are of very recent origin. The gold occurs in the gravels in the form of nuggets, flakes, or dustlike grains, the last being usually hard to catch. The nuggets represent the largest pieces, and the finding of some very large ones has been recorded from time to time in different parts of the world. Two large nuggets are recorded from Victoria : one, the " Welcome Stranger," weighing 2280 ounces ; and the other, the " Wel- come Nugget," weighing 2166 ounces. Since the auriferous gravels of the Pacific coast belt are the most important, they will be specially referred to. These have been derived from the wearing down of the GOLD AND SILVER 347 Sierras, and are found in those valleys leading off the drainage from the mountains. Many were formed during the Tertiary period, when the Sierras were subjected to a long-continued denudation, while violent volcanic outbursts at the close of the Tertiary have often covered the gravels and protected them from subsequent erosion. These lava cappings are at times 150 to 200 feet thick, as in Table Mountain, Tuolumne County. Many of the gravel deposits are on lines of former drain- age, while others lie in channels still occupied by streams. Some show but one streak of gold, while in others there may be several, some of which are on rock benches of the valley bot- tom (Fig. 78). During the early days of gold mining in Calif Or- FIG. 78. Generalized section of old placer, with technical terms, a, volcanic cap; nia the gravels at lower 6, upper lead; c, bench gravel; d, chan- , , , . nel gravel. After R. E. Browne. levels and in the valley bottoms were worked, but as these became exhausted, those farther up the slopes or hills were sought. In the earlier operations the gravels were washed en- tirely by hand, either with a pan or rocker, and this plan is even now followed by small miners and prospectors; but mining on a larger scale is carried on by one of three methods, viz. drift mining, hydraulic mining, and dredging. Drift mining is employed in the case of gravel deposits covered by a lava cap, a tunnel being run in to the paying portion of the bed and the auriferous gravel carried out and washed. 348 ECONOMIC GEOLOGY OF THE UNITED STATES In hydraulic mining, a stream is directed against the bank of gravel and the whole washed down into a rock ditch lined with tree sections, or into a wooden trough with cross pieces or riffles on the bottom. The gold, being heavy, settles quickly and is caught in the troughs or ditches, while the other materials are carried off and dis- charged into some neighboring stream. Mercury is some- times put behind the riffles -to aid in catching the gold. The water which is used to wash down the gravel de- posits is often brought a long distance, sometimes many miles, and at great expense, bridging valleys, passing through tunnels, and even crossing divides, this being done to obtain a large enough supply as well as a sufficient head of water. Owing to the great amount of debris which was swept down into the lowlands, a protest was raised by the farm- ers dwelling there, who claimed that their farms were being ruined; and it soon became a question which should survive, the farmer or the miner, for in places the gravels and sand from the washings choked up streams and accu- mulated to a depth of 70 or 80 feet. The question was settled in 1884 in favor of the farmer by an injunction, issued by the United States Circuit Court, which caused many of the hydraulic mines to suspend operations; and at a later date this was extended by state legislation, adverse to the hydraulic mining industry. Owing to this setback, hydraulic mining fell to a comparatively unim- portant place in the gold-producing industry of California, while at the same time quartz mining increased. The passage of the Caminetti law now permits hydraulic mining, but requires that a dam shall be constructed across PLATE XXII FiG. 1. Hydraulic mining of auriferous gravel. The sluice box in the foreground is for catching the gold. FIG. 2. An Alaskan placer deposit. GOLD AND SILVER 349 the stream to catch the tailings. This resulted in a revival of the industry. Dredging consists in taking the gravel from the river with some form of dredge. The method, which was first practised in New Zealand, has been introduced with great success into California, especially on the Feather River, near Oroville, and its use has spread to other parts of the Cordilleran region. The gravel when taken from the river is discharged on to a screen, which separates the coarse stones, and the finer particles pass over amalgamated plates, tables with riffles, and then over felt. Formerly much placer gold was obtained by hydraulic mining, but the annual supply from this source is slowly decreasing, as is that from drift mining, while the returns of dredger gold have been continually increasing since 1900, being 1200,000 in that year and 11,500,000 in 1903. This is due to the fact that large areas in Yuba, Sutler, Nevada, Butte, and Sacramento counties have been found adapted to dredg- ing processes, while the improvement and enlargement of the dredging machines has greatly decreased the cost of mining. Placer gold is also worked in Idaho, Montana, Oregon, New Mexico, and Colorado, all of the deposits except those of the last two states having been derived from veins of Mesozoic age. Gold also occurs in beach sand of certain portions of the Pacific coast of Washington (86), and placer mining has been carried on since 1894 ; but the supply of gold, which is ob- tained from Pleistocene sands and gravels, is small. In arid regions where the gold-bearing sands are largely the product of disintegration, and water for washing out the metal is wanting, a system known as dry-blowing is some- times resorted to. 350 ECONOMIC GEOLOGY OF THE UNITED STATES BLACK HILLS REGION The gold-bearing ores are found chiefly in the northern Black Hills, and include (1) auriferous schists in pre- Cambrian rocks; (2) Cambrian conglomerates; (3) re- fractory siliceous ores; (4) high-grade siliceous ores; and (5) placers. Of these the first and third are the most important. The surface placers, being the most easily discovered, were developed first, followed by the conglomerates at the base of CEMENT MINES FIG. 79. Section of Homestake belt at Lead, S. Dak., showing relation of ancient and modern placers to Homestake lode. From Min. Mag. XI : 467. the Cambrian. These are found near Lead, occupying depres- sions in the old schist surface, and the material is thought to have been derived from the reef formed by the Homestake ledge in the Cambrian sea. These deposits are of interest as being probably the oldest gold placers known in the United States. The fact, however, that the matrix of the gold-bearing portion of the conglomerate is pyrite rather than quartz, and the occurrence of the gold along fractures stained by iron, has led some to believe that the gold has been precipitated chemically by the action of iron sulphide and is not a detrital product. PLATE XXIII GOLD AND SILVER 351 Hbmestake Belt. The gold ores of the Homestake belt (76, 77), which are the most important in the Black Hills, oc- cur in a broad zone of impregnated schists, containing many quartz lenses, alternating with dikes of fine-grained rhyolite, which also formed sheets in the Cambrian sediments over- lying the schists, and now remain as a resistant cap on many of the surrounding ridges. The ore, which is all low grade, averaging $5 to $6 per ton, is usually a mixture of quartz, CONGLOMERATE ALGONKIAN SCHIST FIG. 80. Typical section of siliceous gold ores, Black Hills, S. Dak. After Irving, U. S. GeoL Surv., Prof. Pap. 26. pyrite, and occasionally other minerals having no definite connection with it, occupying a zone in the Algonkian rocks which shows greater hardness, irregularity of structure, and mineralization than the surrounding schists. The boundaries are poorly defined, and superficial examination may fail to distinguish between ore and barren rock. In the upper levels the ore seems to be with the dikes, but diverges from them in depth, and there is apparently no genetic relation between the two. In the earlier days the ore encountered was oxidized and free-milling, but the appearance of sulphides with depth 352 ECONOMIC GEOLOGY OF THE UNITED STATES has necessitated the introduction of the cyanide method of extraction. In spite of the low grade of its ores the Home- stake mine, due to proper management, stands out as one of the richest mines of the world, its monthly production amounting to about 1300,000 (Curie). The ore was origi- nally worked as an open cut (PI. XXIII), but later by underground methods. Siliceous Cambrian Ores. A second important type is the refractory siliceous Cambrian ore found in the region between Yellow Creek and Squaw Creek, and yielding about two thirds as much gold as the Homestake. The deposits, which occur as replacements in a siliceous dolomite, are found at two horizons, one immediately overlying the basal Cam- brian quartzite, and the other near the top of the Cambrian series. The ore forms flat banded masses known as shoots, and varying in width from a few inches to 300 feet. It is overlain by shale or eruptive rock, and associated with a series of vertical fractures, made prominent by a slight silici- fication of the wall rock. These fractures, which are termed verticals, are supposed to have conducted the ore-bearing solutions. The ore is a hard, brittle rock, composed of secondary silica, with pyrite and fluorite, and at times barite, wolfram- ite, stibnite, and jarosite. Its contents range from $3 or $4 per ton to in rare cases $100 per ton, with an average of $17. Other, but less important, siliceous ores occur in the Carboniferous rocks. Michigan Region (55). A small amount of gold has been found in a quartzose zone in schists, near Marquette, Mich- igan, but the area is of little importance. Eastern Crystalline Belt (82). Gold, with some silver, has GOLD AND SILVER 355 bodies are dikes of albite-diorite, permeated with metallic sulphides and carrying small amounts of gold (14), with a hanging wall of greenstone and a foot wall of black slate. The veinlets, which are thought to have been formed by shearing stresses incident to epeirogenic movements, occur in two sets of fractures at right angles to each other. Spencer believes that the mineralization has been caused by hot ascending solutions of possibly magmatic origin. Fia. 82. Sketch map of Douglas Island, Alaska. After Spencer, U. S. Geol. Surv., Bull. 259:71. Secondary concentration is not in evidence, and it is thought that the depth to which the ores can be worked will depend more on the increased cost of mining at great depths rather than on exhaustion of the ore. At present an almost continuous ore body has been developed for 3500 feet. The placer deposits have been found in many parts of Alaska, but the two regions which have yielded the largest amount are the Yukon region (16) and the Seward Penin- sula (14, 15), the latter being now the first. 356 ECONOMIC GEOLOGY OF THE UNITED STATES Gold was discovered in the Forty Mile district of the Yukon in 1886, and caused a stampede for this region; but the deposits of the Klondike did not become known until 1896, and their discovery was followed by a rush of gold seekers that eclipsed all previous ones. Indeed, it is said that by 1898 over 40,000 people were camped out in the vicinity of the present site of Dawson. The Klondike region proper is situated on the eastern side of the Yukon River, and the richer deposits found have been on the Canadian side of the boundary. The SCALE 1,050 FEET=1 INCH FIG. 83. Cross section through Alaska Tread well mine on northern side of Douglas Island. After Spencer, U. S. Geol. Surv., Bull. 259 gold has collected either at the bottom of the gravel in the smaller streams tributary to the Yukon, or else in gravels on the valley sides, this latter occurrence being known as bench gravel. The metal is supposed to have .been derived from the quartz veins found in the Birch Creek, Forty Mile, and Rampart series of metamorphic rocks lying to the east. Up to the end of 1902 the total production of the Klondike is stated to have been $80,000,000. The annual output has, however, decreased, and mining in that region has settled down to a more permanent basis. Gravels running under $9 per cubic yard cannot be worked at a profit, because the difficulties and expenses of running in such a region are GOLD AND SILVER 357 great, and form an interesting comparison with conditions in California, where gravel carrying 25 cents per yard is considered good, while that running as low as 5 cents per yard can be worked (18). Since the discovery of the rich gold gravels on the Yukon, auriferous gravels have been developed in many other parts of Alaska, where they are being more or less actively worked (Fig. 81), but of these various finds those in the Seward Peninsula, which is now the largest producer, have been the most important. The first of the localities discovered in the last-mentioned region was Cape Nome (15), which for a time proved to be a second Klondike. The gold was discovered here on Anvil Creek, and the following year in the beach sands where Nome now stands. These discoveries caused another north- ward stampede, which resulted in the rapid exhaustion of the beach sands ; but other deposits were found farther inland near Nome, as well as the other localities on the Seward Peninsula. Some quartz veins are also worked. Ophir Creek is now the largest producer on the Seward Peninsula. Up to the end of 1902 the Seward Peninsula had produced $20,000,000 in gold, and in 1903 the produc- tion of the Nome region is given as 4,437,449. Uses of Gold. Gold is chiefly used for coinage, orna- ments, and ornamental utensils. It is also employed to a considerable extent in dentistry and in an alloy for the better class of gilding. Its value for use in the arts depends on its brightness, freedom from tarnish, and its ductility and malleability, which permit it to be easily worked. As pure 24-carat 358 ECONOMIC GEOLOGY OF THE UNITED STATES gold is too soft for use, it is alloyed with a small amount of some other metal, such as copper, to gain hardness. Uses of Silver. This metal was formerly of much im- portance for coinage, but is much less so now. It is, however, widely employed in the arts for making jewelry and utensils such as tableware. Its salts are of more or less value in medicine and in photography. Its bright- ness and white color are valuable properties when the metal is used, but, unlike gold, it tarnishes somewhat readily when exposed to sulphurous gases. There are a number of alloys of silver, those with gold and copper, respectively, being of importance. Production of Gold and Silver : PRODUCTION OF GOLD AND SILVER IN THE UNITED STATES FROM 1845 TO 1903 YEAR TOTAL GOLD SILVER (Coining Value) 1845 ..... $1,058,327 $1,008,327 $50 000 1855 55,050,000 55,000 000 50000 1865 64,475,000 53,225,000 11250000 1875 65,100,000 33,400 000 31 700 000 1885 83,400 000 31 800 000 51 600 000 1895 118,661,000 46 610 000 72 051 000 1900 153,704 495 79 171 000 74 533 495 1901 150 054 500 78 666 700 71 387 800 1902 151 757 575 80 000 000 71 757 575 1903 143 797 760 73 591 700 70 9 06 060 The production by states for 1903 is given below, and shows well the overwhelming importance of the Cordil- leran region : GOLD AND SILVER 359 PRODUCTION AND VALUE OF GOLD AND SILVER IN THE UNITED STATES IN 1903, BY STATES GOLD SILVER TOTAL (Silver at Comniercial Commercial Quantity Value Quantity Value Value) Fiue oz. Dollars Fine oz. Dollars Dollars Alabama . . 213 4,400 4,400 Alaska . . . 416,738 8,614,700 143,600 77,544 8,692,244 Arizona . . . 210,799 4,357,600 3,387,100 1,879,034 6,186,634 California . . 779,057 16,104,500 931,500 503,010 16,607,510 Colorado 1,090,376 22,540,100 12,990,200 7,014,708 29,554,808 Georgia . . 3,000 62,000 400 216 62,216 Idaho . . . 75,969 1,570,400 6,507,400 3,513,996 5,084,396 Kansas . . . 468 9,700 97,400 52,596 62,296 Maryland . . 24 500 500 Michigan . . 50,000 27,000 27,000 Montana 213,425 4,411,900 12,642,300 6,826,842 11,238,742 Nevada . . . 163,892 3,388,000 5,050,500 2,727,270 6,115,270 New Mexico . 11,833 244,600 180,700 97,578 342,178 North Carolina . 3,411 70,500 11,000 5,940 76,440 Oregon . . . 62,411 1,290,200 118,000 63,720 1,353,920 South Carolina 4,872 100,700 300 162 100,862 South Dakota . 330,243 6,826,700 221,200 119,448 6,946,148 Tennessee . . 38 800 13,000 7,020 7,820 Texas . . . 454,400 245,376 245,376 Utah .... 178,863 3,697,400 11,196,800 6,046,272 9,243,672 Virginia . . 654 13,500 9,500 15,130 18,630 Washington . 13,539 297,900 294,500 159,030 438,930 Wyoming . . 175 3,600 200 108 3,708 Total . . 3,560,000 73,591,700 54,300,000 29,322,000 102,913,700 Mr. Lindgren (80) has recently given a most interesting and valuable classification of the figures of gold and silver production, grouped according to the kind of ores from which they have been derived. These are given below, and indicate that the Tertiary quartz veins yield the largest amount of gold, and the lead ores the greatest quantity of silver. 360 ECONOMIC GEOLOGY OF THE UNITED STATES PRODUCTION OF GOLD AND SILVER IN 1904 ACCORDING TO KINDS OF ORE GOLD FINE OUNCES SILVER FINE OUNCES Placers 619 700 64000 Quartzose gold and silver ores Pre-Cambrian Quartz veins 964 000 79000 IMesozoic Quartz veins 1 045 000 860 000 1 727 000 11 000 000 Copper ores . . . .... 206 000 18 600 000 Lead ores 2" 500 23 000 000 4,086,200 53,603,000 WORLD'S PRODUCTION OF GOLD AND SILVER IN 1903 GOLD SILVER TOTAL North and Central America . Australia $104,979,000 89,210,100 $70,235,500 5,228,700 $175,214,500 94,438,800 Africa 67,998,100 185,300 68,183,400 Europe 27,117,800 8,182,100 35,299,900 Asia 25,434,000 359,100 25,793,100 South America .... 10 788 200 7,848 900 18,637,100 Total $325 527 200 $92 039,600 $417,566,800 REFERENCES ON GOLD AND SILVER GENERAL. 1. Blake, Amer. Inst. Min. Engrs., Trans. XXVI : 290, 1897. (Gold in igneous rocks.) 2. Cumenge and Robellaz, L'Or dans la nature (Paris, 1898). 3. Curie, The Gold Mines of the World (London, 1902). 4. Don, Amer. Inst. Min. Engrs., Trans. XXVII : 564, 1898. (Genesis of certain auriferous lodes.) 5. Emmons, Amer. Inst. Min. Engrs., Trans. XVI : 804, 1888. (Structural rela- tions of ores.) 6. Kemp, Min. Indus., VI: 295, 1898. (Telluride ores.) 7. Liversidge, Amer. Jour. Sci., XIV: 466, 1902. 8. Mer- rill, Amer. Jour. Sci., 1 : 309, 1896. (Gold in granite.) 9. Pearce, Ores of Gold, etc., Colo. Sci. Soc. Proc., Ill: 237. 10. Rickard, Min. and Sci. Pr., LXXVII : 81 and 105, 1898. (Minerals ac- GOLD AND SILVER 361 companying gold.) 11. Spurr, Eng. and Min. Jour., LXXVI : 500, 1903. (Gold in diorite.) 12. Spurr, Eng. and Min. Jour., LXXVII : 198, 1904. (Native gold original in metamorphic gneis- ses.) Alabama: 13. Brewer, Ala. Geol. Surv., Bull. 5, 1896; Phil- lips, Ala. Geol. Surv., Bull. 3, 1892. Alaska : 14. Brooks and others, U. S. Geol. Surv., Bull. 259, 1905. (Mineral resources.) 15. Schrader and Brooks, Amer. Inst. Min. Engrs., Trans. XXX : 236, 1901. (Cape Nome.) 16. Spurr, U. S. Geol. Surv., 18th Ann. Kept., Ill : 101, 1898. (Yukon district.) 17. See also various papers on Alaska in U. S. Geol. Surv., Bull. 213, 1903, and Bull. 225, 1904. 18. Peurose, Eng. and Min. Jour., LXXVI: 807, 852, 1903. Arizona : 19. Blandy, Amer. Inst. Min. Engrs., Trans. XI : 286, 1882. (Prescott district.) 20. Comstock, Amer. Inst. Min. Engrs., Trans. XXX: 1038, 1901. (Geology and vein phenomena.) 21. Pratt, Eng. and Min. Jour., LXXI11 : 795, 1902. Literature on Arizona gold ores, especially of recent character, is scarce. 22. See reports of Director of Mint. California: 23. Browne, Calif. State Min. Bur., 10th Ann. Kept.: 435. (River gravels.) 24. Diller, U. S. Geol. Surv., Bull. 260: 45, 1905. (Indian Valley region.) 25. Fair- banks, Calif. State Min. Bur., X: 23, 1890, and XIII: 665, 1896. (Mother Lode district.) 26. Lindgren, U. S. Geol. Surv., 17th Ann. Kept., II : 1, 1896. (Nevada City and Grass Valley.) 27. Lindgren, Geol. Soc. Amer., Bull. VI: 221, 1895. (Gold quartz veins.) 28. Lindgren, U. S. Geol. Surv., 14th Ann. Kept., II: 243, 1894. (Ophir.) 29. Lindgren, U. S. Geol. Surv., Bull. 213: 64, 1903. (Neocene river gravels.) 30. Turner, Amer. Geol., XV : 371, 1895. (Auriferous gravels.) 31. See also various annual reports of Calif. State Mineralogist. Colorado : 32. Comstock, Amer. Inst. Min. Engrs., Trans. XV: 218, 1886, and XI: 165, 1882. (Geology and. vein structure, southwestern Colo.) 33. Emrnons, Eng. and Min. Jour., XXXV : 332, 1883. (Summit district.) 34. Emmons, U. S. Geol. Surv., 17th Ann. Kept., II : 405, 1896. (Custer Co.) 35. Farish, Colo. Sci. Soc., Proc. IV : 151, 1892. (Rico.) 36. Irving, U. S. Geol. Surv., Bull. 260 : 50, 1905. (Ouray.) 37. Irving, U. S. Geol. Surv., Bull. 260 : 78, 1905. (Lake City.) 38. Kedzie, Amer. Inst. Min. Engrs., Trans. XV : 570, 1886. (Red Mt.) 39. Lindgren and Ran- sorne, U. S. Geol. Surv., Bull. 256, 1905. (Cripple Creek.) 40. Pen- rose and Cross, U. S. Geol. Surv., 16th Ann. Rept., II: 111, 1895. (Cripple Creek.) 41. Porter, Amer. Inst. Min. Engrs., Trans. XXVI : 449, 1897. (Telluride.) 42. Purington, U. S. Geol. Surv., 18th Ann. Rept., Ill : 751, 1898. (Telluride.) 43. Ransome, U. S. Geol. Surv., Bull. 182, 1901. (Silverton.) 44. Rickard, Min. Indus., II: 325, 1894, and IV: 315, 1895. 45. Rickard, Amer. Inst. Min. Engrs., 362 ECONOMIC GEOLOGY OF THE UNITED STATES Trans. XXX : 367, 1901. (Cripple Creek.) 46. Schwartz, Amer. Inst. Min. Engrs., Trans. XVIII : 139, 1890. (Cripple Creek.) 47. Skewes, Amer. Inst. Min. Engrs., Trans. XXVI : 553, 1897. (Cripple Creek.) 48. Spurr, U. S. Geol. Surv., Bull. 260: 99, 1905. (Georgetown.) Georgia : 49. Eckel, U. S. Geol. Surv., Bull. 213 : 57, 1903. (Dahlonega district.) 50. Yeates, McCallie, and King, Ga. Geol. Surv., Bull. 4 a, 1896. Idaho : 51. Lindgren, U. S. Geol. Surv., 20th Ann. Kept., Ill: 75, 1900. (Silver City, De Lamar Co.) 52. Lindgren, U. S. Geol. Surv., 18th Ann. Kept., Ill : 625, 1898. (Idaho Basin and Boise Ridge.) Kansas : 53. Lindgren, Eng. and Min. Jour., LXXIV : 111, 1902. (Tests for gold and silver in shales.) Maryland : 54. Weed, U. S. Geol. Surv., Bull. 260 : 128, 1905. (Great Falls.) Michigan : 55. Wads worth, Ann. Kept., 1892, Mich. State Geologist. Minnesota : 56. Winchell and Grant, Minn. Geol. and Nat. Hist. Surv., XXIII : 36, 1895. (Rainy Lake district.) Montana : 57. Lind- gren, U. S. Geol. Surv., Bull. 213 : 66, 1903. (Bitter Root and Clear- water Mts.) 58. Weed, U. S. Geol. Surv., Bull. 213: 88, 1903. (Marysville.) 59. Weed and Barrell, U. S. Geol. Surv., 22d Ann. Rept., II : 399, 1902. (Elkhorn district.) 60. Weed and Pirsson, U. S. Geol. Surv., 18th Ann. Rept., Ill: 589, 1898. (Judith Mts.) Nevada: 61. Becker, U. S. Geol. Surv., Mon. Ill, 1882. (Corn- stock Lode.) 62. Lord, U. S. Geol. Surv., Mon. IV, 1883. (Comstock mining.) 63. Spurr, U. S. Geol. Surv., Bull. 227, 1904, and Bull. 260 : 140, 1905. (Tonopah.) 64. Spurr, U. S. Geol. Surv., Bull. 225 : 118, 1904, and Bull. 260 : 132, 1905. (Gold fields.) 65. Spurr, U. S. Geol. Surv., Bull. 225 : 111, 1904. (Silver Peak quadrangle.) 66. See also annual reports of Director of Mint. New England : 67. Smith, U. S. Geol. Surv., Bull. 225: 81, 1904. (Me. and Vt.) North Carolina : 68. Nitze and Hanna, N. Ca. Geol. Surv., Bulls. 3 and 10. Oklahoma: 69. Bain, U. S. Geol. Surv., Bull. 225: 120, 1904. (Wichita Mts.) Oregon : 70. Diller, U. S. Geol. Surv., 20th Ann. Rept., Ill: 7, 1900. (Bohemia district.) 71. Kimball, Eng. and Min. Jour., LXXIII : 889, 1902. (Bohemia district.) 72. Lindgren, U. S. Geol. Surv., 22d Ann. Rept., II: 551, 1901. (Blue Mts.) 73. See also bulletin on Oregon Mineral Resources issued by Uni- versity of Oregon. South Carolina : 74. Thies and Mezger, Amer. Inst. Min. Engrs., Trans. XIX : 595, 1891. (Haile Mine.) See also No. 82. South Dakota: 75. Carpenter, Amer. Inst. Min. Engrs., Trans. XVII: 570, 1888. 76. Irving, U. S. Geol. Surv., Bull. 225: 123, 1904, and U. S. Geol. Surv., Prof. Paper 26, 1904. (N. Black Hills.) 77. O'Harra, S. Dak. Geol. Surv., Bull. 3, 1902. (Black Hills.) 78. Smith, Amer. Inst. Min. Engrs., Trans. XXVI: 485, 1897. (Cambrian ores.) United States : 79. Lindgren, Amer. Inst. GOLD AND SILVER 363 Min. Engrs., Trans. XXXIII: 790, 1903. (N. Amer. production and geology.) 80. Lindgren, U. S. Geol. Surv., Bull. 260 : 32, 1905. 81. Nitze and Wilkens, Araer. Inst. Min. Engrs., Trans. XXV : 691, 1896. (Appalachians.) 82. Pratt, Eug. and Min. Jour., LXX1V : 241, 1902. (S. Appalachians.) 83. Ransome, Min. Mag., X: 7, 1904. See also annual reports on Precious Metals, issued by Director of Mint, the Mineral Resources issued by U. S. Geol. Survey, the Mineral Industry, and Census Report on Mines and Quarries, 1902. Utah : 84. Spurr, U. S. Geol. Surv., 16th Ann. Kept., II : 343, 1895. (Mercur.) See also annual reports of Director of Mint, all of which contain much general information, partly of statistical character ; also references under Silver-Lead. 85. Warren, Eng. and Min. Jour. LXVIII : 455, 1899. (Daly- West Mine.) Vermont : See New Eng- land. Washington : 86. Arnold, U. S. Geol. Surv., Bull. 260: 154, 1905. (Beach placers.) 87. Smith, Eng. and Min. Jour., LXXIII: 379, 1902. (Mt. Baker district.) 88. Spurr, U. S. Geol. Surv., 22d Ann. Kept., II : 777, 1901. (Monte Cristo.) CHAPTER XVIII SILVER-LEAD ORES THE Silver-Lead Ores form a large class, which are widely distributed in the Cordilleran region, and not only supply most of the lead mined in the United States, but in ad- dition may also and often do carry variable quantities of silver, gold, and copper. The deposits as a whole present a variety of forms. The associated rocks are often faulted, and the ore bodies are commonly oxidized above so that the altered portions re- quire different metallurgical treatment from the sulphide ores found below. Secondary enrichment has in some cases raised the grade of the ore. Deposits of this class are prominent in Colorado, Idaho, and Utah, but are also known in New Mexico, Montana, Wyoming, Nevada, Arizona, Cali- fornia, and South Dakota. Idaho is the largest producer of silver-lead ores, but they average only one third silver, while those of Colorado average three quarters silver, and those of Utah about two thirds silver. A few of the more prominent occurrences are mentioned. Leadville District, Colorado (1, 7). This region lies in the Mosquito range at the headwaters of the Arkansas River in south central Colorado, while the town of Leadville is situ- ated in an old lake basin on the we*st side of the range. The latter is composed of crystalline rocks, Paleozoic sedi- 364 SILVER-LEAD ORES 365 ments, and igneous intrusions, the last in part conforming to the bedding planes of the sedimentary rocks. The Paleozoic section alone is over 5000 feet and involves the following members: Upper Carboniferous limestone . . 1000 to 1500 feet. Weber shales and sandstone . . . 2000 feet. Oldest or white porphyry .... Carboniferous blue limestone (chief ore-bearing stratum) . . . . . 200 feet. Gray porphyry r Quartzite 40 feet. [ White limestone .... 160 feet. Cambrian quartzite 150 to 200 feet. The rocks on the western side of the Mosquito range are folded and faulted, this having taken place during late Cre- taceous times, when the Rocky Mountains were uplifted, and subsequent to the intrusion of the igneous rocks. It is con- sidered that the latter stimulated the ascension of the ore- bearing solutions, the ore being commonly deposited on the under side of the porphyry sheets and in contact with the blue Carboniferous limestones. Later developments have shown its presence along some of the other contacts. The unaltered ore is argentiferous galena with some native gold, but within the zone of oxidation the galena is changed to carbonate and sulphate, with silver chloride and at times containing considerable limonite. The gangue is calcite, barite, and chert. The older mines are mostly east of the city on Fryer, Car- bonate, and Iron Hill, but in recent years the continuation of the deposits has been found under the city. 366 ECONOMIC GEOLOGY OF THE UNITED STATES The origin of the ores has been discussed by several geolo- gists, among them Emmons and Blow (1, 7). The former believes that the ores were originally deposited as sulphides from aqueous solutions ascending from some deep source, and by a process in- volving metasomatic interchange, the ore-bearing solutions following the con- tact because it happened to form a good channel. For many years the oxidized ores of the Leadville district have been an important source of material for the smelters; but latterly the silver ores have shown signs of exhaustion, and their place has been taken to some extent by the discovery of gold ore to the east of the town, as well as of zinc sulphides at greater depths and the shipment of larger quantities of iron and manganese ores than formerly. 1 f r ' iiL_ Even in former years Leadville was a mining I I_ '3 camp of great importance, having indeed given Colorado its first serious start as a mining state. From an area of about a square mile the output of silver was for a number of years greater than that of any foreign country except Mexico, and during the same period the production of lead was nearly equal to that of England and greater than that of any European country excepting Spain and Germany. Although regarded originally as a silver camp, it really ceased being such nearly ten years ago, and is now an important producer of at least eight metals, of which five or six are SILVER-LEAD ORES 367 sometimes all obtained from the same group of properties. It will thus be seen that the successful marketing of one may affect all the others. Leadville began as a gold camp in 1860, when a placer deposit of gold was found in a gulch near there and several million dollars' worth of metal were extracted, resulting in the establishment of a flourishing town called Oro, which, however, soon lost its importance when the gold began to be exhausted. Not until 1875 was the carbonate of lead, which has since been so important, actually recognized. That Leadville is no longer entirely a lead-silver camp is evident from the fact that, in 1901, of the 850,000 long tons of ore mined, 35,000 tons were zinc ores, 70,000 tons manganese iron ores, and the remainder lead and copper smelting ores. Aspen, Colorado (15). Here again the ores are oxidized and occur in highly folded and faulted Carboniferous lime- stone, although the section involves rocks ranging in age from Archsean to Mesozoic. Two quartz porphyries, one at the base of the Devonian, the other in the Carboniferous, are present, but bear no special relation to the ore. At the close of the Cretaceous the rocks were folded into a great anticline, with a syncline on its eastern limit, which passed into a great fault along Castle Creek west of the mines. Contemporaneous with the folding there were also produced two faults parallel to the bedding of the Carbonif- erous dolomite, while at the same time much cross faulting occurred. The ore is found chiefly at the intersection of these two sets of fault planes, and Spurr considers that the ore-bearing solutions followed the bed faults. 1 On account of the intimate association of the dolomite, quartz, and barite with the ore their origin is considered as similar. 1 Weed has suggested that this accumulation of ore at the intersection of fault planes is the result of secondary enrichment, rather than of primary concentration. 368 ECONOMIC GEOLOGY OF THE UNITED STATES The ores are peculiarly free from other metals except lead, and the rich polybasite (Ag 9 SbS 6 ) ores of Smuggler Mountain do not contain even this. The mining camp of Aspen started in 1879, but its development for a time was much re- tarded by lawsuits. The richer ore bodies were not discovered until 1884, and then by un- derground exploration, for owing to the heavy mantle of glacial gravels their outcrops were hid- den. Since also the ore carries no iron or manganese, as do the Leadville ores, its out- crop may be incon- spicuous. The railroads did not reach the camp until 1887, so that during the first few GLACIAL DRIFT I WEBER FORMATION I LEADVILLE DOLOMITE l : '-" ; l PARTING QUARTZITE yV /I YULE FORMATION SAWATCH FORMATION QUARTZ PORPHYRY FIG. 85. Section of ore body at Aspen, Colo. After Spurr, U.S. Geol. Surv., Mon. XXXI. years of its history the ore had to be carried out on burros. In both Aspen and Smuggler mountains long tunnels have been run for drainage and hauling purposes. The Cowenhoven tunnel, which is the largest of these, is over 8300 feet long, and taps a number of mines. Aspen was one of the first mining camps in the West to install electric machinery for hoisting, haulage, etc., and the current was cheaply sup- plied- by the neighboring water power. One shaft 1000 feet deep is operated electrically. PLATE XXIV FIG. 1. General view of Rico, Colo., and Enterprise group of mines. FIG. 2. Ontario mine, Park City, Utah. SILVER-LEAD ORES 369 At the present day the larger ore bodies are worked out, but the camp is still an active producer. From 1881 to 1895 it produced $63,653,989 worth of silver. Other Occurrences. Argentiferous lead ores also occur in the Ten Mile district (8), in Chaff ee County, and along the Eagle River (11). They are also known in Red Mountain (10 a), and in Rico Mountain, Dolores County (4, 12, 13). In the last-mentioned region the mountains, which are the remains of the struc- tural dome arising above the Dolores plateau lying in the San Juan region, contain a series of sedi- mentary beds ranging from Algonkian to Juras- sic in age, which have SANDY SHALE BLACK SHALE BLANKET BLANKET LIMESTONE BLACK SHALE SANDSTONE SANDY SHALE SANDY SHALE SANDSTONE SANDY SHALE SANDSTONE SANDSTONE SANDY SHALE FIG. 86. Diagrammatic section across a northeasterly lode at Rico, Colo., showing " blanket " of ore. After Ransome, U. S. Geol. Surv., 22d Ann. Kept., II. been uplifted partly by the intrusion of igneous rocks, as stocks, sills, and dikes, and partly by upthrows due to faulting. The ore occurs as lodes, replacements in limestone, stocks, and blankets, the last consisting usually of deposits lying parallel to the planes of bedding or to the sheets of igneous rock, and known locally as "contacts," although not such in the true sense. The four types of deposit mentioned may pass into each other. Most of the ore in the district has, however, 2B 370 ECONOMIC GEOLOGY OF THE UNITED STATES come from the blankets, and the bulk of this has been found in the Carboniferous, especially in the Hermosa formation, a striking feature of the deposits being their limited vertical range. The ores are primarily galena, often highly argentifer- ous and associated with rich silver-bearing minerals. In many deposits the more or less complete oxidation of the silver ores has resulted in powdery masses, often very rich in silver. Below the zone of oxidation, the veins have not been success- fully worked. The bulk of the ores can be roughly divided into py- ritic ores, usually low grade, and silver-bearing galena ores, sometimes containing rich silver minerals. Quartz is the commonest gangue mineral, but the beautiful pink rhodochrosite is also conspicuous. The ore deposition is be- lieved to be closely associated with the igneous intrusions of the district, especially with the later ones. Most of the ore produced in the Rico district has been shipped crude or smelted in Rico without mechanical concentration. Par k City, Utah (2), which is located on the eastern FIG. 87. Vein filling a fault fissure, Enterprise mine, Rico, Colo. After Richard, Amer. Inst. Min. Eng., Trans. XXVI: 927. SILVER-LEAD ORES 371 slope of the Wasatch range, about 25 miles southeast of Salt Lake City, has made Summit County famous as one of the important mining centers of this country, as there are here large bodies of rich silver-lead ores carrying minor values of gold and copper. The success of this camp, therefore, depends more or less on the condition of the silver and copper industry. The geological section involves a series of limestones, sandstones, and shales, chiefly of Carboniferous age, and having an aggregate thickness of over 6000 feet, with a general dip of 30 to 40 degrees northwest, and traversed by many fissures, faults, and intrusions, the last being of either dioritic or porphyritic types. The ores, which in the oxidized zone are cerussite, anglesite, azurite, mala- chite, etc., and in the sulphide zone are galena, tetrahe- drite, and pyrite, occur either as lodes or fissures, or as bedded deposits in limestones. The latter, which supply most of the ore, form replacements in certain strata of both the upper Carboniferous and Permocarboniferous, and lie between siliceous members as walls. Both types of ore deposit are frequently associated with porphyry. The fissures carry either silver or lead with or without zinc, and copper or gold with some silver. The replace- ment ores of the limestones hold silver and lead chiefly. The contact ores contain copper and gold with or without silver, and form irregular bodies in metamorphic limestone adjacent to the igneous rock. The ordinary crude ore carries 50 to 55 ounces silver, 20 per cent lead, .04 to .05 ounce gold, 1.5 per cent copper, 10 to 18 per cent zinc. Silver is obtained in the proportion of 3 ounces silver to each per cent iron, 1 ounce silver to each per cent lead, 372 ECONOMIC GEOLOGY OF THE UNITED STATES and .5 ounce silver to each per cent zinc. Bonanzas are known. The low-grade ores are treated at the concen- trating mill, while the rich ores are shipped to the smelter. Tintic District, Utah (16). This district lies in the Tintic Mountains, about 65 miles southwest of Salt Lake City. The ores are argentiferous galena, with small amounts of copper, the average assay of 240,000 tons being .6 per cent copper and 13.5 lead with some gold. The section of nearly 14,000 feet of folded Paleozoic sediments includes chiefly limestones, which after uplift and erosion were covered by Tertiary lavas and tuffs. The ores occur in zones in the limestones, as fissures in the igneous rocks, and along the contact. The minerals in the ore bodies are quartz, barite, pyrite, galena, sphal- erite, enargite, silver and gold minerals and their oxida- tion products. The Tintic is one of the oldest camps in the state, the ore having been discovered in 1869, and it was at first shipped as far as Baltimore and Wales. Since then mills have been erected at the mines. The chief towns are Eureka, Mam- moth, Robinson, Silver City, and Diamond. The same type of ore occurs in Big and Little Cottonwood canons and Bingham Canon, the latter having been worked longer than those of the Tintic district. The camps lie southeast and southwest of Salt Lake City, and the ores are oxidized lead-silver ores, parallel to the bedding of Carboniferous limestones and the underlying quartzite. Galena and pyrite occur in the lower workings below water level. Cceur d'Alene, Idaho (14), lying in the northern part of the state, is one of the most prominent producers in the SILVER-LEAD ORES 373 United States, having, in the fifteen years preceding 1902, produced about 60,000,000 worth of lead and silver. The formations of the region consist of slates, sandstones, and quartzites, which have been bent into east and west folds, the accompanying metamor- phism having been sufficient to produce new minerals. Igneous intrusions are, how- ever, rare. The ore bodies, which are typical veins, con- taining argentiferous galena, associated with much siderite, occupy fault planes, and are oxidized above. The chief FIG. 88. Section of lead-silver vein, Co3ur d'Alene, Ido. (1) Country rock. (2) Sheared rock. (3) Galena and siderite. (4) Fissure with fine- grained galena. (5) Barren , silicified country rock. After Finlay, Amer. Inst. Mln. Engrs., Trans. XXXIII : 249. minerals are quartz, siderite, galena, and sphalerite. The workable deposits carry from 5 to 25 per cent lead, the average of the district being 10 per cent and 7 ounces per ton silver. Montana and Nevada, etc. Montana contains several lead-silver ore localities. Those of Neihart (17) occur as veins in gneiss and igneous rocks, the ores being galena, silver sulphides, and some blende. The veins are best de- nned in the gneiss, and are mostly replacement deposits, which have been subsequently fractured and secondarily enriched. Lead-silver ores also occur at Glendale and in Jefferson County. Some are also known in South Dakota and New Mexico (3). The Eureka district (10) of eastern Nevada, discovered in 1868, is chiefly of historic importance. The ores are oxidized lead-silver ores, carrying some gold. They occur in Cambrian 374 ECONOMIC GEOLOGY OF THE UNITED STATES limestone which is much faulted and crushed, and is part of a Paleozoic section 30,000 feet thick. The ore is associated with a great fault, and is oxidized to a depth of 1000 feet. There are two mining districts, Pros- pect Hill and Ruby Hill. Near the mines are great por- phyry masses which are supposed to have afforded the ores. Up to 1882 the output was not far from $60,000,000 of pre- cious metals and 225,000 tons of lead. REFERENCES ON LEAD-SILVER ORES 1. Blow, Amer. Inst. Min. Engrs., Trans. XVIII : 145, 1889. 2. Boutwell, U. S. Geol. Surv., Bull. 213 : 31, 1903 ; 225 : 141, 1904 ; 260 : 140, 1905. (Park City, Utah.) 3. Clark, Amer. Inst. Min. Engrs., Trans. XXIV : 155. (Lake Valley, New Mex.) 4. Cross and Spencer, U. S. Geol. Surv., 21st Ann. Kept., II: 15, 1900. (Rico Mts., Colo.) 5. Curtis, U. S. Geol. Surv., Mon. VII, 1884. (Eureka, Nev.) 6. Eldridge, U. S. Geol. Surv., 16th Ann. Kept., II : 264, 1895. 7. Emmons, U. S. Geol. Surv., Mon. XII, 1886. (Leadville, Colo. A new report is in preparation.) 8. Emmons, U. S. Geol. Surv., Ten Mile Atlas Folio. (Ten Mile district, Colo.) 9. Farish, Colo. Sci. Soc., Proc. IV: 151. (Rico.) 10. Hague, U. S. Geol. Surv., Mon. XX, 1892. (Eureka, Nev.) 10 a. Kedzie, Amer. Inst. Min. Engrs., Trans. XV : 570, 1886. (Red Mt.) 11. Olcott, Eng. and Min. Jour. XLIII: 417, 436, 1887, and LIII: 545, 1892. (Eagle Co., Colo.) 12. Rickard, Amer. Inst. Min. Engrs., Trans. XXVI : 906, 1896. (Enterprise mine, Rico, Colo.) 13. Ransome, U. S. Geol. Surv., 22d Ann. Kept:, II: 229, 1902. 14. Ransome, U. S. Geol. Surv., Bull. 260 : 274, 1905. (Coeur d'Alene.) 15. Spurr, U. S. Geol. Surv., Mon. XXXI, 1898. (Aspen, Colo.) 16. Tower and Smith, U. S. Geol. Surv., 19th Ann. Kept., Ill : 601, 1899. (Tintic district, Utah.) 17. Weed, U. S. Geol. Surv., 20th Ann. Rept., Ill : 271, 1900. CHAPTER XIX ALUMINUM Ores. This is one of the few metals whose ores do not present a metallic appearance. Many different minerals con- tain aluminum, but it can be profitably extracted from only a few. Common clay, for example, presents an inexhaustible supply, but the chemical combination of the aluminum in it is such that its extraction up to the present time has not been found practicable. The ores of aluminum, together with the percentage of the metal which they contain, are : corundum, A1 2 O 3 (53.3 per cent); cryolite, A1F 3 , 3 NaF (12.8 per cent); bauxite, A1 2 O 3 , 2 H 2 O (34.94 per cent); gibbsite, A1 2 O 3 , 3 H 2 O (34.6 per cent). Of these, corundum is too valuable as an abrasive, and is not found in sufficient quantity to permit its use as an ore of aluminum. Until the discovery of bauxite, cryolite was the chief source of the metal, all of it being obtained from Greenland (8). Bauxite derives its name from Baux in southern France, where it was first discovered, but in recent years large de- posits have been found in the United States. It is usually pisolitic in structure, and may sometimes resemble clay in appearance. The common impurities are silica, iron oxide, and titanic acid ; and the variation in the amount of these ingredients can be seen from the following analyses of both domestic and foreign occurrences : 376 376 ECONOMIC GEOLOGY OP THE UNITED STATES ANALYSES OF BAUXITE 1 2 3 4 5 6 Alumina (A1 2 3 ) .... Ferric oxide (Fe 2 O 3 ) . . . Silica (SiO 2 ) 57.60 25.30 2.80 61.89 1.96 6.01 63-.16 23.55 4.15 59.22 3.16 3.30 61.00 2.20 2.10 62.05 1.66 2.00 Lime carbonate (CaCO 3 ) . . Titanic acid (TiO 2 ) .... Water (H 2 O) .40 3.10 10.80 27.82 8.34 3.62 28.80 31.58 30.31 Moisture 1.90 3.12 3.50 Alkalies (Na 2 O, K 2 O) . . . .79 1. Baux, France. 2. Glenravel, Ireland. 3. Wochein, Germany. 4. Georgia. 5. Rock Run, Alabama. 6. Arkansas. Distribution of Bauxite in the United States. Bauxite in commercial quantity is known to occur in but three districts in the United States. These are the Georgia- Alabama dis- trict, the Arkansas district, and a small area in southwestern New Mexico. The New Mexico deposits are of little com- mercial importance on account of their inaccessibility. Georgia- Alabama (4, 6, 7). The bauxite deposits of these two states form a belt about 60 miles long extending from Jacksonville, Alabama, to Cartersville, Georgia. The ore, which is either pisolitic or claylike in its character, forms pockets or lenses of variable diameter and depth, in the re- sidual clay derived from the Knox dolomite. A pronounced feature is their occurrence close to 900 feet above sea level, few being found above 950 feet or below 850 (4). The bauxite is believed by Hayes (4) to be a hot spring deposit. It is underlain by the Knox dolomite and this in turn by the Connasauga shales which are several thousand feet in thickness, and contain from 15 to 20 per cent of alu- mina, and also pyrite. The region is one of marked faulting. PLATE XXV FIG. 1. View of Bauxite bank, Rock Kuu, Ala. H. Ries, photo. FIG. 2. Furnace for roasting mercury ore, Terlingua, Tex. W. H. Turner, photo. ALUMINUM 377 Alteration of the pyrite by percolating meteoric waters has yielded sulphuric acid, which attacked the alumina of the shale, with the formation of alum and also ferrous sulphate. Both of these have been carried toward the surface by spring waters, but since they had to pass through the higher lying FIG. 89. Geologic map of Alabama-Georgia bauxite region. After Hayes, U. S. GeoL Surv., 16th Ann. Kept., Ill: 552. limestones, the lime carbonate acted on the dissolved alum according to the following equation : l A1 2 (SO 4 ) 3 + 3 CaCO 3 = A1 2 O 3 + 3 CaSO 4 + 3 CO 2 . The alumina thus formed was a light, gelatinous precipi- tate, which was carried upward into spring basins on the surface, where it finally settled. The pisolitic structure is thought to have been caused by the balling together of the gelatinous mass by currents. 1 For clearness, the water combined with the alumina is left out. 378 ECONOMIC GEOLOGY OF THE UNITED STATES The Georgia- Alabama deposits, which represent a unique type of occurrence, were discovered in 1887, and have been worked steadily since that time. There have been some mis- givings regarding the exhaustibility of the domestic supply, but the discovery and development of the next described district have allayed these fears. Arkansas (2,3). The occurrence of bauxite in Arkansas has been known since 1891, but owing to a more accessible eastern supply, there was little development in that region until 1900. The deposits, which are much more extensive than the Georgia- Alabama ones, are confined to a small area FIG. 90. Section of Bauxite deposit, (a) Residual mantle ; (&) Red sandy clay soil; (c) Pisolitic ore; (d) Bauxite with clay; (e) Clay with bauxite; (/) Talus; (g) Mottled clay; (h) Drainage ditch. After Hayes. in Pulaski and Saline counties, north and southwest of Little Rock. They have an average thickness of 10 to 15 feet and show two distinct types. In the southwesterly or Bryant district the lower beds show a granitic structure and rest directly on a mass of kaolin derived from the elseolite- syenite, and it is probable that the bauxite has also been derived directly from this rock. The upper beds are piso- litic and similar in character to the Georgia- Alabama ones. In the Fourche Mountain area only the pisolitic form is found. The granitic type is the purest and corresponds in composition to the formula of gibbsite rather than bauxite, while the white bauxitic kaolins run high in silica. ALUMINUM 379 The origin of the Arkansas bauxites is somewhat obscure, but Hayes (3) considers that subsequent to the intrusion of the syenite into the palaeozoics of that region, the former was exposed by erosion of the latter. This was followed by a submergence of the surface below a body of salt or highly alkaline waters, which in some way penetrated the still partially hot syenite, and dissolved its minerals. On re- turning to the surface they attacked the syenite there, removing silica and alkalies and depositing alumina in its place. Much of the alumina was also deposited from these waters as a gelatinous precipitate on the ocean bottom, over the syenite surface. Some was also deposited with the Tertiary sediments then forming. New Mexico (1). The bauxite deposits which occur near Silver City appear to have been derived from a basic volcanic rock, by decomposition and alteration in place. Uses of Aluminum. The chief use of this metal is for making wire for the transmission of electric currents, but a large quantity of it is also used in the manufacture of articles for domestic or culinary use, instruments, boats, and other articles where lightness is wanted. It is also employed in the manufacture of special alloys, among which may be men- tioned magnalium, an alloy of aluminum and magnesium; and wolframinium, a tungsten-aluminum alloy. One alloy of this type known as partinium is said to have a ten- sile strength of over 49,000 pounds per square inch; Mc- Adamite, an alloy of aluminum, zinc, and copper, is said to possess a tensile strength exceeding 44,000 pounds per square inch ; aluminum silver is an alloy of copper, nickel, zinc, and aluminum ; aluminum zinc includes a series . of 380 ECONOMIC GEOLOGY OF THE UNITED STATES alloys containing various proportions of these two metals. Of growing importance is the use of aluminum for litho- graphic work as a substitute for stone or zinc. Another extending application is that of powdered aluminum for the production of intense heat by combustion, and in this connection it is used for welding tramway rails, or for the reduction of rare metals from their oxides. Aluminum has also been tried for the manufacture of grindstones and whet- stones, for which purpose it is said to be peculiarly suited owing to the property it has for forming under whetting action a very fine mass which adheres strongly to steel. A small amount of aluminum added to steel prevents air holes and cracks in casting. Uses of Bauxite. Aside from being used for the manu- facture of aluminum and alum, bauxite is of some value for the manufacture of refractory products, its heat-resisting qualities being very great. Production of Bauxite. The production of bauxite in the United States has been as follows : PRODUCTION OF BAUXITE IN THE UNITED STATES FROM 1889 TO 1903 YEAR GEORGIA LONG TONS ALABAMA LONG TONS ARKANSAS LONG TONS TOTAL VALUE 1889. . . . 728 728 $2366 1890. . . . 1844 1844 6012 1895. . . . 3756 13,313 17,069 44,000 1899. . . . 15,736 14,499 5045 35,280 125,598 1900. . . . 19,739 3445 23,184 89,676 1902. . . . 22,677 4645 27,322 120,366 1903. . . . 22,374 25,713 48,087 171,306 ALUMINUM 381 The following table shows the annual consumption of bauxite and its value in the United States : PRODUCTION, IMPORTS, EXPORTS, AND CONSUMPTION OF BAUXITE IN THE UNITED STATES TOTAL PRODUCTION IMPORTS EXPORTS CONSUMPTION YEAR Quan- Quan- Quan- Quan- tity Long Value tity Long Value tity Long Value tity Long Value Tons Tons Tons Tons 1901 18,905 $79,914 18,313 $67,107 1,000 $3,000 36,218 $144,021 1902 27,322 121,465 15,790 54,410 nil 43,112 175,875 1903 46,087 171,306 14,684 49,684 nil 62,976 220,990 WORLD'S PRODUCTION OF BAUXITE 1900 1901 1902 COUNTRY QUANTITY QUANTITY QUANTITY METRIC VALUE METRIC VALUE METRIC VALUE TONS TONS TONS United States . 23,556 $89,767 19,207 $79,914 29,785 $128,206 France . . 58,530 92,596 76,620 124,168 96,900 174,685 United Kingdom 5,873 6,750 10,357 14,515 9,192 13,395 Total . 87,959 $189,022 106,184 $218,597 135,877 $316,286 Prior to 1890 nearly all the bauxite consumed in the United States was imported from France. The French ore has a high iron oxide content, and very little is now imported, except during periods of low ocean freights. Most of it is purchased by Germany. 382 ECONOMIC GEOLOGY OF THE UNITED STATES Most of the bauxite used in the United States is for the manufacture of aluminum, but from one fourth to one half of the total is employed in the manufacture of chemi- cal salts of aluminum, and artificial corundum, known as alundum. The Georgia-Alabama bauxites, on account of their freedom from iron, are of special value for the manu- facture of alum. In Europe much is used as a refractory material for lining furnaces. The production of aluminum in the United States since 1883 has been as follows : PRODUCTION OF ALUMINUM IN THE UNITED STATES YEAR QUANTITY POUNDS YEAR QUANTITY POUNDS 1883 83 1900 7 150 000 1885 283 1901 7 150 000 1890 61281 190 9 7 300 000 1895 920,000 1903 7,500,000 The domestic output comes from four large plants. WORLD'S PRODUCTION OF ALUMINUM 18 01 1! )02 COUNTRY QUANTITY METRIC TONS VALUE QUANTITY METRIC TONS VALUE United States . . . France .... 3,244 1,200 $2,238,000 560,000 3,311 1,355 $2,284,900 638,830 United Kingdom . . Switzerland .... 560 2,500 1,225,000 600 2,500 1,201,425 Total 7,504 7,766 MANGANESE 383 REFERENCES ON ALUMINUM AND BAUXITE 1. Blake, Amer. Inst. Min. Engrs., Trans. XXIV : 571, 1895. (N. Mex.) 2. Branner, Jour. Geol., V: 263, 1897. (Ark.) 3. Hayes, U. S. Geol. Surv., 21st Ann. Kept., Ill : 435, 1901. (Ark.) 4. Hayes, U. S. Geol. Surv., 16th Ann. Kept., Ill: 547, 1895. (Ga.-Ala.) 5. Laur, Amer. Inst. Min. Engrs., Trans. XXIV : 234, 1895. (The bauxites.) 6. Watson, Amer. Geol., XXVIII: 25, 1901. (Ga.) 7. Watson, Ga. Geol. Surv., Bull. 11, 1904. (Ga.) 8. For cryolite, see Min. Indus., VI : 251, 1897. MANGANESE Ores. While many different minerals contain this metal, practically the only ones of commercial value are the oxides and carbonates, and in this country only the former. The silicates are not used as a source of manganese, owing to their high silica percentage. The important ores of manganese are the following : pyro- lusite, the black oxide (MnO 2 ; 63.2 per cent Mn) ; psilome- lane (chiefly MnO 2 , H 2 O ; K and Ba variable), one of the most abundant manganese ores; braunite (Mn 2 O 3 ; 69.68 per cent Mn) ; and wad, a low-grade, earthy brown or black ore, with the percentage of manganese varying from 15 to 40 per cent. Wad is often of too low grade, due to impurities, to be used as an ore of manganese ; but it is sometimes em- ployed for paint. Rhodochrosite (MnCO 3 ), though found as a common gangue mineral in some western mines, does not serve as a source of manganese. The several ores of manganese are often intimately as- sociated, the pyrolusite generally assuming a crystalline and the psilomelane a massive character. Manganese oxides are also often intermixed with more or less oxide of iron, and considerable amounts of the metal are obtained from man- 384 ECONOMIC GEOLOGY OF THE UNITED STATES ganiferous zinc, silver, or iron ores. Since much manga- nese is used in iron reduction, the last association is of importance. To be of commercial value a manganese ore should have at least 40 per cent metallic manganese, and should be low in phosphorus and silica. High-grade ores run from 50 to 60 per cent manganese. The price of manganese ores in 1903 was 18.97 per long ton; of manganiferous iron ore, $2.69 (18-32 per cent Mn) and $2.40 (1-10 per cent Mn) ; of manganiferous silver ores, $3.63. Origin. Manganese oxide deposits are usually of second- ary origin, having been formed by weathering processes, which caused the decay of the parent rock containing man- ganiferous silicates, and the change of these latter to oxides. By circulating ground water they have often been concen- trated in residual clays. Although iron also may have been present in the parent rock, and the two are sometimes de- posited together, still they have in many instances been separated from each other, due to the fact that conditions favorable for precipitation are not the same for both (4), or because the soluble compounds of manganese formed by weathering are sometimes more stable than corresponding iron compounds, and hence may be carried farther by cir- culating waters before they are deposited. Distribution of Manganese Ores in the United States. Although manganese ores are widely distributed in the United States, only a few localities are of commercial im- portance. This is partly owing to the uncertainty of the extent of the ore deposits and partly to the high percentage MANGANESE 385 of phosphorus which many of the ores contain, together with their remoteness from lines of transportation. Eastern Area. Manganese deposits are found in the At- lantic States from Vermont to Alabama, and two states in this belt, Georgia and Virginia, lead in the domestic production. The common mode of occurrence in this district is as nod- ules or lumps in residual clay, simi- lar to the limonites of the same area. In Virginia, at Crimora, Augusta FIG. 91. Map showing Georgia manganese areas. County (2), the ore forms pockets 5 to 6 feet thick and 20 to 30 feet long in a bed of clay 276 feet thick. In northern Georgia (1, 3, 7) the ore results from the decay of limestone and shales, Cave Spring and Carters- ville being important localities. The deposits are found in the areas underlain by both the crystalline and Paleozoic rocks, but only those associated with the latter have proven to be of commercial importance. In this region the rocks consist of Cambro-Silurian limestones and quartzites, which have been much folded and faulted, and have then weath- ered down to a residual clay, which is often not less than 100 feet thick. The ore occurs as pockets, lenticular masses, stringers, grains, or lumps, irregularly scattered through the 2c 386 ECONOMIC GEOLOGY OF THE UNITED STATES clay and rarely forming distinct beds. None of the de- posits are large, though some 30 feet in length have been worked. More or less limonite, barite, ocher, and bauxite may be associated with the ore, and, indeed, complete gra- dations from manganese to iron ore are found, as shown by the following analyses : Mn 60.61 54.94 41.98 15.26 2.30 Fe 1.45 3.62 16.22 39.25 52.02 p .052 .034 .227 .193 .24 The better-grade ores are usually low in silica, iron, and phosphorus. In the Cartersville district, which is the more -*' , . ._,_ _* Granite PRE-PALEOZOIC FIG. 92. Section in Georgia manganese area, showing geologic relations of manganese, limonite, and ocher. After Watson, Amer. Inst. Mm. Engrs., Trans. XXXIV: 219. important, the ore is found in residual clays derived from the Beaver limestone and Weisner quartzite, while in the Cave Spring area it occurs only in the clays overlying the Knox dolomite. Penrose (5) thought that the manganese was derived from the underlying Cambro-Silurian sediments, while Watson on the contrary believes that the crystalline rocks to the east and south have furnished the ore, as none is found in the parent rock from which the clays were derived. The manganese was probably taken into solution as a sulphate and concentrated by circulating waters of meteoric origin in the residual clays where now found. MANGANESE 387 The Georgia (7) deposits have been worked for a num- ber of years, and the manganese was formerly marketed chiefly in England ; but the output is now sold entirely in the United States. The ore, which has to be purified by washing and crushing, is used in part for paint and in part for steel manufacture. Arkansas. Manganese ore is found in the region around Batesville (5, 6), associated with horizontally stratified lime- stones and shales, ranging from Ordovician to Carbonifer- ous age (Fig. 93). The Cason shale, of Silurian age, occurring near the middle of the section (Fig. 93 6), carries Eesidual Clay ['Carboniferous J } Silurian Ordovician FIG. 93. Section in Batesville, Ark., manganese region, illustrating geological structure and relation of different formations to marketable and non-market- able ore. After Van Ing en, Sch. of M. Quart., XXII: 324. manganese nodules high in phosphorus, which are not marketable, and others are found in the pits of residual clay derived from it. Farther down the slopes marketable ore (Fig. 93 e), which has been derived by leaching of the first-mentioned ore, is found occurring in residual pockets in the lower lying limestones, while the residual clays (Fig. 93 a), formed at a higher level than the Cason shale, are barren of manganese. Other United States Occurrences. California has a num- ber of manganese deposits, of which some are reported to be of high quality (8) ; they have been used largely in 388 ECONOMIC GEOLOGY OF THE UNITED STATES chlorination works for the reduction of gold ores. Man- ganese occurs in Triassic sandstones near Thompson, Utah, and the locality became a producer in 1901 (8). Much manganiferous iron ore and manganiferous silver ore is annually obtained from the Leadville district of Colorado, the former being used by steel works in making spiegel- eisen and the latter as a flux in smelters. Lake Superior iron ores at times carry manganese, but it usually does not exceed 1 per cent. Uses of Manganese. One of the principal uses of man- ganese is in the manufacture of alloys. Of these, spiegel- eisen, an alloy of iron and manganese with under 20 per cent manganese, and ferromanganese, a similar alloy with over 20 per cent manganese, are important. Other alloys are manganese bronze, manganese and copper with or without iron; silver bronze, an alloy of manganese, alu- minum, zinc, copper, and silver; and manganese-titanium alloys. Manganese is also used as an oxidizing agent in the manufacture of chlorine, bromine, and disinfectants ; as a coloring agent in calico printing and dyeing, in the making of glass, pottery, brick, as well as in paints. It is also employed as a decolorizer in green glass. Production of Manganese. Although much used in mak- ing glass and steel, of which latter material the United States is the largest manufacturer in the world, neverthe- less the domestic production is small. This consequently necessitates the importation of large quantities, which are obtained chiefly from Brazil. MANGANESE 389 PRODUCTION AND VALUE OF MANGANESE ORES IN THE UNITED STATES (IN LONG TONS) YEAR PRODUCTION VALUE 1880 5,761 $86,415 1885 23,258 190,281 1890 25,684 219,050 . 1895 9,547 71,769 1900 11,771 100,289 1901 11,995 116,722 1902 7,477 60,911 1903 2,825 25,335 PRODUCTION AND VALUE OF MANGANESE ORES IN THE UNITED STATES BY STATES (IN LONG TONS) : L901 1 J02 1 903 STATE PRODUC- TION VALUE PRODUC- TION VALUE PRODUC- TION VALUE Arkansas . . . Georgia .... Utah 91 4,074 2 500 $657 24,674 31 250 82 3,500 $422 20,830 500 483 $2,930 2 415 Virginia .... All others . . . 4,275 1,055 52,853 7,288 3,041 824 29,444 10,215 1,801 41 19,611 379 Total . . . 11,995 $116,722 7,477 $60,911 2,825 $25,335 PRODUCTION AND VALUE OF DIFFERENT KINDS OF MANGANESE ORES IN THE UNITED STATES (IN LONG TONS) KIND OP ORE 1901 1902 1903 PRODUC- TION VALUE PRODUC- TION VALUE PRODUC- TION VALUE Manganese ores . 11,995 $116,722 7,477 $60,911 2,825 $25,335 Manganiferous iron ores . . . 574,489 1,475,084 901,214 2,001,626 584,493 1,571,750 Manganiferous silver ores . . 228,187 865,959 194,132 908,098 179,205 649,727 Manganiferous zinc residuum 1 52,311 52,311 65,246 65,246 73,264 73,264 Total . . . 866,982 $2,510,076 1,168,069 $3,035,881 839,787 $2,320,076 1 As this is a by-product in the treatment of zinc ores, the value given to it is nominal. 390 ECONOMIC GEOLOGY OF THE UNITED STATES The imports of manganese ore in 1903 amounted to 146,056 long tons, valued at $1,278,108, and came chiefly from Brazil, but the British East Indies, Cuba, Germany, and Russia also supplied some. REFERENCES ON MANGANESE 1. Brewer, Ala. Ind. and Sci. Soc. Proc., VI : 72. (Ga.) 2. Hall, Amer. Inst. Min. Engrs., Trans. XX : 46, 1892. (Crimora, Va.) 3. Hayes, Amer. Inst. Min. Engrs., Trans. XXX : 403, 1901. (Ga.) 4. Pen- rose, Jour. Geol., 1 : 275, 1893. (Chemical relations of iron and manganese in sedimentary rocks.) 5. Penrose, Ark. Geol. Surv., Kept, for 1890, Vol. I, 1898. (Uses, ores, and deposits.) 6. Van Ingen, Sch. of M. Quart., XXII : 318, 1901. (Batesville, Ark.) 7. Watson, Amer. Inst. Min. Engrs., Trans. XXXIV: 207, 1904. (Ga.) 8. Birkenbine, Mineral Census, 1902, Mines and Quarries. MERCURY Ores. While mercury is sometimes found native in the form of quicksilver, the most common ore is cinnabar (HgS), which contains 86.2 per cent mercury. Native amalgam of mercury and silver is known, and calomel, the chloride, as well as other compounds, are sometimes found. Mode of Occurrence. Mercury ores are not confined to any particular formation, but are found in rocks ranging from the Ordovician to Recent Age in different parts of the world. Nor are they peculiar to any special type of rock, although igneous rocks are often found in the vicinity of them. They occur as veins, disseminations, or as masses of irregular form. Silica, either crystalline or opaline, and calcite are common garigue minerals, while pyrite or mar- casite are rarely wanting, and bitumen is widespread. Distribution in the United States. California has always been the most important, and, in fact, at times, the only MERCURY 391 producing state. Deposits are, however, also known in Texas, Oregon, Utah, Nevada, and New Mexico. California (1,2,7). The California ores occur chiefly in metamorphosed Cretaceous or Jurassic rocks, with some in the Miocene and even Quaternary. The depos- its, which are termed " chambered veins " by Becker, are fissured zones. Eruptive rocks seem in many cases to be involved in the ore formation, and at New Almaden a rhyo- lite dike runs parallel with the ore body. The ore here occurs along the con- tact between serpentine and shale, filling in part the interstices of a brec- cia. These mines, which are the largest in the state, have been worked to a depth of over 2500 feet. Other occurrences are in Colusa County, where the cin- nabar is found in altered serpentine, and in Napa County, where it occurs along the contact of sandstone and slate. The minerals associated with these are bitumen, free sul- phur, stibnite, mispickel, gold and silver, chalcopyrite, py- rite, millerite, quartz, calcite, barite, and borax. At New Idria the ore is the same, but the wall rock is metamor- phic sandstones and shales. A third important mine is the Sulphur Bank, which is of very recent date. The vein is a fissure filled with brecciated fragments, and cuts FIG. 94. Map of California mercury local- ities. 392 ECONOMIC GEOLOGY OF THE UNITED STATES through sandstone, shale, and augite andesite, the cinnabar cementing the breccia together, but at times also impreg- nating the walls. Hot waters which circulate through the vein still deposit gelatinous silica. At Steamboat Springs the waters carry gold, sulphide of arsenic, antimony, and mercury, sulphides or sulphates of silver, lead, copper, zinc, iron oxide, and possibly other metals. They also contain sodium carbonate, sodium chlo- ride, sulphur, and borax. Cinnabar is known in Lane and Douglas counties, Oregon. Texas (3, 4, 5). The Teiiingua district of Brewster County, Texas, has caused much interest in recent years. The ore bodies thus far known lie in a belt 15 miles east and west by 4 miles wide, with Fresno Canon on the west- ern boundary, but the remoteness from the railroad (90 miles) and the lack of water form seri- ous obstacles to the rapid development of this district. The rocks are Cretaceous limestone, which have been broken by several large northwest-southeast faults, with minor parallel ones between. Overlying these are younger sediments and volcanics. Only one of the ore bodies is close to an intru- sive contact. FIG. 95. Map showing Texas mercury region. After Hill, Eng. and Min. Jour., LXXIV: 305. MEBCTJRY 393 Cinnabar is the commonest ore, but other mercury min- erals are present, including quicksilver, which is usually intimately associated with calcite. Hematite and limonite are very common accessories, _^ v _ rv ^__^_ J ^ but pyrite is rare. The ore is most frequently found in fis- sure veins with calcite gangue, these fissures forming two series at right angles to each Other, of which the northeast- FIG. 96. Section of cinnabar vein iu limestone, Terlingua, Tex. After southwest ones are productive. Phillips, Univ. Tex. Min. Surv., The ore also occurs in brec- ciated strips, or as lateral extension veins. The working's are all shallow. Recently an extension of this area has been found in the Chisos Mountains near Terlingua. Origin. The origin of mercury ores has been studied chiefly by Becker (1) and later by Schrauf (6). The for- mer points out that silica (either crystalline or amorphous) and calcite are common gangue minerals, but pyrite or marcasite are almost equally abundant, as is also bitumen. In addition to these, the ores show an irregular association with other metallic minerals, such as antimony, silver, lead, copper, arsenic, zinc, or even gold. Becker believes that the cinnabar has been precipitated from ascending waters by bituminous matter, having come up in solution as a double sulphide with alkaline sulphides. He further sug- gests that the deposits represent impregnations and are not replacements. Uses of Mercury. The most important use of quick- silver is in the extraction of gold and silver by the process 394 ECONOMIC GEOLOGY OF THE UNITED STATES of amalgamation (see Gold and Silver). Its power of form- ing amalgams with other metals makes it of value in the arts for the preparation of a substance used for silver- ing mirrors and for other purposes. Because it is liquid at ordinary temperatures it can be employed in the manufac- ture of thermometers ; and this fact, added to its weight, renders it of special value in the construction of mercurial barometers. In medicine mercury is used in various forms, chiefly as calomel, while cinnabar and other compounds of mercury are valuable in the manufacture of pigments. For this purpose it was used by the American Indians and by the other early races of people. Extraction. The mercury is usually obtained from the ore by the simple process of sublimation, the cinnabar being heated in furnaces, and the fumes of sulphur and metallic mercury allowed to pass off. The latter are caught in condensing chambers, while the former escape into the air. Production of Mercury. California was for many years practically the only domestic source of mercury, but in 1898 Texas became a producer, and will no doubt con- tinue so. The output of mercury is quoted in flasks of 76J- pounds net. That of California since 1850 has been as follows : PRODUCTION OF MERCURY IN CALIFORNIA FROM 1850 TO 1900 (Flasks of 76| pounds) 1850 7,723 1860 10,000 1870 . 30,077 1880 59,926 1890 22,926 1900 26,317 MERCURY 395 PRODUCTION OF MERCURY IN CALIFORNIA AND TEXAS FROM 1901 TO 1903 1901 1902 1903 QUANTITY FLASKS VALUE QUANTITY FLASKS VALUE QUANTITY FLASKS VALUE Texas . . 2,932 $132,438 5,319 $239,350 5;029 $211,218 California 26,720 1,285,014 28,974 1,228,498 30,526 1,330,916 The imports of mercury in 1903 were valued at $1065, and the exports at 446,845. The world's production for 1902 was as follows : COUNTRY QUANTITY METRIC TONS VALUE United States 1,190 $1 467 848 Austria 511 568 929 Italy 260 310,080 1,425 1,941,387 REFERENCES ON MERCURY Becker, Geology of Quicksilver Deposits of Pacific Slope, U. S. Geol. Surv., Mon. XIII, 1888. 2. Becker, U. S. Geol. Surv., Min. Res., 1892: 139, 1893. (Origin.) 3. Blake, W. P., Amer. Inst. Min. Engrs., Trans. XXV : 68, 1896. (Cinnabar in Texas.) 4. Hill, Eng. and Min. Jour., LXXIV : 305, 1902. (Tex.) 5. Phillips, Univ. Tex. Min. Surv., Bull. 4, 1902. (Terlingua district, Texas.) 6. Schrauf, Zeitsch. prak. Geologic, II : 10, 1894. (Origin.) 7. Watts, W. L., Cal. State Min. Bur., XI : 239, 1893. (Lake County, California.) CHAPTER XX ANTIMOirr Ores. Stibnite (Sb 2 S 3 ) is the most important ore of antimony, and the metal is rarely obtained from any other mineral, although native antimony has been sparingly found. The oxide senarmontite (Sb 2 O 3 ) seldom occurs in any quantity. A small amount of antimony is present in some silver-lead ores. The stibnite, together with a gangue of quartz, and sometimes calcite, usually forms veins cutting igneous, sedimentary, or metamorphic rocks. Distribution of Antimony in United States. Antimony has been found at a number of localities in the Cordilleran region, but the great distance of the deposits from the rail- road, together with the fact that the smelting plants are located in the East, make them of little commercial value, and no domestic production has been reported since 1901. Moreover, the large output of antimony ores and metal abroad, combined with low ocean freights and the absence of any import tax on crude antimony, are of themselves discouraging to domestic competition. The large amount of antimony now manufactured in the United States is obtained : (1) as a by-product from the smelting of foreign and domestic lead-silver ores con- taining small quantities of antimony ; (2) antimony regu- lus, or metal from foreign countries ; (8) foreign ore. 396 ANTIMONY 397 Uses. Antimony metal is used chiefly in the manufac- ture of alloys of lead, tin, zinc, etc. Type metal, which is an alloy of lead, antimony, and bismuth, has the property of expanding at the moment of solidification. Britannia metal is tin with 10 to 16 per cent antimony and 3 per cent copper. Babbitt, or antifriction, metal consists of antimony and tin, with small amounts of lead, copper, bis- muth, zinc, and nickel. Tartar emetic, a potassium-anti- mony tartrate, is used in medicine and as a mordant for dyeing, while antimony persulphide is employed for vulcan- izing and coloring rubber. Production of Antimony. The production of metallic antimony from domestic and foreign ores since 1890 was as follows : PRODUCTION OF ANTIMONY FROM DOMESTIC AND FOREIGN ORES YEAR QUANTITY SHORT TONS VALUE YEAR QUANTITY SHORT TONS VALUE 1890 938 $175,508 1901 2639 $539,902 1895 2013 304,169 1902 3561 634,506 1900 4226 837,896 1903 3128 548,433 The production in 1903 was about three fifths of the entire consumption. The hard lead (antimonial lead) produced in the United States in 1903, as a by-product from impure lead-silver ores, was 21,237,440 pounds, con- taining 24 per cent antimony. REFERENCES ON ANTIMONY 1. Blake, U. S. Geol. Surv., Min. Res., 1883-4 : 641, 1885. 2. Comstock, Ark. Geol. Surv., Ann. Kept, for 1888, I: 136. (Ark.) 3. Min. Indus., 2 : 13, 1894. (General.) 398 ECONOMIC GEOLOGY OF THE UNITED STATES ARSENIC Although arsenic-bearing minerals are widely distributed in many countries, the commercially valuable occurrences are few. Arsenopyrite (FeAsS), called also mispickel and arsenical pyrites, is the main source of the metal. Realgar (As 2 S 2 ) and orpiment (As 2 S 3 ) may also serve as ores. Arsenopyrite is mined in Washington, where the mineral is used for making arsenious oxide, and more recently de- posits have been opened up in Floyd and Montgomery counties, Virginia. At the former locality the ore, which is chiefly arsenopyrite, averages about 14 per cent arsenic, .7 ounce gold, and 3 ounces silver per ton (2). Arsenopyrite is used chiefly for the manufacture of arse- nious oxide. It is employed in medicine, as a pigment, and as an alloy with lead for making shot. Arsenious oxide is used for making paris green, in glassware for destroying the iron coloration, in certain enamels, and as a fixing and conveying substance for aniline dyes. The domestic production of arsenious oxide in 1903 amounted to 611 short tons valued at $36,691, and was all made at Everett, Wash. This, however, supplied only one quarter of the domestic demand, and large quantities were imported from Canada, Germany, and Spain. The imports of arsenic and its compounds in 1903 amounted to 8,357,661 pounds, valued at $294,602. REFERENCES ON ARSENIC 1. Min. Indus., II : 25, 1894. 2. Struthers, U. S. Geol. Surv., Min. Res., 1903 : 326, 1904. (General.) 3. Merrill, Non-Metallic Minerals, 30, 1904. CHROMIC IKON ORE 399 BISMUTH Ores. The principal ores of this metal, together with the percentage of metallic bismuth which they contain, are : Bismuthinite (Bi 2 8 3 , 81.2) ; bismite (Bi 2 O 3 , 96.6) ; and bis- mutite (Bi 2 O 3 , CO 2 , H 2 O, 80.6). Although all of these contain a high percentage of metallic bismuth, the content of the ore as mined does not usually exceed ten or fifteen per cent. Bismuth ores are commonly associated with those of gold and silver, and the metal is obtained as a by-product in the smelting of these. Distribution. There are many scattered occurrences of bismuth ores throughout the Rocky Mountain states, but Colorado is the most important, and in 1904 Leadville was the only producing region. Uses and Production. Bismuth is chiefly valuable on account of the easily fusible alloys which it forms with lead, tin, and cadmium ; the melting point of some of these lies between 64 C. and 94.5 C. They are therefore employed in safety fuses for electrical apparatus, safety plugs for boilers, dental amalgams, etc. The production of bismuth in 1904 was 5184 pounds, valued at $314. The imports of metallic bismuth in 1904 amounted to 185,905 pounds, valued at 1339,058. CHROMIC IRON ORE Ores. Chromite (FeO, Cr 2 O 3 ) is the chief source of the compounds of the metal chromium which are used in the arts. This ore occurs sometimes in alluvial deposits, but more commonly in basic magnesian rocks, notably serpentine. 400 ECONOMIC GEOLOGY OF THE UNITED STATES Origin of Chromite. It has been pointed out by Pratt (4) that chromite occurs most commonly around the border of basic magnesian rocks of igneous origin. This is believed to indicate that the chromium existed in the original molten rock, and that, as this basic magma cooled, the chromite, being one of the earliest minerals to crystallize, separated out along the border of the mass because this portion was the first to cool. As the cooling proceeded, convection cur- rents within the molten mass would bring additional supplies to the border. Analyses (5). The following table gives the composition of several of the types of chromic iron ores : COLERAINE, FRANCE CAN. Concentrated ASIA MINOR STYRIA CALIF. RUSSIA Product Cr 2 3 37.00 53.64 53.00 53.00 42.20 59.00 SiO 2 2.53 2.31 2.15 2.50 5.48 2.20 A1 2 3 13.15 14.02 7.62 8.00 13.60 10.00 MgO 12.53 15.75 12.31 11.58 14.88 11.62 FeO 34.79 11.47 24.92 24.92 23.84 18.18 CaO 2.81 The price of chromic iron ore is based on its percentage of chromic oxide, the standard ore containing 50 per cent. Every unit above this is valued at from 75 cents to $1 per ton ; but when the percentage is below 50 per cent, the value decreases at an even greater rate. How- ever, ores carrying only 45 per cent of chromic oxide are easily market- able. Low silica is desirable. Distribution in the United States. In the United States chromite was for a time obtained from Chester and Delaware counties, Pennsylvania, and Baltimore County, Maryland, CHROMIC IRON ORE 401 and the exhaustion of these deposits was followed by the opening of others in San Luis Obispo County, California. Subsequently the importation of Turkish and Russian chro- mite commenced, followed by additional supplies from Canada and Newfoundland. This foreign chrome iron ore, especially the Turkish, can be placed on the American market so cheaply that there has been little development of our own deposits. The importation of chromic iron ore from New Caledonia is also increasing. Chromite occurs in a number of places in California besides the one referred to above ; and also in North Carolina, in a belt of peridotite rock extending from Ashe County to Clay County. In this area, however, the chromite has been found in quantity at only a few localities (3). Uses. Metallic chromium has no direct use; but raw chromite and chromium salts have a variety of applications. Owing to its great heat-resisting qualities, chromite is employed in the manufacture of refractory bricks. Such bricks are sometimes used for lining basic open-hearth fur- naces, and as a hearth lining for water-jacket furnaces in copper smelting. They stand rapid changes of temperature well, and are not attacked by molten metals. In the presence of carbon, chromium makes steel extremely hard and resistant to shocks ; therefore chrome steel is suited to a variety of uses, as in the manufacture of paper, hard-edged tools, etc. An alloy of iron and chromium is used in armor plates, alloys of ferro-chromium and ferro- nickel being added to the molten steel before casting. Most of the chromite mined is used for pigments because of the red, yellow, and green color of its compounds, chromate and bichromate of potash. In these forms the substance is em- 2D 402 ECONOMIC GEOLOGY OF THE UNITED STATES ployed in dyeing, calico printing, and the making of pig- ments useful in painting, printing wall papers, and coloring pottery. Alkaline bichromates are employed for tanning skins, and some chromium salts have a medicinal value. Production of Chromite. The amount of chromite pro- duced in the United States is small, and in 1903 California was the only source of supply. The production for several years was as follows : PRODUCTION OF CHROMITE IN THE UNITED STATES FROM 1900 TO 1903 YEAR QUANTITY LONG TONS VALUE 1900 140 $1400 1901 368 5790 1902 315 4567 1903 150 2250 The value of the imports for the last three years was : YEAR CHROMATE AND BICHROMATE OF POTASH CHROMIC ACID CHROME ORE TOTAL 1901 $29 224 $10 861 $363 108 $403 193 1902 11,115 582,597 593,712 1903 32 174 292 025 3^4 199 REFERENCES ON CHROMIC IRON ORE 1. Glenn, Amer. Inst. of Min. Engrs., Trans. XXXI : 374, 1902. 2. May- nard, ibid., XXVII : 283, 1898. (Newfoundland.) 3. Pratt, U. S. Geol. Surv., Mineral Resources, 1901 : 941, 1902. (General.) 4. Pratt, U. S. Geol. Surv., Bull. 180. (Origin.) 5. Anon., Min. Indus., VI : 147, 1898. (Analyses.) NICKEL AND COBALT 403 MOLYBDENUM Ores and Occurrences. Molybdenite (MoS 2 ) and, less com- monly, wulfenite (FbMoO 4 ), are the chief sources of this metal. Molybdenite forms irregular masses or disseminations in crystalline rocks, and many occurrences are known in the West, for example, in California, Washington, Montana, Utah, Arizona, New Mexico, and in the East, in Maine. An ore to be marketable must contain over 45 per cent of molybdenum and be free from copper, the average price of a 50 to 55 per cent ore being about $400 per ton. Uses. Its chief use is in the manufacture of chemicals, especially ammonium molybdate, and for coloring porcelain green. A nickel-molybdenum alloy is also made. The use of molybdenum for hardening steel is increasing, it being used chiefly for tool steel. Production of Molybdenum. The production of molyb- denite in 1903 was 6200 tons crude ore, but very little of this was concentrated and marketed. REFERENCES ON MOLYBDENUM 1. Crooks, Bull. Geol. Soc. Amer., XV: 283, 1904. (N.Y.) 2. Pratt, U. S. Geol. Surv., Min. Res., 1903 : 307, 1904. (General.) 3. Smith, U. S. Geol. Surv., Bull. 260 : 197, 1905. (E. Me.) - NICKEL AND COBALT Ores. These two metals can best be treated together, for nearly all the ores containing one are apt to carry some of the other, and furthermore, in smelting, the two metals go into the same matte, and are separated later in the refining process. 404 ECONOMIC GEOLOGY OF THE UNITED STATES The ores of nickel and cobalt, together with their composi- tion and the percentage of nickel or cobalt they contain, are : ORE COMPOSITION Ni Co Pyrrhotite (nickeliferous) IVIillsritG Fe n S 12 NiS 0-6 646 Pentlandite G6nthit6 (FeNi)S 2 NiO 2 , 2 MoO 3 SiO 2 6 H 2 O 22 2 9 46 NiAs 43.9 Linricfcite (CoNi),S, 30.53 21 34 The nickeliferous pyrrhotite is the most widely distributed of the nickel ores, and may carry small amounts of cobalt. It is also called magnetic pyrites. The percentage of nickel ranges from a trace to 6 per cent, but an increase above this brings it into pentlandite. The millerite is sometimes found associated with pyrrhotite ores. Of the genthite, the variety known as garnierite forms the ores, and carries from 21 to 45 per cent nickel oxide. Distribution. Very little direct mining for nickel and cobalt is done in the United States, but at Mine la Motte, Missouri, considerable quantities have been obtained annually as a by-product in lead mining. (See under Lead.) Eastern Occurrences of Nickel. The Gap Nickel Mine, Lancaster County, Pennsylvania, is the most important eastern occurrence. It was actively worked from 1863 to 1880, being during that period the only nickel ore mined on this continent. In 1902 the mine was again operated. The ore is pyrrhotite associated with amphibolite, an altered intrusive, the whole inclosed by mica-schist. The pyrrhotite is believed to have originated by magmatic segregation (4). NICKEL AND COBALT 405 Nickel minerals have also been found in the basic magnesian rocks of North Carolina. Western Occurrences. Deposits of nickel and cobalt ores are known in Idaho and Oregon, but they have not yet assumed importance. Nickel ore is found in Ferry County, Wash- ington, and other deposits are reported from Sheridan and Piney Creek, Wyoming, as well as at several localities in Nevada, Idaho, Arizona, and South Dakota ; but none of the occurrences are worked, and the main source of supply on this continent comes from Sudbury, Ontario (1, 2). There, the ore, which occurs in enormous masses, is a nickeliferous pyrrhotite, and the output forms probably one half of the world's produc- tion. The ore occurs on the contact of quartzite and diorite, or forms, more often, scattered irregular masses in the latter. Its origin has been a matter of some dispute, some having regarded it as a product of mag- matic segregation, while others believe the ore to have been deposited in the crushed diorite. A partial analysis shows : Cu, 8.05 ; Ni, 2.97 ; Fe, 26.21; SiO 2 , 26.05; S, 19.08. The second important source of the world's nickel ore is the mines of New Caledonia, in the Pacific Ocean, off the east coast of Australia. The ore is garnierite. Uses of Nickel. The most important and increasing use of nickel is for the manufacture of nickel and nickel-chromium steel. This, on account of its great hardness, strength, and elasticity, is used for making armor plate, gun shields, turrets, ammunition hoists, etc. Krupp steel, which may be taken as a type, has approximately 3.5 per cent nickel, 1.5 per cent chromium, and .25 per cent carbon. Owing to its abrasive resistance, nickel-steel is now much used for rails. Other important uses are for large forgings, marine engines, wire cables, and electrical apparatus. A steel with 25 to 30 per cent nickel shows high resistance to corrosion by salt, fresh 406 ECONOMIC GEOLOGY OF THE UNITED STATES or acid waters, or by superheated steam. German silver is an alloy of zinc, copper, and nickel. Uses of Cobalt. Cobalt steel, while having a high elastic limit and breaking strength, cannot compete with nickel steel on account of its high cost, and the main use for cobalt is as a pigment. Production. The production of nickel from domestic ores and cobalt oxide in the United States from 1892 to 1901 was : PRODUCTION OF NICKEL AND COBALT FROM DOMESTIC ORES YEAR NICKEL COBALT OXIDE Quantity Pounds Value Quantity Pounds 1892 92,252 10,302 9,715 6,700 5,748 114,200 $50,739 3,091 3,886 3,551 2,701 45,900 7,869 14,458 6,471 13,360 3,730 120,000 1895 1900 1901 1902 .... 1903 The amount of nickel produced in Canada in 1903 was 12,505,510 pounds. The imports of cobalt oxide in 1903 were 73,350 pounds, valued at $145,264, while the total value of the nickel imported in the same year was $1, 849,620. The exports of nickel oxide and matte in 1901 were $1,483,889. THE WORLD'S PRODUCTION OF NICKEL QUANTITY VALUE Canada 1903 . . 12 505 510 pounds $5 00 204 France 1902 1 600 met tons 1 080 800 Germany 1902 1 605 met tons 1 122 271 PLATINUM GROUP OF METALS 407 REFERENCES ON NICKEL AND COBALT 1. Barlow, Can. Geol. Surv., Ann. Kept., XIV, pt. H, 1904. (Ontario.) 2. Dickson, Amer. Inst. Min. Engrs., Trans. XXXIV: 3, 1904. (Ontario.) 3. Hodges, Amer. Inst. Min. Engrs., Trans. X : 657, 1882. (Nev.) 4. Kemp, Amer. Inst. Min. Engrs., Trans. XXIV : 620, 1895. (Pa.) 5. Neill, Amer. Inst. Min. Engrs., Trans. XIII : 634, 1885. (Mo.) PLATINUM GROUP OF METALS Platinum. The ores of platinum are native platinum (100 per cent Pt), and sperrylite, PtAS 2 (56.5 per cent Pt). The former is commonly found in placer deposits, but it has also been noted in basic igneous rocks rich in olivine, such as peridotite, or in serpentine derived from it. The sperrylite never occurs in large quantities, but has been found in association with nickel and copper ores. Iridos- mine and osmiridium are also known to carry platinum. The nuggets found in placers are commonly regarded as being pure native platinum, but this, according to Kemp (4), is only true in part, most of those assayed yielding between 70 and 85 per cent, and the richest recorded being 86.5 per cent. The balance is made up largely of iron, the highest percentage of this noted being 19.5 per cent in a Ural specimen. Iridium, rhodium, and palladium are always present. Until the platinum falls below 60 per cent the iridium rarely reaches 5 per cent, rhodium 4 per cent, while palladium is less than 2 per cent. Other elements that have been detected in the nuggets are osmium, ruthenium, cop- per, and even gold, while chromite is a common associated mineral (4). Distribution in the United States. The domestic supply of platinum, never large, has been obtained in recent years 408 ECONOMIC GEOLOGY OF THE UNITED STATES as a secondary product from gold-placer deposits in Trinity and Shasta counties, California, and while its occurrence has been reported in many other gold placers of the Northwest and Alaska, still none of them have proven sufficiently rich to work. Iridosmine and a natural alloy of iron and nickel called josephinite are found associated with the gold. In addition to the above sources, platinum is also found in the copper ores of the Rambler mine, Wyoming, and has been saved from the slimes obtained in treating the copper ore and matte at this locality. The covellite in the ore assays .06 to 1.4 ounces per ton of platinum. Uses. Platinum was first used as an adulterant of gold, and in Russia it was used for coinage from 1828 to 1845. At the present time it is employed for crucibles and other chemical apparatus which are to be subjected to high temper- atures or strong acids. It is also of value in dentistry, for electric lamps and electric apparatus, for jewelry, and in photography. The price of it has risen steadily in recent years, so that it is as valuable as gold. . Production. The production in the United States from 1880 to 1903 was as follows : PRODUCTION OF PLATINUM IN THE UNITED STATES YEAR QUANTITY OUNCES VALUE YEAR QUANTITY OUNCES VALUE 1880 100 $400 1900 400 $2,500 1885 250 187 1901 1,408 27,526 1890 600 2,500 1902 94 1,874 1895 150 900 1903 6,080 PLATINUM GROUP OF METALS 409 Since the close of 1899 platinum has risen steadily in price, reaching a maximum of $20 per ounce in 1902. The imports of platinum, both crude and manufactured, amounted to 11,987,980 in 1902, and 82,055,933 in 1903. The domestic production is entirely inadequate to supply the demand, and the greater portion of the supply of the United States, and in fact the world, is obtained from the platinum placers of the Urals (5). REFERENCES ON PLATINUM 1. Day, U. S. Geol. Surv., 19th Ann. Kept., VI : 265, 1898. 2. Day, Amer. Inst. Min. Engrs., Trans. XXX : 702, 1901. (N. Amer.) 3. Donald, Eng. and Min. Jour., LV : 81, 1893. (Can.) 4. Kemp, Min. Indus., X: 540, 1902; and U. S. Geol. Surv., Bull. 193, 1902. (General.) 5. Purington, Eng. and Min. Jour., LXXVII : 720, 1904. (Russia.) Palladium. This metal is found associated with platinum and also native and alloyed with gold (Brazil). It is of silver-white color, ductile and malleable, and is unaffected by the air. Its great rarity and consequent high value has restricted its use, but a small amount is used for some mathe- matical and surgical instruments, for compensating balance wheels and hair springs for watches, and for finely graduated scales. In the United States it has been reported from the platinum deposits of the Pacific Coast and from the Rambler mine in Wyoming. Osmium. This, the heaviest and most infusible metal known, occurs alloyed with platinum and also with iridium in iridosmine. In the United States small quantities have been found in the platinum placers of California. Iridosmine is employed for pointing pens and fine tools, 410 ECONOMIC GEOLOGY OF THE UNITED STATES while osmic acid is used for staining anatomical prepara- tions in microscopic work. Iridium. Iridium is found chiefly in Russia and Cali- fornia, alloyed with platinum or osmium. It is a lustrous, steel-white metal of great hardness, and is, next to osmium, the most refractory metal known. An alloy of iridium and platinum has been used for standard weights and measures, and iridium is also used in photography. TIN Ores. Oassiterite (SnO 2 ), with 78.6 per cent metallic tin, is the principal ore of this metal, but owing to the pres- ence of impurities the ore rarely shows this composition. Its hardness (6-7), imperfect cleavage, nonmagnetic charac- ter, high specific gravity (6.8-7.1), and brittleness help to distinguish it from other minerals that are liable to occur with it. The mineral stannite, or tin pyrites, a complex sulphide of copper, iron, and tin, rarely serves as an ore. Stream tin is the name applied to cassiterite found in placers. Mode of Occurrence. Cassiterite of primary character is usually found in veins of pegmatite, or, more commonly, greisen (quartz and muscovite or lepidolite), around the edges of granite areas. This, together with the associa- tion of fluorite, tourmaline, and topaz with the ore, indicate quite clearly that it may be the result of fumarolic action. This type of occurrence is, however, of little commercial value, and over 80 per cent of the world's supply comes from placers whose materials have been derived from tin- bearing veins. r TIN 411 Distribution in the United States. Although tin has been found at a number of localities in the United States, only a very few of these can be looked upon as commercial sources. The Black Hills (1, 2, 6) of South Dakota and Wyoming is perhaps the best known tin-producing region of the United States, and although much money has been sunk in its development and many ex- citing rumors have been pub- lished regarding it, the output been ex- ceedingly small. Here the tin oc- curs either in FlG 97> _ pegmatite dikes map showing location of Carolina tin belt. After Graton, U. S. GeoL Surv., Bull. 260. or quartz veins and in placers. The Harney Peak deposits of the northern Black Hills have produced but little, but the Nigger Hill region of Wyoming, in the northwestern part of the hills, seems to be more promising. More recently the tin deposits of North and South Caro- lina (4, 6) have been attracting considerable attention. These lie in a belt extending from Cherokee County, South Caro- lina, to Lincoln County, North Carolina. The cassiterite occurs as an original constituent of pegmatite dikes, but is somewhat irregularly distributed in them. Some of the 412 ECONOMIC GEOLOGY OF THE UNITED STATES mines now being worked at Gaffney, South Carolina, and Kings Mountain, North Carolina, are promising. An inter- esting feature is that the dikes are of undoubted igneous origin. Tin has been reported from a number of localities in Alaska (3), but the production is still very small, that during 1903 and 1904 having amounted to not more than 100 tons. The most important occurrences are on the Seward pen- insula, where it occurs in placers, quartz-porphyry dikes, granites, or in sedimentaries near their contact with the igneous rock. In the dikes the accompanying minerals are tourmaline, topaz, fluorite, zinnwaldite, wolframite, quartz, epidote, pyrite, galena, etc. The amount of tin ore produced in the United States is entirely too small to supply the demand, and the main source of supply for this country, and indeed for the world, is the Malay peninsula, while other regions of commercial importance are Australia, Bolivia, and Great Britain. Uses of Tin. Tin is used chiefly for the manufacture of bronze and tin plate, and to a smaller extent in plumbing as well as less important purposes. Britannia metal is com- posed of from 82 to 90 parts of tin alloyed with antimony, copper, and sometimes zinc. Production of Tin. The world's production for a number of years has been behind the demand, a fact which has not only kept up the price of this metal, but also stimulated prospecting and mining. The world's production for 1904 as given by the Engineer- ing and Mining Journal was : TITANIUM 413 COUNTRY TONS Straits Settlements 65,696 Banka and Billiton 16,394 Bolivia 10,304 Australia and Tasmania 5,692 England , 4,796 Germany and Austria 112 Miscellaneous 140 Total 103,134 The price of tin on the New York market in 1904 averaged about 28 cents per pound. The United States in 1904 con- sumed about 43,120 tons of tin. REFERENCES ON TIN 1. Blake, Amer. Inst. Min. Engrs., Trans. XIII: 601. (Black Hills.) 2. Blake, U. S. Geol. Surv., Min. Res., 1883-84 : 592, 1885. (Ores and deposits). 3. Collier, U. S. Geol. Surv., Bull. 220, 1904. (Alaska and general.) 4. Graton, U. S. Geol. Surv., Bull. 260 : 188, 1905. (N. Ca. and S. Ca.) 5. Hess and Graton, U. S. Geol. Surv., Bull. 260 : 161, 1905. (Occurrence and distribution). 6. Struthers and Pratt, U. S. Geol. Surv., Min. Res., 1903 : 335, 1904. (U. S.) 7. Weed, U. S. Geol. Surv., Bull. 178, 1901. (Texas.) Also Bull. 213 : 99, 1903. 8. Winslow, Eng. and Min. Jour., XL : 320, 1885. (Va.) TITANIUM Ores. Among the minerals carrying titanium the most abundant is ilmenite (FeO, TiO 2 ), which occurs in many deposits of magnetite. Entile (TiO 2 , 60 per cent Ti when pure), though less abundant, is not uncommon. Titanium is also found in a number of other minerals, many of which are rare. Occurrence. For many years Norway has been the chief producer of this metal ; but in 1900 large deposits of rutile were discovered in Virginia, from which, up to the end of 1901, about 40,000 pounds had been extracted. 414 ECONOMIC GEOLOGY OF THE UNITED STATES The Virginia ore (2), which is found in Nelson County, occurs in the form of small granules, disseminated through a ground mass of feldspar or as a segregation in quartz, in a rock of probable igneous origin. Until the discoveiy of the Virginia deposits, the domestic demand, which has been small, was supplied from deposits in Chester County, Pennsylvania. Uses. Titanium is used for producing yellow underglaze colors on pottery, and also in the manufacture of artificial teeth, to give them an ivory tint. Another use is in the alloy ferro-titanium. Its commercial values as a steel-hard- ening metal are not yet thoroughly proven, but from .5 to 3 per cent titanium appear to materially increase the transverse and tensile strength of steel. By the use of the electric fur- nace, ferro-titanium can be produced directly from the ores, which would open a use for our American titaniferous magnetites. REFERENCES ON TITANIUM 1. Merrill, Non-metallic Minerals: 109, 1904. (General.) 2. Merrill, Eng. and Min. Jour., LXXIII : 351, 1902. (Va.) 3. Pratt, U. S. Geol. Surv., Min. Res., 1903 : 309, 1904. TUNGSTEN Ores. The ores of tungsten are wolframite ([FeMn] WO 4 ), hubnerite (MnWO 4 ), and scheelite (CaWO 4 ). Of these wolframite is the most abundant, and scheelite, the most easily reducible ore of tungsten, the least abundant. Schee- lite is found in but few localities in the world, and in the United States occurs in commercial quantity at only one locality. Although the ores of tungsten are rare, the quantity available exceeds the demand. TUNGSTEN 415 Occurrence. Most of the known American deposits of tungsten ores are found in the western states, especially Arizona (1, 2, 6), Nevada, and Colorado. That found near Dragoon, Arizona (6), consists of hiibnerite with subordinate scheelite, and concentrates easily to a product yielding WO 3 , 70.22; SiO 2 , .30; Fe, 1.90; Mn, 19.82; CaO, 4.87; MgO, 3.40. Rich ores are found in White Pine County, Nevada, at some distance from the railroad. In Colorado wolframite and hiibnerite occur in several counties, and have been mined to some extent. Eastern occurrences are rare, but scheelite is found at Longhill, Connecticut (8), where it occurs along the contact of limestone with diorite and hornblende gneiss. Tungsten is also found associated with the Cambrian sili- ceous gold ores of the Black Hills region, South Dakota (4), but this source has not become of great importance. Uses. Tungsten has been used for some years to fix the color in wash goods and make them fireproof. It has also been employed for manufacturing stained paper. But the most important present use is for the alloy ferro-tungsten, or in the manufacture of tungsten-steel. Alloys of tung- sten, aluminum, and copper are also made. The fluores- cent properties of tungstate of lime make it useful in the Rontgen ray apparatus. Tungsten is also employed for coloring glass. Production. In 1903 the production was 2451 short tons, yielding 292 short tons concentrates valued at 143,639, or |149 per ton. This production came from Colorado, Arizona, and Connecticut. In 1903 ferro-tungsten-chrome alloys were imported to the value of 118,136. 416 ECONOMIC GEOLOGY OF THE UNITED STATES REFERENCES ON TUNGSTEN 1. Blake, Eng. and Min. Jour., LXV: 608, 1898. (Ariz.) 2. Blake, Min. Indus., VII : 720, 1899. (Ariz.) 3. Blake, Amer. lust. Min. Engrs., Trans., XXVIII : 543, 1899. 4. Irving, Amer. Inst. Min. Engrs., Trans., XXXI : 683, 1902. (S. Dak.) 5. Pratt, U. S. Geol. Surv., Min. Res., 1903 : 304, 1904. (General.) 6. Rickard, Eng. and Min. Jour., LXXVIII : 263, 1904. (Ariz.) 7. Thomas, Min. and Met., XXIV : 301. (Ores and uses.) 8. Hobbs, U. S. Geol. Surv., 22d Ann. Kept., II : 13, 1902. (Conn.) URANIUM AND VANADIUM Ores. The minerals serving as the ores of uranium metals are uraninite (UO 3 , UO 2 , PbO, N, etc.), gummite (doubt- ful composition), and gamotite. The last-mentioned also carries vanadium, as does also vanadinite [(PbCl)Pb 4 (VO 4 ) 3 ]. The chief sources of uraninite are the mines near Central City and in Montrose County, Colorado. Gamotite occurs in Montrose County, Colorado, and also in Utah, while vanadinite has been found in some quantity in the gold and silver mining districts of Arizona and New Mexico. Uses. Uranium and vanadium increase the strength and toughness of steel, and are used to a small extent in the manufacture of ferro-alloys. Uranium oxides are used for coloring porcelain and glass, and vanadium oxide as a dyeing material. Vanadium compounds are employed in making vanadium bronze. Production. The output of the ores of these minerals in 1901 came chiefly from Colorado, and amounted to 375 short tons. In 1903, as a result of much prospecting and developmental work, there was a production of 432 short tons of crude ore. Thirty tons of concentrates were sold URANIUM AND VANADIUM 417 at a value of 15625. Most of the uranium and vanadium ores mined in the United States are exported, but a large quantity of uranium and vanadium salts are imported, the value of these in 1903 amounting to $13,498. REFERENCES ON URANIUM AND VANADIUM 1. Boutwell, U. S. Geol. Surv., Bull. 260 : 200, 1905. (Utah.) 2. Pratt, U. S. Geol. Surv., Min. Res., 1901. 3. Merrill, Non-Metallic Min- erals : 299 and 320, 1904. (General.) INDEX Abrasives, 158. artificial, 166. production of, 165. references on, 166. See Buhrstones, Whetstones, Pumice, Co- rundum, Garnet, Quartz, Infusorial Earth. Actinolite, as gangue mineral, 295. Adobe clay, defined, 99. ^Eolian soils, 214. Alabama, bauxite, 3T6 ; clinton ore, 266; fuller's earth, 175 ; graphite, 179 ; kaolin, 101 ; limonite, 271 ; phosphate, 153 ; Port- land cement materials, 119; stoneware clay, 103 ; Warrior coal, analysis, 7. Alabaster, ^43. Alaska, coal, 32 ; coal mining, 33 ; copper, 298 ; gold, 353 ; lignite, analysis from, 6 ; magmatically segregated-* ores, 225 ; petroleum, 54 ; tin, 412 ; yield of gold ores, 332. Albertite, properties, 59. distribution, 59. Algeria, onyx marbles, 83. Algonkian, copper in, 295 ; iron in, 260. Alkali soils, 215. Alkalies, effect on clay, 96. Alluvial soils, 214. Almandite, uses as gem, 194. Alumina, effect on clay, 95. in iron ores, 252. in soils, 214. Aluminum, 375. for lithographic work, 182. ores of, 375. production of, 382. references on, 888. uses of, 379. Alundum, 165. Amethyst, as gem, 195. Amorphous phosphates, see Phosphates. Amygdaloids, copper-bearing, 288. Analyses of, anthracite coal, 8; asphaltites, 60 ; bauxite, 376 ; bituminous coal, 8 ; bituminous rocks, 61 ; cement rock, natural, 112 ; chromite,400 ; clays, 98; coal, elementary, 14 ; copper ores, Butte, 285; fuller's earth, 175; glass sand, 177; greensand, 156; gypsum, 143; hematites, 264, 268; kaolin, crude, 101 ; kaolin, washed, 101 ; lig- nite, elementary, 14 ; limestones, 109 ; limonites, 272; lithographic stone, 181 ; magnetites, uon-titaniferous, 257; magnetites, titaniferous, 258; maltha, 60 ; mine waters, 227 ; min- eral waters, 206 ; monazite, 191 ; natural gas, 43 ; peat, elementary, 14 ; petroleum, 41 ; phosphates, 154 ; Portland cement materials, 115 ; Port- land cements, 116 ; proximate, of United States coals, 6; rock salt, 181 ; solid matter in brine, 131 ; waters, sea and ocean, 124. Analysis of, barite, 170 ; bat guano, 155 ; bitu- minous coal ash, 9 ; brick clay, 98 ; calcareous clay, 98 ; copper ore, 298 ; fire clay, 98 ; graphite, 178 ; gypsum, calcined, 144 ; kaolin, 98 ; kaolinite, 98 ; lignite ash, 9 ; molding sand, 189 ; nickel ore, Canada, 405 ; oil shale, 57 ; peat ash, 9; pyrite, 199; shale, 98; stoneware clay, 98 ; tungsten concen- trates, 415; zinc ore, 315; zinc ore, Creede, Colo., 819; zinc ore, Lead- ville, 318 ; zinc ore, New Jersey, 809. Anglesite, 303, 305, 371. Anhydrite, defined, 139. Anthracite, 5, 22. effect of igneous intrusions on, 15. price per ton, 34. properties of, 5. Anthraxolite, occurrence and properties, 59. Antimony, 396. distribution in United States, 396. gangue minerals, 396. mode of occurrence, 396. production, 897. references on, 397. sources, 396. uses, 397. with mercury, 393. Apatite, as a fertilizer, 147. sources, 147. Apex, 239. Appalachian coal field, 20. anthracite area, 22. bituminous area, 21. character of bituminous coals, 22. Appalachian petroleum, distillates from, 42. 419 420 INDEX Appalachian region, copper ores of, 294. depth of oxidation in ore bodies, 244. petroleum in, 48. Apsdin, Joseph, discoverer of Portland cement, 113. Aquamarine, 194. Archaean, iron ores in, 261. Argentite, 286, 325. Argillaceous limestone,for Portland cement,114. Arizona, asbestos, 168 ; fluorspar, 173 ; garnet, 195; molybdenum, 403; rubies (so called), 193 ; tungsten, 415 ; turquoise, 194; vanadium, 416; weathering of ores, 281. Arkansas, bauxite in, 378; bituminous coal, analysis of, 7 ; coal fields, 29 ; fuller's earth, 175 ; lignite, 30 ; lirnonite, 271 ; manganese, 387 ; novaculite, 160 ; phosphate, 153 ; Portland cement ma- terials, 119 ; semi-bituminous coal, analysis of, 7 ; whetstone, 160 ; zinc ores, 315. Arkose, defined, 85. Arsenic, 398. distribution, Virginia, 398 ; Washington, 398. in iron ores, 252. references on, 398. sources of, 398. uses, 398. with mercury, 393. Arsenopyrite, 398. Artesian water, 209. depth below surface, 209. distinction from ground water, 210. distribution, Atlantic coast, 210; Great Plains, 211 ; Mississippi Valley, 211. geologic horizon of, 209. in metam orphic rocks, 210. Asbestos, asbestos minerals, 167. amphibole, mode of occurrence, 167. as mineral pigment, 188. chrysotile veins, origin, 168. distribution, 167 ; Canada, 168 ; Georgia, 167 ; North Carolina, 167 ; Virginia, 167. production, 169. references on, 169. serpentine, mode of occurrence, 167. uses, 169. Ashburner, on origin of petroleum, 44. Ash, coal, analyses of, 9. Ash in coal, 9. Ash soils, 214. Ash, volcanic, see Volcanic Ash. Asia Minor, turquoise in, 194. Aspen, Colo., lead-silver, 307, 367. Asphaltites, defined, 57. properties, 58. uses of, 61. Asphaltum, references on, 67. Astral oil, 56. Atlantic Ocean, analysis of water, 124. Azurite, 278, 281, 291, 293, 371. B Babbitt metal, 397. Bain, on Missouri lead-zinc ores, 317. Ball clay, defined, 99. distribution of, 103. Barite, as mineral pigment, 187. distribution, 170; Connecticut, 170; Mis- souri, 170 ; North Carolina, 170 ; Pennsylvania, 170; Tennessee, 170; Virginia, 170. mode of occurrence, 170. production, 170. references on, 171. uses, 170. Barre, Vermont granite, 77. Bauxite, analyses of, 376. distribution, Alabama, 376 ; Arkansas, 373 ; Georgia, 376 ; New Mexico, 379. production of, 380. properties, 375. references on, 383. uses, 380. Bavaria, lithographic stone, 182. Beaufort, S. C., phosphate deposits, 150. Beaumont, Texas, petroleum, 51. Becker, on mercury origin, 393. Bedding planes, effect on quarrying, 74. Belgium, buhrstones from, 161. Benzine, in petroleum, 42. Berea sandstone, 86. Bessemer ores, defined, 252. Bingham Canyon, Utah, copper, 296, 307. Bisbee, Ariz., copper, 290. Bismite, 399. Bismuth, distribution, Colorado, 399. ores, 399. production, 399. uses, 399. Bismuthinite, 399. Bismutite, 399. Bitumen, with mercury, 390, 393. with zinc, 315. Bituminous coal, price per ton, 34. properties of, 4. See Coal. Bituminous rocks, analyses, 61. California, described, 60. defined, 57. distribution, geographic, 57. geologic, 57. Indian Territory, mentioned, 60. Kentucky, mentioned, 60. origin, 57. Black copper, at base of gossan, 244. Black Hills, 8. Dak., tin, 411. tungsten, 415. Black Sea, analysis of water, 124. Black silver, 325. Blende, as contact ore, 235. See Sphalerite. Bluestone, defined, 85. See Building stones. INDEX 421 Bonanzas, 237, 286, 338, 345. Bone coal, 24. Boracite, 134. Borax, 184. marshes, California, 135. minerals containing, 134. near Daggett, 135. production, 136. references on, 135. uses, 185. Bornite, 278, 279, 286, 292. as contact ore, 235. secondary, 286. Bort, 192. Boulder, Colo., petroleum at, 53. Boulder, Mont., auriferous hot spring, 228. Bradford district, Pa., natural gas in, 54. Brass, 299, 320. Braunite, 383. Brazil, emerald, 193; magnetite sand, 258; monazite, 190; topaz, 194. Breaker, coal, 24. Brick clay, analysis of, 98. defined, 99. distribution of, 104. Brines, natural, 127. Britannia metal, 397. Brittle silver, 325. Bromyrite, 325. Bronze, 299. Brooks, on Lake Superior ores, 262. Brownstone, defined, 85. Buhrstones, characters, 161. distribution, 161. German, 161. Building stones, 69. absorption of, 73. color, 70. crushing strength, 72. cut off, 74. density, 70. distribution, see under Granite, Sandstone, Limestone, Marble, Slate. fading, cause of, 70. hardness, 71. lift, 74. permanent swelling, 73. porosity of, 73. production of, 89. properties of, 69. quarry water in, 73. references on, 90. resistance to frost, 78. to heat, 73. rift, 74. sap of, 73. specific gravity, 71. strength, 71. texture, 70. Bully Hill, Calif., copper, 298. Butte, Mont., copper ores, 282. metasomatism at, 284. Calamine, 303, 305, 310, 313. Calaverite, 339. Calcareous clay, analysis of, 98. Calcite, see Gangue minerals. California, asbestos mentioned, 168; coal, 31, 32 ; copper, 297 ; fire clay, 103 ; infu- sorial earth, mentioned, 162; Kern Kiver oil field, 53; lignite, analysis, 7 ; lithium, 183 ; magriesite, 184 ; mag- netite, 256 ; manganese, 387 ; marble, 82 ; mercury, 391 ; molybdenum, 403 ; natural gas, 56 ; petroleum, 52 ; petro- leum, characters, 53 ; platinum, 408 ; Portland cement materials, 119 ; salt, 130 ; stoneware clay, 103 ; topaz, 194. Californite, as gem, 195. Calomel, 390, 391. Calumet conglomerate, 288. Cambrian, glass sand, 177. gold ores, 329. ocher, 187. silver ores, 329. tungsten, 415. Cambro-Silurian limonite, 271. pyrite, 199. Cannel coal, properties of, 5. Cape Nome, Alaska, 357. Carbonado, 192. Carboniferous, Appalachian section, 21 ; see Coal, Anthracite, distribution ; cop- per, 290, 293, 296; gold ores, 336; gypsum, 140 ; hematite, 268 ; lime- stones for Portland cement, 119 ; petroleum, 53 ; salt, 129 ; shales for Portland cement, 119 ; siderite, 273 ; silver ores, 336 ; silver-lead, 865, 367, 370 ; zinc ores, 314, 319. Carbonite, 25. Carborundum, 165. Cartersville, Ga., manganese, 386. Cassiterite, 410. Cat's eye (oriental), 194. Cavities, depth of occurrence, 229. fault, 28. formation of, 231. in earth's crust, 229. shrinkage, 231. solution, 231. Cement, calcareous, 109. hydraulic, defined, 111. natural, analyses, 113. difference from Portland, 118. properties of, 112. Portland, analyses of, 116. properties, 113. raw materials, 114. pozzuolano, defined, 111. composition, 111. production, 120. references, 121. Eoinan, 112. 422 INDEX Cement continued. Kosendale, defined, 112. uses of, 119. Cement materials, natural rock, Appalachian region, 117 ; Illinois, 118 ; Kentucky, 118 ; Maryland, 117 ; New York, 117 ; Ohio, 117; Pennsylvania, 117; Wis- consin, 118. Portland, Alabama, 119; Arkansas, 119; California, 119; Colorado, 119 ; Indi- ana, 119; Kansas, 119; Michigan, 119; New Jersey, 118; New York, 118 ; North Dakota, 119 ; Ohio, 119 ; Pennsylvania, 118; South Dakota, 119 ; Texas, 119 ; Utah, 119. geologic age, 118. Cement plaster, 144. Cement rock, natural, analyses, 112. Cerargyrite, 325, 336. Cerium, in monazite, 191. Cerussite, 303, 305, 311, 371. Ceylon, graphite from, 179. topaz in, 194. Chalcocite, 278, 281, 285, 286, 291, 292, 297, 298. Chalcocite, secondary, 286. Chalcopyrite, 278, 279, 281, 292, 293, 294. as a contact ore, 235. in pyrite deposits, 199. Chalk, 80. Champion Springs, N.Y., 205. Chara, as aid in marl formation, 119. Chester, Mass., emery deposits, 164. China clay, defined, 99. Chlorastrolite, as gem, 195. Chlorine, in soils, 214. Chlorite, 326. Chrome yellow, as mineral pigment, 188. Chromic iron, 899. Chromite, 399. analyses, 400. as mineral pigment, 188. associated rocks, 399. association with peridotite, 226. distribution in United States, 400; Cali- fornia, 401 ; North Carolina, 401 ; Pennsylvania, 401. origin of, 400. production of, 402. uses of, 401. with platinum, 408. Chrysocolla, 278, 281. Chrysoprase, as gem, 195. Chrysotile, 167. Chrysotile veins, origin, 168. Cinnabar, 390, 393. Cinnabar, as mineral pigment, 188. Classification of, clays, 98. ore deposits, 246. Clay, adobe, defined, 99. JEolian, 95. air shrinkage, 96. alkalies in, 96. alumina in, 95. analyses of, 98. ball, distribution of, 103. classification of, 98. defined, 92. distribution, by kinds, 100. fire, distribution of, 104. fire shrinkage, 97. flood-plain, 94. fusibility of, 97. geologic distribution, 100. glacial, 94. glass pots, sources, 104. iron oxide in, 95. kaolin, defined, 99, 100. lake, 94, 104. lime in, 96. magnesia in, 96. marine, 94. miscellaneous, referred to, 104. origin, 92, 93. paper, sources, 104. physical properties, 96. plasticity of, 96. pottery, 99, 103. products, production of, 105. properties of, 95. references on, 106. residual, 104. sedimentary, 93. silica in, 95. specific gravity, 97. stoneware, distribution of, 103. sulphur trioxide in, 96. tensile strength, 96. titanic acid in, 96. uses of, 105. varieties, 99. water in, 96. Clay soils, properties, 215. Clausthal, Prussia, banded veins at, 237. Clifton, Ariz., copper, 293. Clinton limestone, gas in, 55. Clinton ore, 266. analyses, 268. Birmingham, Ala., 266. character, 266. distribution, 266. origin, 267. Coal, 3. age of, 19. anthracite, defined, 5. bituminous, defined, 4. bone, 24. cannel, defined, 5. Carboniferous, distribution, 19. cretaceous, distribution, 19. distribution, Alabama, 20; Alaska, 32; Appalachian field, 20; Arkansas, 28, 30; California, 32; Colorado, 31 ; INDEX 423 Coal, distribution continued. Dakota, 31 ; Eastern Interior field, 26 ; Illinois, 27 ; Indiana, 27 ; Indian Ter- ritory, 29; Iowa, 29; Kansas, 29; Kentucky, 27; Maryland, 22; Michi- gan, 27 ; Montana, 31 ; New Mexico, 81 ; Northern Interior field, 27 ; Ore- gon, 82 ; Pacific coast field, 31 ; Penn- sylvania, 22; Khode Island field, 25; Rocky Mountain field, 30 ; South Dakota, 31 ; Southwestern field, 29 ; Texas, 30 ; Triassic area, 25 ; United States, 18 ; Washington, 32 ; Western Interior field, 29. elementary analysis, 14. faulting, 18. formation of, chemical changes during, 12. geologic distribution in United States, 19. heat and pressure, effect on, 14. kinds of, 3. origin of, 9. outcrops, 15. price per ton, 34. production of, 33. proximate analysis of, explained, 6. proximate analyses of United States coals, 6. references on, 35. rocks associated with, 16. seams, see Coal beds, semi-bituminous, defined, 5. Triassic, distribution, 19. Coal beds, pinching of, 16. splitting of, 17. structural features, 15. swelling of, 16. thickness of, 16. Coal-blossom, 16. Coal-brasses, 200. Coal-breaker, 24. Cobalt, Missouri, 404. ores, 404. production of v 406. references on, 407. uses, 406. Cobaltite, as mineral pigment, 188. Coke, natural, see Carbonite. production of, 35. Colemanite, 134. Colorado, anthracite coal, analysis of, 8 ; coal, 31 ; coking coal, analysis of, 7 : cop- per, 298 , desilverized lead, 307 : fire clay, 103 ; lignite, analysis, 6 ; limon- ite, 271 ; magnetite, 256 ; manganese, 888 ; petroleum, 53 ; Portland cement materials, 119; stoneware clay, 103; topaz,194 ; tungsten,415 ; uranium,416. Comb structure, 237. Com stock lode, Nevada, 844. Conglomerate, copper-bearing, 288. Connecticut, barite, 170; garnet, 163; kaolin, 101 ; lithium minerals, 183 ; tungsten in, 415. Contact deposits, copper ores, 293, 2T9. examples of, 235. Contemporaneous ores, in igneous rocks, 224. in sedimentary rocks, 225. Copper, 278. in hot spring deposit, 228. in iron ores, 252. mode of occurrence in United States, 279. native, 278, 279, 287, 289, 296. ores of, 278. production, 299. references on, 801. uses, 298. with mercury, 393. Copper ore, analysis, California, 298. analyses of, Montana, 285. distribution, 281; Alaska, 298; Appala- chian region, 294 ; Ariz., 290 ; Bis- bee, Ariz., 290; California, 297; Clifton, Ariz., 293; Colorado, 298; Connecticut, 296; Globe, Ariz., 294; Idaho, 298; Jerome district, 292; Michigan, 287 ; Montana, 282 ; New Jersey, 296; New Mexico, 293; Pennsylvania, 296 ; Utah, 296 ; Wyo- ming, 298. Copper ores, gold and silver bearing, 828. impurities, 280. superficial alteration, 280. Coquina, 80. Corniferous limestone, gas in, 55. Cornwall, England, tin veins, 235. Cornwall, Pa., magnetite, 256. Corsicana, Texas, petroleum, 52. Corundum, ore of aluminum, 375. as abrasive, 163. distribution, 163. Georgia, 164. North Carolina, 164. mechanical concentration, 165. origin, 164. Cottonwood district, Utah, 307. Covellite, 285, 286. carrying platinum, 408. Creede, Colo., 307. Crested Butte, Colo., 15. Cretaceous, glass sand in, 176; green sand in, 155 ; lignite, 19 ; limestone for lime, 116; mercury, 392; petroleum, 58; phosphate, 153; shale for Portland cement, 119. Crimora, Va., manganese, 385. Cripple Creek, Colo:, gold, 338. Crustification, defined, 236. Cryolite, 875. Crystal Falls district, hematite, 261. Culm, defined, 24. uses, 24. Cuprite, 278, 291. Cut-off, in quarries, 74. 424 INDEX Dakota, lignite in, 31. Dead Sea, analysis of water, 124. Descension theory, 240. Devonian, phosphate in, 153. Diamond, properties of, 192. South Africa, 192. United States, 192. Didymium in rnonazite, 191. Dismal Swamp, analysis of peat from, 6. Disseminated ores, 242. Dolomite, see Gangue. defined, 78. petroleum in, 51. Douglas Island, Alaska,, 354. Dredging gold, 348. Drift mining, gold, 347. Duck River, Tenn., phosphate deposits, 151. Ducktown, Tenn., copper at, 295. Dune soils, 214. E Eagle Pass, Texas, coal, 30. Earthenware clay, defined, 99. Earth's crust, zones in, 228. Eld ridge, on Florida phosphate, 149. Embolite, 325. Emerald, distribution, Brazil, 194 ; Ceylon, 193 ; Hindostan, 193; North Carolina, 193; Siberia, 193. lithia, 194. properties, 193. Emery, defined, 163. Massachusetts, described, 164. New York, mentioned, 164. Emmons, cited, 230. Enargite, 278, 279, 284, 372. England, fuller's earth in, 175. Epidote, 295, 326. in contact deposits, 235. Faults, effect on oil reservoir, 53. relation to oil springs, 53. Feather Eiver, Calif., gold in, 349. Ferric sulphate, as a solvent of ores, 244. effect on pyrite, 244. Ferro-chromium, 401. Ferro-nickel, 401. Ferro-titanium, 414. Fertilizers, apatite, 147. listed, 147. production of, 156. references on, 157. See Phosphate, Guano, Gypsum, and Greensand. Findlay, Ohio, oil pressure at, 45. Fire clay, analysis of, 98. defined, 99. distribution in United States, 102. under coal, 16. Fissure veins, apex, 239. bonanzas, 237. boundaries of, 236. comb structure, 237. filling of, 240. foot wall, 239. hanging wall, 239. linked, 239. lode, 239. ores common in, 237. secondary banding, 236. selvage in, 237. strike of, 239. Fixed carbon, effect of, in coal, 8. Flagstone, defined, 85. Flats, 312. Flint clay, defined, 99. Florence oil field, Colorado, 53. Florida, ball clay, 103 ; phosphate, 148 ; phos- phate, uses, 154. Fluorspar, characters, 171. distribution, Arizona, 173 ; Illinois, deposits described, 172 ; Kentucky, 173 ; Ten- nessee, 173. gangue mineral, 172. gems, 195. occurrence, 171. origin, 173. production, 178. references on, 173. uses, 173. Foot wall, 239. Fort Dodge, Iowa, gypsum at, 140. Foster, on Lake Superior ores, 262. Fountain head, 209. France, buhrstones. 161. Franklinite, 303, 304, 808, 810. Fredonia, N.Y., gas, 40. Freestone, defined, 85. Freiberg, Saxony, banded veins at, 237. Fuel ratio, 8. Fuller's earth, analyses of, 175. difference from clay, 174. distribution, Alabama, 175 ; Arkansas, 175 ; England, 175; Florida, 175; Ne- braska, 175; New York, 175; South Dakota, 175. geological distribution, 175. production of, 176. properties, 174. references on, 176. Gaffney, S.C., tin, 411. Galena, as a contact ore, 235. mentioned, 303, 305, 306, 311, 312, 813, 315, 329, 365, 370, 371, 372, 373, 412. Galicia, ozokerite in, 59. Galvanic action, ore precipitation by, 235. Gangue minerals, barite, 311, 315, 336,342, 865, 867, 372. calcite, 311, 312, 815, 842, 865, 890, 393, 396. INDEX 425 Gangue minerals continued. chert, 315, 365. dolomite, 311, 315, 339, 342, 367. epidote, 295, 412. fluorite, 811, 339, 410, 412. garnet, 295. lepidolite, 410. marcasite, 312, 313. muscovite, 410. orthoclase, 339,- 344. quartz, 311, 335, 336, 339, 342, 344, 367, 370, 372, 373, 390, 896, 412. rhodochrosite, 342, 370, 383. topaz, 410, 412. zinnwaldite, 412. Garnet, as an abrasive, 163. as a gem, 194. distribution, Arizona, 195; Connecticut, mentioned, 163; India, 194; New Mexico, 195 ; New York, mentioned, 163 ; North Carolina, 195 ; Tennessee, 163. in contact deposits, 235. uses as abrasive, 163. Gash veins, in Wisconsin, 240. defined, 240. Gasoline, in petroleum, 42. Genthite, 404. Georgia, asbestos, 167 ; bauxite, 376 ; corun- dum, 164; graphite, 179; manganese, 385; ocher, 187; phosphate, 154; stoneware clay, 103. German silver, 321. Germany, buhr stones from, 161. Gibbsite, 375. Gilsonite, 59. analysis of, 60. occurrence, 59. properties, 59. Glacial soils, 214. Glass sand, analyses of, 17T. distribution, Illinois, 177; Iowa, 177; Mary- land, 177 ; Massachusetts, 177 ; New Jersey, 177 ; Pennsylvania, 177 ; West Virginia, 177. effect of clay in, 176. effect of iron oxide on, 176. geologic distribution, 176. production, 177. properties, 176. references on, 178. Glauber salt, 136. Globe, Ariz., copper, 294. Gold, gravels, 346. gravels, Pacific Coast, 347. Gold Hill, N.C., copper at, 295. Gold, in beach sands, 349. native, 325, 336, 339, 365. Gold ores, chlorination process, 330. classification, 327. cyanide process, 330. distribution, Alaska, 353; Alaska, placer deposits, 356 ; Black Hills, 350 ; Crip- pie Creek, Colo., 338 ; Cordilleran re- gion, 332; Homestake belt, S. Dak., 351 ; Idaho, 337 ; Mercur, Utah, 336 ; Michigan, 352 ; Montana, 337 ; Mother Lode belt, Calif., 333; Nevada Co., Calif., 334 ; Oregon, 335 ; Pacific coast belt, 332 ; Washington, 335. eastern crystalline belt, 352. extraction, 329. free milling, defined, 329. geologic distribution, 329. gold-milling centres, 330. igneous rocks associated with. 326. in igneous rocks, 326. in metamorphic rocks, 326. in propylitic veins, 326. listed, 325. mode of occurrence, 326. production of, 358. quartzose, 328. quartz veins, 326. references on, 360. refractory, defined, 329. sands in arid regions, 349. secondary enrichment of, 327. siliceous, Cambrian, South Dakota, 352. uses of, 357. valuation of, 330. wall rocks, 326. weathering of, 327. with mercury, 393. with platinum, 408. Gold-silver ores, distribution, Bohemia district, Ore., 345; Boulder Co., Colo., 345; Central Belt, 335; Clear Creek Co., Colo., 345; Com stock lode, Nev., 344 ; Eastern Belt, Tertiary ores, 337 ; Gilpin Co., Colo., 345; Monte Cristo, Wash., 345 ; Ouray, Colo., 342 ; Owy- hee Co., Ido.,345; San Juan region, Colo., 341; Silverton, Colo., 341 ; Tel- luride, Colo., 342; Tonopah, 343. Gold veins, associations with igneous rock, 230. Gossan, defined, 242. leaching of, 244. Grahamite, analysis of, 60. occurrence, 59. Grand Eapids, Mich., gypsum at, 142. Granites, 75. characteristics of, 75. color of, 75. distribution, California, 77 ; Central States, 77 ; eastern crystalline belt, 77 ; Min- nesota, 77; Missouri, 77; Montana, 77; Oregon, 77; South Dakota, 77; Texas, 77 ; United States, 77 ; Wash- ington, 77 ; western states, 77. durability of, 75. geologic range, 76. uses of, 77. weight of, 75. 426 INDEX Graphite, amorphous, 179. amorphous, Ehode Island, 179. analysis, 178. artificial, 180. as mineral pigment, 188. distribution, Alabama, 179 ; Ceylon, 179 ; Ceylon, origin, 179; Georgia, 179; Michigan, not such, 179; Montana, 179; New Hampshire, 179; New York, 179; North Carolina, 179; Pennsylvania, 179; Wisconsin, not such, 179. occurrence, 178. production, 180. properties of, 178. references on, 181. uses, 179. Grass Valley, Calif., 834. banded veins at, 287. Gravels, auriferous, 346. Gravity of petroleum, 41. Great gossan lead, 295. Great Salt Lake, analysis of water, 124. Greenland, cryolite in, 875. Greensand, analyses, 156. defined, 155. distribution, 155. source of Texas limonite, 271. Virginia, uses of, 155. Greisen, tin bearing, 410. Grindstones, distribution, 159. properties of, 158. Ground water, 208. movements of, 208. Guano, 155. bat, 155. bat, analysis, 155. bat, Texas, 155. kinds, 155. Peru, 155. West Indies, 155. Gumbo clay, defined, 99. Gypsite, defined, 139. distribution, Kansas, 141 ; Oklahoma, 142 ; Texas, 142 ; Wyoming, 142. origin of, 140. Gypsum, absence from Kansas salt beds, 130. analyses before and after calcination, 144. analyses of, 143. as mineral pigment, 187. calcination process, 144. composition, 139. distribution, Arizona, 142 ; California, 142 ; Colorado, 142 ; Idaho, 142 ; Iowa, 140 ; Kansas, 141; Michigan, 142; Mon- tana, 142 ; Nevada, 142 ; New York, 142 ; Ohio, 142 ; South Dakota, 142 ; Vermont, 142 ; Virginia, 142. formed from pyrite, 140. formed from sea-water, 140. geologic distribution, 139. occurrence, 139. origin, 189. production of, 145. references on, 146. uses, 143. volcanic origin of, 140. H Hamilton shales, for Portland cement, 118. Hanging wall, 239. Hayes, on Arkansas bauxite, 379. on Georgia bauxite, 376. on Tennessee phosphates, 153. Hematite, 259. analysis, Lake Superior, 264. as mineral pigment, 186. distribution, Alabama, 268; Lake Superior region, 259; Missouri, 269; Utah, 268; Wyoming, 268; United States, 259. in contact deposits, 235. with mercury, 393. See Clinton ore. Hermann, on weight of stones, 71. Hindostan, emerald in, 193. Hindostan stone, 160. Holston Valley, Va., gypsum, 142. Horn silver, 325. Hot spring, gold-bearing, 228. Hot spring deposits, see Stibnite, Pyrite, Copper. Hot Springs, 204. Hubnerite, 414. Humus, 213. Hungary, opal in, 195. Huronian, iron ores in, 261. Hydraulic limes, see Lime. Hydraulic mining, 348. I Idaho, auriferous lead ores in, 329 ; copper, 298 ; nickel, 405 ; silver-lead ores, 372. Idaho basin, Idaho, 337. Igneous rocks, miscellaneous, for building, 78. Illinois, brick clays, 104 ; bituminous coal, analysis of, 7; coal field, 26; glass sand, 177 ; natural rock cement, 118 ; ocher, 187; sienna, 187; stoneware clay, 103. Ilmenite, 257, 418. India, garnet in, 194. source of mica, 186. Indiana, Brazil coal, analysis of, 7 ; brick clays, 104 ; cannel coal, analysis of, 7 ; coal field, 27 ; petroleum, distillates from, 42 ; natural gas, 55 ; natural gas analy- sis, 43 ; petroleum, 50 ; Portland ce- ment materials, 119 ; stoneware clay, 103 ; whetstones mentioned, 160. Indian Territory, coal field, 29 ; natural gas, 55. Infusorial earth, defined, 162. distribution, California, 162 ; Maryland, 162 ; INDEX 427 Infusorial earth, distribution continued. Missouri, 162; Nevada, 162; New England, 162 ; New York, 162 ; Vir- ginia, 162. German deposits, 162. uses, 162. Iowa, bituminous coal, 7; coal in, 29; glass sand in, 177 ; gypsum, 140 ; lime rock in, 116 ; limonite in, 271 ; lithographic stone in, 182 ; stoneware clay in, 103 ; zinc ores in, 811. Iridium, properties and occurrence, 410. uses, 410. with platinum, 407. Iron, in copper ores, 280. Iron Mountain, Calif., copper, 298. Iron ores, distribution, Alabama, 266, 271 ; Arkansas, 271 ; California, 256 ; Colo- rado, 256, 257 ; Iowa, 271 ; Kentucky, 273 ; Michigan, 256, 261, 265 ; Minne- sota, 257, 261, 264, 271; Missouri, 269; New Jersey, 256, 257; New Mexico, 256, 268; New York, 255, 257, 258, 266, 273; North Carolina, 255 ; Ohio, 266, 273 ; Oregon, 271 ; Pennsylvania, 256, 273 ; Sweden, 270 ; Texas, 271; Utah, 256, 268; Ver- mont, 271 ; Virginia, 271 ; Wisconsin, 261, 266, 271 ; Wyoming, 256, 268. distribution in United States, 254. geologic distribution, 254. impurities in, 252. magnetite, modes of occurrence, 254. magnetites, origin of, 255. modes of origin, 253. non-titaniferous, 254. production of, 273. references on, 276. See Hematite and Limonite. Iron oxide, effect on clay, 95. in soils, 214. Irving, on Lake Superior ores, 262. Japan, solfataric sulphur in, 196. Jenney, on Missouri lead zinc ores, 317. Jennings, La., petroleum, 52. Jerome, Ariz., copper, 292. Jet, 4. Joplin, Mo., zinc ores, 808, 314. Josephinite, 408. Jurassic, gold, 333; lithographic stone, 182 sulphur in, 197. Kansas, coal, 29 ; gypsite, 141 ; gypsum, 141 ; lime rock, 116 ; natural gas, 55 ; petro- leum, 52 ; petroleum, distillates from, 42 ; Portland cement materials, 119 : salt, 130. Kaolin, defined, 99. analysis of, 98, 10}. . , distribution, Alabama, 101 ; Connecticut, 101 ; Maryland, 101 ; North Carolina, 101 ; Pennsylvania, 101 ; Virginia, 101. origin, 93. Kaolinite, 92. analysis of, 98. product of metasomatism, 326. Kemp, cited, 230, 246, 257, 310, 407. Kentucky, ball clay in, 103 ; bat guano, 155 ; bituminous coal, analysis of, 7 ; coal field, 27 ; fluorspar, 173 ; lithographic stone, 182; molding sand, 190; natu- ral gas, 56 ; natural rock cement, 118 ; stoneware clay, 103. Kerosene, in Wyoming petroleum, 53. Kerosene shale, 57. Keweenaw series, Michigan, 287. Klondike River, Alaska, 354, 356. Knox dolomite, 376. Kunzite, as gem, 195. Lake asphalt, 59. Lake Superior ores, 259. analyses, 264. character, 260. development, 265. origin, 263. Lanthanum, in monazite, 191. Lateral secretion theory, 240. Lead, desilverized, occurrences, 307. gangue minerals of, 304. ores of, 303. production of, 321. references on, 323. uses of, 319. with mercury, 393. Lead ores, Colorado, 307. disseminated, 306. distribution, Appalachian belt, 306; Mis- souri, 806, 314; Kocky Mountain states, 818. gold and silver bearing, 828. impurities in, 304. modes of occurrence, 804. superficial alteration, 805. Leadville, Colo., 364. Lepidolite, 183. Lesley, on origin of petroleum, 44. Lift, in quarries, 74. Lignite, 4. age of, 4. areas in United States, 19. Gulf States area, 80. properties of, 4. Lime, effect on clay, 96. effect on soils, 215. in iron ores, 252. properties, 110. references on, 121. uses of, 119. 428 INDEX Limes, hydraulic, distribution, 117. properties of, 112. Limestone, analyses, 109. burning, changes in, 110. Cretaceous, for building, 80. distribution in United States, 80. for lime, distribution, 116. for Portland cement, 114, 118. general characteristics, 78. lithographic, 181. varieties, 78. See Building stones. Limonite, 269. advantage of using, 272. analyses of, 272. bog ores, 269. Cambro-Silurian, 271. distribution, Appalachian, 271; Arkansas, 271 ; Colorado, 271 ; Iowa, 271 ; Min- nesota, 271; Oregon, 271, Texas, 271 ; Wisconsin, 271. Great Gossan Lead, 271. manganiferous, 271. residual, 270. with mercury, 398. Lindgren, cited, 280. on Colorado gold ores, 837. Linked veins, 239. Linnaeite, 404. Lipari, pumice from, 162. Litharge, 819. Lithium, distribution, California, 183 ; Connec- ticut, 183 ; South Dakota, 183. industry, 188. minerals as sources of, 183. production, 183. uses, 188. Lithographic stone, analyses, 181. definition, 181. distribution, Bavaria, 182 ; Iowa, 182; Ken- tucky, 182. physical properties, 182. references on, 183. Lithophone paint, 170. Lode, 239. Loess, defined, 99. Louisiana, petroleum, 52; salt, 129; sulphur, 197. Lower Carboniferous, fluorspar in, 172. Lower Helderberg, limestone for lime, 116. M Magmatic segregation, 224. in acid rocks, 225. in basic rocks, 224. of copper, 279. Magmatic water, effects of, 230. Magnesia, effect on clay, 96. in iron ores, 252. in natural cements, 118. in soils, 214. Magnesite, California, 184. occurrence and properties, 188. production, 184. references on, 184. uses, 184. Magnetite, as a contact ore, 235. non-titaniferous, 254. sand, 258 ; see Iron ores. titaniferous, 257. analyses, 258. distribution, 257. origin, 257. Maine, molybdenum, 403 ; topaz, 194. Malachite, 278, 281, 291, 293, 371. Malay peninsula, tin from, 412. Maltha, analysis of, 60. Manganese, distribution, Arkansas, 887 ; Cali- fornia, 387; Colorado, 388; eastern area, 385 ; Georgia, 385 ; Utah, 388 ; Virginia, 386. in iron ores, 252. ores of, 388. origin, 384. production, 388. references on, 389. uses, 388. Marbles, distribution in United States, 81. general characteristics, 78. See Building stones. Marl, for Portland cement, 114, 119. Marquette range, 261, 263. Marsh gas, in natural gas, 42. properties, 42. Marshes, salt, cause of, 127. Maryland, coal, referred to, 37 ; glass sand, 177 ; infusorial earth, 162; kaolin, 101; marble, 82 ; natural rock cement, 118. Marysville, Mont., 337. Massachusetts, emery in, described, 164 ; glass sand, 177 ; marble, 82 ; pyrite, 199. Mechanical concentration, 289, 310, 318, 315. Mediterranean Sea, analysis of water, 124. Melaconite, 278, 295. Mendeljeff, on petroleum origin, 46. Menominie range, 261. Mercur, Utah, 336. Mercury, 390. associated minerals, 893. distribution, California, 390; Oregon, 892; Texas, 392. extraction, 394. mode of occurrence, 890. ores of, 390. origin, 893. production of, 394. references on, 395. Merrill, G. P., on chrysotile veins, 169. Mesabi range, Minnesota, 261, 262. Mesozoic, auriferous gravels, 327 ; clays of, 100 ; petroleum, 53 ; quartzose ores, 328. INDEX 429 Metals, disseminated in granite, 226. disseminated in limestone, 226. disseminated in quartz-porphyry, 226. distribution in rocks, 226. precipitation, conditions governing, 232. Metasomatism, denned, 233. pressure accompanying, 233. temperature during, 233. variation in process of, 233. Meteoric waters, importance in secondary con- centration, 230. Mexico, opal in, 195 ; solfataric sulphur in, 196. Mica, distribution, North Carolina, 185. in kaolin, 100. mode of occurrence, 185. production of, 185. references on, 186. species of economic value, 185. value of, 185. Micanite, 185. Michigan, bituminous coal, analysis of, 7j brick clays, 104 ; coal field, 28 ; cop- per ores, 28T ; gold, 352 ; graphite, so- called, 180; gypsum, 142; magnetite, 256 ; Portland cement materials, 119 ; salt in, 129. Millerite, 404. Millstones, characters, 161. distribution, 161. Mine Hill, N.J., zinc ore, 809. Mine waters, analyses of, 22T. vadose, 227. Mineral pigments, 186. asbestos, 188. barite, 187. graphite, 188. gypsum, 187. hematite, 186. ochers, 186. production, 188. references on, 189. slate, 187. Mineral springs, volume of discharge, 205. Mineral waters, analyses, 206. classification, 205. denned, 204. distribution, 205. origin and occurrence, 204. production of, 206. references on, 207. thermal springs, 204. Mineralizing vapors, 234. in contact deposits, 235. Minerals, in contact deposits, 235. Minnesota, hematite, 261, 264 ; limonite, 271. Miocene, petroleum, 53 ; phosphate, 150. Mississippi, lignite in, 80. Mississippi delta, soils of, 214. Missouri, bituminous coal, analysis of, 7; ball clay, 103 ; barite, 170 ; hematite, 269 : infusorial earth, 162 ; lime rock, 116 ; stoneware clay, 103. Moisture In coal, 8. Molding sand, analysis, 189. distribution, 190. mechanical composition, 189. properties, 189. references on, 190. Molybdenite, 339, 403. Molybdenum, 403. in Maine, 403. in western states, 403. ores and occurrences, 403. production of, 403. references on, 403. uses, 403. Monazite, analyses, 191. composition, 190. distribution, Brazil, 190; North Carolina, 190 ; South Carolina, 190. magnetic separation' of, 191. occurrence, 190. production of, 191. references on, 191. uses, 191, Montana, asbestos, 168 ; silver, 284 ; coal, 31 ; copper ores, 282 ; graphite, 179 ; lignite analysis from, 6 ; molybdenum, 403 ; sapphire, 193 ; silver-lead ores, 373. Monte Cristo, Wash., 335. direction of veins at, 238. Montezuina, Colo., zinc concentrates, 819. Moss agate, as gem, 195. Mother lode, California, gold, 333. Muscovite, as source of mica, 185. N Naphthas, in petroleum, 42. Natural gas, analyses of, 43. anticlinal theory, 43. distribution, California, 56; Indiana, 55; Indian Territory, 55; Kansas, 55; Kentucky, 56 ; New York, 54 ; Ohio, 55; Pennsylvania, 54; Texas, 56; West Virginia, 55. exhaustion of, 54. geologic distribution, 48. history of development, 40. occurrence of, 43. pressure in well, 44. properties of, 42. references on, 67. uses of, 56. Natural rock cements, see Cements. Nebraska, fullers earth in, 175. Nevada, infusorial earth, mentioned, 162 ; mag- matically segregated ores in, 225 ; sol- fataric sulphur, 197 ; silver-lead ores", 373 ; tungsten in, 415. Nevada City, Calif., 384. Newberry, on temperature petroleum forma- tion, 47. New Brunswick, albertite In, 59. New Caledonia, nickel supply from, 405. 430 INDEX New England, infusorial earth, mentioned, 162. lime rock in, 116. New Hampshire, graphite in ; 179 ; whetstones mentioned, 160. New Jersey,ballclay,103; copper,296; glass sand, 177; greensand, 155; magnetite, 256 ; molding sand, 190 ; Portland cement materials, 118 ; stoneware clay, 103. New Mexico, anthracite coal, analysis of, 8 ; bauxite, 879 ; coal, 30, 31 ; copper, 298; garnet, 195; magnetite, 256; molybdenum, 403 ; silver-lead ores, 373 ; turquoise, 194 ; vanadium, 416. New York, Clinton ore, 266 ; emery, mentioned, 164; fuller's earth, 175; garnet, 163; graphite, 179 ; gypsum, 142 ; infuso- rial earth, mentioned, 162 ; limestone ; 116 ; magnetite, 255 ; marble, 82 ; mill- stones, 161 ; molding sand, 190 ; natu- ral gas, 54 ; natural rock cement, 118 ; petroleum occurrence, 48; Portland cement materials, 118 ; production of gypsum, 145 ; pyrite, 199 ; salt, 127 ; siderite, origin of, 273 ; sienna, 187 ; talc, 202 ; whetstones, mentioned, 160. New Zealand, magnetite sand, 258. Niccolite, 404. Nickel ores, 404. Nickel, analysis of, 405. distribution, Missouri, 404 ; North Carolina, 404; Ontario, Canada, 404; Pennsyl- vania, 404 ; western states, 404. production of, 406. references on, 407. uses of, 405. Nile Valley, alluvial soils, 214. Nitrogen, in natural gas, 214. in soils, 214. Norite, New York, 78. North Carolina, asbestos, 167; barite, 170; corundum, 164 ; emerald, 193 ; garnet, 195 ; graphite, 179 ; kaolin, 101 ; mag- netite, 255 ; mica in, 185 ; millstones in, 161 ; monazite in, 190 ; phosphate in, 154 ; pyrophyllite, 203 ; rubies, 19 talc, 201 ; tin, 411 ; Triassic coal, 25. North Dakota, Portland cement materials, 119. Norway, titanium in, 413. Novaculite, 160. origin, 160. Nuggets, gold, 346. O Ocher, as mineral pigment, 186. classification, 187. composition, 187. distribution, 187. origin, 187. Ochsenius, on origin of salt, 125. Qgdensburg, New Jersey, zinc ore, 309. Ohio, brick clays, 104; brines, 129; Clinton ore, 266; gypsum, 142; Hocking Valley coal, analysis of, 7; molding sand, 190 ; natural gas analysis, 43 ; natural gas, 55 ; natural rock cement, 118 ; petroleum, 50 ; Portland cement materials, 119 ; siderite, 273 ; stoneware clay, 103 ; whetstones, mentioned, 160. Oil rock, capacity of, 44. Oil shales, analysis, 57. distillation of, 57. geographic distribution, 57. properties, 56. references on, 67. Oil springs, 52. Oilstones, defined, 159. distribution, 160. Oklahoma, gypsite in, 142. Oliphant, on petroleum distillates, 42. Ontario, anthraxolite in, 59. Ontario, nickel, 404. Onyx marbles, 83. characters, 83. distribution. 83. for lithographic work, 182. references on, 91. Oolitic, limestone, defined, 80. Opal, composition and occurrence, 195. distribution, Hungary, 195; Mexico, 195; Oregon, 195 ; Washington, 195. Orange Spring, Fla., 205. Ordovician, lead in, 306 ; limestones, 116. Ore deposits, bedded, 241 ; bonanzas, forma- tion of, 245; chamber deposits, 242; classification of, 246 ; contact de- posits, 241 ; contemporaneous origin of, 224 ; disseminations, 242 ; Fahl- band, 241 ; fissure veins, 236 ; forms of, 236 ; impregnations, 241 ; linked veins, 239 ; ore channel, 241 ; origin of, 224 ; oxidation, 243 ; oxidation, depth of, 244. references on, 249 ; sec- ondary alteration in, 242; secondary enrichment, 245 ; weathering, 242 ; weathering, chemical changes, 243 ; weathering, conditions affecting depth, 243 ; weathering, minerals affected, 242. Oregon, coal, 32 ; gold ores, 335 ; limonite, 27 ; mercury, 392; nickel, 404; opal in, 195 ; solfataric sulphur, 197* Ores, concentration in rocks, 225. value of, 245. Organic matter, as reducing agent, 317. Oriskany, glass sand in, 177 ; limonite in, 271 ; phosphate in, 153. Orpiment, 398. Orton, on petroleum origin, 47. Osmium, properties and occurrence, 409. uses, 409. with platinum, 407. Osmotic pressure, ore precipitation by, 236. Ouray, Colo., 307, 342. Ozark region, 314. Ozokerite, properties, 59. occurrence, 59. INDEX 431 Palladium, properties and occurrence, 409. uses, 409. with platinum, 40T. Paper clay, defined, 99. Paraffin, 56. Paragenesis, 313, 315. Park City, Utah, 307. Peace River, Fla., phosphate, 148. Peale, on mineral waters, 205. Peat, analyses of, 4, 6. defined, 3. references on, 38. sections in bog, 3. Peckham, on temperature petroleum forma- tion, 47. Pegmatite, tin-bearing, 410. Pennsylvania, anthracite coal, 8, 22; barite, 170; bituminous coal, 7; cement ma- terials, 117, 118; chromite, 401 ; Clin- ton ore, 266 ; copper, 296 ; fire clays, 102 ; glass sand, 177 ; graphite, 179 ; iron ore, 256, 273 ; kaolin, 101 ; mag- netite, 256; natural gas, 54; ocher, 187 ; petroleum, 50 ; phosphate, 154 ; Portland cement materials, 118 ; ser- pentine, 84; siderite, 273; sienna, 187 ; stoneware clay, 103 ; titanium, 414; zinc, 311. Penokee-Gogebic range. 261, 262. Penrose, on Georgia manganese, 386. Pentlandite, 404. Permian, gypsum, 141; rock salt, 127; salt, 130. Persia, turquoise, 194. Petroleum, analyses, 41. anticlinal, 43. asphaltic, 40, 42. uses, 42. boiling point, 42. distillates, percentages of, 42. distribution, Alaska, 54 ; Appalachian field, 48 ; California, 52 ; Colorado, 53 ; Kansas, 52 ; Ohio-Indiana, 50 ; Penn- sylvania, 50 ; Texas-Louisiana, 51. flashing point. 41. geologic distribution, 48. gravity of, 41. gushers, in Beaumont field, 45. history of development, 39. movement in rocks, 47. nitrogen in, 40. origin, inorganic theory, 46. organic theory, 46. paraffin in, 42. pool, defined, 44. pressure in well, 44. production, 62. properties of, 40. references on, 66. rock pressure, 45. sands, defined, 44. solidification temperature, 41. uses of, 56. wells, depth of, 45. Phlogopite, as source of mica, 185. Phosphate, analyses, 154. distribution, Alabama, 153 ; Arkansas, 153 ; Florida, 148; Georgia, 153; North Carolina, 153; Pennsylvania, 153; South Carolina, 150 ; Tennessee, 150. geological distribution, 148. impurities, 153. land pebble, 149. mode of occurrence,. 147. river pebble, 149. rock, 148. soft, 149. uses, 154. Phosphoric acid, in soils, 214. Phosphorus, in copper ores, 280. in iron ores, 252. Pipe clay, defined, 99. Pipe lines, West Virginia, 55. Pitches, 312. Placers, 327. Plaster of Paris, 144. Plasticity, clay, 96. Platinum, associated metals, 407. composition, 407. distribution, California, 408; Wyoming, 408. native, 407. ores, 407. production, 408. references on, 408. uses, 408. Pleistocene, clays, 100 ; glass sand, 176 ; stone- ware clays, 108. Pneumatolysis, defined, 234. Polybasite,'325, 344, 368. Portland cement, see Cement. Posepny, on ore deposits, 246. on vadose water, 281. Potash, in soils, 214. Potsdam, glass sand, 177 ; sandstone, 87. Pottery clay, defined, 99. distribution, 103. Pozzuolano, Italy, cement from, 111. Pratt, on chromite, 400. on chrysotile veins, 169. on corundum, 163. Pre-Cambrian, auriferous gravels, 327 ; clays, 100 ; gold, 329 ; iron ores, 260. Precious stones, defined, 192. occurrence, 192. production, 195. references on, 195. Proctor, Vt., marble, 82. Proustite, 325. Psilomelane, 383. Pulpstones, properties and uses, 159. Pumice, 161. sources, 162. 432 INDEX Pumpelly, cited, 262. Pyrargyrite, 325. Pyrite, 286, 339, 371, 412. analysis, 199. as contact mineral, 235. distribution, Massachusetts, 199 ; New York, 199 ; Virginia, 199. in hot spring deposit, 228. occurrence, 199. references on, 200. uses, 200. Pyrolusite, 888. Pyromorphite, 803. Pyrope, as gem, 194. Pyrophyllite, composition, 203. North Carolina, 203. uses, 203. Pyroxene, as gangue mineral, 295. Pyrrhotite, 404. as contact ore, 235. Ducktown, Tenn., 295. in Virginia pyrite deposits, 199. Sudbury, Ont, 405. Quarries, bedding planes in, 74. Quarrying, structural features affecting, 74. Quarry water, 73. Quartz, crystalline, uses, 163. in kaolin, 100. Quicksilver, 390, 391, 393. Quincy, Mass., granite, 77. R Realgar, 398. Red Sulphur Springs, Va., 205. Regolith, 213. Replacement, defined, 233. Residual soils, 218. Residuum, petroleum, 42. Retort clay, defined, 99. Rhigolene, 56. Rhode Island, coal field, 25 ; graphite, 179. Rhodium, with platinum, 407. Rico, Colo., 307. banded veins at. 237. zinc concentrates, 319. Rift, 74. Road materials, 217. clay, behavior under traffic, 217. gravel, characteristics, 217. methods of testing, 218. references on, 218. requisite qualities, 218. sand, characteristics, 217. shale, 217. Rock crystal, as gem, 195. Rock pressure, Orton on, 45. Rock salt, occurrence, 125. Rocky Mountain region, yield of silver, 832. coal fields of, 30. Ruby, properties, 193. Arizona, 193 ; North Carolina, 193 ; United States, 193. Ruby silver, 825. Ruthenium, with platinum, 407. Rutile, 413. S Salina, gypsum, 142 ; salt, 129. Salines, 124. Sail Mountain, Ga., amphibole asbestos, 167. Salt, analyses of salt and brines, 131. analyses of sea waters, 124. association with gypsum, 126. distribution, California, 130; Kansas, 130; Louisiana, 129; Michigan, 129; New York, 127 ; Texas, 130 ; Utah, 180. extraction, 131. impurities, 126. occurrence in waters, 124. production, 132. references on, 134. rock, origin, 125. sources of, 124. uses, 132. San Bernardino Hot Springs, Calif., 204. Sandberger, on dissemination of metals, 228. Sandstone, 84. arkose, 85. Berea, 87. bluestone, 85. distribution, 86. flagstone, 85. general properties. 84. Potsdam, 87. varieties of, 85. Sandusky, Ohio, gypsum, 142. San Juan region, Colorado, gold-silver, 841. Sap, 73. Sapphire, 193. distribution, Montana, 193 ; North Carolina, 193 ; Siam, 193. properties, 193. Sagger clay, defined, 99. Saucon Valley, Pa., zinc ores, 811. Scheelite, 414. Schrauf, on mercury origin, 393. Sea water, pyrite precipitation from, 225. limonite precipitation from, 225. manganese precipitation from, 225. Selvage, 237. Semi-bituminous coal, defined, 5. Senarmontite, 396. Sericite, 826. Serpentine, for building, 83. characteristics, 83. distribution, 84. Seward peninsula, Alaska, 857 ; tin in, 412. Shale, analysis of, 98. Shutes, 237. Siam, sapphire, 198. Siberia, emerald, 193; turquoise, 194. Sicily, sulphur, 191. INDEX 433 Siderite, 272, 3T3. distribution, Kentucky, 273 ; New York, 273 ; Pennsylvania, 273. geologic distribution, 272. mode of occurrence, 272. Sienna, defined, 187. Silica, as an abrasive, 163. deposition from water, 393. effect on clay, 95. in iron ores, 252. in soils, 214. Silurian, manganese in, 387. Silver, Butte, Mont., 284. ores of, 325. production, 358. uses of, 357. with mercury, 393. Silver Cliff, Colo., analyses of mine waters, 227. Silver glance, 325. Silver ores, classification, 327. distribution of, see Gold-silver. extraction, 329. geologic distribution, 329. mode of occurrence, 826. production of, 358. references on, 360. secondary enrichment, 827. wall rocks, 826. weathering of, 327. Silver-lead ores, 364. assays of, 372, 373. distribution, Aspen, Colo., 867 ; Coaur d'Alene, Ido., 372; Eagle River, Colo., 369 ; Eureka, Nev., 373 ; Glen- dale, Mont., 373; Leadville, Colo., 864 ; Neihart, Mont., 373 ; New Mex- ico, 373 ; Park City, Utah, 370 ; Red Mountain, Colo., 369 ; Rico,Colo.,369 ; South Dakota, 373 ; Ten Mile district, Colo., 369 ; Tintic district, Utah, 372. references on. 374. Silverton, Colo., 341. Slate, as mineral pigment, 187. quarrying, waste in, 89. uses, 89. Slates, for building, 87. bleaching of, 88. cleavage, 87. distribution, 88. Smithsonite, 303, 305, 310, 312, 319. Smut, of coal, 16. Soapstone, 201. in southern Appalachians, 201. See Talc. Soda, in soils, 214. Soda niter, properties, 136. references on, 186. Sodium sulphate, 186. Soils, 213. seolian, 214. alkali in, 215. 2p alluvial, 214. chemical properties, 214. defined, 213. distribution, 216. dune, 214. flocculated, 215. glacial, 214. loamy, properties, 215. loess, 216. marsh, 216. origin, 213. physical properties, 215. prairie, 216. puddled, 215. references on, 216. residual, 213. sandy, 215. structure, 215. ' subsoil, 216. temperature, 216. texture of, 215. transported, 213. volcanic, 214. Solenhofen, Bavaria, lithographic stone, 182. Solid bitumens, 57. South Carolina, mouazite, 190 ; phosphate, 150 ; tin, 411. South Dakota, fire clay, 103 ; gold, 350 ; fuller's earth, 175; lithium, 188; Portland cement materials, 119 ; silver-lead ores, 873 ; tungsten, 415. Specularite, as contact ore, 235. S perry lite, 407. Spessartite, as gem, 194. Sphagnum, 3. Sphalerite, 303, 305, 811, 812, 313, 315, 819, 872, 373. Spodumene, 183. Spurr, on magmatic segregation, 225. Stannite, 410. Stassfurth, Prussia, salt at, 126. Steamboat Springs, Nev., 392. Stephanite, 325, 844. Stevenson, on anthracite formation, 15. Stibnite, 336, 339, 396. in hot spring deposit, 228. Stoneware clay, analysis of, 98. defined, 99. distribution of, 103. Stream tin, 410. Strontian Island, celestite on, 201. Strontium, minerals containing, 200. references on, 201. uses, 201. Subcarboniferous, salt, 129; limestone for lime, 116; zinc, 814. Subsoil, 216. Sudbury, Ont., nickel, 405. Sulphides, in contact deposits, 235. Sulphur, distribution, Louisiana, 197 ; Japan, 196; Mexico, 196; Oregon, 197; Utah, 196. 434 INDEX Sulphur continued. geologic age, 197. gypsum type, 197. in coal, 9. in copper ores, 280. origin, 197. production, 198. references on, 198. solfataric type, 196. uses, 198. Sussex County, N.J., zinc ores, 808. Sweet Springs, W. Va., 204. Sylvanite, 325, 339. Table Mountain, Calif., 347. Talc, 201. analyses of, 202. as alteration product, 201. distribution, New York, 202; North Caro- lina, 201. origin and occurrence, 201. production, 203. references on, 203. uses, 202. Tellurides, 325. unknown in contact deposits, 235. Tellurium in copper, 280. Tennantite, 285. Tennessee, ball clay, 103; barite, 170; fluor- spar, 173 ; Jellico coal, analysis of, 7 ; garnet, 163; phosphate, 150; stone- ware clay, 103. Terlingua, Texas, mercury, 892. Terra alba, 143. Terra-cotta clay, defined, 99. Tertiary, fuller's earth, 175; gold-silver ores, 337 ; glass sand, 177 ; greensand, 155 ; lignite, 19 ; limonite, 271 : phosphates, 148, 153 ; sulphur, 197. Tetrahedrite, 278, 285, 297, 321, 331, 339. Texas, bat guano, 155 ; bituminous coal, analy- sis, 7; coal, 29; fuller's earth, 175; gypsite, 142 ; lignite, 6, 30 ; lime rock, 116 ; limonite, 271 ; mercury, 392 ; natural gas, 56 ; petroleum, 51 ; Port- land cement materials, 119 ; salt, 130 ; stoneware clay, 103. Thermal springs, origin, 204. Thorium, in monazite, 190, 191. Tin, association with granite, 226. distribution, Alaska, 412 ; Black Hills, 411 ; Malay Peninsula, 412; North Caro- lina, 411 ; South Carolina, 411. mode of occurrence, 410. ores, 410. production of, 412. references on, 418. uses of, 412. Titanic acid, in clay, 96. Titanium, distribution, Norway, 413 ; Penn- sylvania, 414 ; Virginia, 414. in iron ores, 252. occurrence, 413. ores, 413. references on, 414. uses, 414. Tonopah, Nev., 343. Topaz, distribution, Brazil, 194; California, 194; Ceylon, 194; Colorado, 194; Maine, 194 ; Urals, 194. properties, 194. Torbanite, 57. Tourmaline, as gem, 195. with tin, 412. Transported soils, classification, 214. origin, 213. Trap, 78. Travertine, defined, 80. Trenton, limestone for lime, 116; petroleum in, 51. Triassic, coal, 25 ; magnetite, 256. Trinidad, asphalt in, 59. analysis of, 60. Tripoli, see Infusorial earth. Tully limestone, for Portland cement, 118. Tungsten, analysis. Arizona, 415. distribution, Arizona, 415; Black Hills, 415 ; Colorado, 415; Connecticut, 415; Nevada, 415. ores, 414. production, 415. references on, 416. uses, 415. Turquoise, distribution, Arizona, 194; Asia Minor, 194 ; New Mexico, 194 ; Per- sia, 194 ; Siberia, 194. properties and occurrence, 194. Type metal, 897. U Uintaite, 59. Ulexite, 134. Umber, defined, 187. Underground waters, 207. references on, 211. sources of, 207. Urals, topaz in, 194. Uranium, distribution, Colorado, 416 ; Utah, 416. ores, 416. production, 416. references on, 417. uses, 416. Utah, coal, 31 ; copper, 296 ; desilverized lead, 307 ; hematite, 268 ; magnetite, 256 ; manganese, 388 ; molybdenum, 403 ; Portland cement materials, 119 ; salt, 130 ; silver-lead ores, 372 ; sulphur, 196 ; uranium, 416. Vadose water, defined, 227. Vanadium, distribution, Arizona, 416; New Mexico. 416. INDEX 435 Vanadium continued. ores, 416. production, 416. references on, 417. uses, 416. Van Hise, on Lake Superior ores, 262. on meteoric waters, 228. on ore deposit classification, 246. Veins, see Fissure veins. Vermilion, as mineral pigment, 188. Vermilion Range, Minn., 261. 264. Vermont, asbestos, 168 ; marble, 82 ; whet- stones, 160. Vesuvianite, in contact deposits, 235. Virgilina, Va., copper, 291. Virginia, arsenic, 398 ; asbestos, 167 ; barite, 170 ; brines, 129 ; coal, 25 ; green- sand, 155; gypsum, 142; infusorial earth, 162 ; kaolin, 101 ; limonite, 271 ; pyrite, 199 ; titanium, 414. Virginia City, Nev., 344. Vogt, on magmatic segregation, 224. Volcanic ash, 161. United States deposits, 162. soils, 214. W Wad, 383. Warm Springs, Tenn., 204. Warm Sulphur Springs, Va., 205. Washington, arsenic, 398 ; bituminous coal, analysis of, 8 ; coals, 32 ; gold, 335 ; lignite, analysis, 6; molybdenum, 403 ; nickel, 404. Water, artesian, 209. as carrier of ores, 226. circulation of meteoric, 229. distribution in earth's crust, 228. hot, agent in ore formation, 228. in clay, 96. mine, analyses, 227. mineral, 205. of igneous origin, 229. of meteoric origin, 228. underground, source of, 228. Water lime beds, cement rock in, 117. Water table, 208. Watson, on Georgia manganese, 386. Weathering, building stones, 70, 75, 79, 85. ore deposits, 242. Weed, cited. 228, 230, 246. West Virginia, brines, 129 ; gas, 55 ; glass sand, 177 ; grahamite, 59 ; natural gas, 55 ; petroleum, 48. Westerly, R.I., granite, 77. Whetstones, defined, 159. distribution, 160. White, I. C., on anticlinal theory, 43. White lead, as mineral pigment, 188. White metal, 320. Whiting, as mineral pigment, 188. Whitney, on Lake Superior ores, 262. Willernite, 303, 304, 308, 310. Winslow, on Missouri lead and zinc, 226. Wisconsin, Clinton ore, 266; graphite, 180; hematite, 261, 264 ; limomite, 271 ; natural rock cement, 118; zinc ores, 312. Wolframite, 414. Wollastonite, 235. Wulfenite, 403. Wyoming, asbestos, 168 ; copper, 298 ; gypsite, 142; hematite, 268; magnetite, 256; nickel, 404; petroleum, 53; platinum, 408. Y Yellow ocher, see Ocher. Yukon valley, Alaska, 353. Zinc, Butte, Mont., 285. ores of, 303. production of, 321. with mercury, 393. uses of, 320. Zincite, 303, 308, 310. Zinc ores, analysis of, Leadville, 318. Missouri, 315. New Jersey, 80S. distribution, Creede, Colo., 319 ; Iowa, 811 ; Missouri, 314 ; New Jersey, 308 ; New Mexico, 319 ; Pennsylvania, 311 ; Vir- ginia-Tennessee, 309 ; Wisconsin, 311. impurities in, 304. mechanical concentration, 313. references on, 323. residual, 310. superficial alteration, 805. Zinc oxide, manufacture in Colorado, 318. Zone of flowage, 228. Zone of fracture, 228. . UNIVERSITY OF CALIFORNIA LIBRARY