THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES IN MEMORY OF Dr. Harold . Fairbanks PRESENTED BY Miss Helen K. Fairbanks The RALPH P., REED LIBRARY DEPARTMENT OF GEOLOGY UNIVERSITY of CALIFORNIA L08 ANGELES, CALIF. "- SYLLABUS A COURSE OF LECTURES ELEMENTARY GEOLOGY JOHN C. BRANNER, PH. D. Professor of Geology in Leland Stanford Junior University Second Edition STANFORD UNIVERSITY 1902 STANFORD UNIVERSITY PRESS Library CONTENTS. PAGE TEXT-BOOKS OF GEOLOGY 4 THE DATA OP GEOLOGY 6-8 PART I. DYNAMIC GEOLOGY, OR ROCK-MAKING AGENCIES .... 10-210 PART II. STRUCTURAL GEOLOGY, OR THE MODIFICATIONS OF ROCKS . . 212-288 PART III. HISTORICAL GEOLOGY, OR PALEONTOLOGY. THE ORDER OF EVENTS AND LIFE AS RECORDED IN THE ROCKS .... 290-326 PART IV. PHYSIOGRAPHY, OR TOPOGRAPHIC GEOLOGY. THE SURFACE FEAT- URES OF THE EARTH 328-356 INDEX . 362-369 775680 INTRODUCTION. The method of presentation followed in these lectures is not intended to be a strictly logical one from a geological point of view. It is not thought that the logic of the subject as a whole is of any particular importance to the student until he shall have gained a good general knowledge of geologi- cal phenomena and of geological principles. It is the aim to begin with those phenomena with which the average student is most likely to be familiar, and by using this familiarity to branch out so as to cover the whole field, in so far as it can be done in such an elementary course of lectures. The order of presentation is approximately that followed in the text- books. The student cannot be too deeply impressed with the fact that, if he is to get a real knowledge of geology, he must go out of doors and see it face to face. No amount of book study, however important and thorough it may be, can take the place of this field study. But neither must books be neglected, for they contain the results of what others have seen and thought. The foot-note references will enable students to extend their knowledge by reading. These references are not intended to be full, but the papers cited almost invariably mention others upon the same subject, and some of them contain full bibliographies. TEXT-BOOKS OF GEOLOGY. MANUAL OF GEOLOGY. By James D. Dana. Fourth edition, New York, 1895. 1087 pages. Price, $5.00. AN INTRODUCTION TO GEOLOGY. By W. B. Scott. New York, 1897. 573-(-xxvii pages. Price, $1.90. TEXT-BOOK OP GEOLOGY. By Sir Archibald Geikie. Third edition, Lon- don and New York, 1893. 1147+xvii pages. Price, $7.50. PHYSICAL GEOLOGY. By A. H. Green. London, 1882. 728-4-xxiv pages. Price, $6.00. GEOLOGY, CHEMICAL, PHYSICAL, AND STRATIGRAPHICAL. By Joseph Prest- wich. Oxford, 1886. 2 vols., 1083+lii pages. Price, $15.00. PRINCIPLES OF GEOLOGY. By Sir Charles Lyell. Eleventh edition, 2 vols., New York, 1889. 1323+xxxix pages. Price, $8.00. TKAITE DE GEOLOGIE. Par A. de Lapparent. 2me edition, Paris, 1885. 1504+xv pages. 4me edition, Paris, 1900. 3 vols., 1912+xxiii pages. Price, $10.00. . TH*: STUDENT'S HAND-BOOK OF PHYSICAL GEOLOGY. By A. J. Jukes-Browne. London, 1884. 514+xii pages. Price, $2.40. New edition, London, 1902. ELEMENTE DER GEOLOGIE. Von Dr. Hermann Credner. Leipzig, 1887. 808+xx pages. Price, $6.00. ELEMENTS OF GEOLOGY. By Joseph Le Conte. New York, 1896. 640+xvii pages. Price, $4.00. REVISED TEXT- BOOK OF GEOLOGY. By James D. Dana. Fifth edition, edited by Wm. North Rice. New York [1898]. Price, $1.40. A TEXT-BOOK OF GEOLOGY. By A. P. Brigham. New York, 1901. Price, ,*1.50. ELEMENTARY GEOLOGY. THE DATA OP GEOLOGY. Geology has to do with the structure and history of the earth. Geologic reasoning is based on the supposition that the operation of geologic agencies is constant under given conditions. Geology deals with two classes of phenomena : I. OBJECTIVE PHENOMENA, or the materials, structure, and forms of the earth. These phenomena are : 1. Rocks and their constituents. The earth is made of rocks. Geologic definition of rocks. The rocks are made of minerals. Examples of different kinds of rocks: Conglomerates, pebbles, pudding-stones, sands, sandstones, clays, shales. Igneous rocks. 2. Structural features, or the internal conditions and changes of the rocks. What is meant by the earth's structure. Examples exposed in canons, gorges, gullies, road and railway cuts, mines, tunnels, and wells. Fig. 1. Vertical section in the Ozark mountains of Arkansas, showing horizontal, bent, and broken layers of rocks. 3. Topographic forms, or external changes of rocks. What is meant by topography or physiography, or the external modifications of rocks. Examples of various types of topography and the relations of these forms to geology. 8 DATA OF GEOLOGY. In order to understand the forms, we must understand the structure ; to understand the structure, we must understand how the rocks are made and modified. That branch of geology which deals with the topographic forms and surface features of the earth, their origin and modification, is called Topo- graphic Geology, or Physiography. It will be treated of in Part IV. Fig. 2 Example of parallel ridges and valleys due to folding and denudation of alternate hard and soft layers of rock. (Means.) II. SUBJECTIVE PHENOMENA, or the processes by which those materials of which the earth is formed have reached their present conditions. The agencies and processes of rock-making are called DYNAMICAL GEOL- OGY, and are discussed in Part I. The earth's history as preserved in rocks is but fragmental at best. These fragments are contained in the materials, structure, and forms of the earth. The rock records are not everywhere the same, nor everywhere equally accessible, while enormous portions of them have been obscured, or en- tirely wiped out by the changes of time. 10 PART I. DYNAMICAL GEOLOGY. Dynamical geology is that branch which deals with rock-making and rock-destroying agencies. Rocks may be classed as 1. Mechanical sediments, or rocks deposited mechanically, either by air or by water. They are usually called sedimentary rocks. 2. Chemical deposits, or precipitates from solution in gases or in water. 3. Igneous rocks, or those cooled and hardened from a fused condi- tion. 4. Rocks of organic origin, or those made by accumulations of organic matter. These embrace all the kinds of rocks in all parts of the globe. All rocks have peculiarities or characteristics due to the methods of their formation. It is, therefore, necessary to understand these methods or agencies, in order to know how and under what circumstances the rocks were formed. GEOLOGIC AGENCIES. Geologic agencies are those that either make or destroy the rocks. They may be grouped, like the rocks themselves, as follows : Agencies -< ( Atmospheric Mechanical < ( Aqueous I Solution Chemical < Igneous (Precipitation (high temperature) Organic ( Direct (indirect 11 12 ATMOSPHERIC AGENCIES. THE DIRECT WORK OF THE ATMOSPHERE.* The work of the atmosphere is called seolian, and the deposits are known as aeolian rocks. The direct geologic work of the atmosphere in done chiefly in arid regions and on sandy shores. It consists of carrying, wearing, and deposit- ing. I. The Carrying Done by the Wind. Distribution of volcanic dust or cinders. For miles around Mount Shasta; Vesuvius; wide-spread tuff beds of Arizona. In Iceland ;t in South America. i In August, 1883, eruption of Krakatoa, in Straits of Sunda; ashes fell nearly 1,000 miles southwest of there. (> Skies made red all over the world, till November of that year, by the fine dust, H which rose to an elevation of 85,217 feet in Venezuela, and 106,250 feet at St. Helena. Dust- and sand-storms If are common in arid regions, but they also occur in regions that are not arid.** Burying of roads and railway tracks. Filling of railway cuts; wind-breaks. Burial of forest on the shores of Lake Michigan. Burial of farms of west Portugal ; Bermuda. tt In Asia and Africa towns and cities have been buried, ii Sphinx of Egypt half buried in sand; some oases being buried. In the arid parts of the United States seolian deposits are sometimes 2,000 feet thick. Stamp-mill buried by sand on desert one hundred and twenty miles east of San Bernardino, California, 1896. Church buried. |||| * Earth sculpture. By James Geikie. Chap, xii : Land-forms modified by asolian action, 250-265. New York. 1898. t Across the Vatna Jokull, or scenes in Iceland. By W. L. Watts. 105-108 160. London, 1876. J Travels amongst the Great Andes of the equator. By Edward Whymper 125, 141, 326, 328. New York, 1892. I Nature, April 24, 1884, XXIX, 595. | Nature, December 6, 1883, XXIX, 130-133. - Krakatoa Com. Rep., 375. \ Dust-falls and their origins. Nature. May S, 1902, p. 41. "Observations on dirt storms. By E. O. Hershey. Am. Geol., June 1899, XXIII, 38M-382 tt The Atlantic. By Wyville Thomson. Vol. I, 291 et seq. it Logons de geologic pratique. Par E. de Beaumont. I, 193-194. Paris, 1845. In Palestine, see Mount Seir, Sinai and Western Palestine. By E Hull. 145-146. Lon- don, 1889. n I. C. Russell, Geol Mag., 1889, pp. 289, 342. III! See cases cited in Woodward's Geology of England and Wales, 2d ed., 546-547. London, 1H87. 14 ATMOSPHERIC AGENCIES. In the Argentine Republic dust produces darkness and obliterates landmarks and roads.* Darkness caused by mineral matter in the air.t Estimated that such storms carry at least 2,000 tons to the cubic mile.t In April, 1863, several inches of dust fell at Peking, China; it came from the cultivated fields of Asia. In February, 1898, worn sand, probably from Sahara, fell on shipboard nine hundred miles off the coast of Africa. || Distribution of plants by seeds blown over the earth, if Seeds with wings, etc. " Tumbleweed." Russian thistle.** Diatoms. Distribution of animals. Birds, blown out to sea. Spiders, locusts, butterflies. Origin of insular floras and faunas. ft Influence of plants and animals upon geology. II. The Wearing Done by Wind. Wind alone does not wear rocks; it wears with what it carries. tt Effect of the impact of single particles. Dulling of car windows in arid regions. Wearing through of glass panes near dunes. Wearing and rounding of telegraph-poles in deserts. Polishing of rocks in mountain passes. Faceting of pebbles. |||| Examples. Effect upon vegetation. Toadstool-shaped rocks supposed to be so made ; often due to softer layers. 1T1F Origin of the sand-blast used for grinding and ornamenting glass, stone- carving. Wear of the sand grains themselves.*** * Woodbine Parish's Buenos Ayres and the Provinces of the Rio de la Plata. 127-128. t The earth as modified by human action. By G. P. Marsh. 525-581 New York, 1885. t Dust and sand storms in the West. By J. A. Udden. Pop. Sci. Mo., Sept. 1896, p. 655. Across America and Asia. By R. Pumpelly. 59-60; 138-139. London, 1870. Wind as a factor in geology. By G. P. Merrill. Eng. Mag., Feb. 1892, II, 596-607. | Nature, March 17, 1898, LVII, 463. I Darwinism. By Alfred R. Wallace. 362-374. London and New York, 1889. ** The Russian thistle in California. Bui. 107, Univ. Cal. Agr. Exper. Sta. Tumbling mustard, circular no. 7, U. S. Dept. Agr., Div. Bot. ft Island life. By Alfred R. Wallace. London, 1880. it Erosion by flying sand on the beach of Cape Cod. By A. A. Julian. Science. Jan. 3, 1902, pp. 27-28. II 40th parallel rep. II, 159. Blake, Reconnaissance in California, 91-93. Am. Jour. Sci., Sept. 1855, LXX, 178-181. Wind action in Maine. By G. H. Stone. Am. Jour. Sci., 1886, CXXXI, 133-138. II J. Walther. Denudation in der Wtiste. Plates IV, V. Leipzig, 1891. Max Verworn Neues Jahrb. f. Min., 1896, I, 200-210.- Davis. Proc. Boston Soc. Nat. Hist., XXVI, 166-175; plates. T,j Bui. U. S. Geol. and Geog. Surv. Ter., IV, 1878, p. 831; 1873, pp. 32-6; 1874, pi. IV; 1875, p. 156. Wheeler's survey, III, 82. ral erosion by sand in Western Territories. By G. K. Sci., XXIII, 26-29. Die Denudation in der WUste. Von J. Walther. Leipzig, . . , , . Natural erosion by sand in Western Territories. By G. K. Gilbert. Am. Assn. Adv. 1891. On the laws that govern the rounding of particles of sand. By Wm. Mackie. Trans. Edin. Geol. Soc., 1897, VII, 298-311. 16 ATMOSPIIKRIC AGKNCIKS. III. The Depositing of Wind-Borne Material.* Why wind-borne material is deposited. If volcanic dust falls in water, or is bedded, it makes tuffs. If rain falls through dust, it falls as mud.t Wind-blown sands make dunes. Fig. 3. Sand-dunes on the Sergipe coast, Brazil. (Hartt.) Formation and shifting of sand-dunes. i Movement of dunes; burial of houses; invasion of towns and forests ; dune helped across a railway. || Forms. 1. Lines at right angles to wind in unobstructed regions. 2. Lines parallel with winds in regions of isolated obstructions, such as bushes. Angle of repose of dry Band, 35; wet sand, 40. Height. Probably limited only by accidents. On the coast of Holland, 260 feet. Western Palestine, 200 feet.H On Cat Island, one of the Bahamas, the dunes are nearly 400 feet high ; on the coast of West Africa, near Cape Bajador, they are 500 feet and more.** * The mechanical composition of wind deposits. By J. A. Udden. Augustana Library. Publication no. 1. Rock Island, 111., 1898. t Woodbine Parish's Buenos Ayres, 137-128. J On the formation of sand-dunes. By V. Cornish. Geog. Jour., Mar. 1897, pp. 278- 309. (Comprehensive discussion.) Die Denudation in der Wiiste. Von J. Walther. Das Wandern der Dunen, 513-22. Leip- zig, 1891. Desert sand-dunes bordering the Nile delta. By V. Cornish. Geog. Jour., Jan. 1900, XV, 1-32. -Nature, Feb. 22, 1900, LXI, 403. I Report on a botanical survey of the Dismal Swamp region. By T. H. Kearney. Contributions U. S. Nat. Mus.. vol. V, no. 6, pp 332-337. Washington, 1901. | Climbing and exploration in the Bolivian Andes. By Sir Martin Conway. 55. London, 1901. f The survey of Western Palest inc. By E. Hull. 88. London, 1886. On the maritime dunes of the Low Countries. By F. C. Winkler. Report of the International Congress of Geologists for 1878, pp. 181 et seq. reconnaissance of the Bahamas. By ** A reconnaissance of the Bahamas. By Alex. Agassiz. Bui. Mus. Comp. Zool., XXVI, no. 1, p. 34. Cambridge, 1894. 18 JEOLIAN ROCKS. Structure. Due to methods of deposition. Variations produced by shifting winds. Length. Examples : Monterey, southwest France, Holland.* Damming of streams on west coast of France and in northeast Brazil, t Fig. 4. Sand-dune structure exposed in jeolian sandstone. JEolian rocks. JEolian rocks are those formed of wind-blown materials, usually sands. They are not necessarily different from other sandstones. Mostly of quartz sand. In Carson Desert, Nevada, dunes of minute crustacean shells. Near Fillmore, Utah, of gypsum. Fig. 5. ^Eolian sandstones forming the top of a bluff and resting upon lava. Fernando de Noronha, South Atlantic. *For physiographic value of wind, see London Geog. Jour., 1896, VIII, 264-278. Subserial deposits of the arid region of North America. By I. G. Russell. Geol. Mag., 1889, pp. 289, 342-350. t Les Lacs francais. Par A. Delebeoque. Paris, 1898. 19 20 CHANGES OF TEMPERATURE. Bermuda* and Bahamas made of seolian calcareous sandstone. Process by which such rocks are hardened. Supposed atolian origin of the loess of China; 2,500 feet thick. t Cut by streams into gulches 30 to 100 feet deep and 4 to 20 feet wide; houses cut in these walls. Influence of vegetation on seolian deposits.* Probable origin of the " hog-wallows " of the San Joaquin Valley, Cali- fornia. Similar phenomena to be seen in most deserts. INDIRECT WORK OF THE ATMOSPHERE. The indirect work of the atmosphere is more important than its direct work. It may be included under the following heads : 1. Changes of temperature. 2. Evaporation. 3. Production of waves on large bodies of water. 4. Effect on the water level. 5. Effect on ocean currents and climates. 6. Its work as a water carrier. I. Changes of Temperature. All changes of temperature cause rocks and minerals to contract and expand. In massive or crystalline rocks the crystals expand and contract differently along their different axes. Some even contract along one axis while expanding along another. || The rocks are composed of several minerals interlocking ; the expan- sion and contraction at different rates cause the minerals to slip on each other, and the mass to loosen and disintegrate. * Am. Geol., May, 1897, XIX, 293. The geology of Bermuda. By Wm. North Rice. Bui. U. S. Nat. Mus., no. 25, p. 7. Wash- ington, 1884. The Bermuda Islands. By A. Heilprin. 32. Philadelphia, 1889. The seolian sandstones of Fernando de Noronha. By J. C. Branner. Am. Jour. Sci., April 1890, XXXIX, 247-257. The Atlantic. By Sir C. Wy ville Thomson. I, 285-295. New York, 1878. tChina. By F. F. von Richthofen. Reviewed in Am. Jour. Sci., 1877, CXIV, 487^91. F. B. Wright. Science, July 13, 1900, XII, 71-72.- G. F. Wright. Bui. Geol. Soc. Am., 1902, XIII, 127-128. Geological researches in China, Mongolia, and Japan. By R. Pumpelly. 40-41. Wash ington, 1866. The distribution of loess fossils. By B. Shimek. Jour. Geol., VII, 122-140. Loess as a land deposit. By J. A. Udden. Bui. Geol. Soc. Am.. 1897, IX, 6-9. Eolian origin of loess. By C. R. Keyes. Am. Jour. Sci., CL.VI. 299-304. I Across Vatna Jb'kul. By W. L. Watts. 76 London, 1876. Die Denudation in der Wilste u. ihre Bedeutung. Von J. Walther. 377. Leipzig, 1891. Further contributions to the geology of the Sierra Nevadas. By H. W. Turner. 17th ann. rep. U. S. Geol. Surv., 1895-96, pt. I, 681-683. Washington, 1896. The hillocks or mound formations of San Diego, California. By G. W. Barnes. Am. Nat., Sept. 1879, XIII, S65-571. Hog wallows, or prairie mounds. By J. Le Conte. Nature, April 19, 1877, XV, 530-531. | Smithsonian miscellaneous collections, XIV, no. 289. Tables of expansion by heat for solids and liquids By F. W. Claru. Washington, 1876. 21 EXFOLIATION. Changes of temperature affect surface layers especially. This produces spalling, chipping, and exfoliation in layers. Tendency to produce rounded blocks ; reason for the rounding of cor- ners. Rounding of basaltic columns; examples. Called "boulders of decomposition."* Same effect produced on hills and mountains of massive rocks no- ticeable in granite region. Ex- amples: Yosemite Valley, Serra do Mar, Rio de Janeiro, interior Fig. 6.-The weathering of mas- .... _. . ._ sive rocks along joints and Of Africa, Greorgia,t and North the formation of boulders Carolina.* of decomposition. Granite and gneiss expand one part in about 200,000 for every ad- ditional degree at ordinary temperatures. Annual change in temperate regions is about 150 ( 25 to +125 Fahr.) for exposed surfaces. Linear expansion for 103 over a surface of 300 feet = 1.85 inches. Fig. 7. Granite boulders of decomposition in the Bay of Riode Janeiro. (Benest.) * Winslow's report on Iron Mountain sheet. Missouri Geol. Surv., IX, 6-8, plates. The rocks of the Sierra Nevada. By H. W. Turner. 14th ann. rep. U. S. Geol. Surv., 480, and plate 53. Washington, 1895. t Merrill's Rock-weathering. Frontispiece. j North Carolina and its resources. Winston, 1896. Plate of Stone mountain. Opp. p. 115. 23 24 EXFOLIATION. Rifts found in granite quarries caused by this expansion and con- traction.* (See Plate II.) When the temperature falls below freezing another set of phenomena is intro- duced by the expansion of water on freezing. Lifting of sidewalks. Crumbling of damp earth by needle-ice. Enlargement of crevices in rocks. Throwing down of loose fragments and blocks from cliffs. Case of Cleopatra's Needle in New York City. Formation of talus slopes. Disintegration of porous rocks. Kig. 8. -A granita peak rounded by exfoliation, Victoria, Brazil. (Hartt.) Importance of alternate freezing and thawing. "Creep" of soil, and how it lowers slopes; examples of the "knob- stone " hills of southern Indiana. FORMATION OF SOIL IN PLACE. Relations of rocks and soils. Residuary soils formed partly through changes of temperature and freez- ing, and partly through the chemical action of water and plants. The process is called " weathering." t *See example of Raymond quarry in 12th ann. rep. State Min. Bur. California, 1894. 384. Sacramento, 1894. Decomposition of rocks in Brazil. By J. C. Branner. Bui. Geol. Soc. Am., 1896, VII, 255-314. Principles of rock weathering. By G. P. Merrill. Jour. Geol., 1896, IV, 704-724; IV, 850. Boulders formed in situ. By G. H. Barton. Technology Quarterly, V, 401-405. Boston, 1892. Plate XIV in monograph XXVII, U. S. Geol. Surv. A treatise on rocks, rock- weathering, and soils. By G. P. Merrill. New York, 1897. t Concentric weathering in sedimentary rocks. By T. C. Hopkins. Bui. Geol. Soc. Am., IX, 427-428. Weathering of diabase in the vicinity of Chatham, Va. By T. L. Watson. Am. Geol., Dec. 1899, XXIV, 355. Plate III. A cave room, made by the exfoliation of granite, in San Jacinto Mountains, Riverside County, California. (McMillan.) 25 26 EVAPORATION. Why some blocks of rock are left undecayed.* Why soil is often thin on slopes and deeper in the valleys. Alluvial soils derived from residuary soils. Method of accumulation. Origin of soil belts. Glacial soils are derived largely from residuary soils. Accumulation and modification. t Fig. 9. Talus slopes on the side of Mount Sneffels, Colorado. II. Evaporation. The geological work of evaporation consists in the concentration and deposition of minerals dissolved in water, the drying up of streams in arid regions, and in the drying out of certain soils, which causes them to open in cracks that admit water and gases to the soils and the underlying rocks. The chemical deposition of minerals will be treated at length under the head of Chemical Agencies. Formation of efflorescence. t Illustrated by efflorescence on brick buildings. Effect of the formation of efflorescence upon certain rocks. The origin of "fret- work." "Alkali " of arid regions. * U. S. Geol. Surv., monograph XXVII, plate XIV, 286. Washington, 1896. fThe origin and nature of soils. By N S. Shaler. 12th ann. rep. U. S. Geol. Surv., 213-545. Washington. 1892. Geology of England and Wales. By H. B. Woodward. 518-550. 2d ed., London, 1887. t Journal of the Franklin Institute, CVI, 52. American Architect, 1884, XVI, 207-208, 267-268; 1893, XXXIX, 30. The Clay Worker, April 1893, pp. 497-509; Dec. 1896, pp. 443-444; Feb. 1897, pp. 124-125; June 1897, p. 517; Oct. 1897, p. 265. The Clay Record, Nov. 15, 1897, XI, 17: July 8, 1898, XIII, 15. g See example in monograph XXXIII, U. S. Geol. Sury., 362. ORIGINAL CONDITION OF THET ROCKS. *~k^"T"'fcL "f~-r.- r t '"r'""\~ g ''T .*;";";_. '."" '.''- "\ : i^g& - h- _ *-,. t i ^ ^ i _ ^-1 fa r> &=_ r=^- f=- - =--=- i^iirE^ _ zp^T^-T -^=ri = -_^T=-- feJl &= FIRST STAGE OF DECOMPOSITION. SECOND STAGE: OF DECOMPOSITION, THIRD STAQE OF DECOMPOSITION. IBOONE CHERT MANGANESE-BEARING CLAY EEaizARD LIMESTONE I ST.CLAIR LIMESTONE; IZi3sACCHARoiDAL SANDSTONE Plate IV. Theoretical sections showing the process of irregular rock decomposition and the formation of soil. (Penrose.) 27 28 EVAPORATION. All spring, well, or surface waters contain mineral matter in solution. How demonstrated. Water passing through rocks and soils dissolves some of the soluhle minerals. In arid regions surface evaporation causes water to come to the surface from below or within, and its evaporation leaves the mineral in small crystals over the surface. Called "alkali"; various sub- stances, such as sulphate of magnesia, sodium chloride, etc.* Fig. 10. Fret-work in the yellow sandstone of the Santa Cruz Mountains. * Alkali lands. By Milton Whitney and T. H. Means. Farm. Bui. 88, U. S. Dept. Agr. Washington, 1899. The alkali soils of the Yellowstone Valley. By M. Whitney and T. H. Means. Bui. 14, Div. Soils, U. S. Dept. Agr. Washington, 1898. 30 WINDS AND WAVES. Efflorescence often causes rock surfaces to disintegrate and cavities to form. Efflorescence, being soluble, is washed off by rain. Origin of the "whitewash" of brick buildings. III. Production of Waves on Large Bodies of Water. Waves are one of the most im- portant geologic agents. Most waves are produced by wind moving over water. The geologic work of waves is done at the shore line. If water were undisturbed it would not cut land. (The geologic work of waves is treated at length un- der the head of Aque- ous Agencies.) Abruptness of sea and lake shores due chiefly to the under- cutting of waves. Skeleton islands off coasts and attacked shores. Transportation of shingle and sand along shores. Formation of spits. (Discussed under Aqueous Agencies.) Damming of river mouths by wave-driven sands. California. Fig. 11. Streams near Oceanside dammed by beach sands heaped across their mouths. Example: Oceanside, IV. Effect of Wind on Water Level. Blowing of wind for a long time in one direction over a body of water tends to pile up the water. Examples in long, narrow lakes, such as the "finger lakes" of New York; on Bala Lake; Mediterranean Sea;* Red Sea. In October, 1886, the west wind on Lake Erie raised the water 8 feet at Buffalo and lowered it 8 feet at Toledo, Ohio.t September 8, 1900, the city of Galveston, Texas, destroyed by a flood blown by southeast winds 8 or 9 feet above usual high- water level. t Similar earlier disasters. * Karamania. By F. Beaufort. 20, 21, 116. 2d ed., London, 1818. t Nat. Geog. Mag., Sept. 1897, VIII, 238. I The lessons of Galveston. By W. J McGee. The West Indian hurricane of Sept, 1-12, 1900. By E. B. Garriott. Nat. Geog. Mag., Oct. 1900, XI, 377-392. Gen. A. W. Greeley, in Nat. Geog. Mag., Nov. 1900, XI, 442-445. 31 32 WINDS AND CURRENTS. Tides are unusually high when the wind helps. Effect of southeast winds on the tides in the Bay of Fundy.* Higher tides increase the range of wave-cutting. V. Effects of Winds on Ocean Currents and Climate. t Character and direction of ocean currents. Ocean currents are produced partly by the lagging of water on the re- volving globe. The atmosphere as a whole lags in much the same way, but, being heated at the equator, it rises and flows toward the cold poles. This produces currents in contact with the globe, chiefly a water sur- face, which, as they move toward the equator, lag, and hence swing westward. These air currents help on the ocean currents which tend to pile up the water. In the Gulf of Mexico it escapes as the "Gulf Stream" into the North Atlantic. Probably only the surface currents are determined by winds, while the deep currents are due largely to convection.! In 1882 severe northwest gales pushed aside the warm gulf waters off the New England coast, and the coldness of the waters killed the tile-fish by the millions.^ Climatic effect of the warm waters carried into polar regions. Example of northwestern Europe and Iceland. VI. The Atmosphere as a Water Carrier. The air is never still. The great air currents are more or less definite, but they are influenced by the seasons (owing to changes of temperature), and, to some extent, by topographic forms. || Warm air takes up moisture. When this air is cooled the moisture is condensed and dropped. Cloud banners on mountain peaks. Moisture on the inside of window-panes in cold weather. Causes of the sweating of roi-ks. Warm air rises. In the tropics, over warm seas, it absorbs the moisture and carries it upward. This afterward comes down as rain. Abundant rains of the Andes due to east winds. Why it is dry on the west slope of the Andes. * G. P. Matthew. Canadian Naturalist, new ser., IX, 369, foot-note. t The influence of the winds upon climate during the Pleistocene epoch. By F. W. Har- mer. Quar. Jour. Geol. Soc., LVII, 405-478. London, 1901. t W. M. Davis. Scot. Geog. Mag.. Oct. 1897. g C. C. Nutting. Science, May 31, 1901, XQI, 843. B The circulation of the atmosphere. By W. M. Davis. Quar. Jour. Roy. Meteor. Soc., April 1899, XXV, no. llu. 34 WIND A WATER CARRIER. When the temperature into which the water-laden air is brought is below freezing the precipitation is frozen that is, it is in the form of frost, hail,* or snow. Frost on window-panes, instead of water, when it is freezing cold on the pane. Why there is snow only about the poles and on the highest mountains. Why there is usually no snow in the coldest weather. Sleet and hail start high and freeze before reaching the earth. Importance of water to life. Water is one of the first conditions of existence : no life without it. The most important geologic work done by the atmosphere is that which it does as a water carrier. All the geolgic work done by water is indirectly the work of the atmosphere . Of the atmosphere in general. The exposure of rocks to the air is fatal to the rocks. They are almost universally broken up and destroyed. They can last only when protected from the atmosphere. Rock destruction is chiefly a subaerial process. Fig. 12. Stone-capped columns of earth and rock fragments near Canyon City, Colorado. (Purdue.) * Method of formation of hail. Nature, Jan. 31, 1901, LXIII, 337. 35 AQUEOUS AGENCIES. MECHANICAL AQUEOUS AGENCIES. The mechanical work of water is done by 1. Rain (in its direct work). 2. Streams. 4. Seas and oceans. 5. Ice in forming and as glaciers and icebergs. I. The Mechanical Work of Rain. Most of the mechanical work of rain is done after the water gathers in The impact of rain, however, .produces certain peculiar topographic forms, illustrated by the stone-capped columns, or earth pillars, of Tyrol,* and of La Paz Valley, Bolivia.! Aside from that which evaporates, the water of rain runs off as streams (p. 38), or soaks into the ground and emerges as springs, either on land or beneath the ocean. Landslides, or landslips. Landslides are mechanical effects produced by rain-water soaking the ground. Common in railway cuts, and wherever the natural support of the soil has been removed. Overwhelming villages in Switzerland,} Russia,? Colorado, || Washing- ton.^ The bursting of peat- bogs** in Ireland. Mud avalanches in India.tt the Alps,}* and the Andes.$ Landslips sometimes dam streams and thus form lakes. |||| * Geikie's Text-book of geology, 354-356. t The Bolivian Andes. By Sir Martin Conway, 93. London, 1901. t Science, Jan. 1, 1897, p. 21. Bui. Soc. Geol. de France, 2me ser., VII. 188. Paris, 1850. Ueber Bergstttrze in den Alpen. Von Dr. A. Baltzer in Zurich. Sep. Abdr. Jahrbuch des S. A. C., X, Zurich, 1875. g Guide des excursions du VII Cong. Gtk>l. Internat. XX, 30, and plate C. St. Peters- burg, 1897. II W. Cross. Science, Dec. 25, 1896, IV, 962. 11 1. C. Russell. Bui. 108, U. S. Geol. Surv., 47-48. 20th ann. rep. U. S. Geol. Surv., part II, 193-200. ** G. A. J. Cole. Nature, Jan. 14, 1897, IV, 254-256. G. Henry Kinahan. Nature, Jan. 21, 1897, LV, 268-269. Jour. Geol., 1901, IX, 639. tt Climbing and exploration in the Karakorum Himalayas. By W. M. Conway. 118, 129. 130. New York, 1894. t Bonney. Geol. Mag., Jan. 1902. p. 8. : The highest Andes. By E. A. Fitzgerald. 23-24. New York, 1899. G. K. Gilbert. Science, Jan. 19, 1900. XI, p. 99. ' i Nation, Mar. 4, 1897. 37 38 WORK OF STREAMS. Conditions favoring landslides : 1. Topographic form; only in mountains and hills. 2. Geologic structure. 3. Mineralogic composition. Clays, kaolin, decayed shale, serpentine, steatite, soapstone, graphite, mica, and peat are all slippery when wet. 4. Water present.* 5. Earthquakes.! How to prevent landslides. 1. By draining and turning the water away from the slippery earth. 2. By planting trees where roots will hold the soil. 3. By protecting the natural supports of land liable to slip. Case of the reservoir at Rio de Janeiro. II. The Mechanical Work of Streams. Origin of streams. Relation to underground water supply. Relation to surface waters. The mechanical work of streams. 1. Erosion, or wearing. 2. Transportation, or carrying. 3. Deposition. The whole process of removal is generally spoken of as denudation. The laws of flow in open streams. Different rates of surface, bottom, and sides of streams. Different rates at bends. Difference due to internal friction as well as to friction against the channel. i I. STREAM EROSION. Stream erosion is produced in two ways : 1. By impact of the water. 2. Scour, or abrasion, by the transported materials. I. Erosion by impact against soft materials affects the bottoms and sides of stream channels. Illustrated by hydraulic mining. * On landslides in Switzerland, see Neues Jahrb. fur Min. u. Geol., 1877, p. 916; 1875, p. 15. Modern denudation in North Wales. By J. R Dakyns. Geol. Mag., Jan. 1900, pp. 18-20. Notes on the late landslip in the Dendenong Ranges, Victoria. By F. D. Power. Proe. Austral. Assn. Adv. Sci., 1893, IV, 337-340. Articles on landslides cited in British Assn. Rep., 1885, pp. 448, 451, 458. Edin. New Phil. Jour., 1840, XXIX, 160. Topographic features due to landslides. By I. C. Russell. Pop. Sci. Mo., Aug. 1898, LIII, 480-489. Geology of the Cascade Mountains in Northern Washington. By I. C. Russell. 20th ann. rep. U. S. Geol. Surv., part II. Landslides, 193-204. Thecauseof the Darjeeling landslips. Nature. Dec. 7, 1899, LXI, 127. Dawson, in Bui. Geol. Soc. Amer., 1899. X, 484-490. t The great Indian earthquake of June 12, 1897. By J. Milne. Nature, Oct. 13, 1898, p. 586. I See results of Seddon, Trans St. Louis Acad. Sci., 1898, VJII, p. xxiv. 40 WORK OF STREAMS. Lateral erosion undercuts banks of soft materials. Centrifugal force on the outside of a stream's curves. Lateral erosion operates chiefly in the lower part of a river's course. Produces winding streams. Swinging of streams from side to side. Ox-bows and " cut-offs " of the Mississippi River. Mompox, an old Spanish city, fifty years ago stood on the bank of the Rio Magdalena. Owing to the shifting of the stream it is now twenty miles from that river.* An old adobe town that formerly stood on the banks of the Colorado river below Needles is now (1902) five miles inland. The falling of the undercut river banks may be heard all night. (V. L. Kellogg.) Terras cahidas of the Amazonas.t Formation of river terraces. (See under Physiography.) II. Erosion by scour, or abrasion (of bottom and sides), by transported ma- terials.* Materials moved : Blocks ) ~ , , , }- Boulders. Cobbles ) Pebbles. Sand. Clay. Effects of moving stones and sand. Clear, clean water cannot cut hard rocks mechanically. 1. To grind rock beds and sides of streams. (Abrasion.) In eddies below cataracts and falls, form pot-holes, Methods of grinding. Searsville Creek. Archbald pot-hole, 40 by 20 feet.$ Lucerne, Switzerland. Pot-holes are purely local. General effect of the grinding of the bottom is to cut stream channels deeper in the rocks. The loose stones, sand, etc., are pushed along down stream, and as they go they wear and cut the bottom and sides. Bottom cutting is done chiefly in the upper and steeper parts of stream channels. * Colombian and Venezuelan Republics. By W. L. Scruggs. 44. Boston, 1900. t The pororoca or bore of the Amazon. Science, Nov. 28, 1884. t The erosive power of rivers and glaciers. By R. M. Deely. Geol. Mag., Sept. 1897, p. Glaciation of the Wyoming and Lackawanna valleys. By J. C. Branner. Proc. Am. Phil. Soc., 1886, pp. 353-356. Archbald pot-hole. By C. A. Ashburner. 2d Geol. Surv. of Pa., ann. rep. for 1885, pp. 615-635, and plates. Glacial pot-holes in California. By H. W. Turner. Am. Jour. Sci. Soc., Dec. 1892. XLJV, 453-489, and plate. Open-air studies. By G. A. J. Cole. 30-32. London, 1895. A glacial pot hole in the Hudson river shales near Catskill, N. Y. By H. F. Osborn. Am. Nat., Jan. 1900, XXXIV, 33-36. 41 42 WORK OF STREAMS. 2. To bump together the materials moved . (Corrasion.) Process one of wearing, chipping, and rounding.* Illustrated by the manufacture of playing marbles.t Pebbles and boulders are rounded in the same way. Fig. 13. The glacial pot-hole at Archbald, Pa. From a photograph taken with the camera pointing straight upward. * Description of apparatus and methods used by the Mass. Highway Commission et By T. C. Mendenhall, etc. Stone, April 1899, XVIII, 207-210 * The non-metallic minerals. By G. P. Merrill. Rep. U. S. Nt. Mus., 1899, p. 370. 43 44 WORK OF STREAMS. Rounded worn pebbles are made only by the action -of water as streams or waves. Why some pebbles are round, some flat, and some long and slender. How water-worn stones throw light on the history of rock beds. Rounding of sand grains can be produced only when the current is not strong enough to suspend the grains, but yet strong enough to move them. This allows them to bump over each other like pebbles. Very fine sand is angular. Size of sand grains in relation to form. Specific gravity. Hardness prevents rapid wearing. Distance traveled. Agent of transportation,* wind, water, ice. The power of a stream to wear its channel is increased or kept up by the removal by the current of the material thus produced. II. STREAM TRANSPORTATION. Muddy color of some streams, and milky color of glacial streams, due to matter carried. Law of the transporting power of water: Erosive power, or power to overcome cohesion, varies as the velocity squared. That is, velocity doubled quadruples the force of the current. Transporting power, or power to overcome weight, varies as the sixth power of the velocity. That is, double the current and it will move sixty-four timer as big a block. Or, increase the velocity ten times and it will transport a block one million times as large.t Vast importance and enormous increase of work done by increase of velocity of streams. Currents required to move materials in rivers : Clay requires 0.25 feet per second Fine sand 50 " " Pebbles size of pea 1.00 " " Pebbles 1 inch in diameter 2.25 " " Blocks of 5 tons 15. " " Blocks of 320 tons 30. " " Result of dumping all these in a stream at once. * On the laws that govern the rounding of particles of sand. By Wm. Mackie. Trans. Edin. Geol. Soc.. 1897, VII, 298-311. t Prestwich's Geology. I, 83. Quar. Jour. Geol. Soc., IV, 92-93. Geologic pratique. Par Elie de Beaumont. Du regime des rivieres. Tome II, 63-134. Paris, 1849. Ann. rep. U. S. Engineers, 1875, II, 481. A treatise on hydraulics. By M. Merriman. 251-252. New York. 1891. The suspension of solids in flowing water. By E. H. Hooker. Trans. Am. Soc. Civ. Eng., 1896, XXXVI, 239-340. (The last work contains a valuable bibliography of the subject.) 45 46 WORK OF STREAMS. The total result of these varying carrying capacities is the sorting action of water, and the deposition at separate places of coarse and fine materials. Importance of the varying currents caused by fluctuation in the volume of water during freshets. In regions of concentrated rainfall the stream work is likewise concen- trated very large part of the time, and nil the rest of the year. The materials carried mechanically by streams are mostly submerged. Some streams upon swelling, especially in arid regions, carry sand and small stones upon the surface of the water, held up by tension.* Determination of the amount of transportation by streams. I. By reconstruction or restoration of the topography, or of matter removed. In canons of horizontal rocks. In folded regions by restoring the arches and folds. Of limited application owing to ignorance of the upper limit of the surface removed. Only part of the record preserved. II. By measuring the discharge of drainage, and estimating the amount of sediments carried out. Origin of the silts of any stream. Relations to its hydrographic basin. Observations on the amount carried in each gallon, and the number of gallons discharged. Method of measuring discharged Collecting samples at various depths, and in various parts of the stream. Objects of the method. Illustrated by work on the Arkansas river. How to determine the amount of silt in discharge. The Arkansas river in 1887-88 carried 2 grains of silt per gallon at the lowest stage, and 713 grains per gallon at the highest stage. In November, 1887 (lowest discharge in any month), the total dis- charge of silt was 16,449 tons (dry). In May, 1888, it was 6,208,717 tons. Total for the year was 21 ,471 ,578 tons.t III. By direct measurement of wear on stream beds. Rates of erosion and transportation by streams. Erosion of the hydrographic basin of the Arkansas above Little Rock (= 140,000 square miles) takes place at the rate of one foot in 9,433 years. Over the Mississippi basin (1,317,500 square miles) the rate is one foot in 4,640 years. * Floating sand. By F. W. Simonds. Am. Geol., Jan. 1896, XVII, 29-37. "Floating stones." Nature, Feb. 1, 1900, LXI, 318; Feb. 8, 1900, LXI, 346. Science, Mar. 30, 1900, XI, 510-512; June 8, 1900, XI, 912-913. t Instruments and methods of hydrographic measurements. By F. H. Newell. Proc. Am. Assn. Adv. Sci., XLVII. 248-249. I Erosion in the hydrographic basin of the Arkansas river above Little Rock. By J. C. Branner. Ann. rep. Geol. Surv. of Ark. for 1891, II, 153-166. Little Rock, 1894. t> The rate of erosion of some river valleys. By C. C. Brittlebank. Geol. Mag., July 1900, y-JT w*rt rtArt 47 48 WORK OF STREAMS. Amazon basin 2,264,000 square miles. Drainage is not always propor- tional to the area. Amazon hydrographic basin has twice the area of Mississippi and five times the water, owing to greater rainfall under the tropics. The rate of mechanical erosion by streams depends on 1. The volume of water. Small stream cannot carry much. 2. The slope of the land, which determines the velocity of the streams. 3. Character of the rocks. The softer rocks are cut faster. 4. Quality and quantity of detritus, or load. The hard rocks cut faster; too much chokes up or overloads the stream. 5. Climatic conditions. Differences between dry and wet climates, and especially difference between a region of concentrated rainfall and one having the same rainfall distributed throughout the year. Differences between tropics and cold climates. Freezing loosens soil and rock. The results of erosion and transportation are local and general. I. LOCAL RESULTS. The local result of erosion and transportation is to produce gullies, chan- nels, gorges, waterfalls, and valleys. The smallest ones we see made ; larger ones take more time, but the process is the same. The Colo- rado canon, a most striking illustration, is 2,000 to 6,000 feet deep. The Colorado river rises in the Uintah and Rocky Mountains in rainy areas, but it flows through an arid region where there is but little frost to break up, and but little rain to wash down the banks. Origin of waterfalls. Waterfalls are necessarily in stream channels. I. Caused by a more resisting bed overlying less resisting ones. Niagara as a type. Why most waterfalls are in gorges. Time is required to cut back. II. Caused by a new escarpment formed across stream channel. These escarpments may occur 1. On coasts where encroachment is more rapid than the cutting of the streams. 2. In rapidly cut canons, with falls in the side streams. 3. On the up-stream sides of faults across streams. All valleys are more or less the results of stream erosion. Some valleys, though modified by stream erosion, are formed as 1. Fault valleys. 2. Synclines. 3. Between volcanic mountains. 4. Glacial valleys. These are small.* * Technology Quarterly, X, fig. 27, opp. p. 242. 50 STREAM DEPOSITION. II. GENERAL RESULTS. The general result of erosion and transportation (or of denudation), as distinguished from the local result, is a lowering of land surfaces. Demonstrated in cases of large streams. Origin of the silts carried by streams. They come from the whole basin, though some parts are attacked more rapidly than others. Every part of the land above water is attacked by agencies of decom- position and denudation. The present contour of the land reveals little or nothing of its original form. The base level of erosion or peneplain.* III. DEPOSITION. t Deposition by a stream takes place in accordance with the laws of trans- portation. If the stream were uniform in velocity throughout there would be no deposition ; but, When any part of a loaded current is checked, deposition takes place. In winding streams silts deposit on the inside : s of curves. Why ox-bows are silted up next to the main stream and then cut off and left as crescent-shaped lakes. Eddies silt up when the current is slack, but keep clear when the cur- rent is strong, so that there is alternate removal and deposition at any single place. SOME IMPORTANT INSTANCES OF STREAM DEPOSITION. 1. Deposition over flood-plains. \ Flood-plain, that part of a valley that is covered by water when the stream is in flood. General silting up of bottom-lands. 2. Formation of natural levees. Levee bank is raised next to the stream. How the current on an overflowed flood-plain clings to its channel. A little of the main current constantly leaving the channel is checked by the quiet waters; this causes silts to sink along the margin of the main stream. When the main stream overflows, the side stream deposits part of its load as soon as it is checked. * The peneplain. By W. M. Davis. Am. Geol., April 1899, XXIII, 207-239. t Denudation and deposition. By G. J. Stoney. Phil. Mag., XLVII, 372-375; 557-565. London, 1899. Denudation and deposition. By Ch. Chree. Phil. Mag., XLVII, 494-496. London, 1899. I Recognition of river and flood deposits. By W(arren) U(pham). Am. Geol., May 1900, XXV, 313-314. The suspension of solids in flowing water. By E. H. Hooker. Trans. Am. Soc. Civ. Eng., XXXVI, 239-340. New York, 1896. The floods of the Mississippi river. By Wm. Starling. New York, 1897. 51 52 LAKES. 3. Formation of deltas. (See under Lakes.) 4. Formation of bars at mouths of streams and estuaries. Two sets of bars in streams flowing into the ocean. One at the contact of stream current with quiet ocean waters. Another at the contact of the stream with the high- tide limit. Shifting of bars due to a. Varying discharge of the stream. b. Storms and waves at sea. c. Any variation of the currents. 5. Spits formed in streams.* Deposition by overloaded streams. An overloaded stream is one that receives more silt than it can carry, and hence cannot keep its channel open. In a sense, parts of every stream are overloaded where they deposit. Such channels are kept open by freshets, or by some increase of volume and current. Overloaded streams cut no channels, but fill them up; they are constantly damming up their own courses and seeking new channels. This leads to the spreading out of their materials as a broad, flat bed. Illustrations: Southern California, where streams emerge from tor- rents of mountains on the plains ; currents strong in the moun- tains, but are overloaded for the lower grade of the plains where they deposit. McGee calls this "sheet-flood erosion."! It is rather a mode of deposition by overloaded streams. III. Mechanical Aqueous Agencies in Lakes. Fresh-water lakes. Fresh and salt lakes differ somewhat on account of difference in specific gravities of water, and on account of the flocculation produced by the salt in the water. (On flocculation see Mechanical agencies in seas and oceans.) Coarse silts sink more rapidly in fresh water, but fine silts, ow- ing to flocculation, settle more rapidly in salt water. Deltas. Origin and cause. Illustrated by the filling of mill-ponds and reservoirs from the entrance of the supply streams. Illustrated by settling-pools on water-supply ditches. Lakes are all settling reservoirs. Why the St. Lawrence river is clear. Rhone waters flow into Lake Geneva muddy, but flow out clear at Geneva; delta at its upper end building constantly outward. * Tidal sand-cusps. By F. P. Gulliver. Science, Nov. 22, 1895, II, 705. t W. J. McGee. Bui. Geol. Soc. Am., VIII, 87-112. 53 54 SEAS AND OCEANS. At Interlaken, Switzerland, a delta formed by silt-laden lateral streams has cut the lake in two. A delta deposited at the mouth of the Colorado river has cut off the northern end of the Gulf of California, and this northern end has evaporated. The extension of deltas into lakes turns them into marshes, and event- ually into dry land. Many of the marshes and meadows of the Sierras are silted-up lakes. Such are the American Valley, at Quincy; Sierra Valley, and many other flat-bottomed valleys. Salt-water lakes. Salt lakes behave like other bodies of salt water, except that they are tideless, and consequently produce less erosion. The amount of cutting on shores depends on the width of the play of the eroding agent; hence there is less on lakes than on open seas. Salt lakes have no outlets; they lose water by evaporation. Changes of level recorded by the old shore lines and deltas about Salt Lake.* Present Salt Lake area, 2,170 square miles; depth, 49 feet. Former area (Lake Bonneville), 19,570 square miles; depth, 1,050 feet. Area of Lake Erie, 9,900 square miles; depth, 210 feet. IV. Mechanical Aqueous Agencies in Seas and Oceans. Depth. The oceans are deeper than the average height of mountains. The Atlantic is from 12,000 to 20,000 feet; the Pacific's deepest is 27,930 feet. Mt. Whitney, Cal., 14,898 feet; Illimani, 22,200 feet; Orizaba, Mexico, 18,314 feet; Aconcagua, Argentina, 23,080 feet;t Mt. St. Elias, Alaska, 18,092 feet; J Himalayas, Asia, 29,000 feet. Temperature. Challenger map, 3>^ south of the equator in the Atlantic Ocean, shows the following decrease of temperature with depth : Fahr. Fahr. Surface 78 2,460 feet 39 270 feet 68 6,600 " 37.4 360 " 59 9,000 " 36.5 960 " 50 12,000 " 33.7 1,920 " 41 13,200 " 33 The isotherms follow the contour of the bottom. In many places the temperature is below 32 Fahr. Salt water freezes at 27.4 ; but varies with salinity and pressure. * Lake Bonneville. By G. K. Gilbert. Monograph I, U. S. Geol. Surv. t The highest Andes. By E. A. Fitzgerald. 29-30. New York, 1899. | Nature, May 3, 1900, p. 1. \ The voyage of the Challenger. By Wyville Thomson. The Atlantic. I, temperature charts. New York, 1878. 55 56 SEAS AND OCEANS. CURRENTS.* The ocean's waters are everywhere in motion. The currents flow in definite channels. Four miles an hour off the north- west coast of Cuba. Theory of the causes of the ocean's currents.* Combination of 1. Rotation of the earth and lagging waters. 2. Trade winds, that also lag. 3. Unequal temperature of the water, producing convection. Salinitv has been appealed to, but though evaporation increases salin- ity, and hence density, this occurs mostly in warm regions, and is compensated by temperature. Also, there is a marked increase of salinity only in a few enclosed places, like the Mediterranean and Red seas. Effects of ocean currents. Effect on the distribution of life.\ Effect on climates. , Isotherms carried north and south on the surface. The Gulf Stream carries half as much heat from the tropics as the artics get from the sun. The Gulf Stream carries more water than all the rivers of the Effect on the North Atlantic and Northwestern Europe. || Effect on rocks formed by corals and other warm-water life-forms. THE TIDES. IT Tides are the periodical fluctuations of the water-level in seas and oceans. Very small on lakes.** At Chicago three inches at most. Caused by moon's and sun's attraction of the fluid covering of the globe. Spring tides occur when the two act together. Neap tides occur when these attractions tend to connteract each other. Height in the open ocean, 3 to 4 feet. On shores the height depends largely upon shore configuration. * Les courants oceaniques, leur causes et leur effets. Par M. le Major Hennequin. Soc. Beige de Geographic. Bui. 4me an., 1880, pp. 5-40. Bruxelles, 1880. t The origin of the Gulf Stream. By P. T. Cleve. Am. Jour. Sci , April 1900, CLIX, 310- 311. The Gulf Stream. By J. R. Bartlett. Bui. Am. Geog. Soc., 1881, no. 1, pp. 29-46; 1882, no. 2, pp. 69-84. t Nature, Nov. 21, 1895, LIII, 64-66, 534. Darwinism. By A. R. Wallace. 361. London and New York, 1889. Island life. By A. R. Wallace. 79,262. London, 1880. ? The Atlantic. By Sir C. Wyville Thomson. I, 332-391. New York, 1878. | See H. M. Watts in Scribner's Mo. Mag., June 1902, XXXI, 689-699. H The tides and kindred phenomena in the solar system. By. Geo. H. Darwin. Boston, Manual of tides. By R. A. Harris. Rep. U. S. Coast and Geodetic Survey for 1897, pp. 477618. ** Nat. Geog. Mag., Sept. 1897, VIII, 239. 57 58 SEAS AND OCEANS. Puget Sound, 20 feet; at Chepstow, near Bristol, England, 53 feet; Bay of Fundy, 70 feet.* Importance of height due to the greater range of wave action. Power. Tides have no erosive power except in shallow water. They keep narrow channels open,t and increase the vertical range of the work of waves. MECHANICAL WORK DONE BY SEAS AND OCEANS, i Destructive work or erosion. The destructive work (i. e., erosion) is done by waves and tides. Kinds of waves. 1. Ordinary, or storm waves. 2. Extraordinary, or "tidal waves." a. Bore, or pororoca, true tidal waves, produced by submarine topography. 6. Extraordinary waves (improperly called "tidal"), pro- duced by earthquakes or other submarine disturbances. I. The destructive work of ordinary storm waves.fy On the Bahama Islands blocks of 300 cubic feet thrown 125 feet on shore, and 25 feet above high water. || Work confined to from 50 feet below to 100 to 200 feet above tide, or as high as undermining may affect the shore. Fig. 14. Blow-holes on the sea coast. Waves catch the air beneath the rock shelf in tl foreground and force it out through two openings. * Tides in the bay of Fundy. Nature, Sept. 14, 1899, p. 461. On bay of Fundy tides. Ann. rep. Geol. Surv. Canada, new series, VII, 1894, pt. M., 14. t Tidal erosion on the bay of Fundy. By G. F. Matthew. Canadian Naturalist, new series, IX, 1881, pp. 368-373. I The sea-coast. By W. H. Wheeler. Chaps, i-iii. London and New York, 1902. ? Geikie's Text-book of geology. 3d ed., 438, and references. I Alex. Agassiz. Bui. Mus. Comp. Zool., XXVI, no. 1, pp. 46, 58, 60, 66, 69, 74, 76. 59 60 SEAS AND OCEANS. 1. Work below tide. Violently destructive 50 feet below tide, scattering stones and haul- ing out by undertow.* Dana thinks but little breaking is done below the depth bared for the plunge, and that a depth of 20 feet is rarely exceeded. " Displacement at 240 feet is only a few inches." t Scott thinks it ceases to be effective "not far below low-tide mark."* Agitation during storms to 1800 feet. Air caught under ledges and forced out through blow-holes. 2. Work at and above tide. a. Alternate compression and expansion of air in crevices tend to loosen rock fragments, even though not reached by the water. b. Impact of the water thrown against the shore. Fig. 15. Notch cut by the surf in Ilha Raza, Fernando de Noronha group. (From a photograph taken at low tide.) * Capt. Thos. Dickenson's Narritive of the . . . recovery of the ... treasure sunk in H. M. S. Thetis, at Cape Frio, Brazil. 38, 42, 48, 59, 139. London, 1836. Tidal action as a geological cause. By T. Mellard Reade. Proc. Liverpool Geol. Soc., 15th session, 1873-74, II, 50-72. t Am. Jour. Sci., 1885, CXXX, 176. t An introduction to geology. By W. B. Scott. 119. New York, 1897. I The scenery of England. By Lord Avebury. 137-138. New York, 1902. Development of the profile of equilibrium of the subaqueous shore terrace. By N. M. Fenneman. Jour. Geol. Jan.-Feb. 1902, X, 1-32. 61 62 SEAS AND OCEANS. c. Shingle dashed against rocks does much cutting. Blocks weigh- ing from two to five tons hurled against the banks ; all ex- posed shores undercut. d. Shingle rolled up and down the shore. The grinding sound to be heard upon a beach covered with loose stones. Milky color of water due to wear. e. Spray washes mechanically, and dissolves chemically,* some rocks. Thrown over island at Rio de Janeiro ; in the north of Scotland lighthouse windows broken at 300 feet. The jagged surfaces sometimes produced by the solution of the shore rocks by spray. /. Hydrostatic pressure of water in crevices at heights of 50 to 300 feet. II. The destructive work of tidal waves. 1. The bore, at the mouth of the Amazon, and of the Ganges. Its destruction of banks, forests, islands. Produced by topography of the bottom over which a tide wave trips up.t 2. Extraordinary waves (improperly called tidal waves). Produced by earthquakes or other submarine disturbances. Ships left aground at St. Croix in 1867. t Destruction by waves during the Lisbon earthquake. June 15, 1896, on the coast of Japan, 175 miles of coast was struck by a wave 10 to 30 feet high ; some say 80 to 100 feet. It killed 26,- 975 persons; wounded 5,390 others; wrecked 9,313 houses, 300 larger and 10,000 smaller boats, and destroyed $3,000,000 worth of property. Land washed off, rocks broken, shore lines changed. All this happened in less than two minutes. It was probably caused by a submarine volcanic eruption 500 miles off the coast. Pumice was found floating on the sea, and an earth- quake was felt that day a few hours before the wave. The destructiveness of waves depends upon 1. The direction of the winds, especially during gales and storms. Islands half cut away off the west coast of Ireland, where storms come mostly from the west. * Alex. Agassiz. Bui. Mus. Comp. Zool., XXVI, no. 1, pp. 48 et seq. t The porordca, or bore of the Amazon. By J. C. Branner. Science, Nov. 28, 1884, IV, 488 -492. Sur les mouvements extraordinaires de la mer, etc. Par M. Babinet. Nouvelles An- nales des Voyages, vol. 137, pp. 338-352. Paris, 1853. Nature, June 7, 1900, p. 126; Feb. 13, 1902, p. 344; Feb. 20, 1902, p. 366. For photograph of bore see Ann. rep. Geol. Surv. Canada. New ser. VII, 1894, part M, p. 11, plate I. t Am. Jour. Sci., XC, 133-135. New Haven, 1868. g The recent earthquake wave on the coast of Japan. By Miss Eliza R. Skidmore. Nat. Geog. Mag., VII, Sept. 1896, pp. 285-289, 310^312. Letter of Mabel Loomis Todd. The Nation, July 30, 1896, p. 84. Report of the Krakatoa committee of the Royal Society, London. 93. 63 64 SEAS AND OCEANS. 2. The exposure of the coast, as at Santa Cruz. 3. Position of the bedding planes of rocks, or structure of the shore. 4. Character of the rocks. Shown by variations in the same beds at Santa Cruz. 5. Depth of the water off shore. Deep oceans have big waves which break on shore; shallows cause them to break and form surf outside before they reach the land. Fig. 16. The sea-caves of the La Jolla near San Diego, California. Fig. 17. Cathedral Rock, the remnant of a shore near San Diego, California, like the sea-caves of La Jolla. 65 66 SEAS AND OCEANS. Shore forms produced by wave action. Like destructiveness of the waves, the forms produced on shores depend more or less upon a. The direction and force of the waves. b. The nature and structure of the rocks. 1. Often there is a notch cut at the line of greatest activity.* 2. Shelves or terraces are sometimes cut at high and at low tide. This can only occur when the nature of the rock favors it. 3. Caves and natural arches are cut where the variation in the resist- ance of the rocks and the structure favors them. Portao, Fer- nando de Noronha. Fig. '18. The Portao or big door, an opening forty feet wide cut by the surf through an isthmus of eruptive rocks, Island of Fernando de Noronha. * For good examples of undercut limestone coasts, see Bui. Mus. Comp. Zool., Nov. 1900, XXXVIII, plate 13. 87 68 SEAS AND OCEANS. 4. The forms are sometimes the results of protective agents on the rocks, such as seaweeds, millipores, corallines, polyps, mollusks.* Passing of land through beach condition. General results of destructive wave work. (See p. 60.) CONSTRUCTIVE MECHANICAL WORK OF SEAS AND OCEANS, OR MARINE TRANS- PORTATION AND DEPOSITION. In general, transportation and deposition take place in seas and oceans in obedience to the laws of transportation ; that is, the transporting power varies with the sixth power of the velocity. Transportation in the ocean is done by 1. Tidal currents. 2. Waves. 3. Undertow. 4. Ocean currents. I. Tidal currents keep inlets open by the sweep, or ebb and flow, of the tides.t II. Waves carry beach materials where they strike the beach at an angle. They are most important where the wind blows regularly in one direction. Sands and gravels are carried long distances. (See this Syllabus, un- der head of Spits.) III. The undertow is the return oceanward of waters dashed on shore as waves; it is below the surface. It is always equal to the influx of waters on the surface as waves or surf. It hauls shore-made silts seaward. J IV. Ocean currents are usually so far from the land that they carry but little sediment. In the case of the Amazon river, however, the sediments are swept far north by the ocean current and widely distributed over the sea floor. Deposition in seas and oceans. Deposition in seas and oceans takes place in obedience to the law of transportation, P Oc V 6 . Except that 1. The salt water, being more dense than fresh, with a given velocity, carries heavier materials, which lose one-fortieth of their weight. 2. The salt in sea water causes flocculation, and consequently a more rapid settling of the ./me silts. (Flocculation, see under Deltas.) Silts sink in one-fifteenth of the time required in fresh water. * Across America and Asia. By R. Pumpelly. 188. London, 1870. A visit to the Bermudas. By Alex. Agassiz. Bui. Mus. Comp. Zool., XXVI, no. 2, p. 245. Cambridge, 1895. t The action of waves and tides on the movement of material on the sea-coast. By W. H. Wheeler. Geol. Mag., Feb. 1899, pp. 70-71. British Assn. Rep., 1898. t Development of the profile of equilibrium of the subaqueous shore terrace. By N. M. Fenneman. Jour. Geol., Jan.-Feb. 1902, X, 1-33. 70 MARINE DEPOSITS. FORMS AND ORIGINS OF MECHANICAL MARINE SEDIMENTARY DEPOSITS. Mechanical marine sediments, when deposited, take on the following forms : 1. Beaches. 4. Sand-barrier islands. 2. Spits. 5. Submarine banks. 3. Bars. 6. Deltas. IRgJiWater. Fig. 19.^ A section across a stone reef or hardened beach, coast of Brazil. (Hartt.) I. Beaches are of two kinds: ordinary beaches and storm beaches. 1. Ordinary beaches are of sand, or other loose materials, derived from the land. Some materials are thrown up by the waves ; some are drawn sea- ward by the undertow. Sands and silts swept into coves and bays, accumulate and fill out the land. Dunes often originate on sandy shores. Beds on beaches slope seaward. Sometimes hardened by carbonate of lime. Fig. 20. The stone reef of Pernambuco, Brazil, formed by the.hardening of a sand beach. 71 72 STORM BEACHES. 2. Storm beaches are those thrown up by storm waves, and beyond the reach of ordinary waves. " Sir John Coode has stated as the result of his experience that a heavy gale of wind of twenty-four hours duration would bring about far greater changes in the conditions of sand- banks and foreshores than ordinary weather in twenty-four months."* They often dam rivers and form fresh-water or brackish lakes at their mouths. Examples : Oceanside marshes, California. Lake Merced, near San Francisco. Lakes on the Brazilian coast. Fig. 21. Cusps on the beach at Santa Cruz, California. Fig. 22. Diagram illustrating the formation of beach cusps. The concentric lines represent two sets of wave crests; the heavy line is the curve of a beach which with these waves would yield cusps of uniform size. * W. H. Wheeler. Brit. Assn. Rep., 1898. 73 74 SPITS AND BAES. The form, or line, of the beach is determined partly By wind and waves. Beach cusps, their forms and origin.* By ocean currents. Cuspate beaches of North Carolina and South Carolina.! II. Spits.t Spits are lengthwise extensions of beaches into the water. Spits are formed 1. By waves sweeping shingle and silts into quiet waters at the turn of the shore. Examples: Cape Cod; Dutch Harbor spit, Anamak Island, Alaska. Fig. 23. Dutch Harbor, Anamak Island, Alaska, protected by a long natural spit. 2. By conflict between waves and stream currents. These cross the mouths of streams. Vistula, Baltic Sea. Sea of Azov. 3. By the throwing up of storm beaches on shoals. These often connect islands. Example: St. Paul Island, Pribilof group. (H. L. Elliott's Pribilof Island, p. 80.) They sometimes cause rivers to flow parallel with coast. (Gregory's Great rift valley, p. 31.) III. Bars. (Already discussed under Streams, p. 52.) They are formed by the combined action of streams and seas. Common in most streams flowing into seas. * The origin of beach cusps. By J. C. Branner. Jour. Geol., Sept.-Oct. 1900, VIII, 481-484. See illustration in Brigham's Text-book of geology, 126. An example of wave-formed cusp at Lake George, N. Y. By F. M. Comstock. Am. Geol., Mar. 1900, XXV, 192-194. t Remarks on the cuspate capes of the Carolina coast. By Cleveland Abbe, Jr. Proc. Boston Soc. Nat. Hist., May 14, 1895, XXVI, 489-497. J Lake Bonneville. By G. K. Gilbert. Monograph I, U. S. Geol. Surv. Washington, 1890. I Nature, Mar. 12, 1896, LIII, 445. Wave-formed cuspate forelands. By R. S. Tarr. Am. Geol., July 1898, XXII, 1-12. 75 76 BEACHES, BANKS AND DELTAS. IV. Barrier beaches. Long, narrow, and parallel with the coast. These merge into spits and bars. Formed by heavy waves hurling back land silts along shallow shores.* Eventually form islands. Examples: Texas, Mexico, Yucatan, North Carolina, Baltic Sea, Adriatic Sea. Behind these barriers the land gains on the sea by the silting up of the lagoons. Examples: Pamlico and Albemarle sounds and the New Jersey coast. V. Submarine banks. Formed wherever silts settle in the ocean for a long time. Example : off Golden Gate are the Sacramento Valley sediments. Distinguish between a submarine bank and a wave-cut shelf. When submarine banks come near the surface the waves pile the ma- terials above the water, and land begins. VI. Deltas. Deltas built in seas are formed in the same general way as those in lakes. Sediments are brought from the land by streams. Deltas at the mouths of some streams, not of others. Probable determining causes : 1. Character of the water of the stream. Clear streams can have no deltas. Example : St. Lawrence river. 2. Presence or absence of marine currents on the coast, whether , ocean or tidal currents. t At the mouth of the Mississippi the tide is 15 inches, and there are no ocean currents. At the mouth of the Amazon ocean currents sweep past it, and sediments discolor the sea 300 miles out. Rio de la Plata current flowing northward. Hoang-Ho discolors the water 200 miles from its mouth ; fill- ing the Gulf of Peleche.t Ganges and Bramapootra have deltas. Silts probably thrown back by tides. History of the Nile delta. General form of deltas fan-shaped. * N. S. Shaler, in Physiography of the U. S., 151-154. t Marine currents and river deflection. By K. A. Daly. Science, June 14, 1901, XIII, 952- 954. t Across America and Asia. By R. Pumpelly. 803. London, 1870. I The physical geology and geography of Arabia, Petraaa, Palestine, and adjoining dis- tricts. By Edward Hull. [London,] 1886. See also Bui. Soc. G6ol. de France, 1898, XXVI, 558. lif ZM 77 78 MARINE SEDIMENTS. Building of marine deltas. Reason of certain forms in Mississippi delta. They are the continuation of the natural levees. As the silts push seaward in deeper water, the checking of the current is at the sides and bottom, so that the bottom fills below, the sides build up at the sides, but the top silts are swept into the deeper water. Influence of salt water on silts.* Flocculation. Produced by salt, alum, acids, alkalis, cold, heat. Acids are more active than alkalis. (Joly, 330.) Alum used to flocculate city water-supply before filtering. Why waters containing much lime are clear. The influence of flocculating substances upon the deposition of sed- iments brought down by streams. Flocculation hastens sinking of fine silts; sediments sink in one- fifteenth of the time required in fresh water, though they lose one-fortieth of their weight. Rate of delta growth. Varies with conditions. That of the Mississippi, one mile in sixteen years. That of the Po, twenty miles since the time of Augustus. Bay of San Francisco filling about the ends. The origin of Salton Lake, California. Delta on a rising shore. Example : at Palo Alto, California. Position of marine sediments. Beach deposits slope gently seaward. Most deposits are approximately horizontal, and tend to flatten their beds by filling depressions. May cover larger areas. Coarse ones near shore, along a narrow belt, and nearer their origin. Fine ones farther out and farther from their source. * Experiences sur la sedimentation. Par M. J. Thoulet. Annales des Mines. 8me s6r., XIX, 5-35. Paris, 1891. On the inner mechanism of sedimentation. By J. Joly. Proc. Roy. Dublin Soc., Nov. 1900, IX, 325-332. W. Skey. Chem. News, London, 1868, XVH, 160; 1876, XXXIV, 142. Proc. New Zea- land Inst., 1871, IV, 380-382; 1878, XI, 485-490. D. Robertson. Trans. Geol. Soc. Glasgow, IV, 257-359. C. Barus. Bui. 36, U. S. Geol. Surv. W. H. Brewer. Nat. Acad. Sci., II, 165. J. Fleming. Trans. Roy. Soc. Edin., 1815-18, VIII, 507. E. W. Hilgard. Am. Jour. Sci., 1873, VI. 288, 333; 1879, CXVII, 205. T. S. Hunt. Chem. and Geol. Essays, 10. Proc. Boston Soc. Nat. Hist., 1874, XVI, 302. L. S. Griswold. Ann. rep. Geol. Surv. Ark. for 1890, III, 192. H. Leffman. Proc. Eng. Club Phila., 1894, XI, 293. G. E. Ladd. Am. Geol., Nov. 1898, XXII, 282. H. S. Allen. Nature, July 18, 1901, LXIV, 279-280. (Bibliography.) 79 80 MECHANICAL SEDIMENTS. GENERAL CONSIDERATIONS CONCERNING MECHANICAL SEDIMENTS. 1. The sediments of streams are only the decayed and broken rocks of the land. 2. The ocean's bottom is the destiny of all the land. 3. The rate of removal depends on a. Topography. (The steeper slopes go faster.) This is true both of stream erosion and ware erosion, for (1) Velocity is greater, hence transporting power is greater on the steeper land-slopes. (2) On steep coasts the waves reach the shore with greater force, and the undermining is more effective on account of the greater masses undercut. On coasts having low grades the off-shore shallows break the force of the waves before they reach the beach. b. Climate. Freezing and thawing hasten removal. c. Structure and character of the rocks. 4. Most removal (erosion, or denudation) is done during storms, or in times of freshets, owing to the increased volume and velocity of streams, and to additions from temporary side streams. 5. Erosion stops at, or not far below, the surface of the ocean. 6. Hence eroded surfaces tell of a land condition. 7. The hardening of a rock is, in a sense, an accident. 8. The laws of transportation and deposition by water determine the dis- position of the load of a current. 9. Thus coarse sediments can be moved only by strong currents, and fine ones can be laid down only in weak currents. 10. The nature of the sediments thus reveals the nature of the currents depositing them. 11. In an off-shore area o. Coarse sediments are near shore. 6. Finest sediments are farther out. c. Coarse sediments are in lines parallel to the coast. d. Finer sediments cover wider areas than coarse ones. 12. Examine rock sediments for evidence of their origin. 13. Water-wearing and water-bedding are done only by water, and tell of water conditions. 81 82 GLACIERS. V. Ice as a Geologic Agent. The geologic work of ice is done 1. In the mechanical expansion on freezing, whereby rocks are chipped off and disintegrated, and earth-slopes altered. (Discussed on p. 24.) 2. By glaciers or ice streams. 3. By icebergs and floe-ice. GLACIERS.* Outline of glaciers and their work. Moisture precipitated where the temperature is below freezing, falls as snow. Snow packs as ice, and flows as streams of ice. These streams are called glaciers. (See Plate VII.). They obey the law of flowing streams in general, so far as movements are concerned, though they move very slowly. Debris falling on the side of a glacier is carried down on top, or sinks into the body of the ice. Flowing down to warmer regions the ice melts, and when it melts more rapidly than it is replaced by snow, the glacier ends and the de- bris makes a moraine or heap, while the ice, turned to water, flows away heavily charged with mud. Origin of glaciers. All glaciers originate above the line of perpetual snow. The line of perpetual snow at sea-level is about the poles; in passing from the poles toward the equator it rises higher and higher above sea-level. Height of the perpetual snow line : In Switzerland, 8,500 to 9,000 feet a. t. Kites sent up at Cambridge, Mass., September 19, 1897, show that the temperature decreased 1 degree for 370 feet, when it was 63 Fahr. at the surface.t At this rate the freezing point would be at 11,470 feet. At the equator the freezing point is at 16,000 feet a. t. In mountainous regions snow collects as ice in the valleys. In high latitudes (polar regions) it collects on table-lands and buries the topography. Example: Greenland. * The great ice age. By James Geikie. 3d ed. London, 1894. (The foot-notes contain many references.) Handbuch der Gletscherkunde. Von L)r. Albert Heim. Stuttgart, 1885. The Canadian ice age. By Sir J. W. Dawson. Montreal, 1893. The forms of water in clouds and rivers, ice and glaciers. By John Tyndall. New York, 1872. (International Science Series.) The ice age in North America. By G. F. Wright. New York, 1889. Glaciers of Mt. Rainier. By I. C. Russell. 18th aun. rep. U. S. Geol. Surv., pt. II, 349. t Science, Oct. 8, 1897, new series, VI, 562; Oct. 22, 1897, p. 628. Plate VII. The Fiescher glacier, in the Bernese Alps, Switzerland. 83 84 GLACIERS. Compacting of snow to ice by warmth and pressure. Illustrated by squeezing snow. Blue ice in tunnels. Hence the conditions necessary to the formation of glaciers are 1. Region extending above the perpetual snow line. 2. Abundant precipitation. 3. Difference of temperature to hasten flow. MOVEMENTS OF GLACIERS. Rate of movement. Swiss glaciers move 150 to 400 feet per year. Aar glacier moves 330 feet per year. Boisson glacier moved 210 feet a year for 41 years. Muir glacier moved 7 feet per day,* x 365 = 2,555 feet per year. Greenland glaciers move 8 feet to 8 miles per year. Rates vary according to 1. The slope of the bed. 2. The warmth of summer. 3. The snowfall or mass of the glacier that presses behind. Method of determining the rate of movement. Transit and stakes. General law of glacial flow is the same as that of streams. t 1. Move more rapidly at top than at bottom. (Owing to fricton on bottom.) 2. Move more rapidly in middle than at sides. (Owing to friction on sides.) 3. Swing around curves with the rapid current on the outside. 4. Flow more rapidly on steep slopes. (Less friction.) Explanation of ice movement (or how solid matter flows). Theories offered to explain. i 1. In 1705 Scheuchzer suggested the freezing and expansion of water in the cracks in the ice. 2. Sliding along its bed by gravity. This would work like a pile of marbles or shot, since the ice conforms to its bed. 3. Pressure lowers the freezing point and makes slush of the bot- tom. This probably helps ice movement. 4. Plasticity or viscosity of the ice (Forbes). Examples of viscosity: pitch, tar, rosin, candy, asphalt. * Studies of Muir Glacier. By H. F. Reid. Nat. Geog. Mag., IV, 43-44. Washington, 1892. t The flow of glaciers. W. Upham. Am. Geol., Jan. 1896, XVII, 16-29. Deely and Fletcher. Geol. Mag., 1895, II, 153-162. T. C. Chamberlin, editorial in Jour. Geol., Ill, 963-967. Chicago, 1895. The mechanics of glaciers. By H. F. Reid. Jour. Geol., IV, 912-928. Chicago, 1896. t Glaciers of North America. By I. C. Russell. 163-189. Boston, 1897. 1 See VVm. Ludlow's experiments, Proc. Eng. Club of Philadelphia, IV, no. 2, pp. 93-99. Philadelphia, 1884. 86 GLACIERS. Trinidad lake. But these substances, though brittle, stretch; ice does not stretch. 5. Regelation or refreezing theory of Tyndall. Process shown by pressure into various forms, by cutting with wire, by the refreezing of the small broken fragments. Glaciers are like ice fragments in a mold. The pressure is all produced by gravity. Hence large glaciers flow faster than smaller ones on the same slope. Glaciers are not smooth and clean, but irregular and dirty. Irregularities made by crevasses. CREVASSES. Crevasses are cracks in the glacier. Produced by tension. 1. Where the ice increases its slope or flows over a ridge. These ridges may either cross, or be parallel with, the glacier. 2. Where there is a different rate of movement of one part over another. Producing a. Transverse lateral crevasses. Transverse lateral crevasses point diagon?lly up-stream. Why they point up-stream and not down. How they swing down-stream and are crossed by new ones. b. Transverse vertical crevasses. Transverse vertical crevasses within the ice point up- stream from the bottom, but their tops swing grad- ually down stream. Principle the same as for transverse lateral crevasses. 3. Where the ice stream widens, as sometimes happens, at the end of the glacier. Longitudinal crevasses. ' 1. Where there is a longitudinal ridge on the glacier's bed. 2. At the ends of spreading glaciers. MORAINES.* Rock fragments, soil, etc., falling upon the sides of glaciers, accumulate along the sides as the glaciers move forward. This material is called a lateral moraine. How and why debris on one side may differ from that on the other. Medial moraines are formed at the confluence of two glaciers by two lateral moraines running together. Sometimes there are many medial moraines of many colors. Baltoro glacier, in Hindu Rush, has fifteen moraines of different colors. Number of moraines varies with the number of glaciers uniting to form the large one. * Geschichte der Moranenkunde. Von Dr. A. B. Edlen von Bomersheim. Abh. der K. K. Geog. Gesell. in Wien. Ill, B, no. 4. Wien, 1901. 87 88 GLACIERS. Terminal moraines are the accumulations of debris at 'the ends of the glacier They are made of the lateral and medial moraines, and of all the sol: matter carried in the body of the ice. Forms of terminal moraines determined by the form of the end of the glacie Circular when the glacier is lobate. Not water-sorted, but a heterogeneous mixture of unsorted material. Ground moraine is the debris, soil, clay, etc., on which the ice sometim rests. Glacier often slides over the moraine, and over part of its own mat at the end.* ERRATICS OR GLACIAL BOULDERS. Blocks of rock carried by ice, and left scattered by the melting of the ice Erratics often occur in large numbers. Sometimes they are of very large size. In Switzerland, 40 to 73 feet long by 20 feet high. One of 240,000 cubic feet is biggest. The Madison, N. H., boulder, 70,000 cubic feet.t STRIDE, t Strix are scratches made on the bed-rock over which ice moves, or on i blocks held in the ice. ( See Plate VIII, opp. p. 94.) Rock fragments held in the grip of the ice and pushed forward scrat the bed-rock. The striae cut deep at one end show the direction of the movement glaciers. Fragments held in the ice, ground against the bottom, are striated a faceted. Why several faces are worn on a single block. Differences between ice-worn, water-worn, and wind-worn pebbles. Why all glacial pebbles are not faceted. Some never reach the bottom of the ice. Some have been water- worn since they were grooved. Deep grooves of stream channels sometimes striated by ice pressed ii them. Polishing is produced when the ice is filled with sand and fine debris. THE CROSSING OF STRLE. Caused by 1. Spreading at the end of an ice-lobe. Produced by change of volume. 2. Increase and decrease of confluent ice-streams. * Glacier motion and erosion. By R. M. Deeley. Qeol. Mag., Dec. 1898, pp. 564-565. t Crosby. Appalachia, VI, 61-70. t For examples, see University of the State of New York, Sate Museum Report 49, pi 1895, p. 324. I Ann. rep.-Geol. Surv. Canada, new ser. VII, pt. M, 75-81. Ottawa, 1895. 89 90 GLACIERS. 3. Turning of stones. 4. Bringing of glacier under local topographic influence. Difference between water-wearing and ice-wearing of rock in place.* GLACIAL STREAMS. Superglacial streams. Formed by the melting of the ice. Plunge into crevasses, forming moulins, and grinding out pot-holes. Lucerne glacier garden . Archbald pot-hole. t Subglacial streams are the superglacial streams after passing beneath the ice through crevasses. Wind and cut narrow, deep channels in the bed-rock. Channels exposed at Grindelwald and Zermatt, Switzerland. On large glaciers they sometimes come to the surface again. J GEOLOGIC WORK OF GLACIERS. Geologic work of glaciers is done as erosion, transportation, and deposition. I. Erosion.^ Rock-set ice grinds its bed ; grooves, striae, polish. Streams cut pot-holes, wear channels. Color and character of water ; gletscher-milch. Amount of wear shown approximately 1. By topography. 2. By gletscher-milch examination. 3. By glacial debris, or drift, left over the country on the retreat of the ice. II. Transportation. The materials carried are either in the form of lateral or medial moraines, materials scattered through the ice, or silts washed along by glacial streams. III. Deposition. Glacial deposits are 1. Terminal moraines. 2. Lateral moraines. 3. Isolated boulders. 4. Water deposits. Between lobes in pools. In ice-dammed lakes in their lower courses. || * The rock-scorings of the great ice age. By T. C. Chamberlin. 7th ann. rep. U. S. Geol. Surv., 1876-85. Washington, 1888. Glacial erosion. By W. M. Davis. Proc. Boston Soc. Nat. Hist., 1882, XXII, 19-58. t Branner. Proc. Am. Phil. Soc., XXIII, 353-356. Philadelphia, 1886. Ann. rep. Geol. Surv. Pa. for 1885, pp. 615-625. Harrisburg, 1886. Giants' Kettles near Christiania and in Lucerne. By W. Upham. Am. Geol., Nov. 1898, XXII, 291-299. } See photograph, Jour. Geol., 1896, IV, 809. ? Glacier motion and erosion. By R. M. Deeley. Geol. Mag., Dec. 1898, pp. 564-565. The eroding power of ice. By J. S. Newberry. Proc. Am. Assn. Adv. Sci., 1883, XXXII, 200-201. Science, 1883, II, 330. Trans. N. Y. Acad. Sci., 1885, III, 51-52. School of Mines Quarterly, 1885, VI, 142-153. Proc. Am. Phil. Soc., 1882, XX, 91-95. J. P. Lesley. Report Z, Geol. Surv. Pa., XIII-XIV; Proc. Am. Phil. Soc., XX, 95- 101. II Climbing iincl exploration in the KaraUorum-Himalayas. By W. M. Conway. 106-179 London, 1894. 91 92 EXISTING GLACIERS. Effect of glaciation on the topography. Effects of erosion on hills. Roches moutonnees. Exceptional cases of angular rock fronts facing the ice cur- rents; caused by the ice packing against them, and thus preventing erosion. Clearing off of soil. Fig. 24. Map showing the lobate forms of the principal moraines of the Mississippi Valley region. Effects of deposition of drift. Moraines. Lateral. Terminal. Interlobate. Erratics. Silts in old lakes; in ice pools. Parallel roads of Glen Roy.* Kettle-holes.t ADVANCE AND RETREAT OF EXISTING GLACIERS. Evidences of advance and retreat. 1. Observations of residents; glaciers invade fields occasionally. Photographs at Grindelwald. * W. Upham. Am. Geol., May 1898. XXI. 294. t Kettles in glacial lake deltas. By H. L,. Fairchild. Jour. Geol., Sept. -Oct. 1898, VI, 93 94 ANCIENT GLACIATION. 2. Striae and drift below the present ends of glaciers. 3. Trees, that were cut off by ice, below present glaciers.* 4. Difference in vegetation on old and newly glaciated surfaces. t Swiss glaciers reached a maximum about 1820; retreated till 1840; advanced till 1850-60. Reports from glaciers in all parts of the world showed many of them retreating in 1899 ; a few were ad- vancing.! Evidence of the unquestionable origin of glacial phenomena. Striae on bed-rock. Striae on boulders. Old moraines; forms; mixing of material not water-sorted. Transported blocks. PLEISTOCENE OR ANCIENT GLACIATION. These phenomena led to the discovery of the former glaciation of Switzerland: 1. Striae down the valleys. (See Plate VIII.) 2. Erratic blocks from the Alps on the sides of the Jura mountains. Time required to carry blocks suggests the length of the glacial epoch: 1,000 to 2,000 years, as glaciers now move. Probably moved faster. The ice rose 4,400 feet on the Jura mountains, and flowed to Lyons, France, a distance of more than 200 miles. Another branch flowed eastward toward Zurich about 200 miles. Reluctance rvith which theory of glacial epoch was accepted. Extension by Agassiz of the theory to England, Scotland, and Ireland. Shown by topography, drift, and striae. Extension to America. Confirmed by Agassiz landing at Halifax, N. S., in 1846. || GLACIATION IN NORTH AMERICA. Evidences of glaciation in North America. Striae, or furrows. Striated boulders. Till, or boulder clay. Moraines. Erratics. Area of glaciation. Includes parts of the Rocky mountains and of the Sierra Nevada moun- tains. Driftless area of Wisconsin.^ * I. C. Russell. 13th ann. rep. U. S. Geol. Surv., pt. II, 63. t Glacier Bay and its glaciers. By H. F. Reid. 16th ann. rep. U. S. Geol. Surv., 421-461. Washington, 1896. t The variations of glaciers. By H. F. Reid. Jour. Geol., 1901, IX, 250-254, and earlier reports there cited. g See map of the glaciers of Switzerland and France, in his Equisse g^ologique du ter- rain erratique . . . du bassindu Rhone. Par A. Falsan. Lyon, 1883. l sketches. By L. Agassiz. II, 77. Boston, 1886. The driftless area of the upper Mississippi. By T. C. Chamberlin and R. D. Salis- bury. 6th ann. rep. U. S. Geol. SurV., 205-322. Washington, 1885. 95 96 ANCIENT GLACIATION. Origin of the ice. The ice did not come from the north pole, but from three principal centers of accumulation. The ice moved southwest up the St. Lawrence valley. Local origin of the ice in the Rocky mountains, Sierras, etc. Fig. 25. -The glaciated area of North America (shaded) and the centers of general distribution during the glacial epoch. (Chamberlin.) Direction of ice movements shown by 1. Ice marks. Why some ice marks go up-hill. 2. Shapes of terminal moraines. 97 98 ANCIENT GLACIATION. 3. Wearing of hills on ice- ward side. 4. Distribution of material. Granites in Indiana and Illinois. Copper from Lake Superior.* 5. Effect on drainage. Streams that flowed toward the ice source were dammed up and left terraces around the ancient lake margins. Some stream channels were entirely obliterated as surface features. Lobate forms of the ice shown by 1. Forms of terminal moraines and interlobate moraines. 2. Direction of striae. Thickness of the ice. In the eastern United States the thickness is shown on the mountains. Elk Mountain, northeastern Pennsylvania, glaciated 2,700 feet a. t., and 1,500 feet above the valley.t Mt. Washington 6,000 feet a. t., boulders on top. Ice thinned as the epoch waned, and finally came under the influence of local topography. Cross striae (see p. 88). Retreat of the ice, Concentric parallel moraines. t Evidence that the country was formerly higher to the north . 1. The fjord-like bays of Maine.$ 2. Hudson river gorge out at sea could only be made by subaerial ero- sion. || 3. Preglacial channels of Cuyahoga at Cleveland, Ohio. Wells strike bed-rock at 228, 333, 470, 203, 392 feet below Lake Erie water-level (see p. 102). These must have been made before the glacial epoch, for they are now filled with glacial drift. 4. Possibly the drowned valleys of California, Puget Sound, and north, stood higher during the glacial epoch and sank at its end. IT Elephants' teeth from St. Paul island, of the Pribilof group, an island about 275 miles from the mainland, and in a shallow sea. 5. Terraces, or old shore lines, around Lake Ontario, show that that lake, since the glacial epoch, has sunk on the north more than on the south. The " ridge road " of northern New York. * Copper mines of Isle Royale, Lake Superior. By W. H. Holmes. Am. Anthropolo- gist, III, 684-696. Washington, 1901. t Branner. Am. Jour. Sci., 1886, CXXXII, 363-366. t See maps in Monograph XXXVIII of U. S. Geol. Surv., and Monograph XXXIV, opp. p. 392. ? Gannett. Physiography folio I, U. S. Geol. Surv. I Geology of the sea-bottom in the approaches to New York bay. By A. Lindenkohl. Am. Jour. Sci.. 1885, CXXIX, 475-480. 1i The submerged valleys of the coast of California. By George Davidson. Proc. Cal. Acad. Sci., I, no. 2, pp. 73-103. San Francisco, 1897. Drift phenomena of Puget Sound. By Bailey Willis. Bui. Geol. Soc. Am., 1898, IX, 99 100 GLACIATION IN NORTH AMERICA. Some of the results of glacialion in North America. The region affected varies between 1. The narrow valleys of New England, New York, and Pennsylvania. !?. The broad, flat plains east of the Rocky Mountains. 3. The basin regions of the Great Lakes, now reaching (Huron) 121 to 492 feet (Ontario) below ocean level. 4. The far inland Rocky Mountain ranges. n. The Pacific ranges of the Cascades* and Sierras. t It is to be expected that in so varied a region the influences would vary. Fig. 26. -Ice-marked granite near Lake Tahoe above Glen Alpine Springs, California. (Holway.) Influence of glaciation on 1. Vegetation. 2. Faunas. 3. Drainage and topography. 4. Agriculture. 5. Roads. 6. Mining. 7. Architecture. * Geology of the Cascade Mountains in northern Washington. By I. C. Russell. 80th nu a n ' rep " U ' S ' GeoL Surv -' Pt- n - Glaciation, 150-192 t The Pleistocene geology of the south central Sierra Nevada, with especial reference l * W ' TUrner ' PTOC - CaL A 101 102 INFLUENCE OF GLACIATION. I. Influence on vegetation.* Cold climate crowded vegetation southward. Retreating ice left behind arctic forms. Arctic forms left on mountain tops. Cases of Mt. Washington, Teneriffe, and Java. Swiss mountains have many forms that could only have come from the north when it was cold in the valleys. t II. Influence on faunas. Insects left on Mt. Washington. i They cannot live in the valleys now. Fresh-water fishes and mollusks migrated northward from the Missis- sippi drainage, and passed over the present divides when the drainage flowed into the Mississippi. III. Influence on topography and drainage. Moraines. Long Island, N. Y., largely a terminal moraine resting on Cretaceous rocks. || Kettle-holes and lakes in the moraines. During the ice age former streams were buried and their channels tilled with drift after the retreat; new channels had to be established : IT Cuya- hoga (see p. 98), Chicago,** Niagara. New drainage developed as the ice melted. Lake Michigan drained southward; buried channels ;tt impossibility of locating many of them. Fig. 27.-Preglacial topography of the coal region of Indiana baried under glacial drift. (Ashley.) Wabash drainage. Terraces at Terre Haute, Indiana. Evidences of a much larger stream. Floods from the melting ice. Proc. Am. Assn. Adv. Sci., 1872, XXI, 14. Wyoming 647. as to the public water supplies. . Pierce. Am. Geol., Sept. 1897, X F. A. Hill. Ann. rep. Geol Surv. Pa. for 1885, pp. 637- '. Leverett. Monograph XXXVUI, U. S. Geol. Surv., Ste 7 itS Chica e ^18^ area ' By Ffank Leverett - BuL 103 104 INFLUENCE OF GLACIATION. Mohawk-Hudson drainage. Terraces. Origin of Niagara gorge. St. Lawrence drainage last.* Lake Agassiz.i Ponding back of the water by the ice. Winnipeg on the old lake bed. Postglacial lakes.* Origin of glacial lakes. Left by morainal dams. Left in scooped-out rock basins. " Finger Lakes," of New York. The former northward drainage dammed by drift. Glacial lakes of the Sierras. Donner Lake. Fallen Leaf Lake. IV. Influence of glaciation on agriculture. Nature of glacial soils : mixed, pulverized, hence more fertile and more valuable. In Ohio the glacial border separates the less productive from the more productive parts. Drift soils of the Northwest noted for fertility. || In the driftless area of Wisconsin the land is worth $10 an acre, or less. Loess of the Mississippi valley. Origin from flooded streams? IT At Louisville, Ky.; St. Louis, Mo.; Omaha, Neb.; Kansas City, Mo.; Des Moines, Iowa; Vicksburg, Miss.; Memphis, Tenn. Fine soil. V. Influence on roads. Glacial gravels make good roads. Roads as an index of civilization. VI. Influence on mining. Pot-holes at Archbald. (See p. 42.) Nanticoke disaster.** Buried river channels. (See p. 102.) VII. Influence on architecture. Milwaukee cream-colored bricks from glacial clays containing lime. St. Louis and Memphis red bricks from the loess. At many places in the Northwest glacial boulders used for houses. * Glacial waters in the Finger Lake region of New York. By H. L. Fair-child. Bui. Geol. Soc. Am., 1899, X, 27-68. t Monograph XXV, U. S. Geol. Surv. Tyrell, Jour. Geol., 1895, IV, 811-815. | Ann. rep. Geol. Surv. Canada. New ser., VII, 1894, pt. B, 306. I Glacial lakes in central New York. By H. L. Fairchild. Am. Jour. Sci., April 1899, VII, 249-263. Bui. Geol. Soc. Am., 1893, V.348.-F. B. Taylor. Am. Geol., July 1899, XXIV, 6-38. \ Geology of 'Wisconsin. II, 189. Madison, 1877. Geology of Minnesota. I, 351-385. Minneapolis, 1884. ! Origin of the loess of the Mississippi valley. T. C. Chamberlin. Jour. Geol., Nov.-Dec. 1897, V, 795-802. Abstract, Am. Geol., Sept. 1897, XX, 197; Oct. 1897, 274-275. T. O. Mabry, Jour. Geol., 1898, VI, 273-302. - 12th ann. rep. U. S. Geol. Surv., 401-404. B. Shimek, Am. Geol., Dec. 1901, XXVIII, 344-358. Jour. Geol., VII, 122-140.- Sardensen, Am. Jour. Sci., CLVII, 58-60. Keyes, Am. Jour. Sci., CLVI, 299. ** Buried valley . . . near Nanticoke. Ann. rep. Geol. Surv. Pa., 1885, pp. 626-636. Har- risburg, 1886. 105 106 THE GLACIAL EPOCH. OTHER THEORIES ADVANCED TO EXPLAIN GLACIAL PHENOMENA. (These are mentioned as illustrating the process by which a natural explanation is sought for natural phenomena.) 1. The deluge of biblical account.* 2. Tipping up of the north end of America, and the elevation of the Alps.t 3. Waves of folding rocks.% 4. Iceberg theory. 5. Destroyed planet and the tail of a comet.\\ OBJECTIONS FORMERLY URGED TO THE GLACIAL THEORY. I. The striae show that the ice moved up-hill. Some up-hill movements are local. In the St. Lawrence valley the slope has changed since the glacial epoch. II. Present climate would be colder. But 5 to 6 lower temperature would bring the Swiss glaciers to Ge- neva; hence a very slight change of the annual temperature would cause a glacial epoch. III. Agassiz's theory of South American glaciation. This theory was that a glacier formerly flowed down the Amazon valley. IT This proved too much ; life would have been extinct. This theory not found correct.** DATE OF THE GLACIAL EPOCH. Can be shown by the geologic work done since glaciation. Case of Niagara Falls: estimates range from 3,500 years to hundreds of thousands of years, ft Case of St. Anthony's Falls, Minneapolis, about 8,000 years.it * For geological explanation of the deluge, see La face de la terre. Par E. Suess. 25-95. Paris, 1897. t Poggendortf's Annalen, 1827, IX, 575. Bui. des Sci. Nat., Mai 1828, pp. 5-7. t H. D. Rogers. Am. Jour. Sci., 1844, XL VII, 274 et seq. \ Acadian geology. By J. W. Dawson. 64-73, 2d. ed. 1868. I Kruger. Bui. des Sci. Nat. et de G6ol., Sept. 1826, p. 6. Ragnarok. By Ignatius Donelly. 1i Atlantic Monthly, July and August, 1866. Geological sketches. By L. Agassiz. II, 153. Boston, 1886. ** The supposed glaciation of Brazil. By J. C. Branner. Jour. Geol., I, 753-772. Chicago, tt Niagara Falls and their history. By G. K. Gilbert, Physiography of the United States, 235-236. Guide to the geology and paleontology of Niagara Falls and vicinity. By A. W. Grabau. Bui N. Y. State Mus., no. 45, vol. IX, pp. 82-85. Albany, 1901. U N. H. Winchell. The geology of Minnesota. Vol. II of the final report. 313-341. St. 107 108 THE GLACIAL EPOCH. LENGTH OF THE GLACIAL EPOCH.* Was man here during or before the glacial epoch f Implements should be in the drift if he was here. The Trenton gravels, in which human implements have been found, are far south of the ice margin. t Minnesota. Stump and root holes. Burrowing of animals. In Europe.* WILL THE GLACIAL EPOCH RECUR? Depends on cause or causes. If the cause recurs, the epoch will. If the cause is astronomic, its return is to be expected. Evidences of interglacial epoch. Several lignite beds in the glacial deposits near Zurich, Switzerland. Topographic variation and difference in oxidation in Illinois, Indiana, and Yosemite Valley region. Shells in wrinkled loess. Nature of marine fossils inter bedded with drift. || Evidence of previous glacial epochs.^ In the Mesozoic rocks of India.** In the Carboniferous rocks of India and South Africa. In Tertiary, or pre-Tertiary, rocks in South Australia, tt Hence the glacial epoch may return. The conditions move slowly. CAUSES OF A GLACIAL EPOCH. Evidently the climate must have been different, though not necessarily arctic. In Alaska forests are growing alongside of glaciers, and even in the moraines upon the ice.ii * See F. B. Taylor, Jour. Geol., 1897, V, 421-465. Makes retreat from Cincinnati, Ohio, to Makinac 75,000 to 150,000 years, and glacial epoch 150,000 to 300,000 years or more. W. Upham, Am. Geol., Oct. 1897, XX, 268. Geikie's Great ice age. 812-815. t G. F. Wright and A. Hollick. Science, Oct. 29 and Nov. 5, 1897. W. H. Holmes. Jour. Geol., 1893, I, 15-37 and 147. Science, new ser., vol. VI, 1897. Several papers in Proc. Am. Assn. Adv. Sci., 1897, XLVI, 344-390. F. Russell. Am. Nat., XXXIII, 143-153. t Man in relation to the glacial period. By Dr. H. Hicks. Nature, Feb. 24, 1898, LVII, 402. Nature, Oct. 6, 1898, p. 559. 2 Interglacial deposits in Iowa. By S. Calvin. Proc. Iowa Acad. Sci., 1898, vol. V. II On the interglacial submergence of Great Britain. By H. Munthe. Bui. Geol. Inst. Univ. of Upsala, 1898, III, 369-411. 11 Neues Jahrb. f. Min., 1896, II, 61-86, and plate V. Bibliography. Geol. Mag., 1886. Ill, 492-495. For bibliography, see Am. Geol. Mag., 1889, III, 299-330. The great ice age. By James Geikie. 3d ed., 817-826. London, 1894. Am. Geol., Mar. 1902, XXIX, 169-170. Molengraaff, in Trans. Geol. Soc. South Africa, IV, pt. V, pp. 104- Geologie de la Republique Sud-Africaine du Transvaal. Par M. G. A. F. Molengraaff. Bui. Soc. G6ol. de France, 4me Se~r. I, 71-81. Paris, 1901. ** C. H. Hitchcock. Am. Geol., April 1899, XXIII, 252. n Glaciated boulders at the base of the Permo-Carboniferous, etc. By T. W. E. David, Jour, and Proc. Roy. Soc. N. S. W., 1899, XXXIII, 154. U I- C. Russell. 13th ann. rep. U. S. Geol. Surv., pt. II, 66. 109 HO THE GLACIAL EPOCH. Leblanc thinks an average of 7 degrees Centigrade lower than now would produce glacial epoch.* Temperature falls 1 degree Centigrade for 188 metres in elevation. Snow line in the Alps is at 1,200 metres; a decrease of 5 degrees in the temperature of that region would bring the ice down to 260 metres, or below Geneva. Difference of temperature may have been due to geographic or astronomic causes. Suggested geographic causes .t 1. Change of ocean's currents. 2. Change of trade winds. 3. Elevation of land above snow line. The sea bottom of Norway was at least 2,600 metres higher than at present.* That northern North America was higher is shown by the fjords of Maine and British Columbia and by the ice flowing up the St. Lawrence valley; Canada was at least 1,200 feet higher than at present. 4. Change in distribution of land and water. We have no evidence of such changes during the glacial epoch. Supposed astronomic causes.^ 5. Increase of the obliquity of the ecliptic. 6. Combined effect of precession of equinoxes and of the eccentricity of the earth's orbit. 7. Changes in position of earth's axis. In Tertiary times it was warmer near the north pole, as fossil plants show. 8. The turning of an exterior crust over a fixed core.|| 9. Variation of the heat radiated by the sun. 10. Variation of the temperature of space. The planetary system may pass through cold and hot belts. 11. Decrease of the original heat of the earth. We have to account for many glacial epochs. Certainly due to lowering of the snow line, whatever may have caused that. * Bui. Soc. G6ol. de France. ler seYie. XIV, 600-611. Paris, 1843. t Chamberlin. Jour. Geol., Nov.-Dec. 1899, VII, 751-787. H. N. Dickson. Geog. Jour., XVIII, 516-523. London, 1901. t Om de senglaciale og post-glaciale Nivaforandruger i Kristianiafeltet. Af W. C. Brog- ger. 683. Kristiania, 1901. \ Discussions on climate and cosmology. By James Croll. Edinburg, 188.V Climate and time in their geological relations. By James Croll. Edinburg, 1875. Island life. The causes of glacial epochs. By A. R. Wallace. 121-162. London, 1880. Mars on the glacial epoch. By P. Lowell. Proc. Am. Phil. Soc., XXXIX, 641-664. Phila- delphia, 1900. I Sir John Evans. Proc. Roy. Soc. 1866. Ill 112 ICEBERGS. ICEBERGS. Formed by sea-water lifting the ends of glaciers. Humboldt glacier, Greenland, 60 miles across at the end. Muir glacier, Alaska, two miles across at the end. Bottoms set with stones and debris. Floating, they carry away this debris for thousands of miles. Icebergs melt and the stones they carry fall to the bottom. Banks of Newfoundland. Stranding of bergs in shallow water.* Only one-eighth to one-seventh part of the ice remains out of the water. Icebergs can ground in 2,000 feet of water. Contorting of drift by the dragging of icebergs. A large area south of the glaciers probably affected by bergs. FLOE-ICE. Work of the ice in streams when the ice breaks up in the spring. Stones and earth are carried down. Ice piled on the spits of the Great Lakes. * Striation by dragging bergs. Chalmers, Geol. Surv. Canada, VII, part M, 104-106. Ottawa, 1895. Proc. Liverpool Geol. Soc., 1895, pp. 383-386. 113 114 CHEMICAL AGENCIES. CHEMICAL AGENCIES. Under the head of Chemical Agencies come the decomposition and re- composition of minerals and rocks, and the formation of many of our most valuable mineral deposits. The operations of chemical agents are, for the most part, invisible ; but the results of such operations become apparent with time. When rainfalls on the earth the water does either mechanical or chemical work. 1. It flows off over the surface as freshets (doing mechanical and chem- ical work), and returns to the air by evaporation. 2. It soaks into the ground, to emerge as springs, or to be evaporated from the soil surface (doing chemical work). 3. It reaches the sea by underground channels (doing chemical work). All stream, spring, and well waters contain mineral matter in solution. This is shown by evaporation of the water. Mineral matter is derived from the rocks passed through. Many of these minerals are considered insoluble in water. Why the minerals are in solution. The water is not simple, pure water. The solvent power of water is increased by 1. Carbonic acid (CO 2 ) derived from the air. 2. Nitric acid derived from the air. Produced by electric discharges. More abundant in the tropics. 3. Organic acids in the soil. Carbonic acid from the decay of plants ; from the breath of bur- rowing animals. Humic acids from the decay of organic matter.* 4. Increase of pressure on the water column, which increases its dis- solving power. 5. Increase of temperature, which increases the dissolving power with minerals. 6. Decrease of temperature. Amount of dissolved matter in streams. The streams come chiefly from springs, and all spring waters contain minerals in solution. The amount dissolved varies greatly. * Phillips' Ore deposits. 2d ed., 37. London, 1896. On the geological action of the humus acids. By Alexis A. Jnlien. Proc. Am. Assn. Adv. Sci., 1879, XXVIII, 311-410. 115 116 CHEMICAL EROSION. No two streams are alike. The same stream varies from time to time. How the amount is determined. Measure of discharge frequently. Determination of matter in samples. Examination of the Arkansas river water. Matter in solution varies from 11 to 71 grains per U. S. gallon. Re- moved in solution in one day from 13,000 to 68,000 tons; in the year 1887-88 the total removed in solution was 6,828,350 tons. All of this is invisible.* Minerals in solution mostly salt, gypsum, epsom salt, lime carbonate. Difference between streams. Due to rock differences of the hydraulic basins. Due to the nature of the water (i. e., the contained acids). Streams from swamps and marshes usually contain much organic acid. Tropical streams often carry much organic acid on account of the rapid decay of vegetation. Difference in the same stream due to Drainage coming at different times from different parts of the basin, where the rocks differ. Drainage sometimes from underground, sometimes from surface water. Concentration of water by evaporation in dry weather. EFFECTS OF CHEMICAL EROSION. Rocks are minerals; some minerals are easily soluble, some are nearly in- soluble, but all are soluble with time. Materials removed are minerals dissolved from the rocks. Chemical action results in the decomposition and removal of rocks. The chemical operations of decomposition and alteration of roe&t result in 1. Soils (residuary). Depth of rock decay. 2. Kaolins (from feldspar). Nature and form of kaolin beds. Only in region of feldspathic rocks, or redeposited. 3. Clays (largely kaolin). 4. Concentration of some minerals by the removal of others. The mechanical results of solution and rock removal. 1. Etching.* Examples. 2. Fluting. 3. Fret- work (see p. 28). 4. Caves. ! w 0n( i ra?h XI PJ - U ' S ' GeoL Surv - for wat er of twenty rivers. (Table A.) 176. t W^^ering of diabase near Chatham, Virginia. By. T. L. Watson. Am. Geol., Aug. 1898 XXII, 85-101. - Bui. Geol. Soc. Am., XII, 9JM08. Van den Broeck. Compt. Rend. Cong. Interval de Geol., 1878, pp. 1-11. Paris, 1880. Am. Jour. Sci., 3d ser., XXVI, 196. - Am. Naturalist, IX, 1875, p. 471. - Annales des mines, 7me ser., VIII, 698. Paris, 1875. | Mount Seir, Sinai, etc. By E. Hull. 20. I Branner Bui. Geol. Soc. Am., 1896, VII, 280. - Bauer. Neues Jahrbuch f. Min. 1898, 11, iy-, puite XI. 117 118 FORMATION OF CAVES. THE FORMATION OF CAVES.* Natural caverns are formed in four ways : 1. By the removal of rock in solution. 2. By the underflow of lava beneath hard crust. 3. By the mechanical action of waves on coasts. 4. By the differential weathering of cliffs. Fig. 28. Ideal section in a limestone region, showing the relations of caves to sink- holes and natural arches. (Shaler.) I. Differential solution and removal of rock, aided by mechanical wear. Mammoth Cave, Kentucky, has '65 to 40 miles of tunnels along which one can walk, besides many miles of smaller ones along which one can creep. Cavern 70 to 200 feet high. 500 caves in Edmonson county, Ky.t The limestone regions of Kentucky extend into Indiana, Tennessee, Arkansas, and Missouri. Wyandotte cave, Indiana ;+ Nicajack cave, Tennessee; Luray cave, Virginia.^ Fig. 29. Plan of the limestone caves of Lapa Vermelha, State of Minas, Brazil (Lund.) * La sp61(ologie on science des cavernes. Par E. A. Martel. 126 pp. Paris, 1900. Mar- tel. Ann. des Mines, 9me ser. X, 5-100. Paris, 1896. - Stainier. Bui. Soc. Beige de ijeol., 1897, XI, mem. 251-272. t The Mammoth Cave of Kentucky. By H. C. Hovey and R E Call " _ Am. Geol., Oct. 1896, XVIII, 228. 1st ann. rep. Dept. of Geol. (of Abstracts of papers by H. C. Hovej I Indiana caves and their fauna. By W. S. Bla'tchley. Indiana), 121-175. Indianapolis, 1897. Observations on Indiana caves. By O. C. Farrington. Pub. 53 Field Columb Mus I no 8, Geol. Surv. Chicago, 1901. g Am. Geol., Oct. 1896, XVIII, 228. 119 120 FORMATION OF CAVES. Why the great caves are in limestone regions. The processes of solution and removal. Such caves formerly supposed to be formed only above ocean-level. But waters from the land discharge beneath the ocean, hence there must be rock removed below sea-level.* II. By the underflow of lava beneath a cooled hard crust. Method of formation. Such caves are formed only in volcanic regions. The lost streams of volcanic regions in some cases flow through these caverns. Kildii river, in Iceland, is only two miles long; the rest of it is below ground. t III. By the mechanical action of waves on coast lines. Processes of the wave work. Chemical action of sea-water often aids mechanical work.t Caverns made in this way seldom go far into the rocks. Examples: at Santa Cruz, California; at Santa Cruz Island; at Fernando de Noronha. (See Figs. 15 and 16, pp. 60 and 62.) IV. By differential weathering in cliffs. Processes of weathering. Why caves are formed in one bed and not in another. Uses made of cliff caverns.^ (See Plate IX.) BLOWING, "BREATHING," AND SUCKING CAVES. Movements of air due to varying temperatui-es inside and outside of the caverns. In summer the inside air is cooler and descends. In winter it is warmer and rises. Flows out of Mammoth Cave at 54 in summer. || ICE CAVES, if SINK-HOLES. Sink-holes are formed by the solution and downward removal of rocks at the surface, or by the falling in of roofs of caves. * For instance of fresh water discharging beneath the ocean, see Shaler in Bui. Geol. Soc. Am., 1895, VI, 155. t Iceland; its volcanoes, geysers, and glaciers. By Charles S. Forbes. 112,145-148. Lon- A summer in Iceland. By C. W. Paijkull. 273-274. London, 1868. Kilauea, the home of Pele. By Wm. Libbey. Harper's Mag., Oct. 1897, p 719 For illustration of Hawaii caves see Scott's Introduction to geology 44-45 t See Agassiz, Bui. Mus. Comp. Zool., XXVI, no. 1, p. 48, and plates. 2 The cliff ruins of Canon de Chelly, Arizona. By C. Mendeleff. 16th ann. rep. Bur. Am. Ethnology, 79-198, with plates. Washington, 1897. A summer among cliff-dwellers. By T. M. Prudden. Harper's Mag., Sept. 1896, XCIII, II The Mammoth Cave of Kentucky. By Hovey and Call. 9; 4. II The origin and occurrence of cave ice. Nature, April 19, 1900, LXI, 591. Ice caves and frozen wells. By W. J. McGee. Nat. Geog. Mag., Dec. 1901, XII, 433-434. Plate IX. Natural caverns used as houses by the "Cliff-dwellers." Walnut Canon, near Flagstaff, Arizona. 121 122 CHEMICAL DEPOSITION. Found chiefly in limestone regions. Due to solubility of limestone. Examples found in the cave regions of Kentucky, Indiana, Tennessee, Virginia, Missouri, and Florida.* Eden Valley, Ky., covers 2,000 acres ;t 1,000 sink-holes in that county. Ponds made by puddling clays in sink-holes. Underground drainage of cave regions. Mammoth Springs. Why they fluctuate so little in volume. Method of tracing streams by the use of fluorescein. NATCRAL ARCHES. I. Formed by the destruction of caverns. Natural Bridge of Virginia in synclinal fold. In limestone or volcanic regions.* (See Fig. 28, p. 118.) II. Formed by encroachment of sea on isthmus or peninsula. Examples: Santa Cruz, California; Fernando de Noronha. (See Fig. 18, p. 66.) Chemical Deposition. It has been shown that solution is due to 1. Acids in the water (derived from various sources). 2. Pressure. 3. High temperatures. 4. Low temperatures. 5. Chemical reaction. 6. The solubility of rock-forming minerals under ordinary conditions. It follows that if these causes be removed the mineral matter can no longer remain in solution, and must be deposited. Deposition from solution takes place I. When the solvent escapes. Especially true of carbonic acid gas. Origin of stalactites ; stalagmites; stone pillars. Frozen cascades. Origin of spring deposits of lime (tufa and travertine) by the escape of CO 2 ; especially when sprayed at falls. * Alex. Agas'siz. Bui. Mus. Comp. Zool., XXVI, 215-216. Shaler. Bui. Mus. Comp. Zool., XVI, no. 7, pp. 144-145, 151. t The Mammoth Cave of Kentucky. By Hovey and Call. 4. t Natural arches of Kentucky. By A. M. Miller. Science, June 24, 1898, VII, 845-846, illustration. The Natural Bridge of Virginia. By C. D. Walcott. Nat. Geog. Mag., V, 59-62. Wash- ington, 1893. Voyage de Humboldt et Bonpland, premiere partie. Atlas pittoresque, pp. 9-13. Paris, I Stalactites, etc. By G. P. Merrill. Proc. U. S. Nat. Mus., XVII, 77-81 (illustration). Washington, 1894. 123 124 SALT LAKES. Terraced lime deposits.* Hardening of beach sands by ocean water containing CO 2 . Examples on the northeast coast of Brazil. (Plates V and VI, and p. 70.) Hardening of dunes of calcareous sands by CO 2 from the air. II. When the temperature is lowered. Hot water dissolves more mineral matter (except carbonates) than cold. Hot waters usually deep seated, and on approaching the surface cool and deposit. Example: box from the Comstock mines. Some hot springs and geysers deposit tufas. Quicksilver deposited in cool neck of retort. When hot water is alkaline it dissolves silica and deposits siliceous sinter. t III. When the temperature is raised. Examples : marls of Michigan and Indiana. i Effect of heating hard water in boilers. IV. When the pressure decreases. All underground water is under hydrostatic pressure. Pressure decreases as the water approaches the surface. Cooperates with lower temperature, in the case of waters from depths, to help fill cavities with mineral matter from depths. V. When chemical reactions take place. Any reaction that causes precipitation. Examples: oxidation of iron in solution, and deposition of bog iron. Probable relations to certain ore deposits. Some deposits appear to have been formed at the confluence of underground streams. VI. When solutions are allowed to stand long undisturbed. Examples: geodes; some veins. VII. When there is a concentration of the water by evaporation. This is chiefly a surface phenomenon. Efflorescence, or "alkali," thus produced (see p. 28); salt, borax, and alkaline lakes made in this way. "Hard-pan" sometimes formed by waters rising toward the surface. SALT LAKES. Origin of the salt in salt lakes. 1. From the cutting off of an arm of the sea. 2. By the concentration of fresh water. 3. By some combination of the two. * The origin of travertine falls and reefs. By J. C. Branner. Science, Aug. 2, 1901, XIV, 184-185. t Am. Geol., Sept. 1897, p. 165. Weed. Folio 30, U. S. Geol. Surv., 1896. t Deposits of calcareous marls. By I. C. Russell. Science, Jan. 19, 1900, XI, 102. i The caliche of southern Arizona. By W. P. Blake. Trans. Am. Inst. Min. Eng., vol. XXXI, p. . New York, 1901. 125 126 SALT LAKES. I. Cutting off an arm of the sea. Origin of the salt in the ocean : it was all originally in the hot rocks of the earth. Water leached it out and concentrated it in seas. Effect of the separation of any part in dry climate. Examples : salt spray pools on sea beaches. Influence of an arid climate. Waters of the Red Sea, and of Mediterranean Sea,* now denser than ordinary ocean water, in spite of the constant influx of fresh water. Cause of greater density of waters of the tropics. Results of isolation depend on the relations of influx to evaporation. A salt lake may wash out and become fresh. San Francisco bay, if cut off, would wash out. Sea of Galilee kept fresh by inflow and outflow to Dead Sea. The Caspian Sea was formerly connected with the Black Sea; it is now isolated and concentrating. II. Concentration from fresh-water streams. River waters contain salt, epsom salt, and carbonate of lime, etc. Waters flowing from sedimentary rocks all contain salt, etc. If such waters evaporate, the salt is deposited. If their basins overflow, the water remains fresh. It is therefore a question of evaporation or of aridity. The western tributaries of the Paraguay river are more or less salty, because they flow 'from an arid region. The eastern tributaries are fresh, owing to the greater rainfall.t Salt Lake, Utah, covers 2,000 square miles; it formerly covered 50,000 square miles, and was fresh. J Its waters are now more dense than those of the ocean. Freshness indicated by its former outlet.^ Lakes having outlets are fresh. III. Combination of the isolation of salt water and the concentration of fresh water. Salton Lake, formerly part of the Gulf of California, and since added to by the influx of fresh water from the Colorado river. || * Double currents in the Bosphorus, etc. By S. Makaroff. Nature, July 13, 1899, pp. 261- t Buenos Ayres and the provinces of the Rio de la Plata. By Sir Woodbine Parish. 2d ed., 233. London, 1852. t The Great Salt Lake. By J. E. Talmage. Scottish Geog. Mag., Dec. 1901, XVII, 617- Monograph I, U. S. Geol. Surv. I J. W. Powell. Scribner's Mag., Oct. 1891, X, 463-468. Salton Lake. By E. B. Preston, llth ann. rep. State Mineralogist of Cal., pp. 387-393. Sacramento, 1897. The Colorado desert. By D. P. Barrows. Nat. Geog. Mag., Sept. 1900, XI, 337-351. Lands of the Colorado delta in the Salton basin. By Snow, Hilgard, and Shaw. Bui. 140, Univ. Cal. Agr. Exp. Sta. Sacramento, 1902. 127 128 SALT LAKES. "V *'<* CALfFOR Fig. 30. The shaded portion of the map shows the area formerly covered by the Gulf of California. Association of salt and gypsum in salt lakes. Salt can not be deposited in the open sea; sea-water is too fresh. In sea-water gypsum is deposited only after eighty per cent, of the water is evaporated, and salt after still further evaporation. Gypsum not soluble in strong brine; hence it precipitates first.* In part of the Caspian Sea (Gulf of Karabougas) gypsum is now de- positing. Middle has beds of mirabilite (Glauber salt), sulphate of soda.t * Dieulafait. Pop. Sci. Mo., Oct. 1897. t Eng. and Min. Jour., Oct. 9, 1897, LXIV, 428. 130 ALKALINE LAKES. Thickness of salt beds (maximum) : Syracuse, N. Y., Warsaw, N. Y., 65 to 318 feet Kansas,* 200 feet. Michigan, 32 feet. Goderich, Canada, at 964 to 1,180 feet it is 14 to 40 feet. Orange Island, Louisiana, 1,865 feet. Spain, 300-400 feet in hills near Barcelona. Stassfurt, Germany.t 4,794+ feet. Explanation of great thickness of salt beds. Influx of sea-water at high tide and during storms. Examples : Lag6a de Freitas, Rio de Janeiro. Influx due to evaporation in shallow marginal pools.* Interpretation of gypsum and salt beds. Indicate salt lakes and arid climates at those places at the time of their deposition. ALKALINE LAKES. Alkaline lakes have been formed by the concentration by evaporation of waters flowing over igneous rocks (in which alkaline carbonates pre- dominate). Mono Lake, California;^ area 87 square miles in 1887, but varying. Strong solution of salt and carbonate of soda (42.53 per cent, of the total constituents). Carbonate of lime, and borate of soda. Old shore line 680 feet above water (higher in glacial epoch), and hydrographic basin of 7,000 square miles. Region arid mostly; the minerals will precipitate soon. Owen's Lake, California. Water used to manufacture soda. BITTER LAKES. Bitter lakes are a further concentration of salt lakes. Those containing bittern, or liquor, left after the deposition of salt. Contain Epsom salts, Glauber salt. Such lakes cut on Suez canal. They were below the level of the Red Sea. The Dead Sea is a bitter lake. BORAX LAKES. Borax lakes are formed by the concentration of waters flowing from igne- ous rocks containing borax minerals. Borax now made from the water of wells sunk in basins. This water has flowed from igneous rocks, and has been concentrated in lakes now dried up. * Gypsum deposits in Kansas. Am. Geol., Oct. 1896, XVIII, 236. t The salt deposits of Stassfurt. By H. M. Cadell. Trans. Edin. Geol. Soc., V, pt. I, 93. Edinburg, 1885. The theory of the Stassfurt salt deposits. Nature, Feb. 16, 1899, t Karamania, or . . . the south coast of Asia Minor. By F. Beaufort. 2d ed., 283. Lon- don, 1818. ? 8th ann. rep. U. S. Geol. Surv., 287-299. Bui. 60, U. S. Geol. Surv. Russell's Lakes of North America. 83-89. 131 132 PENETRATION. Resume. The matter of chief geologic importance regarding all lakes, and other bodies of mineral waters, is that their mineral contents have been dissolved from the rocks over and through which they have passed, and that the nature of their contents must vary with the nature of the rocks. THE DEPTH TO WHICH WATERS PENETRATE THE EARTH'S CRUST. Depth to which waters penetrate suggested by I. Hot waters. Earth's temperature increases downward. Not uniform; varies with crust and place. Average about 1 degree for 50 feet in depth below constant line. Reasoning from temperatures of hot springs. Thermal Springs of Bath, England, 120 Fahr. If surface temperature of water were 40, the additional 80 would be had at 80 X 50 feet = 4,000 feet. Hot Springs of Arkansas, temperature: 142 40 temperature at surface. 102 above normal temperature. 102 X 50 feet = 5,100 feet, depth from which the water would have come if the conditions were average. II. Depth to which rocks are altered by decay. Suggests the depth to which surface waters penetrate. In Brazil, cuts of 100 feet; drill holes, 393 feet; mines, 400 feet.* Certain minerals (iron and copper sulphides) susceptible of change to carbonates, oxides, etc. In mines some are found changed to depths of 600, 1,000, and 1,500 feet.t In some of the mines of West Australia the rocks and ores are altered to a depth of 400 feet.t These changes are produced by surface waters. GENERAL RESULTS. 1. Meteoric waters dissolve rocks in one place and deposit them in another, or carry them to the sea. 2. They remove the more soluble, and leave the less soluble. 3. They form cavities, caves, sink-holes, and channels. 4. These waters deposit their dissolved materials in crevices and veins, and form surface accumulations. * Branner. Bui. Geol. Soc. Am. , VII, 255. f Penrose. Jour. Geol., 1894, II, 295. t H. C. Hoover. Trans. Am. Inst. Min. Eng., XXVIII, 758-765. New York, 1898. 133 134 135 136 THE INTERIOR OF THE EARTH. IGNEOUS AGENCIES, OR HIGH TEMPERATURES. The Interior of the Earth. Evidences of the heated condition of the earth's interior. 1. Downward increase of temperature in wells and mines. (See page 138.) 2. Volcanoes with their accompanying phenomena. Explosions, steam, hot vapors and gases, molten rocks. 3. Geysers and other hot springs, bringing high temperatures to sur- face. 4. Positions and characters of certain rocks, such as dikes and lava sheets, which appear to have been fused, and to be connected with masses penetrating the earth's crust. Influence of interior heat on climate. Not felt now ; in one year would not melt 1 mm. of ice over the globe. Its influence felt only during the early history of the earth. THEORIES CONCERNING THE INTERIOR CONDITION OF THE EARTH. I. Fluid molten interior, with hard crust. Reasons for the theory. Outflow of lavas and hot waters ; high temperatures. Objections to the theory. Physicists show that there would be tides in such a globe. It does not behave like a molten globe. II. Solid crust and center and molten layer between. Would answer geologic conditions unless affected by tides. III. Solid as a globe of glass or steel. Because of behavior. Objections. Evidences of elevation and depression. Our sedimentary rocks here are marine, including those in the mountain tops. IV. Solid throughout, except local pockets of molten rocks. Physicists and geologists can agree on this.* Rate of increase of temperature downward. Temperature of the ground surface varies daily and yearly. This variation is due to outside, or solar, influence. * Earth movements. By C. R. Van Hise. Trans. Wis. Acad. Sci., XI, 475, on " Condition of the interior of the earth." Madison, 1898. 137 138 THE INTERIOR OF THE EARTH. Level of no change in the tropics is about 4 feet deep ; at New York it is about 50 feet deep. Further north it is deeper. Difference due to climatic fluctuations. Below the line of uniformity the temperature rises. The increase is constant, but the rate varies at different places, and at different depths. On volcanic cones the high temperature is near the surface. Comstock Lode, Yellow Jacket mine.* 1 for every 28 feet, down to 3,000 feet. Artesian wells increase 1 for about 50 feet. North of England, 1 for 49 feet.t Committee of the British Associa- tion prefers 64 feet for 1.J New South Wales, 1 for 80 feet.t Schladebach hole, near Leipzig, 6,560 feet, 1 to 56+ feet. Idaho-Maryland mine, Grass Valley, California, 1 to 107 feet. Wheeling, West Virginia, 5,386 feet, Feb. 1897, 1 to 80-90 feet in the upper half; 1 to 60 feet in the lower half.|| Calumet and Hecla copper mines, Michigan, 1 to 224 feet, to a depth of 4,700 feet. If In Dakotas varying from 17}^ to 45 feet to a degree.** Variations may be due 1. To varying conductivity of the rocks (which are not everywhere the same). 2. To varying conditions that produce high temperatures. tt Temperature of 3,000 would fuse rocks. 3,000 50 feet descent for each degree. 150,000 feet = nearly 30 miles, the depth at which a temperature of 3,000 would be reached at this rate. But 30 miles of rock increases pressure greatly, and raises the fusing point. Rocks expand on fusion. Greater depth is therefore required to fuse them. But this depth increases the pressure and raises fusing point. Difficulty of reasoning on the interior conditions of the earth. We can not reproduce the conditions. Possibility of error regarding such temperatures and pressures. * Becker. Monograph III, U. S. Geol. Surv., 229. Washington, 1882. t Nature, 1896, LIV, 137. 1 Reports British Association. 1882, pp. 72-90. I Lindgren. 17th ann. rep. U. S Geol. Surv., 1896, II, 171. II Am. Jour. Sci., 1892, CXLIII, 231. School of Mines Quar., Jan. 1897, XVIII, 148-153. H Am. Jour. Sci., 1895, CL, 503. The geothermal gradient in Michigan. By A. C. Lane. Am. Jour. Sci.. June 1900, CLIX, 434-438. ** Geothermal data, etc. By N. H. Darton. Am. Jour. Sci., CLV, 161-168. . New Haven, 1898. 1t Sollas suggests (Geol. Mag., Nov. 1901, p 502) that the irregular downward increase of temperature may be due to the irregular distribution of molten rock below. This can be of but little importance, because many rocks are quite as hot as some molten on.es, but owing to pressure are hard. 139 140 VOLCANOES. Possibility of fusion being due to local relief of pressure, as in the case of the steam of geysers. Lava supposed to come from a depth of less than 30 miles.* Ridging of the crust by contraction of the globe. Pressure at six miles makes rocks plastic and closes cavities. t Volcanic activity is mostly confined to regions of breaking, slipping, faulting, and thrust. In any case the igneous, or high temperature, phenomena are mostly deep seated, though they manifest themselves at the surface. Volcanoes and Their Geologic Work.} Volcanoes may be classified as 1. Active. t 2. Dormant, or extinct. The periodicity of volcanoes is so irregular and uncertain that such a classification is quite arbitrary. Dormant, and even extinct, vol- canoes become, or are liable to become, active. I. ACTIVE VOLCANOES. Definition. A volcano is usually a conical hill or mountain, with an opening (one or more) through which molten rocks, gases, and cinders escape from the hot interior to the surface. The mountain is the result, not the cause, and is not an essential part of a volcano. ERUPTIONS. I. Conditions of eruptions. Eruptions are supposed to be more or less affected by barometric pres- sure. This could occur only when the eruption was on the point of taking place. * J. L. Lobley. Geol. Mag., April 1897, p. 189. t Flow and fracture of rocks as related to structure. By L. M. Hoskins. 16th ann. rep. U. S. Geol. Surv., 859. C. R. Van Hise. Same vol., 593. Washington, 1896. I Volcanoes: what they are and what they teach. By J. W. Judd. New York, 1895. Volcanoes of North America. By I. C. Russell. New York, 1897. Characteristics of volcanoes. By J. D. Dana. New York, 1891. The eruption of Krakatoa and subsequent phenomena. Report of the Krakatoa commit- tee of the Royal Society. Edited by G. J. Symons. London, 1888. The South Italian volcanoes. By H. J. Johnston-Lavis. Naples, 1891 (With bibliog- raphy.) The geology and extinct volcanoes of Central France. By G. Poulett Scrope. London, Aspects of the earth. By N. S. Shaler. 46-97. New York, 1889. Volcanoes, the character of their phenomena. By G. P. Scrope. London, 1862. I. a face de la terre. Par E. Suess. Tome I, 185-223. Paris, 1897. The ancient volcanoes of Great Britain. By Sir Archibald Geikie. 2 vols. London. 1897. The volcanoes of Japan. By John Milne. Trans. Seismological Soc. of Japan, IX, pt. II. Yokohama (1886). Les volcans et les tremblements de terre. Par K. Fuchs. 6me ed. Paris, 1895. Volcanoes: their structure and significance. By T. G. Bonney. The Science Series. London and New York, 1899. Dutton. 4th ann. rep. U. S. Geol. Surv. Hitchcock. Bui. Geol. Soc. Am., 1900, XI, 15-60. Hurlburt. Bui. Am. Geog Soc., XIX, 233-253. 1887. 141 142 ACTIVE VOLCANOES. Lava is brought to the surface by gravity, or the difference between the weight of the lava and that of the overlying rocks. The flow- stops when equilibrium is again established. II. Periodicity. Stromboli, once in 4 to 10 months. Kilauea, in Hawaii, once in 8 to 9 years. III. Sequence of events. Rumbling. Earthquakes. Rumblings and earthquakes are frequent in many volcanic regions, and do not necessarily indicate an approaching eruption. Vapors. Explosions. Rise of lavas. Overflow. IV. Phenomena accompanying eruptions. Lava flows quietly when dry. Sheets on slopes, or in valleys. Cones of lava, or lava and " ashes," or cinders. Lava breaks through fissures on sides ; due to hydrostatic pressure. Pressure on the sides when the craters are high. Height of South American craters. Cotopaxi, 19,613 feet.* The following have long been extinct: Chimborazo, 20,498 feet; Antisana, 19,335 feet; Cay- ambe, 19,186 feet. When the rocks contain much water the eruptions are explosive and scatter cinders and blocks. t Gases.* Earthquakes. Geysers. Elevations. Jorullo, a volcanic peak in Mexico, rose 513 metres in a night (Sep- tember 29, 1759). Depressions. V. Materials of volcanic eruptions. 1. Lavas and lava streams. || Rate of flow depends partly on slope and partly on the fluidity of the lava. * Travels amongst the great Andes of the Equator. By Edward Whymper. 126-127, 342- New York, 1892. t Verrill. Science, May 23, 1902, p. 824. Verrill. Am. Jour. Sci., XIV, 72-74, July 1902. Gordon. Science, June 27, p 1033-1034. t Observations on Mt. Vesuvius, etc. By Sir William Hamilton. 164-167,118-119. Lon- don, 1774. Santorin et ses eruptions. Par F. Fouque' 225 232 A description of active and extinct volcanoes. By Charles Daubeny. 160, 375. London. Death Gulch, a natural bear trap. By T. A. Jaggar, Jr. Pop. Sci. Mo., Feb. 1899, I.IV, 475-481. - Ward. Science, Mar. 24, 1899, p. 459. ? Vues des Cordilleres, etc. Par A. de Humboldt. 242-244. Paris, 1810. I Kilauea, the home of Pele. By W. Libbey. Harper's Mag., Oct. 1897, vol. 95, pp. 714-723. 143 144 ACTIVE VOLCANOES. Size and shape of streams.* Temperature. Effect on drainage. Dams causing lakes and diverting streams. t The topography is sometimes overwhelmed.* The great lava floods of the northwestern United States cover an area of 150,000 square miles. Formation of cavea with striated sides. 2. Fragmental ejectamenta. Composition of the dust and "smoke," "sand," and " ashes. " Some ascend 20,000 feet,|| and even 164,000 feet in the case of the very fine dust of Krakatoa. Lapilli. Tuff\i deposited in water. Pumice in windrows. If Blocks and other fragments blown from throat. Thrown 12 miles.** Bombs. Mud produced by rains in ashes; by melting ice on high peaks. tt Burying of Pompeii and Herculaneum under showers of frag- mental material ; Herculaneum 70 to 112 feet deep. it Destruction of St. Pierre, Martinique, May 8, 1902. 3. Inclusions. Brought up from below. Show relative age of eruptions. 4. Gases, steam.^ Volcanic peaks (of construction) built up by ejectamenta. Largest volcanoes are those of the Andes, 17,000 to 19,000 feet high. Aconcagua, the highest peak of South America, 23,080 feet, is of volcanic rock.|||| Orizaba, Mexico, 18,314 feet. (See Around the world, opp. p. 24.) * A summer in Iceland. By C. W. Paijkull. 341. London, 1868. The Bolivian Andes. By Sir Martin Conway. 338, and plate. New York and London, t Observations on Mt. Vesuvius, etc. By Sir W. Hamilton. 12, foot-note. London, 1774. See Lindgren, in Truckee folio, U. S. Geol. Surv., 6. t Cadell, on New Zealand volcanic zone. Trans. Edin. Geol. Soc., 1897, VII, 183. 2 Diller and Steiger. On dust from Martinique, etc. Science, June 13, 1902, p. 947. I Whymper. Travels amongst the great Andes. 125, 141, 326-328, 330. Report of the Krakatoa committee of the Royal Society, 375, 379, 282. H J. P. Iddings. Science, Feb. 8, 1884, III, 144. Across Vatna Jokul. By W. L. Watts. 105-108, 160. London, 1876. ** Hamilton's observations. 49, note. tt Travels amongst the great Andes of the Equator. By Edward Whymper. 126-127. New York, 1892. U On ashes about Vesuvius, see Observation on Mt. Vesuvius, etc. By Sir Wm. Hamil- ton. 34, note; 46, 94-95, 116. London, 1774. Pompeii, its life and art. By August Mau. Translated by F. W. Kelsey. New York, ?? J. Milne. Nature, May 15, 1902, LXVI, 56-58; May 29, 1902, LXVI, 107-112; June 12, 1902, LXVf, 151-155; June 19, 1902. LXVI, 178-181. See also references under foot-note t on p. 142. The Antillean volcanoes. By W. J. McGee. Pop. Sci. Mo., July 1902, LXI, 272-281. For a full account of the recent Martinique and St. Vincent eruptions see articles by R. T. Hill and I. C. Russell, Nat. Geog. Mag., XTII, July 1902. - Century Mag., July 1902, pp. 473-483. || The highest Andes- By E. A. Fitzgerald. New York. 1899. Charts. 145 146 PEAKS AND CONES. Fig. 31. The cinder cone and lava field of the Lassen Peak district, California. (Diller.) Ash and cinder peaks are steeper than Java cones (except locally). The angle of repose of dry sand is 40; of gravel is 35 to 38. Mt. Hood, Oregon, 11,225 feet; Columbia river cuts 4,000 feet in its lava. Mt. Tacoma, or Rainier (14,449 feet). Mt. Shasta (14,440 feet) and vicinity. Volcanic region between Lassen Peak and Mt. Shasta. Lava cone* are not so steep. Angle of the slope of Mauna Loa. Fig. 32. The cinder cone of the Lassen Peak district, California. (Diller.) 147 148 SUBMARINE VOLCANOES. VOLCANIC ROCKS. Lavas, mostly dark colored. On decay they often turn red, rusty brown, a purplish red, terra rocha. Some are glassy, like obsidian. Some "blistered" in appearance. Small, angular, or rounded fragments. Inclusions among ejectamenta. Some lavas cool in columns, commonly hexagonal, called basaltic. Examples at the Columns and at the Stone Crusher near Stanford University, Giant's Causeway. (See Plate XI.) (For the explanation of the forms of basaltic columns see Part III of this Syllabus. Fig. 33. Horizontal basaltic columns on the island of Fernando de Noronha. SUBMARINE VOLCANOES.* Peaks all over the sea bottom, and many volcanic islands, lead us to sup- pose that many of them have been made by submarine eruptions. * Ueber submarine Erdbeben u. Eruptionen. Inaug. Diss. von E Rudolph. Stuttgart, 1887. On the geological investigation of submarine rocks. By J. Joly. Sci. Proc. Roy. Dublin Soc., VIII, 509-514. Dublin, 1898. 149 150 VOLCANIC ACTIVITY. Submarine lavas are the same as terrestrial ones.* Santorin and Theresia Islands, in Grecian Archipelago, rose from the st-a 237 B. C. (Sir Wm. Hamilton, 158-9; Daubeny, L'29). One of the Azores near St. Michael in 1628 (Sir Wm. Hamilton, 159). In 1783 one (Nyoe) 6 or 8 miles off Iceland (Forbes, 286). Island a mile in circumference, washed away and only a shoal in less than one year. (Daubeny, 224.) In 1831 Graham's Island, Sicily,t 200 feet high (a. t.), and 800 feet above bottom, three miles around. Active three weeks. Demolished in two years. Bogoslof island in Behring sea.} Volcanic islands, all deeply wave-cut. St. Helena cliffs, 1,000 to 2,000 feet. Teneriffe, Fernando de Noronha. Subaqueous volcanoes on a small scale sometimes produce "mud vol- canoes.'^ DISTRIBUTION OF VOLCANOES. By sides of deepest and largest oceans. Wallace suggests that they "take away the foundations of the sur- rounding district," and thus make the neighboring seas deep.|| The distribution of certain volcanic phenomena are simulated by the outflow of water on frozen lakes. If VOLCANIC ACTIVITY ATTRIBUTED TO : ** 1. Presence of water (they follow oceans). tt 2. Contraction of the earth's crust where strains cannot be resisted, and the relief of downward pressure. 3. Permanent lines of weakness of earth's crust. The volcanic lines are approximately the same as formerly, as if these lines were fixed. Why this is possibly true. * Fouqu6. Santorin et ses eruptions, XVI. t A bibliography of Graham's Island is given in Johnston-Lavis' " South Italian vol- canoes," 105-107. 1 1. C. Russell's Volcanoes of North America. 276-281. Kotzebue's Voyage of discovery. II, 180-181. 1821. Volcanic eruptions in the Bering Sea. By Geo. Davidson. Bui. Am. Geog. Soc., 1890, XXII, 267-272. I Barrows. Nat. Geog. Mag., Sept. 1900, XT, 348-350. Scottish Geog. Mag , May 1901, XVII, 263-264. I The Malay Archipelago. 9. London, 1894. II Ice ramparts. By E. R. Buckley. Trans. Wis. Acad. Sci., XIII, 156-157. ** Les volcans et les causes qui paraissent les determiner. Par Virlet d' Aoust. Con- eres International de Geologic, 1878, pp. 239-248. tt J. W. Judd. The eruption of Krakatoa. Rep. Krakatoa Com. of the Roy. Soc., 46. Lon- don, 1888. 151 152 DORMANT VOLCANOES. II. DORMANT OR EXTINCT VOLCANOES. 1. Some volcanoes always active. 2. Some are quiet for years. Mont Pel6e, Martinique, had no eruptions from 1851 to 1902. 3. Some are quiet for centuries. Once extinct, a volcano crumbles rapidly. If the climatic conditions are favorable, volcanic rocks usually make good soils. Examples of extinct volcanoes. Crater lake,* southwest Oregon ; surface, 6,239 feet a. t. ; 5-6 miles in diameter; no outlet; maximum depth of water, 2,000 feet ; walls above water, 500 to 2,200 feet; total depth of crater, 2,900 to 4,200 feet. Theories of its origin. The San Francisco mountains near Flagstaff, Ariz. Many cones to be seen from the Santa Fe and Southern Pacific railways through the Colorado desert. Marysville buttes, California, t The latest eruptions on the Pacific coast of the United States have taken place within historic times. t The cones of central Fr-ance and Germany. || Ancient lavas. Cascade range volcanic. In the Sierras on top of auriferous gravels; capping many mountains in Arizona. Sheet near Stanford University ; Frenchman's Lake, basaltic columns. The Palisades of the Hudson is the edge of a lava sheet. Giant's Causeway, Ireland ; sheet covers 2,000 square miles. Great sheet from northwest Wyoming down Snake river, 2,000 to over 4,000 feet thick, and covering an area of more than 180,000 square miles. In India the Deccan lava sheet covers an area of 200,000 square miles to a depth of 2,000 to 6,000 feet. IF Dikes. Lavas cooled in crevices.** Effect of temperature of rocks on size of dikes. Stand out as walls ;tt Spanish Peaks of Colorado. U * Science, 1886, VIII, 179-182. 8th ann. rep. U. S. Geol. Surv., 157-158. Washington, 1889. Crater Lake special map. By J. S. Diller. U. S. Geol. Surv., n. d. t Marysville folio, U. S. Geol. Surv. By W. Lindgren and H. W. Turner. J J. S. Diller. Science, May 5, 1899, p. 639. ? Scrope's Volcanos of France. 57-67. London, 1862. 8 Major-General Nelson. Jour. Roy. Geol. Soc. of Ireland, II, 107-109. Edinburg, 1871. t Geology of India. Am. Jour. Sci., XIX, 140, p. 300. New Haven, 1880. ** Open-air studies. By G. A. J. Cole. Plate VII, opp. 181. London, 1895. tt Across Vatna Jokul. By W. L. Watts. 101,109,119,153-157. London, 1876. On veins and dikes, see Crosby in Tech. Quar., Dec. 1896, IX, 355. U Spanish Peaks folio, U. S. Geol. Surv., 71. By R. C. Hills. 153 154 Fig. 34. Trap dikes cutting granite, Bear Island (100 feet high), Labrador. (Daly.) Laccolites.* Lavas intruded between beds. Tuffs. Fragmental ejectamenta, often covering large areas. Fig. 35. West Spanish Peak, Colorado, from the northwest, with vertical dikes. (Hills.) * Geology of the Henry Mountains. By G. K. Gilbert. Laccolites in Colorado. By G. K. Gilbert. Jour. Geol., IV, 816. Chicago, 1895. The laccolitic mountain groups of Colorado, Utah, and Arizona. By W. Cross. 14th ann. rep. U. S. Geol. Surv , 157-341. Washington, 1895. 155 156 IGNEOUS ROCKS. Fig. 36. The great north dike of West Spanish Peak, Colorado. At this point it forms a wall 100 feet in height. (Hills.) AGES OF VOLCANOES. Why the rocks contain no fossils except in cases of tuffs and inclusions. Age shown by relations to adjacent rocks. ECONOMICS OF IGNEOUS ROCKS. Fertility of soils.* Vesuvius and Etna covered with vines and towns. Volcanic cinders quickly make excellent soils when the fall is not more than six or seven inches thick. Java and Japan thickly populated. Sulphur deposits of Sicily, Italy, and Iceland. Ores often concentrated next to dikes and in eruptives. Use of basalt for road material at Stanford. Tuffs and fragmental andesites do not hold water. Examples: Frenchman's Lake; Sierra ditches. Used for railway ballast in Arizona. Pozzuolana used in making hydraulic cement. * Lavas and soils of the Hawaiian Islands. By W. Maxwell, etc. Exp. Sta. Rec. U. S. Dept. Agr., X, no. 6, pp. 525-531. Washington, 1899. 157 158 Geysers.* Geyser, a gusher. Forbes says it means "a rager"; it is applied to any noisy water in Iceland. (Forbes, Iceland, 230.) " Geysir is a common name for all fountains, and is derived from the Icelandic word geysa, to ascend violently, though it is now al- most exclusively applied to the great gey sir." t Geysers are periodically eruptive hot springs. Always hot. Distribution. Iceland. U. S. Colombia, near Cartagena on Rio Magdalena.i New Zealand. Yellowstone National Park. All in regions of former, or recent, volcanic activities. Phenomena of eruption of the great geysers of Iceland remarkably like volcanic eruptions. 1. Cannonading steam bubbles collapsing like singing of kettles. 2. Bulging of water and overflow. 3. Leaping upward of water, about 100 feet. 4. Escape of steam with noise. Frequency diminishing . || In 1804 the geysers of Iceland erupted every hour; now the interval is of a few days. Dying out less marked in the Yellowstone region. In Yellowstone National Park there are more than 3,000 vents. Basin three miles wide, honey-combed. Grand geyser temp. 150, throws water 200 feet and steam 1,000 feet. Giantess throws a column 20 feet in diameter and 60 feet high. Smaller pits throw water 250 feet high. Some erupt for hours. * Bibliography of geysers in Peale's 12th aim. rep. U. S. Geol. Surv. of the Territories. 1878, pt. II, 427-149. Washington, 1883. Geysers. By W. H. Weed. School of Mines yuar., July 1890, XI, 289-306. Yellowstone National Park folio, U. S. Geol. Surv., no. 30. Washington, 1896. t A summer in Iceland. By C. W. Paijkull. 320. London, 1868. t Vues des Cordilleres, etc. Par A. de Humboldt. 239, 241, and plate opp. p 239. Paris, II The rapid decline of geyser activity in Yellowstone Park. By E. H. Harbour. Jour. Franklin Inst., Mar. 1900, CXLIX, 236. Abstract. Proc. A. A. A. Sci, vol. 48, p. 230. 'i A visit to the New Zealand volcanic zone. By H. M. Cadell. Trans. Edin. Geol. Soc., 1897, VII, 183-200. 159 160 GEYSERS. THEORIKS OF THE CAUSES OF ERUPTIONS. Mackenzie's theory.* Bunsen's theory. t Downward removal of boiling-point. The greater the pressure, the higher the temperature required. Artificial geysers. Relations of the overflow to eruptions.! Fig. 37. Mackenzie's diagram illustrating his theory of the cause of geyser periodicity. CONDITIONS NECESSARY TO GEYSERS. 1. Igneous acid rocks, hot above the boiling-point beneath the surface, and cooler at and near the surface. 2. Meteoric waters having access to hot rocks, or to vapors ascending from hot rocks. 3. Tube for escape of water and steam. * Travels in the island of Iceland. By Sir George Steuart Mackenzie. 2d ed., 226-229. London, 1812. t Heat as a mode of motion. By J. Tyndall. 168. New York, 1888. j Some conditions affecting geyser eruption. By T. A. Jaggar, Jr. Am. Jour. Sci., May 1898, V, 323^333. 161 162 KARTHQUAKKS. Effect of soaping geysers. Resemblance of geyser eruptions to " bumping." Bumping more marked in dense liquids. Soaping increases the viscosity of the water.* Geologic work of geysers. AVhy cones are built around vents. Relief of pressure and cooling. Fire-hole fork of Madison river deposits silica. Petrifying of trees, twigs coated. Gardiner's river deposits travertine in terraces. t Hot Springs. The high temperature of hot springs caused by surface waters coming in contact with hot rocks before the waters emerge. When the conditions of supply and emergence are favorable, geysers are formed, but otherwise only hot springs. In most cases hot springs never have been geysers, and there is little or no evidence of hot rocks about them. Terraces formed by hot springs. Method of formation. Possibility of heat being caused by 1. Chemical reaction. 2. Burning coal. Hot springs vary little in flow; they are deep-seated. Supposed medicinal properties of hot springs.; Earthquakes.^ Earthquakes are vibrations, or jars, rock- or earth-waves, propagated through the earth's crust. These are produced by concussions in the crust. The science of earthquakes called Seismology. * Experiments with an artificial geyser. By J. C. Graham. Am. Jour Sci., Jan. 1893, CXLV. 54. Soaping geysers. By Arnold Hague. Trans. Am. Inst. Min. Eng., t Some geological causes of the scenery of Yellowstone National Park. By A. R. Crook. Am. Geol., Sept. 1897, XX, 159-167. A visit to the New Zealand volcanic zone. By H. M. Cadell. Trans. Edin. Geol. Soc., VII, 192. Edinburg, 1897. t The mineral waters of Arkansas. By J. C. Branner. 10. Little Rock, 1892. 2 Les tremblements de terre. Par F. Fouque. Paris, 1889. Great Neapolitan earthquake of 1857. The first principles of observational seismology. By Robert Mallet. 2 vols. London, 186-2. Transactions of the Seismological Society of Japan. Vols. I to XVI, 1880 to 1892. Seis- mology in Japan. By J. Milne. Nature, April 18, 1901, pp. 588-589. The Charleston earthquake of August 31, 1886. By C. E. Dutton. 9th ann. rep. U. S. Geol. Surv., 203-528. Washington, 1889. La face de la terre. Par E. Suess. Tome I, 96-137. Paris, 1897. John Milne, observer of earthquakes. By Cleveland Moffett. McClure's Mag., May 1898, pp. 17-27. Seismology. By John Milne. Internal. Sci. Series. London, 1898. Methods of studying earthquakes. By Charles Davison. Jour. Geol., VIII, 301-308. Chi- cago, 1900. 163 164 EARTHQUAKES. Concussions may be caused by 1. Snapping of rocks under strain. Exemplified by the suddenness with which ice breaks in lakes.* 2. Slipping of rocks on each other. Readjustment. 3. In vicinity of volcanoes, by explosions within, possibly the forming and collapsing of steam. To understand earthquakes it is necessary to study propagation of waves through rocks under complex conditions of various structures, com- positions, and strains. Wherever faults are common in the rocks earthquakes must have occurred, even though they may now be extremely rare.t Every readjustment must cause jars. Note folded and faulted Appalachians; faults 10,000+ feet ; Scotland; Alps ; faults of California. Irregularity of sea bottom and possible slips there. Hence, jars are to be expected along lines of weakness and readjust- ment. Volcanic regions are regions of readjustment. But the wave travels at different rates, owing to the difference in the con- ductivity of rocks. In loose sand, 984 feet per second; sandstone, 7,400 feet per second; granite, 9,200 feet per second.} Explosions at Hell Gate, New York, observed in Boston, Mass., gave a rate of transmission of 4,500 to 20,000 feet per second. The form of the wave at the surface is determined by these differences in conductivity. Epicentrum. Location of epicentrum. Coseismal lines. The form of coseismal lines found by time observations. Focus. Depth of focus. Charleston earthquake 12 miles.$ Some foci are about 4 miles below the surface. Displacement. The amount of displacement of an earth particle is seldom more than 3 or 4 millimeters; sometimes it is only a fraction of a milli- meter. The maximum displacements observed at the Lick Observatory have been June 20, 1897, 0.20 inch. March 30, 1898, 22 inch. The average is about 0.03 inch. * Ice ramparts. By E. R. Buckley. Trans. Wis. Acad. Sci., XIII, 160. t The Hereford earthquake of December 17, 1896. By Charles Davison. Birmingham, 1899. Nature, June 29, 1899, pp. 194-195. t On the velocity of seismic waves in the ocean. By Charles Davison. Phil. Mag.. Dec. 1900, p. 579. Am. Jour. Sci., Jan. 1901, p. 95. Propagation of earthquake waves through the earth. By C. G. Knott. Proc. Roy. Soc. Edinburg, XXII, 573-585. Dutton. 9th ann. rep. U. S. Geol. Surv., 311. Washington, 1889. 165 166 EARTHQUAKES. A displacement of 0.01 inch is readily perceptible. (Director Campbell.) One was reported in Japan in 1891 as " not less than one foot." * (This does not refer to vibrations of swinging objects, or to the dis- placement where a crack or fault is produced.) Form of movement. Shown by seismograph. t Comments on the direction of the movement. Influence of position in relation to focus. At Riobama in 1797 bodies were thrown several hundred feet in the air. Reflex action. Effect in mines and at surface. Sometimes not felt as strongly in mines as on top. Cause of variation. Frequency.^ The frequency varies with locality ; there are two a day in Japan. Common in volcanic regions. California is a region of faults and extinct volcanoes. Has the weather any influence upon earthquakes? $ 18279 records in Japan show that earthquakes originating on land in that country are affected by barometric pressure; yet pressure may be high without producing them.jl Limits of area. Sometimes shocks are felt over areas of thousands of square miles, even over the whole world. If In California they are often felt over a few miles only. Sounds produced by earthquakes.** RESULTS OF EARTHQUAKES.-!-)- Fissures and faults. Japanese earthquakes and faults. it Sonora, Mexico, shock in 1887 ; crack 100 miles, fault 8 feet. Arizona. || || New Zealand, 1848; 60 miles long, 18 inches throw. New Madrid, Missouri, chasm opened. Inyo, California, shock of 1872; crack 40 miles long, fault 25 feet. If IT * Geol. Mag., Sept. 1898, p. 429. t See records in the Journal of Seismology. 1 The periodicity of earthquakes. By R. D. Oldham. Geol. Mag., Oct. 1901, VIII, 449. \ Personal narrative of travels. By A. de Humboldt. II, 215-220. London, 1822. | Milne. Nature, June 26, 1902, p. 202. \ Observations of earthquakes. By H. F. Reid. Johns Hopkins University, circular no. 152, p. 3, May 1901. The propagation of earthquake motions to great distances. By R. D. Oldham. Am. Jour. Sci., April 1900, CLIX, 306-307. Proc. Roy. Soc., LXVI, 2. Nature, Oct. 13, 1898, p. 586. ** Earthquake sounds. By C. Davison. Am. Jour. Sci., Apr. 1900, p. 307. ft Some remarkable earthquake effects. Nature, Nov. 22, 1900, pp. 87-88. +t On the cause of the great earthquake in central Japan, 1891. By B. Koto. Jour. Coll. Sci., Imperial University of Japan, V, pt. IV, plates. Tokyo, 1893. ?? Science, Aug. 12, 1887, X, 81. HI Kemp's Ore deposits. 15. New York, 1893. VS Nature, Nov. 8, 1883, XXIX, 45. 167 168 EARTHQUAKES. The deluge of the Bible lower Euphrates by an earthquake.* Joints in rocks. Rocks bend slowly, but snap when under strain, or from a sud- den jar. Earthquake waves (im- properly called tid- al waves) may be due to sudden lift- ing or lowering of the water surface. Destruction wrought by wave. Examples : Ja- pan, t Lisbon. Landslides, if in wet weather. supposed to be due to the inundation of the Fig. 38. Fault having both vertical and horizontal dis- , formed during an e in Japan. (Koto ) . placement, formed during an earthquake (Ko Fig. 39. Fissure and fault in Arizona produced at the time of an earthquake. * La face de la terre.. Par E. Suess. Tome I, 25-95. Paris, 1897 t Across America and Asia. By R. Pumpelly. 107. London, 1870. Nat. Geog. Mag. Sept. 1896, VII, 285-289, 310. 169 170 CHANGES OF LEVEL. Lakes and pools formed. Slides dam streams; breaking of such dams is dangerous. Case in India in 1897. Drying up of springs. Water turned into other channels. Terrors of earthquakes due to the fact that there is no means of predicting the time or nature of the shock, and to the instability of the earth, which is the very type of stability. No courage or skill can prevent them. From the faulted and slicken-sided condition of the rocks it is inferred that California always has been and probably always will be a region of earthquakes. PRECAUTIONARY MEASURES. Destruction of life mostly caused by the falling of walls of houses. Catania, Sicily, earthquake in 1693; 100,000 killed.* Lisbon earthquake, 1755, killed 60,000, but largely by wave on wharves. Japan earthquake of 1896 killed 26,975, mostly by wave dashing upon the shores. Riobamba, Equador. (See Whymper.) The city of Mendoza, Argentine Republic, entirely destroyed in 1861. t Japanese houses built of wood. Earthquake houses placed on balls. Destruction in California really very small. Changes of Level.* Is it possible that the sea-level itself may change? Changes of level, either elevation or depression, sometimes accompany earthquakes and volcanic eruptions. Sometimes abrupt, as at St. Thomas, W. I. Sometimes quiet, slow, and uniform. In any case they are due in part, at least, to agencies connected with the interior condition of the earth. EVIDENCES OF ELEVATION. 1. Dead marine organisms, or their skeletons, on dry land. 2. Work of marine animals on land. 3. Work of waves (either constructive or destructive) on shore lines now out of the reach of waves. 4. Human records. 5. Eroded surface of marine sediments. * Sir W. Hamilton's Observations. 59. London, 1774. t The highest Andes. By E. A. Fitzgerald. 19-20. New York, 1899. t Untersuchungen iiber das Aufsteigen und Sinken der Kusten. Von Friederich Gustav Hahn. Leipzig, 1879. Travels in Peru. By J. J. Von Tschudi. 41-46. London, 1847. I Oscillations in the sea-level. By H. W. Pearson. Geol. Mag., April 1901, VIII, 167-174; May 1901, VIII, 223-231; June 1901, VIII, 253-264. 171 172 EVIDENCES OF ELEVATION. I. Dead marine organisms, or skeletons, on land. Coral reefs of St. Thomas, W. I. Raised reefs of Mombasa, East Africa.* Raised reefs of Cuba, 1,000 to 1,100 feet a. t. Raised reefs of Peru, 3,000 feet a. t. ;t of Lau Islands, Fiji, 1,000 feeU Fossils (oysters, barnacles, and sea-urchins) on the basaltic columns near Stanford University. Shells of Baffin Land. Elevation 270 to 300 feet. II. Work of marine animals on land. Sea-urchin holes about the bay of Rio de Janeiro, 3 feet a. t., and on the coast of Pernambuco. (See Plate XII.) Pholas holes with shells at Purissima. Pholas and worm-tubes on the Page Mill road. Lithodomus of the temple of Jupiter Serapis, Italy. || III. Wave work (either constructive or destructive) now beyond the reach of waves . Terraces and old beaches at Santa Cruz. Fig. 40. A line of erosion about the base of a granite peak at Victoria, Brazil. The notch is now about two meters above tide-level. * Gregory's Great drift valley. 45. 51, 55. London, 1896. t A. Agassiz. Proc. Am. Acad. Sci.. XI, 287. 1876. t A. Agassiz. Am. Jour. Sci., April 1902, p. 308. g Elevations of Baffin Land. By T. L Watson. Jour. Geol., 1897, V, 17-33. - Partial bibliography for North America, 32-33. I Le temple de S6rapis a Pouzzoles. Chap, ix of La face de la terre. Par E. Suess. II, 173 174 EVIDENCES OF DEPRESSION. San Pedro hill, near Los Angeles, terraced. Santa Catalina islands. Drift timber on Hudson bay above tide.* Conflicting evidenced Terraced fjords of Norway.* Raised beaches of Baffin Land. IV. Human records. Precise levels disclose relative land movements. Scandinavia rising north of Stockholm at the maximum rate of 5-6 feet per century, or 0.72 of an inch in a year. V. An eroded surface of marine sediments. (Unconformity is explained at length in Part II.) AMOUNT OF ELEVATION. The amount of elevation is sometimes shown approximately by the heights of marine sedimentary rocks above the sea. EVIDENCES OF DEPRESSION. Evidences of depression are more difficult to see, because the land surface goes beneath the water. Often it is re-elevated and uncovered. I. Land plants in place covered by marine deposits, or below sea-level. Stalactites, lignite, and erect stumps found 45 feet below sea-level in Bermuda. || Peat below tide on the bay of Fundy.H Stumps beneath marine deposits in Louisiana. In New Jersey cedar stumps on beach reached by salt water.** Trees in Muir inlet exposed at low tide.ft Coal beneath the sea in Peru. Coal in Pennsylvania overlain by marine fossils. II. Corals faund (in wells) below depth at which they live (150 feet). Recent boring (Oct. 1897) in northeast Australia, 698 feet in coral.it III. Submerged valleys, or river channels.^ Valleys can be cut in certain forms only on land. * Robert Bell. Am. Jour. Sci., Mar. 1896, CLI, 219-228. t Stability of the land around Hudson Bay. By J. B. Tyrrell. Geol. Mag., June 1909, p. 266. t Raised shore lines at Trondhjem. By W. Upham. Am. Geol., Sept. 1898, XXII, 149-154. Etud sur le soulevement lent actual de la Scandenavie. Par A. Badoureau. Ann. des Mines, 9me ser., VI, 239-275. Paris, 1894. The glacial period and oscillations of land in Scandinavia. By N. O. Hoist. Geol. Mag., VIII, 205-216. London, 1901. g Evidences of recent elevation of the southern coast of Baffin Land. By Thos. L. Wat- son. Jour. Geol., 1897, V, 17-33. I Notes on the geology of Bermuda. By A. E. Verrill. Am. Jour. Sci., May 1900, CLIX, 325. Recent observations in the Bermudas. By J. M. Jones. Nature, VI, 262. II Canadian Naturalist, 2d ser., 1881, IX, 373. ** Ann. rep. State Geol. New Jersey, 1885, p. 93. -( Reid. 16th ann. rep. U. S. Geol. Surv., I, 440. Washington, 1896. It Nature, Mar. 24, 1898, LII, 494-495; July 7, 1898, LIII, 221. ?g T. Codrington. Submerged rock valleys in South Wales, Devon, and Cornwall. Quar. Jour. Geol. Soc., Aug. 1898, LIV, 251-278. 175 176 EVIDENCES OF DEPRESSION. Firths of Scotland. England.* Fjords of Norway ;t coast of Maine.* Filled-up bays of Ocean side, California; of New Jersey. Drowned valleys of the west coast of the United States.^ Drowned valley at New York.|| IV. Distribution of plants and animals. Identity of Santa Catalina island plants with those of the mainland. Elephants' teeth found on Santa Rosa island and on mainland. Elephants on St. Paul island show sinking to disconnect it from main- land. Great Britain's former connection with Europe. f Wallace's work on Malay archipelago. Professor C. H. Gilbert's work on the distribution of Pacific coast fishes. Case of the Isthmus of Panama.** Resemblance of the faunas of South America and New Zealand. V. Historical records. In Scania, south Sweden, some of the streets are below water. Dunkirk fields. ft Tilting of the region of the Great Lakes. Observations, from 20 to 37 years, show changes from 0.061 to 0.239 feet.iJ Spanish building at the mouth of the Mississippi river. Leveling in France shows the southeastern part of that country to be fixed, while the northwest and northeast have sunk between the years 1863 and 1899. |||| VI. Great thickness of sediments. Sediments of great thickness could accumulate only during a long and gradual depression. Example: Arkansas Valley trough, where the coal measures (sedi- ments) are 23,780 feet thick. if IF * Submerged terraces and river valleys bordering the British Isles. By E. Hull. Geol. Mag., Aug. 1S>8, pp. 351-357. Jukes-Brown. Geol. Mag.. Sept, 1898, p. 429. t Fjords and submerged valleys of Europe. B. W. Upham. Am. Geol., Aug. 1898, XXII, 101-108. Topographish-geologische Studien in Fjordgebieten. Von Otto Nordenskiold. Bui. Geol. Inst. Univ. Upsala, IV, 157-228. Upsala, 1900. Science, June 28, 1901, p 1034. Die Fjordbildungen. Ein Beitrag zur Morphologie der Kiisten. Iiiaug. Diss. von Paul Dinseaus. Berlin, 1894. t Henry Gannett. Physiographic types. Folio 1, Physiography. Topographic Atlas U. S. Washington, 1898. ?, The submerged valleys of the coast of California, etc. By George Davidson. Proc. Cal. Acad. Sci., 3d ser., I, 73-101. San Francisco, 1897. W. E. Ritter. Science, Oct. 11, 1901, XIV, 575. A topographic study of the islands of Southern California. By W. S. T. Smith. Bui. Dept. Geol., Univ. California, II. 179-230 Sept. 1900 LLindenkohl. Am. Jour. Sci , 1885, CXXIX, 475-480. Wallace's Malay Archipelago. 8, 10-14. London and New York, 1894. The geological history of the Isthmus of Panama. By R. T. Hill. Bui. Mus. Comp. Zool., 1898, XXVIII, 266-270. tt L'atlaisement du sol des Pays-bas. Par Jules Girard. Bui. Soc. Geog., Oct. 1879, pp. U Modification of the Great Lakes by earth movement. By G. K. Gilbert. Nat. Geog. Mag., Sept. 1897. VIII, 233-247. ?? Nat. Geog. Mag., VIII, 352. Hi Le nivellement general de la France. Par Charles Lallemand. Ann. des mines, 9me se>., XVI, 227-306. Paris, 1899. Affaisement du sol de la France. Par E. Van den Broeck. Bui. Soc. Beige de G&>1., V, 13-20. Bruxelles, 1891. iH Thickness of the Paleozoic sediments in Arkansas. By J. C. Branner. Am. Jour. Sci., Sept. 1896, pp. 229-236. 177 178 RATE OF CHANGES. VII. Faults with large vertical displacements. A fault in the coal fields of Alabama has a throw of 10,000 feet or more, and the downthrow side, with coal beds, is carried far below ocean-level.* VIII. Wide distribution of heavy conglomerates. Heavy water-worn boulders could be formed over a wide area only by the place passing through a beach condition, and this would re- quire a gradual depression of the land.t Distribution of changes. No part of the earth's crust is quiet. Behavior of delicately adjusted seismoscopes. Some parts change more rapidly than others. RATE OF CHANGES. The rate must necessarily vary greatly. Darwin mentions flat island of Santa Maria raised at a jump, and he found on land " gaping, putre- fying mussel-shells, still attached to the bed on which they had lived, "t St. Thomas raised at a jump, bringing up live corals to perish on the beach . Gilbert cites tilting about the Great Lakes at the rate of 0.42 feet a century in 100 miles. The Niagara river will cease to flow in 3,000 years, if the present rate of tilting continues. Norway, north of Stockholm, rising 5 to 6 feet per century. New Jersey coast, from Long Island to Cape May, is sinking at the rate of 2 feet per century. CAUSES or ELEVATION AND DEPRESSION. Theories. 1. Internal heating and cooling of the rocks. 2. Denudation and deposition. Theory of isostacy.|| 3. Change of physical condition of the interior. Contraction of rocks on changing to crystalline condition. 4. Loss of water, air, and gases. 5. Thrusts or stresses, however produced, that cause bending or fault- ing of the beds. * Branner. Am. Jour. Sci., Nov. 1897, IV., 364-365. t Shaler. Monograph XXXIII, U. S. Geol. Surv., 57-58. t Geological observations. By Cbas. Darwin. 216. ? G. K. Gilbert. Nat. Geog. Mag., VIII, 245. Washington, 1897; 18th ann. rep. U. S. Geol. Surv., pt. II, 601-47. I The great valley of California, a criticism of isostacy. By F. L. Ransome. Bui. Geol. Dept. Univ. Calif., I, 371-428. Earth movements. ByC. R. Van Hise. Trans. Wis. Acad. Sci., XI. Theory of isos- tacy on pp. 469-475 and foot-note ; 478. Madison, 1898. The connection of the glacial period with oscillations of the land, especially in Scan- dinavia. By Dr. N. O. Hoist. Geol. Mag., May 1900, VIII, 205-216. 179 180 ORGANIC AGENTS. ORGANIC AGENCIES, OR THE WORK OF ORGANISMS IN GEOLOGY. Organic agencies are destructive, preservative or protective, and constructive. 1. Destructive organic agencies are those that produce or hasten rock decay, such as organic acids. 2. Preservative agencies are those that protect rocks from destruction, such as seaweeds and mollusks, that prevent waves from cutting the shores. 3. Constructive agencies are those that form new rocks, such as peat from plants and limestone from coral. I. Destructive Organic Agents. Decay of plants and animals produces humic acids that attack minerals.* The streams of southern Florida are charged with carbon dioxide from decaying vegetation, and as they pass through and over the lime- stones the waters attack and dissolve them rapidly .t Roots of plants. Roots etch the rocks. Sachs' experiments on marble slabs. Roots pry rocks apart.* Ivy prying boards from the sides of houses. Sidewalks lifted by the roots of trees. Water follows down roots. (Luther Wagoner, of San Francisco, tells of several roots of pine, or some other conifer, % inch in diameter, found 60 feet below the surface of the ground in a mine in Nevada county, California; rocks decayed.) General tendency of plant roots to break up rocks and minerals. The decay of roots produces destructive organic acids. Roots penetrate more deeply in arid regions. Liverworts. Sea-urchins bore holes in the hardest rocks. Example from the coast of Brazil. (See Plate XII, opp. p. 172.) * A. A. Julien. Proc. A. A. A. S., 1879, XXVII, 324. Rock, rock-weathering, and soils. By G. P. Merrill. 190, foot-note. - Merrill. Jour.Geol., 189o, IV, 856. t The topography of Florida. By N. S. Shaler. Bui. Mus. Comp. Zool., XVI, 144-145. t Notes on the geology of the Bahamas. By J. I. Northrop. Trans. N. Y. Acad. Sci., X, 15-16. New York, 1891. I The conservation of soil moisture. By E. W. Hilgard and R. H. Loughridge. Bui. 121, t4 " 7 -" Hilgard "* Loughridge ' Rep. Agr. Exp. St.. 181 182 ORGANIC AGENTS. Fig. 41. Hard rock bored by sea-urchins. From the coast of Brazil. Boring mollusks, Lithodomus and Pholas, bore rocks. Examples from the coast of California. Burrowing insects, ants of the tropics.* Worms, t Other burrowing animals. Rabbits, squirrels, ground-hogs, gophers, let in water and gases. Crayfish on canals and rivers. Some cause levee breaks of the Mississippi. Fig. 42. Mounds made by ants in the state of Minas, Brazil. * Decomposition of rocks in Brazil. By J. C. Branner. Bui. Geol. Soc. Amer., 1895, VII, 295. Ants as geologic agents in the tropics. By J. C. Branner. Jour. Gcol., Mar. 1900, VIII, 151-153. t Vegetable mould and earthworms. By Chas. Darwin. New York, 1882. 183 184 ORGANIC AGENTS. II. Preservative Work of Organic Agents. Protection of coasts by animals. Corals, serpulse,* and mussels. t Protection by plants.* Seaweeds ; corallinese (calcareous seaweeds). Mangrove swamps of the tropics, || 5 to 20 miles wide. (Plate XIII.) Bamboos of the Amazonas break the force of the current. Bushes generally along stream and lake shores. Water hyacinth, introduced in Florida in 1890, helps to check streams and to check scour, and to cause deposition. IT Plants on dunes prevent the blowing of sand. Roots of willows on canals and creeks prevent wash. Turf protects soil from wash, and rocks from exposure and decay. Forests on mountain slopes prevent snowslides and landslides. Forests generally prevent the rapid melting of snow in the spring ; pre- vent rapid flow of rain waters, and thus decrease floods and ero- sion. III. Constructive Organic Agents. Deposits. Plants. Carbonaceous: sphagnum, peat, lignite, coal, oil, gas. Sulphurous. Ferruginous: iron. Nitrogenous: nitre. Siliceous: diatoms (algee), chert, ooze, eilicified wood. Calcareous: corallinese of the algse. Animals. Calcareous: corals, shells, bones, ooze. Siliceous: sponges, radiolaria.** Phosphatic: guano, bones. Plants as Constructive Organic Agents. Carbonaceous deposits. The rocks of carbonaceous plant origin are as follows (note relations of oxygen and carbon) : * A. Agassiz. Bui. Mus. Comp. Zool., XXVI, 253-272. t Across America and Asia. By R. Pumpelly. 188. London, 1870. J The conservative action of animals, etc. By W. A. Hardman. Proc. Liverpool Geol. Soc , 1889, V, 46-51. ? Phyllospadix as a beach builder. By R. E. Gibbs. Am. Nat., Feb. 1902, XXXVI, 101- 110. | Fresh-water morasses. By N. S. Shaler. 10th ann. rep. U. S. Geol. Surv.,pt. I, 291. Washington, 1890.- A. Agassiz. Bui. Mus. Comp. Zool. ,300, XXVI, 53. Cambridge, II The water hyacinth ... in Florida. Bui. 18. Bot. Div. U. S. Dept. Agr. Washington, 1897. E. de Beaumont. Geologic Pratique. II, 165. ** Geikie's Text book of geology. 439. 3d ed. London and New York, 1893. 185 186 CARBONACEOUS DEPOSITS. Rocks of carbonaceous Oxygen, Carbon, plant origin. percentage. percentage (Wood 44 49) 1. Peat 30-40 59 2. Lignite 20-35 68 3. Bituminous coal 10-15 81 Anthracite coal l%-%/4 95 4. Graphite 100 5. Diamond 100 Petroleum, asphalt, gas, and related carbonaceous minerals, are derived by distillation from organisms, but probably not from any one kind.* The carbonaceous parts of rocks are derived from either plants or ani- mals chiefly from plants. Wood contains 49% carbon and 44% oxygen (+ 6% hydrogen). PKAT.f Peat is woody matter that has lost oxygen, and is thus altered part way to lignite. Antiseptic property of peat prevents decay. Peat made of mosses (sphagnum) grows in marshes, and floats on, and fills, shallow ponds. Moss dies below, grows above; generations of plants. Changes at bottom to brownish black, cheese-like muck. Penetrated by roots of plants growing over surface. Covers large areas, 5 to 50 feet thick. Rate of growth varies with conditions; 1 foot in 5 to 10 years. Some of the European bogs have grown in 1800 years, and have stumps, roads, coins, etc., beneath them. These bogs have grown from one inch to several feet per century. Extent. Peat-bogs cover one-seventh of Ireland 4 The moss of Shannon, Ireland, is 50 miles long and from 2 to 3 miles wide. Dismal Swamp of Virginia and North Carolina contains 300 square miles of peat-bog. Sol way moss in northwest England, near Scotland, 7 miles across. In Norfolk, England, 500 square miles of peat; clay and sand separate the beds. United States and Canada to Montana ; New England. Bursting of peat-mosses or peat-bogs. Peat-bogs become water-logged, burst, and flow. * The production of an asphalt by the distillation of a mixture of fish and wood. By W. C. Day. Proo. Am. Phil. Soc., 1898, XXXVII, 171. t The formation of peat-mosses. By Hampus von Post. Bui. Geol. Inst. Univ. Upsala, 1892-93, 1, 284.- G. Hellsiner. II, 345. On peat and its uses. By T. S. Hunt. Canadian Naturalist, Dec. 1864, 2d ser., I, 436-441. 1 Geikie's Text-book. 480. 3d ed. London and New York, 1893. I Nature. Jan. 14, 1897, LV, 254-256; Jan. 21, 1897, LV, 268. 187 188 CARBONACEOUS DEPOSITS. LIGNITE. Lignite, or brown coal, is common in rocks of Tertiary and Cretaceous age. Appears to be a further change of peat. Change takes place very slowly and can not be observed. Evidences of peat origin of lignite. 1. Spores found in lignite like those in peat. 2. Plant impressions the same in peat and lignite. 3. Intergadation of peat and lignite. 4. Clays beneath lignite contain roots like those penetrating the clays beneath peat. 5. Experimental demonstration.* Interbedding of lignite and sediments. Sections often show several beds of each. Must have been flooded ; or, if there are marine fossils, the peat-moss must have been covered by the sea. BITUMINOUS COAL.* Intergradation of lignite and bituminous coal. Change very slow ; not in man's time. Coal not derived from marine plants, for fucoids contain 75 to 80% water. Coal usually has clay below, with roots penetrating it. Stumps found standing; in some cases these stems extend into the overlying clays. t Sediments interbedded with the coal show changes by submergence and new growths. Splitting of coal beds accounted for.J ANTHRACITE COAL. Daubree's experiments with wood. Changed form of bituminous coal. Plants preserved as coal in some cases. Relations of the anthracite fields of Pennsylvania to the bituminous ones of the same state. Change in the upper ends of synclines at Forest City, above Carbon- dale. Ultra change of Rhode Island anthracite. || * See abstract of work of Adams and Nicolson. Science, Jan. 21, 1898, new ser., VII, 83. Vegetable origin of coal. By Leo Lesquereux. Ann. rep. Geol. Surv. Penn., 1885, pp. 95- 124. Harrisburg, 1886. t Coal plants, etc. By W. S. Gresley. Geol. Mag., Dec. 1900, VII, 538-544. t Lapparant. Traite" de ge"ologie. 841. Paris, 1885. g Les eaux souterraines aux e~poques anciennes. Par A. Daubr^e. 297 Paris, 1887. || On the origin of anthracite. By E. T. Hardman. Jour. Roy. Geol. Soc. Ireland, IV, new ser., 200-209. Edinburg, 1877. 189 191 192 CARBONACEOUS DEPOSITS. Theories advanced to explain the origin of coal. 1. Marine plants. Marine plants have no wood, but cellular tissue only. 2. Blown into lakes from the land. Too widespread ; area of North American coal fields. 3. Floated timber of deltas. ' Too much and too widespread ; the coal beds are of rather even thickness; driftwood irregular and mixed with mud. 4. Timber floated into the sea. Stumps beneath the coal are rooted in place. 5. Peat-bog theory of origin now accepted.* Carbon from the air. Renewed from the crystalline rocks and from the sea. Air not necessarily overcharged with carbon. t GRAPHITE. Graphite is produced in some cases by a still further change of coal. Too much changed to be available for fuel. Changed in some cases by excessive heat. Found in the oldest rocks. Origin of the graphite found in pig-iron; derived from coal. DIAMONDS. Diamonds are crystalline forms of carbon, probably formed by change of graphite by pressure and heat. Graphite found in the diamond ma- trix of Brazil. i DRIFT-TIMBER. Enormous quantities of drift-timber washed down by freshets. Rafts in rivers ; common in delta regions. Atchafalaya, La., raft 10 miles long by 700 feet wide, 8 feet thick ; 50 years' accumulations. Floating islands of the Amazonas and of the Paraguay. Water hyacinth of Florida. || * Discourses. Biological and geological essays. By Thos. H. Huxley. 137-161. New Origin of coal. ' By R. Dakyus. Geol. Mag., 1901, p. 135; Jan. 1901, VIII, 29-34; Mar. 1901, VIII, 135. t Microscopical light in geological darkness. By E. W. Claypole. Am. Geol., Oct. 1898, XXII, 217-228. Chamberlin. Jour. Geol., Oct. 1898, VI, 609-621. On the gases enclosed in crystalline rocks and minerals. By W. A. Tilden. Chem. News, April 9, 1897. | O. A. Derby. Jour. Geol.. VI, 121-146. Chicago, 1898. g The great raft. By A. C. Veatch. Prelim, rep. on the Geol. of La., 160-173. [Baton Rouge, 1899.] " || Bui. 18, U. S. Dept. Agr., Div. Bot. Washington, 1897. 193 194 DEPOSITS FROM PLANTS. SULPHUROUS DEPOSITS FROM PLANTS. Certain bacteria extract sulphur from sulphuretted water (sewage works and factory effluents) and store it up as globules, known to engi- neers as " sewage fungi."* In hot springs in Japan ;t temperature 154 to 157 Fahr. Only in water with hydrogen sulphide. FERRUGINOUS DEPOSITS FROM PLANTS. Iron carried in solution in streams as carbonate, loses CO 2 through the agency of bacteria, and ferric oxide is precipitated. NITROGENOUS DEPOSITS FROM PLANTS. Nitre or saltpeter, formed by nitrifying bacteria. i SILICEOUS DEPOSITS FROM PLANTS. Diatoms are low forms of microscopic plants (alg?e) living in salt or fresh water. Abundant in fresh warm waters of Yellowstone National Park. Temperatures up to 185 Fahr. Deposits there 3 to 6 feet thick ; called " sinter." || Silica extracted from the water. Deposits consist of accumulations of skeletons. Marine diatom beds at Santa Cruz, California, are 700 feet thick. In Nevada, 200 to 300 feet thick. Rocks of diatoms IT are earthy like chalk, harsh to the touch; used to polish metals. Often found in swamps beneath peat. Called tripolite, tripoli powder, infusorial earth.** The distribution of marine diatom deposits in existing seas suggests that they may be cold-water deposits. ft Relations of the diatom beds of California to the petroleum deposits. In many places the materials are altered to cherts. Silicified wood is not properly a siliceous deposit made by plants, but a re- placement of wood by silica from solution. Enormous quantities in Yellowstone region. U (Plate XIV.) * Bennett and Murray's Cryptogamic botany. 454. London and New York, 1889. t Am. Nat., June 1898, XXXII, 456-457. t Microbes, ferments and moulds. By E. L. Trouessart. 121-122. Internal. Sci. Ser. New York, 1892. A. M. Edwards. Microscopical Jour., 1899, pp. 49-55. II W. H. Weed. 9th ann. rep. U. S. Geol. Surv., 650-676. Washington, 1889. 11 On diatoms, see Zittel. Paleontologie, pt. II. Set t>cq. (French edition.) **The tripolite deposit of Fitzgerald Lake near St. John, New Brunswick. Tech. Quar., June 19ul, XIV, 124-127. ft Maps of Mem. Mus. Comp. Zool., XXVI, no. 1. Cambridge, 1902. II Monograph XXXII, pt. II, U. S. Geol. Surv., 755-760, and plates. Plate XIV. Bridge formed by a petrified tree trunk near Holbrook, Arizona. (Vroman.) Plate XIV6. - Petrified logs, Chalcedony Park, near Holbrook, Arizona. Petrified wood covers an area of more than a thousand acres at that place. 195 196 CORAL REEFS. CALCAREOUS DEPOSITS FROM PLANTS. Nullipores or Corallime are coral-like calcareous algse growing in salt water. They help build up coral reefs and coral sand-beaches. Other calcareous algse contribute to marine calcareous deposits.* Calcareous tufas of Great Basin formed through the agency of low plant life.t One calcareous spring in Yellowstone Park (Mammoth Hot Spring) ; de- posits made by algse. i Some calcareous oolites and marls are lime secretions of algse. " Water-biscuit" of Canandaigua Lake formed by algse taking up CO^ and causing the precipitation of the lime from the water.|| Animals as Constructive Organic Agents. Calcareous rocks made by animals. 1. Corals and serpuhe whose skeletons are attached. IT 2. Shells of microscopic marine organisms living at or near the water's surface; foraminifera. 3. Shells of univalves (gasteropods), bivalves (lamellibranchs), worms, echinoderms, crustaceee, and all animals having calcareous skel- etons, whether vertebrates, such as fishes, or invertebrates, such as crinoids. CORAL REEFS.** Importance of the subject. 1. Large areas of the globe covered by coral reefs and islands. Aus- tralian reef 1,250 miles long by 10 to 90 miles wide. 2. Coral makes much of the lime rock of the earth. * Proc. and Trans. Nova Scotia Inst. of Sci., IX, XCII-XCIII, 1897. 1 1. C. Russell. Bui. 108, U. S. Geol. Surv., 94-95. Washington, 1893. t W. H. Weed. 9th ann. rep. U. S. Geol. Surv., 628-649. Washington, 1889. ? A. Rothpletz. Am. Geol., 1892, X, 279-282. For bibliography of oolites see The Bedford oolitic limestone of Indiana. By T. C. Hopkins and C. E. Siebenthal. 21st ann. rep. State Geol. Indiana, 397-410. Ind- ianapolis, 1896. The lakes of northern Indiana, etc. By W. S. Blatchley and G. H. Ashley. 25th ann. rep. Geol. Indiana, 33, 43-48. Indianapolis. 1901. A contribution to the natural history of marl. By C. A. Davis. Jour. Geol., VIII, 485- 497; 498-503. Sept. 1900. | Clarke. Bui. N. Y. State Mus., VIII, W5-198. Albany, 1900. 11 Some recent views on the theory of the formation of coral reefs. By A. Agassiz. Bui. Mus. Comp. Zool., XXVI, 170-187. Cambridge, 1894. Nature, Nov. 10, 1898, LIX, ** The structure and distribution of coral reefs. By Charles Darwin. 3d ed. London, 1889. Corals and coral islands. By James D. Dana. 3d ed. New York [1890]. On the structure and origin of coral reefs and islands. By John Murray. Proc. Roy. Soc. Edinburg, 1880, X, 505. The islands and coral reefs of the Fiji group. By Alexander Agassiz. Am. Jour. Sci., Feb. 1898, CLV, 113-123. Nature, Nov. 10, 1898, LIX, 29. Some recent views on the theory of the formation of coral reefs. By A. Agassiz. Bui. Mus. Comp. Zool., XXVI, 170-187. Cambridge, 1894. 197 198 CORAL REEFS. Coral rocks are formed from the skeletons of polyps. Animals are soft, gelatinous, often transparent, of various colors. Radiate structure with tentacles. Carbonate of lime deposited in the lower part, which is fixed. Form and deposition of the lime by polyps are vital functions, and not subject to will. The growth of coral reefs is produced by growth of these deposits. Forms of corals. 1. Loosely branching. 2. Solid, spherical, or hemispherical. 3. Tabulate. Reproduction . 1. By eggs having power of locomotion, and floating away in the water till they attach themselves to the rocks. 2. By branching or budding. Conditions of growth of the reef-building corals. (Reference is made here only to what are known as the reef-building corals; other corals live at great depths in the ocean, and in very cold waters, but they do not form reefs.) 1. Temperature at or above 70 Fahr. 2. A range of temperature not exceeding 12 Fahr.* 3. Depth, 150 feet and less; most favorable at 50 feet and less. 4. Clear salt water. Effects of elevation and depression, mud, volcanic ashes, and fresh water. 5. Constant change of water; necessity of lime and oxygen. Fig. 44. A coral reef on the coast of Brazil. (Hartt.) * Murray and Irvine. Nature, June 12, 1890, XLII, 162. 200 CORAL' REEFS. Forms of coral reefs. 1. Fringing: join the land. 2. Barrier: form barriers between sea and land. 3. Circular: approximately circular; enclose water; sometimes en- closed lagoons fill up. (These forms are not sharply distinguishable, but merge into one another.) Size of coral reefs. The great reef of Australia is 1,250 miles long by 10 to 90 miles wide. Theories of reef formation. 1. Subsidence theory of Darwin. a. Intergration of reef forms. b. Actual subsidence of some existing islands. c. Depths at which reef rocks are found. A bore-hole sunk in 1897, at Funafuti, northeast Australia, passed through 987 feet of coral without reaching the bottom of the reef.* d. Elevation of some reefs. For depression is as common as elevation. 2. Murray's theory of submarine peaks. Conditions. a. That the coral polyps take possession of submarine peaks. 6. That when the depth is too great, accumulations of micro- scopic organic remains build up the peaks till they come within reach of the corals. Murray thinks atolls grow larger by building be} r ond the growing depth. Darwin thinks atolls grow smaller. Murray's theory is not improbable. Rate of growth of reefs. Can be determined by observation. Agassiz's estimate, 1 inch in 8 years, or 1 foot in a century. Others estimate 2 feet in a century. Coral 987 feet deep is 837 feet below growing depth for living corals. At 2 feet in a century it would require 41,850 years for the reef to attain the thickness of 837 feet below the level of growth. Change by crystallization from original form. All fossil reefs must have grown under more or less similar conditions of depth and temperature. Reefs at the falls of the Ohio. Tertiary reef near Bainbridge, Georgia, t and on the island of Oahu.J * Nature, Dec. 9, 1897, L VII, 137; Mar. 24, 1898, LVII, 494-495; July 7, 1898, LVIII, 221; Nov. 10, 1898, p. 29. Proe. Roy. Soc. N. S. W., Oct. 5, 1898, p. IV. In opposition to the theory of subsidence, see A. Agassiz in Am. Jour. Sci., Feb. 1898, V, 113-123; and same for Aug. 1898, VI, 165-167. Bui. Mus.Comp. Zool., XXVI, 170-187. t T. W. Vaughan. Science, Dec. 7, 1900, pp. 873-875. | W. H. Dall. Bui. Geol. Soc. Am., XI, 57-60. 201 202 . DEPOSITS FORMED BY MARINE ANIMALS. Possibility of other conditions. Temperatures are constantly lowering. Life began in warm seas and climates. The tendency is to adapt to colder conditions, rather than to originate in cold climates, and to change from colder to warmer. Coral reefs teach that 1. Coral limestone is made by animal growths, assisted by wave work and consolidation. 2. Coral limestones are of marine shallow-water origin. 3. They attain great thickness by subsidence. 4. Our limestones contain near-shore life, and are, therefore, of near- shore and shallow-water, rather than of deep-sea origin. SERPUL*:.* MICROSCOPIC MARINE ANIMALS. Foraminifera have (mostly) calcareous skeletons. Live near surface of seas.t Dying, their skeletons sink to bottom, forming "ooze. 1 ' Chalk made up of such calcareous skeletons. Skeletons found to depths of 13,800 feet.* Below that depth these skeletons are dissolved by pressure and the carbon dioxide in the water. Bryozoa lenses of limestone. || MOLLUSCAN AND OTHER CALCAREOUS SHELLS AND SKELETONS. IT (Worms, echini, crabs, crinoids, etc.) Examples: coquina of Florida ; conch shells on the Bahamas.** Encrinital limestone. Siliceous deposits formed by animate. ft Spicules of sponges accumulate. Form cherts, flints, or hornstones. Extensive deposits of chert in Missouri, Tennessee, Arkansas, Eng- land, etc. The cherts of California are derived largely from the skeletons of diatoms. * A. Agassiz. Bui. Mus. Comp. Zool., XXVI. 253-272, and plates XXTT, XXIII, XXVI. tOp. cit.,56. t On foraminifera see Zittel's Text-book of paleontology, Eastman's translation. Vol. I, pt. I, 18-37. London and New York, 1896. Has bibliography. The Atlantic. By C. Wy ville Thomson. I, 199-203, 249. New York, 1878. Discourses. Biological and geological essays. By T. H. Huxley. 1-36. New York, 1897. 'i See also Dittmar, in Challenger reports. Physics and chemistry. I, 222. \ Reef structures in Clinton and Niagara strata of western New York. By C. J. Sarle. Am. Geol., Nov. 1901, XXVIII, 282-299. 1i Mechanically formed limestones from Junagarh and other localities. By J. W. Evans. Quar. Jour. Geol. Soc., LVI, 559-583. Derived limestones. By J. W. Sollas. Geol. Mag., June 1900, pp. 248-250. ** Agassiz. Op. cit., 70. tt Zittel's Paleontology, Eastman's translation. I, pt. I, 42 et seq. Colloid silica. Jukes-Brown and Hill. Quar. Jour. Geol. Soc., Aug. 1889, XLV, 403. On fossil sponges of the flint nodules in the Lower Cretaceous of Texas. By J. A. Merrill. Bui. Mus. Comp. Zool., July 1895, XXVII, 1-26. Review Am. Geol., Jan. 1896, XVII, 52-53. Keyes. Am. Jour. Sci., Dec. 1892, CXLIV, 451. Hovey. Am. Jour. Sci., Nov. 1894, CXLVIII, 401. Lawson. loth U. S. Geol. Surv., 1895, p. 420. 203 204 MAN AS A GEOLOGIC AGENT. PHOSPHATIC DEPOSITS FORMED BY ANIMALS. Droppings and bones of marine animals or birds. Accumulate on sea bottom or on arid land. Guano on the islands of Peru in an arid region. No rain to wash it away.* Phosphate rocks of Tennessee and Arkansas. Sometimes concentrated, as in the rivers of South Carolina. Marine organisms are most abundant in shallow waters and near shore. This is especially true in the tropics. In polar regions the fauna is more abundant in depths of 50 to 150 fathoms than in depths of less than 50 fathoms.* We have now gone over all the different methods by which rocks are made. All rocks fall under one of these heads, and are made in one of these ways. / Mechanical sediments deposited in water, or by wind. All rocks have I Chemical deposits, deposited from solution, originated as \ igneous rocks from fusion. I Organic deposits made by plants and animals. All these deposits are subject to metamorphisms and change of position of bed- ding. (See Structural Geology, Part IV.) Man as a Geologic Agent.; Man's work is confined to modifying the operations of nature. Of comparatively little importance, because the element of time is wanting for his works. 1. Man's influence on plants and forests. 2. Man's influence on animals. 3. Man's influence on land changes. MAN'S INFLUENCE ON PLANTS. Domesticated and cultivated plants, formerly all wild. Distributed over the world by man intentionally. Examples: wheat, oats, rye, beans, corn. Potatoes only since the discovery of America. Cocoanuts, bananas, date-palms, rice, sugar-cane, cotton, coffee, oranges, in warm climates only. Ornamental plants imported and scattered by dealers. Forest trees. Examples : eucalyptus and palms. * Note on Clipperton atoll. By W. J. Wharton. Quar. Jour. Geol. Soc.. LJV, 228-229. London, 1898. t Murray. Nature, Mar. 25, 1897, p. 501. I The earth as modified by human action. By G. P. Marsh. New York, 1885. ^'influence de 1'homme sur la terre. Par A. Woeikof. Ann. de Geographic, 15 Mars 1901, 10e an., 97-114; 15 Mai 1901, pp. 193-215. 205 206 MAN AS A GEOLOGIC AGENT. Other plants accidentally distributed. Tumbleweed, Russian thistle. Weeds along roads and railways.* Cockle in wheat. MAN'S INFLUENCE ON THE FORESTS. By planting. Eucalyptus, introduced from Australia; Lombard}- poplars from Europe. In Switzerland, forests planted to prevent avalanches. On the west coast of France, for resin and to stop the shifting of sand- dunes. Willows planted on canals and streams to prevent cutting. To prevent landslides. By cutting away. Destruction of forests for lumber, charcoal, tan-bark. Destruction by forest fires ; by grazing. 1. Effects of forests on the scour of streams. Cutting of bamboos along streams permits scour. Cutting mangrove swamps permits scour of the coast : no filling. 2. Effects of forests on floods by Holding back water in leaves and debris. Holding back snow from melting rapidly. 3. Removal of forests exposes the soil to sun and drouth, and it cracks and lets in decomposing agents. Questions to be considered. Do forests change climate? What is climate? Annual variations. Long series of observations necessary to determine the climate. MAN'S INFLUENCE ON ANIMAL LIFE. Some animals cared for and domesticated. Others decimated or exterminated. I. Animals preserved and distributed voluntarily. Horses, sheep, camels, cows, pigs, chickens, geese, bees. Preservation of game. Oysters planted in brackish water. Fishes hatched and distributed over the country. Slavery. Africans carried to America. Mingling of European, American, African, and Asiatic races. Mingling of races in South America through the enslavement of Africans and aborigines. * The water hyacinth. Bui. 18, U. S. Dept. Agr., Div. Hot. Washington, 1897. Tumbling mustard. Circular no. 7, U. S. Dept. Agr., Div. Hot. Washington, 1896. 207 208 MAN AS A GEOLOGIC AGENT. II. Animals distributed involuntarily. 1. Injurious or parasitic insects. Colorado potato-beetle. Hessian fly. Scale insects imported on fruit. Of 73 injurious insects of primary importance in the United States, 37 are introduced, all but one, accidentally.* Gipsy-moth, introduced in 1869 in Massachusetts, has cost a million dollars, and will cost one and a half millions more to get rid of it. 2. Harmless animals developing into pests. English sparrows in United States since 1850-67. Parrots of Australia. Rabbits. Marine life likely to be modified by the Suez canal and the Panama canal. III. Animals exterminated, or nearly so. 1. Dangerous or injurious: squirrels, snakes, panthers. 2. Game valuable for food, fur, or hides. Bears, beavers, buffaloes, whales, fur-seals. 3. Wanton destruction. Birds of the guano islands. Buffaloes. IV. MAN'S INFLUENCE ON THE LAND. Reclaiming land. Marshes and swamps drained (elevated marshes). Sea marshes of Holland. Lowering Swiss lake for land. Raising river banks. Levees of the Po bring it above the farms. Levees of the Mississippi. Protection of land. From the sea by dikes and sea-walls. Example: Holland, extensive works. From streams, by paving and straightening channels. Modification of land. By building dams and reservoirs that silt up. By cutting bars, dredging basins. By cutting timber from sandy lands and thus starting dunes. By planting on dunes and stopping them. By irrigation : Egypt, Spain, California. Placer mining. Method of work, and amount of earth washed down. Fills streams and overflows valleys. * Spread of land species by the agency of man. By L. O. Howard. Science, Sept. 10, 1897, new ser., VI, r 1 209 210 MAN AS A GEOLOGIC AGENT. Cultivation of the soil* Cultivation greatly increases chemical activity in soil. 1. Erosion hastened; ground not protected by plants. 2. Erosion is checked where the land is terraced, as in Switzerland. Checking stream erosion. Mattrasses and piles at Pine Bluff, Arkansas. Levees of the Mississippi river, confining it to channel. Straightening and paving the Rhone and other swift streams in Switzer- land. Using the falls for power and thus checking the cutting. Example : Niagara Falls. Future water storage. Will prevent or check floods, and retard erosion. Geological deposits made by man. Refuse heaps about cities and towns. Those of large cities dumped into the sea from scows and ships. Cities buried. By dust-storms of Africa. Sand-dunes of Bermuda. Volcanic dust of Vesuvius. Example : Herculaneum and Pompeii. Ocean deposits are receiving the rejectamenta of civilization and preserving them as fossils. Distribution over the entire globe by means of navigation. * The economic aspects of soil erosion. By N. S. Shaler. Nat. Geog. Mag., Nov. 1896, VII, 36&-S77. 211 212 SEDIMENTARY ROCKS. PART II. STRUCTURAL GEOLOGY, OR THE MODIFICATION OF ROCKS. Structural Geology treats of the kinds and arrangements of rocks, and the changes to which they are subject. Rocks are any materials forming the earth's crust. They are (1) sedimentary or stratified; (2) igneous or unstratified; and (3) vein deposits. SEDIMENTARY, OR STRATIFIED ROCKS. UNCONSOLIDATKD. CONSOLIDATED. ' - ' Shingle. Breccia.* Arenaceous, Gravel. Conglomerate, or sandy. pudding-stone. ^Ssind. Sandstone, ( Shallow-water or quartzite. deposits. Argillaceous, Clay. Shale, or clayey. or slate. Calcareous, Oozie, Chalk, limestone, or limy. shells. marble Stratified rocks. < Deep-water deposits, 600 feet and over. Tufaceous. 1 Skeletal- Cinders, ashes. Ooze, Tuff. Diatom shale, flint, siliceous. (silic- chert, jasper. eous). r Carbonaceous. Peat. Lignite, coal. 1 Arenaceous. t Land deposits. J 1 Argillaceous. Sand. Clay. jEolian sandstone. Loess. t Tufaceous. Cinders. Tuff. * llth ann. rep. U. S. Geol. Surv.,319, 320, 321. Monograph XXVIII, U. S. Geol. Surv., plates VIII, XXVI. Arthur Winslow. Lead and zinc deposits of Missouri. 464-467. Jefferson City, 1894. Branner. Zinc and lead region of Arkansas. 21-23. Little Rock, 1900. Gordon. Jour. Geol., Ill, 307. Chicago, 1895. On the relation of certain breccias, etc. By T. G. Bonney. Quar. Jour. Geol. Soc., LVIII, 185-206. London, May 1902. On a remarkable inlier among the Jurassic rocks, etc. By J. F. Blake. Quar. Jour. Geol. Soc., LVIII, 296-312. London, May 1902. I y a. -JL. I M eVtone^ Fig. 45. Breccia of dolomite, zinc blende and dolomite spar (natural The forms of deposits are determined by the origin of the materials, and by the place and manner of deposition. The rock masses are known by various names, such as layers, beds, strata, veins, dikes, deposits, formations, etc., all of which are rather loosely applied. BEDDING. Stratified rocks are laid down in beds, ^Ei or approximately parallel layers. ej 4 Fig. 46.-Diagram illustrating a meth- btratum (plural strata), beds, layers, od of breccia-making. (Chamberlin.) a 215 216 SEDIMENTARY ROCKS. Lamina, a very thin layer. Lenticular beds are lens-shaped. False bedding, or plunge and flow structure,* is characteristic of nearly all coarse sediments. Produced by wind-bedding in any kind of materials. Conformity. Rocks conform to each other (or are conformable) when laid down in successive layers in a continuous deposition. Unconformity indicates interruption^ (See Plate XVI.) Fig. 47. An unconformity (&) between Tertiary (c) and later (a) beds. (Harris.) Impressions during deposition. Ripple-marks are found in sediments in the bottom of rather shallow water. They are made by the vibration of the water up to a depth of 450 feet.t Ripple-marks are visible on the bottom of Lake Geneva, caused by the paddle-wheels of steamers. Giant ripples caused by wave interference in shallow water. Fig. 48. Ripple-marks in loose sands exposed at low tide. * Dutton's High plateaus of Utah. 152, 208. Washington, 1880. Ann. rep. Geol. Surv. Iowa. VII, plate p. 218. Des Moines, 1897. t Ann. rep. Geol. Surv. Iowa. V, plate I, opp. 52. Des Moines, 1896. Univ. State N. Y. State Mus. Rep. 49, 1895. 444. t Lapparent Trait6 de Geologic. 254. Paris, 1900. Sorby. The Geologist, II, 137-147. London, 1859. Bui. 19, vol. IV, N. Y. State Mus., 172. Rippelmarken. Inaug. Diss. von ErnsfBertololy. Frankenthal, 1894. V. Cornish. Geog. Jour., XVIII, 170-202; July-Dec. 1901. Scot. Geog. Mag., Jan. 1901. Nature, Apr. 25, 1901, pp. 623-625. I G. K. Gilbert. Bui. Geol. Soc. Am., X, 135-140. -Fairchild. Am. Geol., XXVIII, 9-14. Branner. Jour. Geol., IX, 535-536. 217 218 SEDIMENTARY ROCKS. Rain-prints. Sun-cracks. Tracks of birds and other animals.* Fossils are the hard parts, or impressions, of animals or plants that die in the water, or are washed down from the land. Alternation of beds is produced by the 1. Varying conditions of supply. 2. Changes of currents. Persistence of strata. Some strata extend for hundreds of miles. Beds are more likely to persist parallel with the coast from which the material is derived, and in any deep-sea deposits where the con- ditions of supply are alike. Intergradation of beds of different materials. EVIDENCES OF THE SLOW DEPOSITION OF SEDIMENTARY ROCKS. 1. Lamination of shales. 2. Evidences of objects having lain long uncovered on the sea bottom. 3. Beds formed from microscopic organic remains which commonly ac- cumulate slowly. 4. The rate in observed cases. The silting up of bays, etc. 5. The wearing of pebbles of conglomerate requires time. Great thickness of some conglomerate beds. 6. Great conglomerate beds made by the passing of the land through a beach condition are evenly distributed. Example : Pottsville conglomerates of Pennsylvania. 7. The rate of denudation which supplies the materials of mechanical sediments. The thickness of beds suggests, but does not show positively, the length of time they were forming. HARDENING OF ROCKS. The hardening of rocks may be produced either chemically or mechani- cally, or by some combination of both methods. Chemically. 1. By the deposition of lime carbonate, silica, iron, or other mineral. 2. By the elevation of temperature in the presence of water. Mechanically. 3. By pressure. Hardening is now going on.t 1. Bog-iron and maganese deposits. 2. Hardening of road-metal with iron. * Footprints in the rocks. By C. H. Hitchcock. Pop. Sci. Mo., Aug. 1873, pp 428-441 t Woodward's Geology of England and Wales. 3d ed. 546-550, London, 1887. 219 220 SEDIMENTARY ROCKS. 3. Stone reefs of Pernambuco, Brazil, and western Palestine. (See p. 70.) Coquina of the coast of Florida. ^Eolian sandstone of Bermuda. Glacial gravels locally. Spring deposits cementing gravels. 4. Hardening of building-stone after quarrying. 5. Experimental determination by Adams and Nicolson.* The laws of matter show that 1. Stratified rocks must have accumulated by means of the same agencies, and under the same conditions, that govern the deposi- tion of similar materials at the present time. 2. The oldest beds must have been laid down first, and the newer ones next on top, and so on. 3. The stratified rocks were laid down as soft sediment in an approxi- mately horizontal position, and all changes in them, whether by consolidation, folding, faulting, or otherwise, have taken place subsequently, and are, in a sense, accidental. UNSTRATIFIED, OR ERUPTIVE ROCKS. Distinctions between sedimentary and igneous rocks. IGNEOUS, OR UNSTRATIFIED ROCKS. Crystalline from fused state. Massive; different flows may have bedded appearance. No fossils except in inclusions and in tuffs. Flow structure. Gas cavities. Texture varies according to condi- tions of cooling. Under pressure are coarsely crystalline. Without pressure, or quickly cooled, are more glassy. t * Science, Jan. 21, 1898, new ser., VII, 82-83. Bui. Geol. Soc. Am., 1898, IX. t Size of grain in igneous rocks in relation to the distance from the cooling wall. By A. L. Queneau. School of Mines Quar., Jan. 1902, XXIII, 181-195. Variation of texture, etc. By J. E. Spurr. Jour. Geol., Nov. 1901, IX, 586-606. Causes of variation, eto. By T. L. Walker. Am. Jour. Sci., Nov. 1898, OLVI, 410-415. Plutonic rocks of Garabal Hill, etc. By Teall and Dakyns. Quar. Jour. Geol. Soc., Home. Nature, Sept. 19, 1901. SEDIMENTARY, OR STRATIFIED ROCKS. Clastic, or of fragments Bedded Contain fossils No flow structure No gas cavities Texture varies according to currents in which deposited. 221 222 IGNEOUS ROCKS. GROUPING OF IGNEOUS ROCKS. 'With reference j to conditions of { cooling. Those cooling under pressure at great depths. They are, or have been, deep-seated, and have been exposed here and there by eros- ion. Igneous rocks may be grouped With reference to composition. ' Volcanic. /Acid, containing 60 to 75% of silica.] Granites. They are light colored. 1 Gneisses. Fuse with difficulty. Stiffen readily, and form glasses. Basic, containing less than 60% of silica, and high percentages of fluxes, lime, soda, pot- ash, iron, etc. They are dark colored, and 1. Easily fusible (basalts). 2. Medium fusibility (andesites). 3. Difficult to fuse (trachites). FOKMS OF IGNEOUS DEPOSITS. Ejected as local lava flows of fragmental material, they form 1. Lava cones; angle varies with fluidity, 3 to 25. 2. Cinder cones, 35 to 40. Craters are the cup-shaped mouths of volcanoes. Origin of the cup shape.* Lava sheets often spread over wide areas. Overwhelm topography. Deccan trap of India covers 200,000 square miles, 100 to 6,000 feet thick. Oregon, Washington, and California, 150,000 square miles. Lava surfaces are usually very rough. Origin of the Table Mountains of California. Often called trap, from the Swedish trappa, stairs. The lava-capped hills of western Arizona. Columns may be horizontal and in piles. Examples: Fingal's Cave, Scotland ; Giant's Causeway, Ireland. They may curve.t (See Plate XVII.) Intrusions. Between beds. Vertical. Horizontal. * The moon's face. By G. K. Gilbert. Phil. Soc. of Wash., 1892, Bui., vol. XII, 241-292.- Lassen Peak folio, U. S. Geol. Surv. By J. S. Diller. Washington, 1895. t Iddings. Am. Jour. Sci., 1886, CXXXI, 321-324. Humboldt. Atlas Pittoresque, 123-124. Paris, 1810. 223 224 IGNEOUS ROCKS. Fig. 49. Horizontal columns of basalt exposed on the shores of Fernando de Xoronha. Laccolites. (See page 154.) Across beds. Dikes. Irregularities of dikes. (See page 152.) Tuffs. Fragmentary materials ; take the slope of loose sands or cinders. Sometimes deposited in water; may have fossils. Gross forms of tuffs are like those of sedimentary rocks, but they are limited in extent to the vicinity of the volcanoes from which they are derived. Mineral Veins. Mineral veins are of small extent, but of great economic importance. Minerals of economic importance, however, do not always occur in veins. 225 226 MINERAL VEINS. The position of mineral veins among economic geologic deposits will be understood from the following : ( 1. Organic accumulations: coal, lignite, limestone, chalk, phos- phates. 2. Mechanical accumulations: placer gold, diamonds, tin, mag- .bconomic . . , . , netic iron sands. "\ 3. Igneous, or metamorphosed deposits: certain building-stones, slates, some iron ores. 4. Bedded chemical deposits: salt, gypsum. 5. Vein deposits or lodes. Veins are sheets of rocks filling fissures in other rocks.* Difference between veins and dikes. Dikes are crevices in the rock filled with molten rocks. Dikes of sandstone exceptional. (See page 238.) Veins are crevices filled with mineral deposited from solution in under- ground waters. t False veins are crevices filled from above or below. (See Sandstone dikes, p. 238.) If veins are made by minerals filling crevices and cracks in the rocks, it becomes important to understand the forms, sizes, and depths of cavities in the rocks. Origin of crevices. 1. By torsion, or twisting of the rocks. t 2. Earthquake jars when the rocks are under tension. 3. Faults. 4. Openings along the crests of anticlines and the bottoms of synclines when the beds are folded. 5. Shrinkage due to dolomitization and loss of water. Shrinkage cracks, however, are irregular and meandering. 6. Pressure in any direction exceeding the crushing strength of the rocks. Such pressure is often accompanied by faults, but such faults are frequently so small as to be almost imperceptible. Enlargement of fractures. What were originally mere cracks sometimes becomes greatly enlarged. This enlargement may be produced by 1. The expansion due to crystallization of minerals in the incipient crevice. Example: geodes. 2. The solution and removal of the rock walls. Example : the brecciated beds and deposits of the Ozarks. * Mining geology of the Cripple Creek district, Colorado. By R. A. F. Penrose, Jr. 16th ann. rep. U. S. Geol. Surv., pt. II, 144-150. Washington, 1895. t The movements of underground waters of Craven. Geol. Mag., Feb. 1901, VIII, 72-75; Feb. 1901, VIII, 75-77. | Daubree, Geologic experimentale, 307-314. Paris, 1879. 227 228 MINERAL VEINS. Fig. 50. Geodes formed in the stem of a crinoid. The deposition of quartz began in the hollow stem which was finally broken asunder. Natural size. Depth of crevices. Rocks closely confined flow under great pressure. At certain depths, about six miles, crevices can not remain open.* Experiments of Adams and Nicolson.t Veins formed in open crevices must have formed within the zone of rock stability. Thickness of veins. Varies from a fraction of an inch to many feet. Forms of veins. t May be single or in sets, and parallel. Some veins anastamose is all directions. Vary in size in different parts of the same vein. Materials of veins. Various minerals carried in and deposited from solution. Banded. Brecciated. * Flow and fracture of rocks. By L. M. Hoskins. 16th ann. rep. U. S. Geol. Surv., 845- , 874. Washington, 1896. Metamorphism of rocks and rock flowage. By C. R. Van Hise. Am. Jour. Sci., July 1898, CLVI, 75-91. Bui. Geol. Soc. Am., 1898, IX, 269-328. t Science, Jan. 21, 1898, VII, 82^; Jan. 18, 1901, XIII, 95-97. An experimental investigation into the flow of marble. By F. D. Adams and J. J. Nicolson. Phil. Trans. Roy. Soc., London, 1901, vol. CXCV, 363-401. Ueber die Plasticitiit der Gesteine. Von E. Weinschenk. Centralblatt f. Min. Geol. u. Pal., 1902, pp. 161-171. t The gold quartz veins of Nevada City and Grass Valley districts, California. By W. Lindgren. 17th ann. rep. U. S. Geol. Surv., pt. II, 158-170. Washington, 1897. ? Quar. Jour. Geol. Soc., L, plate 27, p. 658. London, 1894. 229 230 MINERAL VEINS. Occurrence of veins. Veins are more abundant in metamorphosed rocks, and in some moun- tain regions, because these are often the seats of dynamic action and the rearrangement of minerals. Mineralizing agencies often more active in such regions. The filling of veins. Theories concerning the source of the vein materials.* 1. From below (Posepny, Newberry, and others). 2. From above (Werner and Wallace). 3. From sides, or lateral secretions! (Sandberger,} Win slow, Van Hise). Processes of filling. 1. From volatilization, i. e., from gases or fumes. Example: sulphur. 2. From hot waters holding minerals in solution. Examples: box-pipe from Comstock lode ; hot springs deposits. 3. From deposits by waters containing mineral in solution at ordinary temperatures. How minerals change in depth. Oxides and free gold above. Sul pli ides below. * Fig. 51. Section of a box-pipe used for ten years in the Comstock mines to carry mine water from one level to another. The box is lined with aragonite more than half an inch thick, deposited by the water. * Kemp's Ore deposits, 42-55. New York, 1893. t Trans. Am. Inst. Min. Eng., 1893, XXII, 634, 735. Winslow. Jour. Geol., 1894, I, 617. Posepny's Genesis of ore deposits. 174-176. New York, 1895. Branner. Zinc and lead deposits of Arkansas. 15-24. t Canadian Naturalist, new ser., 1877, VIII, 345-362. \ The superficial alteration of ore deposits. By R. A. F. Penrose, Jr. Jour. Geol., 1894, II, 288-317. 231 232 MINERAL VEINS. Uncertainties in mining for precious metals, in so far as they depend upon the extent of the ore deposits, are due to 1. Irregularity of veins, fractures, or crevices in which the ores exist. 2. Irregularity of the conditions of deposition. 3. Irregularities due to displacements since deposition. The risks of mining are due largely to these uncertainties. If rocks were uniform in texture and composition, and if we knew the conditions and stresses under which they have been formed, the positions of the veins might be calculated. Certainty of mining bedded deposits. Coal, lignite, and gypsum; salt, asphaltum, etc. South African gold beds.* Fig. 52. Bedded ore deposits (black) interstratifled with other horizontal rocks. Fig. 53. Section of the Glencairn property in the Rand, showing portions of four reefs or bedded ore deposits. (Hatch and Chalmers.) Fig. 54. Section through shafts in the Rand gold field, showing the regularity of the structure. (Hatch and Chalmers.) * Gold mines of the Rand. By F. H. Hatch and J. A. Chalmers. London, 1895. Les mines d'or du Transvaal. Par L. de Launay. Paris, 1896. 233 234 JOINTS IN ROCKS. Terms used. Lode; mother lode. Foot- wall. Hanging-wall. Country rock. Gangue (quartz common). Horse. Placer deposits. Origin of the gold in placer deposits. How the original quartz veins were discovered. How rich placers may be derived from poor vein deposits. Diamond placers of Brazil ; tin placers of the Malay peninsula. STRUCTURAL FEATURES COMMON IN ROCKS. Joints in Rocks.* Joints are fractures, or clean-cut faces, that pass through rocks regardless of the bedding planes. All rocks have more or less of them. They are common in shales ; " block coal " of Indiana. Exposed and used in quarries. Pass through pebbles. They may lie in two or more directions; they frequently occur in sets. Joints often influence topography. t Cliffs of Cayuga lake; in loess ;{ with veins in them. (See Plate XVIII.) Joints are not confined to hard rocks, but occur in sands and clays. Joints of basaltic columns. Horizontal sheets of lava are sometimes vertically jointed so as to form hexagonal columns. Why the columns are approximately hexagonal. || A plane surface can be covered by only three regular figures : square, equilateral triangle, and hexagon. These form about a point the respective angles : 90, 60, and 120. * Daubrge. Geologic experimentaie. 300-318. Paris, 1879. On the fracture system of joints. By J. B. Woodworth. Proc. Boston Soc. Nat. Hist., 1896, XXVII, 163-183. Crosby. Proc. Boston Soc. Nat. Hist., XXII^ 72-85. Boston, 1884. XXIII, 243-248, Bos- ton, 1888. t Button's High plateaus of Utah. 280. Washington, 1880. Erosion forms in Harney Peak district, South Dakota. By E. O. Hovey. Bui. Geol. Soc. Am., XI, 581-582, plates. t Ann. rep. Geol. Surv. Iowa, VII, 235. Des Moines, 1897. 2 Freeland. Trans. Am. Inst. Min. Eng., XXI, 491. \ J. Lomas. Proc. Liverpool Geol. Soc., 1895, VII, pt. 3, pp. 323-325. Open-air studies. By G. A. J. Cole. Plates VI and VIII, opp. pp. 172 and 183. London, "S 13 *1 235 236 JOINTS IN ROCKS. Fig. 55. Jointed shales on the east shore of Cayuga Lake, N. Y. (Martin.) Fig. 56. A vertical dike of sandstone cutting inclined beds of diatomaceous shales, Graves creek, San Luis Obispo county, Gal. (Newsom.) 237 238 JOINTS IN ROCKS. Sandstone dikes.* Joints or cracks in the rocks are occasionally filled with what are called sandstone dikes. These are usually carried by water, or some other fluid, from soft sands into open crevices. Sandstone dikes are common near Santa Cruz, and on Graves creek, San Luis Obispo county, California. (Plates XIX and XX.) Theories of the causes of joints (other than those of basaltic columns). 1. Contraction, as sun-cracks in mud. These are not straight and clean-cut. 2. Torsion. DaubreVs experiments with ice.t 3. Earthquakes. Effect of sharp snaps on rocks under strain. 4. Pressure. Fig. 57. -Fractures in blades of ice produced by torsion. * Sandstone dikes. By J. S. Oilier. Bui. Geol. Soc. Am , 1889. I, 411-442. Intrusive sandstone dikes in granite. By W. Cross. Bui. Geol. Soc. Am., 189-4, V, 225- Dikes of Oligocene sandstone ... in Russia. Ill, 49-53. R. Hay. Bui. Geol. Soc. Am. Sandstone pipes, etc. By E. Greenly. Geol. Mag., Jan. 1900, pp. 20-24. Ransome. Trans. Am. Inst. Min. Eng., XXX, 227-236. New York, 1900. t Geologic experimentale. Par A. Daubrge. 300-314. Paris, 1879. By A. P. Pavlow. Geol. Mag., Feb. 1896. , Ill, Plate XX. A sandstone dike cutting Miocene diatomaceous shales, on the beach six miles west of Santa Cruz, California. In the foreground the dike material has been removed from the cavity by the waves. (Newsom.) 239 240 CLEAVAGE OF ROCKS. The Cleavage of Rocks.* Cleavage is the easy splitting of rocks in parallel planes. Kinds of cleavage peculiar to rocks. 1. Crystalline cleavage. Examples: gypsum, mica. Confined to crystalline forms. 2. Bedding is due to water sorting, and follows bedding planes ; some- times called " flagstone cleavage." 3. Slaty cleavage. General facts regarding slaty cleavage. 1. It is always associated with folded and contorted beds. 2. It cuts across the bedding planes at various angles. 3. It occurs only in fine-grained rocks. 4. The included particles are parallel to the cleavage planes. Experiments show that 1. Iron cooling without pressure is granular; when drawn like wire it is fibrous; when rolled it has cleavage structure, or is scaly; that is, the granules are flattened. 2. Parallel re-arrangement of mica scales in clay after pressure. 3. Pressure on beeswax causes it, to separate into folia, or scales. These facts all suggest that slaty cleavage is caused by pressure at right angles to the cleavage planes. This is borne out 1. By finding wrinkled sand-beds in slates. 2. By the general folding of the rocks of slate regions. 3. By the deformation of fossils in the slates. 4. By the minerals in the slates all lying parallel to the cleavage. It is also thought that pressure alone is not capable of producing slaty cleavage, but that chemical action accompanies it.t SCHISTOSITY. Schistosity is a parallel splitting of the rock in thin layers, but, unlike slaty cleavage, the layers are more or less wrinkled. The rocks often have a felted appearance. Schistosity is supposed to be due to squeezing or shearing } at depth. * On cleavage, joints and folds, see Dale in 16th ann. rep. U. S. Geol. Surv., pt. I, 549- 570. Cleavage and flssility. By C. R. Van Hise. 16th ann. rep. U. S. Geol. Surv., pt. I, 633. (Bibliography.) Washington, 1896. Deformation of rocks. By C. R. Van Hise. Jour. Geol., 1895, IV, 449-483, 593-629. On slaty cleavage and allied rock structure, etc. By Alfred Barker. Rep. Brit. Assn., 1885, pp. 813, 852. (Many references.) t The phyllades of the Ardennes compared with the slates of North Wales. By T. Mel- lard Reade and Philip Holland. Proc. Liverpool Geol. Soc., 1899-1900, pp. 463-478. Reade. Proc. Liverpool Geol. Soc., 1900-1901, pp. 101-128. t Hoskins. 16th ann. rep. U. S. Geol. Surv., pt. I, 870. Washington, 1896. 241 242 CONCRETIONS. Concretions.* Concretions commonly occur as round or lenticular masses of various sizes, from that of a pin-head to several feet in diameter. (Plate XXI.) How they differ from pebbles and boulders. Due to the tendency of certain minerals in solution, or fusion, to segre- gate as they are deposited or crystallized. They may occur in either igneous or sedimentary rocks. 1. Contemporaneous with, or part of, enclosing beds. Rogenstein, bauxite. 2. Formed subsequently. Bedding planes sometimes pass through concretions. Commonly formed along certain beds. Concretions in sandstone are apt to be of lime ; those in limestone are apt to be of silica. Liable to form about bones or shells. Loess-puppets, fantastic forms, of lime concretions in the loess. Geodes, or hollow concretions. Geode beds of Warsaw, Illinois; Keokuk, Iowa; Indiana, etc. Geodes may be empty or filled with calcite, dolomite, gypsum, chal- cedony, quartz, zinc blende, pitch, petroleum. Formed after the deposition of the beds. The " iron pots," or iron geodes, of Arkansas. t Fig. 58. Concretions of iron and clay from the Tertiary beds of South Arkansas. (Harris.) * Merrill. Proc. U. S. Nat. Mus., XVII, 87-88, and plate. Washington, 1895. John Ruskin Geol. Mag., 1867, pp. 338, 481; 1868, pp. 12, 156. 208; 1869, p. 529. T. S. Hunt. Canadian Nat., 1881, IX, 431-433 Gratacap. Am. Nat., 1884, XVIII, 882-892. Bell. Am. Jour. Sci., Apr. 1901, XI, 315-316. Concretions from the Champlain clays of the Connecticut Valley. By J. M. Anns Sheldon. With 160 illustrations. Boston, 1900. Stocks. Geol. Mag., Jan. 1902, IX, 44-45. Stocks. Quar. Jour. Geol. Soc.. LVIII, 46-58. London, 1902. t On the ... siliceous nodular brown hematite (Gothite) in the Carboniferous lime- stone . . near Cookstown, county Tyrone, etc. By E. T. Hardman. Jour. Roy. Geol. Soc., Ireland, II, new ser., 1870-73, pp. 150-158. Plate XXI. A spherical calcareous concretion from sandstone. Piru, Ventura County, California. 243 244 CONCRETIONS. Fig. 59. Concretions from the Champlain clays of the Connecticut Valley; natural size. (Mrs. Sheldon.) 245 246 CONCRETIONS. Oolites * and pisolites (pea-stones) are concretions of smaller size. Formation of pisolite at Carlsbad, where it is called rogenstein. Siliceous oolite from Pennsylvania. Oolitic limestones of Indiana. Concretionary structure in crystalline rocks. Due to concentric arrangement of the crystals in cooling. " Orbicular granite." t Note that 1. Concentric staining is not properly a concretion. It is caused by penetration of mineral-charged waters, and the oxida- tion or deposition of the minerals. 2. Exfoliation, or spheroidal weathering, produces rounded forms which are not concretions, though resembling them.; STYLOLITES, OB CONE-IN-CONE. Stylolite is a columnar, or tooth-like structure, from a fraction of an inch to three inches long, sometimes found in limestones; it is caused by pressure of the overlying beds. FULGURITES.II A fulgurite is a tube one or two inches in diameter formed by lightning fusing soil or sand. It is sometimes formed in hard rock. * Bibliography of oolites. By T. C. Hopkins. 21st aim. rep. Indiana Geol. Surv., 409-410. Indianapolis, 1897. The Geologist, 1858, pp. 73-73. (Insect eggs as oolites.) Nature, Nov. 12, 1896, LV, 40. (Bacterial origin of oolite.) E. B. Wethered. Quar. Jour. Geol. Soc., 1891, LI, 196. (Organic origin.) E. H. Barbour and Jos. Torrey. Am. Jour. Sci., 1890, CXL, 246-249. G. R. Wieland. Am. Jour. Sci., 1897, CLIV, 262-264. (Pennsylvania siliceous oolites.) Rothpletz. Am. Geol., 1892, X, 278-282. Griswold and Agassiz. Bui. Mus. Comp. Zool., vol. 38, no. 2, pp. 29-62. (Florida oolites.) Jour. Geol., V, 312-313. t Bulletin de la Commission Geologique de Finland, no. 4, plates 1 and 2. Concretions in Canadian rocks. By T. C. Weston. Trans. Nova Scotia Sci., 1894-95, The hollow spherulites of the Yellowstone and Great Britain. By John Parkinson. Quar. Jour. Geol. Soc., May 1901, LVII, 211-225. Geikie's Ancient volcanoes of Great Britain. I, 22. Illustration. London, 1897. t On spheroidal structure in Silurian rocks. By J. D. La Touche. Jour. Roy. Geol. Soc. Ireland, II, 1867-70, pp. 229-232. Edinburg, 1871. ? Am. Jour. Sci., 1885, pp. 130, 78-79. Geol. Mag., Nov. 1892, IX, 505-507. H. C. Sorby. Trans. Brit. Assn., 1859, p. 124. 20th ann. rep. Indiana Geol. Surv., 82. Indianapolis, 1896. 21st idem, 305-308; bibliography. Indianapolis, 1897. - Ind. rep. for 1873, p. 275. Gresley. Quar. Jour. Geol. Soc., 1894, L, 731-739, 2 plates. Abstract Am. Geol., 1894, XIV, 399-400. Cole. Mineralogical Mag., X, 136. A. J. Sachs. Proc. Austr. Assn. Adv. Sci., 1893, IV, 327-328. I A spiral fulgurite from Wisconsin. By W. H. Hobbs. Am. Jour. Sci., CLVIII, 17-20. Fulgurites from Tupungato and the summit of Aconcagua. By T. G. Bonney. Geol. Mag., Jan. 1899, pp. 1-4. A study of the structure of fulgurites. By A. A. Julien. Jour. Geol., Dec. 1901, IX, 673- 693. 247 248 DISPLACEMENTS OF ROCKS. Displacements of Rocks. EVIDENCES OF ELEVATION AND DEPRESSION. (Plate XXII.) 1. Evidences that most sedimentary beds were deposited in the ocean. a. They are water-bedded. b. They contain remains of marine animals. 2. As they are now on land, in hills and mountains, they must have been elevated.* But it has been shown that while the earth's surface rises in one place it is depressed at another, so that there must be a warping of the beds. This may produce tilting , folding , or faulting. , 60. Section across the saddle- reef folds at Hargreaves, New South Wales, showing the ores in the anticlines. (Watt.) Theory of isostacy. Isostacy refers to a state of equilibrium. (This is discussed at length under Physi- ography, Part IV.) Geologic importance of folds and faults. Economic importance. Examples : the mining of bedded deposits, like coal and iron. The broader structural features of the earth are exhibited in folds and faults. Means of studying rock beds. 1. Artificial sections are exposed in mines, shafts, and wells. These seldom penetrate more than 3,000 feet. Well near Leipzig 6,560 feet. mm^-^ Hat Fig. 61. Section across a saddle reef, Victoria, Australia, showing the ore in the crest of the anticline. (Rickard.) * Fairbanks. Am. Geol., Oct. 1897, XX, 213, 245. 249 250 DISPLACEMENTS OF ROCKS. \Lower HeWerbero Limestone \Louoe_r., XVI, 227-306. - Bui. Soc. Beige de Geologic, 1891, V, 13-20. t The mechanics of Appalachian structure. By Bailey Willis. 13th ann. rep. U. S. Geol. Surv., pt. II, 211-282. Washington, 1893. The folds of the mountains. Open-air studies. By G. A. J. Cole. 283-313. London, 1895. Deformation of rocks. By C. R. Van Hise. Jour. Geol., 1896, IV, 312-353. A fold-making apparatus, etc. Nature, Aug. 31, 1899, p. 411. t Geological structure ... of the Vermilion range. By H. L. Smith and J. R. Finlay Trans. Am. Inst. Min. Eng., XXV, 595-645. g Torsion structure in the Alps. Nature, Sept. 7, 1899, p. 443. 253 254 DISPLACEMENTS OF ROCKS. Fig. 66. Sections showing types of structure and topography in the Paleozoic region of southwest Arkansas. No. 5 is a section across two anticlines and one syncline. (Ashley.) DISPLACEMENTS OF ROCKS. 255 Fig. 67. Sections across anticlines showing types of structures and topography in the Paleozoic region of southwest Arkansas. The dotted areas represent sandstones, and the shaded parts shales. (Ashley.) 256 DISPLACEMENTS OF ROCKS. Anticline. Syncline. (Middle of No. 5. in Fig. 66.) Monocline, or a slope in one direction (but not an overturn). Location of axes by the use of the dips, when the exposures are many or few. Dip is the slope of a bed of rock down which water or a ball would run. Dip is measured by the angle it makes with the horizon, and is Clinometer and compass. Caution against false-bedding. Caution against apparently horizontal beds. Caution against " creep." * Use of dip in locating beds in depth. Width of the outcrop varies with the dip. Use of dip in determining thickness of rocks. Strike of rocks. Direction on the surface. The water-line against the face of a bed. Use of strike in tracing beds on the surface. Dying out of folds. In length ; the overlapping of folds. In depth, as shown in mines, where the rocks crush or compress in depth, instead of folding. The anticlines are elevated more than the synclines are depressed.* What is meant by rocks being geologically higlier. Not a matter of hypsometry. How outcrops with various dips look on geological maps. Meaning of colors on geological maps. Appearance of eynclines ; of anticlines. How outcrops in folded areas follow the hills according to dip. a Fig. 68. Diagram illustrating the effect of horizontal pressure upon a horizontal homogeneous bed. (Ashley.) * For illustration of creep, see Scott's Geology, 82. t Van Hise. Jour. Geol., 1898, VI, 19. Buckley. Tr rans. Wis. Acad. Sci., XIII, 156. 257 258 A GEOLOGICAL MAP. A TYPICAL EXAMPLE OFTHB GEOLOGY OF NORTH ARKANSAS LOWER CARBONIFEROUS I IOHDOVICIAN MILE! Fig 69. Type of dendritic exposures caused by the streams cutting through the upper and exposing the underlying strata in a region of horizontal beds. OVERTURNED ANTICLINES. 259 6 xat/t j> 3 Fig. 70. North-south sections, ten miles apart, across an anticline in the Coal Meas- ures of Indian Territory. The section at the topis farthest west; toward the east the fold merges into a fault. (Drake.) Fig. 71. An overturned anticline. The resisting beds are sandstones. (Ashley.) 260 STRUCTURE. b // _ b Fig. 72. Diagrams showing the effect of original dip upon ultimate structure. (Ashley.) Fig. 73. Profiles of an anticlinal ridge, Antoine mountain, Pike county, Arkansas. (Ashley.) 261 262 FAULTS. Overturns.* Influence of original dip upon overturns. Overthrust folds form more readily than underthrust folds, because of the easier relief being upward.t Effects of folds on topography. 1. Anticlinal valleys. 4. Monoclinal hills. 2. Synclinal valleys. 5. Anticlinal hills. 3. Synclinal hills. Weak structures. Strong structures. 6. Isoclinal ridges. FAULTS.* Faults are displacements of the rocks along lines of fracture. They are of much more importance in economic geology, partly because ore deposits are often formed along faults, and partly because they frequently displace ore bodies after they have been deposited. Faults may run in any direction. They can only take place after the formation of the beds so faulted. They occur singly or in sets. These sets may cross each other at various angles. Faults are called normal, or reversed, according to the nature of the dis- placement. NORMAL OR GRAVITY FAULTS. Produced by tension of the beds, allowing one side to settle. "Faults hade to the downthrow," a rule originating in a region of normal or gravity faults, and of approx- imately horizontal beds. Meaning of this expres- sion. Gravity faults occur in regions of surface contraction, or of vertical pressure ; they sometimes occur in soft materials.|| Contraction may be due to Fig. 74. Section across normal faults showing the repetition of the same beds at different elevations. 1. Drying, or loss of water. 2. Cooling of hot rocks. Fig. 75. Section across normal faults. * 16th ann. rep. U. S. Geol. Surv., pt. I, 550. Washington, 1896. t Van Hise. 16th ann. rep. U. S. Geol. Surv., pt. I, 621. Washington, 1896. Buckley. Wis. Acad. Sci., XIII, 159. I Fault-rules. By F. T. Freeland. Trans. Am. Inst. Min. Eng., XXI, 491-502. New York, 1892-93. Contains short bibliography. La face de la terre. Par E. Suess. Tome I, 138-184. Paris, 1897. Heim and De Margerie. Dislocations. Zurich, 1888. (Bibliography.) Slickensides and normal faults. By T. Mellard Reade. Proc. Liverpool Geol. Soc., 1889, VI, 92-114. I On the origin of normal faults, etc. By Joseph Le Conte. Am. Jour. Sci., Oct. 1889, pp. 257-263. aGe || Iowa Geol. Surv. Rep., 1889, X, 365-368. Freeland. Trans. Am. Inst. Min. Eng., XXI, 491. 263 264 FAULTS. Oregon lakes,* Dead Sea, and the Jordan.t California valleys, but widened by erosion. Deceptive thickness. REVERSED OR THRUST FAULTS.* Importance of this rule Thrust faults are caused by pressure. Rule regarding the dip of the fault is reversed. in the location of veins and beds. Folds often merge into faults. Sled-like turned up ends of beds on faults Fi - 76. Both depression and elevation of fault blocks produced by pressure and faults dipping in different directions. Fig. 77. Section across folds that become faults repeating the same beds along their outcrops. (Heim and de Margerie.) Fig. 78. A thrust fault displacing a quartz vein. In this case the fault dips toward the downthrow. Topographic features due to landslides. By I. C. Russell. Pop. Sci. Mo., Aug. 1898. th America. By I. C. Russell. 29-31. Boston, 18 London, 1886. Lakes of North America. By I. C. Russell. 29-31. Boston, 1895. t See maps in the survey of Western Pal stine. By E. Hull t Ashley. Bui. Geol. Soc. Am., 1897, IX, 429-431. 265 Fig. 79. An artificial fold passing into one large and many small faults. (Willis.) Amount of displacement in faults. From the fraction of an inch to thousands of feet. Faulted pebbles. 15,000 feet in Sierras. 20,000 feet in Appalachians. 40,000 feet in Wasatch Mountains, Utah. Overthrust faults of Scotland. Continuity of displacements. Faults die out below. Die out longitudinally. They vary in length from a few feet to hundreds of miles; one in Africa is 120 miles long,* another is 270 miles long. There are many long faults in California. Owens Lake fault 150 miles; Salinas valley fault about 120 miles; Santa Clara valley fault more than 200 miles. A shear fault has varying displacements at different parts of the fault. Direction of displacement is not necessarily vertical, but may be lateral, or side thrust ; or it may be twisted, one side moving one way, the other the other, forming a double shear fault. How vertical displacement of tilted beds may give the appearance of a lateral displacement. * Nature, Apr. 22, 1897, LV, 581. 267 268 FAULTS. I North S^cale of feet %-'"' ''W \ Fig. 80. Plan of a laterally faulted calcareous stratum, San Lorenzo river, Ben Lo- mond, California. (Newsom.) Ages of faults. A fault must be newer than the rocks affected by it. If Cambrian and Carboniferous rocks are faulted, the fault must be post-Carbonif erou s . Faults in Nova Scotia since the glacial epoch.* At some places faults are now forming.f Edges of faults are not straight, but ragged and more or less crooked. Slickensides are striae, or scratches, on the rocks between faces that have slipped over each other. Slickensides resemble glacial striae. DETECTION OF FAULTS ON THE SURFACE. 1. By the abrupt termination of beds along a strike. Examples: map of France; Pennsylvania county maps. 2. By newer rocks apparently dipping beneath older ones. Rush creek fault. 3. By mineralization on fault-line. * G. F. Matthew. Bui. XIII, Nat. Hist. Soc. of New Brunswick, Nov. 1894, pp. 34-42- t Spurr. Monograph XXXI, U. S. Geol. Surv., 148-150. Washington, 1898. 269 270 FAULTS. 4. By certain springs emerging on the fault-line. (See no. 2.) 5. By changes of topography. 6. By change of rock or soil on the strike of the fault. ECONOMIC IMPORTANCE OF FAULTS. Mineral veins are often formed in or near fault-lines. Mineral deposits are displaced by .faults. It is therefore frequently important to determine both the direction and amount of displacement by a fault. Fig. 81. A normal fault in the Ozark Mountains displacing beds of zinc ore. Fig. 82. Section across two faulted reefs of the Rand. (Hatch and Chalmers.) Plate XXIII. A ledge of siliceous mineralized rock along a fault-line in the Ozark zinc regions. 271 V LIMESTONE tv.Hj COAHSE SANDSTONE J FINE GRAINED SANDSTONE OCUABTZ < RHODOCH80SITE S) ORE 1 SELVAGE ENTERPRISE MINE, COLORADO. Fig. 83. Ore deposited in a fault, Enterprise mine, Colorado. (Rickard. 272 METAMORPHISM. The Alteration of Rocks. Rocks do not remain the same, but are subject to changes. Metamorphism is one of these changes. METAMORPHISM.* The change, whether chemical, mineralogical, or other rearrangement, that rocks undergo after their original formation or deposition. It often obscures the 1. Original form. 2. Method of formation. Not all changes are spoken of as metamorphism, though the distinction is sometimes quite arbitrary. / Decay. Example : formation of kaolin. Coloration : mottling of rocks. Hydration. (See page 280.) Changes other than meta- morphism Sandstone is sometimes changed to quartzite at the sur- face by a process of weathering or local meta- morphism. Limestone and fossils of lime carbonate change to crys- talline marble. Lignite changes to coal. Coal changes to anthracite, graphite, and natural coke. f Changes may be 1. In form and texture, but not in composition. Aragonite to calcite. Clastic to crystalline rocks; grits to schists. 2. In chemical composition, by replacement. Wood to silica. Calcareous shells to silica. Effects of metamorphism. 1. Bleaching. 2. Change of color. 3. Hardening and consolidation. Sandstone to quartzite. Clay and shale to slate. * Metamorphism of the sedimentary rocks. By C. R. Van Hise. 16th ann. rep. U. S. Geol. Surv., pt. I, 683-716. Washington, 1896. Metamorphism of rocks and rock flowage. By C. R. Van Hise. Am. Jour. Sci., July 1898, CLVI, 75-91. - Bui. Geol. Soc. Am., 1898, IX, 269-328. Physics of metamorphism. By A. Harker. Geol. Mag., 1889, VI, 15. Judd. Geol. Mag., 1889, VI, 243. The greenstone schist areas of ... Michigan. By G. H. Williams. Bui. 62, U. S. Geol. Surv. Washington, 1890. Lea eaux souterraines aux dpoques anciennes. Par A. Daubre'e. 181 et e.q. Paris, 1887. Callaway. Quar. Jour. Geol. Soc., 1898, L.IV, 374. Am. Naturalist, XXXIII, 176. 273 274 METAMORPHISM. 4. Expulsion of water and vaporizable ingredients. 5. Melting, baking. 6. Crystallization, with or without change in constituent minerals, including Marmarosis. 7. Production of new minerals. 8. Production of foliation and schistosity. 9. Obliteration of fossil contents. The fossils are not always obliterated.* 10. Obliteration of bedding planes. Causes of metamorphism. 1. Hot waters with CO 2 and minerals (alkalis) in solution. 2. Hot vapors and gases beneath the surface. 3. Movements in rocks, such as pressure, crushing, and shearing.! 4. Intrusion of hot eruptive rocks. Heat and moisture are the chief agents of metamorphism. Amount of heat. But little heat is necessary to produce metamorphism, and there are some minerals in metamorphosed rocks that can not withstand much heat. Amount of moisture. But little moisture is necessary in metamorphism. Dry heat, however, does not affect rocks far. Certain minerals contain water. Time an important element. The oldest rocks are usually most metamorphosed. How heat may be produced in rocks. 1. By chemical action. 2. By the crushing and shearing of the rocks. 3. Intrusion of hot rocks from below. 4. Rise of interior heat. (See pages 136-140.) Metamorphism j Local, or contact. may be I General, or regional. I. LOCAL OR CONTACT METAMORPHISM. Local metamorphism is produced by the altering effect of hot rocks on those with which they come in contact. Igneous rocks penetrating coal in southeast Colorado have produced coke or powdery graphite. Sometimes other beds are only reddened. Limestone much changed near a dike, but less away from it. * Daubr^e. Geologic experimentale. 140-142. t Account of a series of experiments showing the effects of compression in modifying the action of heat. By Jas. Hall. Edin. Phil. Trans., VI, 1812. Daubre'e. Geologic experimentale. 132. Adams and Nicolson. Phil. Trans. Roy. Soc. London, vol. 195, pp. 363-401. London, 1901. 275 276 METAMORPHISM. A dike in chalk in County Antrim, Ireland, has altered the chalk to the following rocks, beginning next to the dike : 1. Dark- brown crystalline limestone. 2. Saccharoidal limestone. 3. Fine-grained limestone. 4. Porcelanous limestone. 5. Blue-gray limestone. 6. Yellow-white limestone. 7. Grades into chalk. Alteration of the slates of the Sierras by granite dikes ; in places the meta- morphism has affected the rocks as much as a mile from the dikes. Sedimentary beds are sometimes baked to " an intensely hard and ex- quisitely white porcelain " by a lava sheet.* These changes vary greatly in degree, from incipient metamorphism to a change of the form and of the chemical composition of the rocks. Experiments of Daubr6e.t Great changes, however, are not always produced. Near the crest of the Siskiyou Mountains, on the north side, there are many exposures in the railway cuts, showing granites containing inclusions that stili preserve their bedding planes ; the inclusions are of all sizes up to 20 feet or more in diameter. II. REGIONAL OR GENERAL METAMORPHISM. J This name is applied to wide areas where there is apparently no connec- tion between local igneous phenomena and the metamorphism. Of the same nature as local metamorphism, but different in extent. Great regions of schists fall under this head. Examples: New England, Wisconsin, Michigan, and Minnesota. North of Scotland.^ Interior of South America. Regional, or general, metamorphism is supposed to be due to the presence of metamorphosing conditions in rocks over wide areas. Regional metamorphism is most common in regions of stress, folding, crump- ling, and shearing. It is often unequal in degree and character. Why some beds are metamorphosed while others in the same series are not. Due to difference 1. In contained water. 2. In condition of or size of the particles. 3. In composition. * The great rift valley. By J. W. Gregory. 137. London, 1896. t Etudes synthetiques de geologic experimentale. Par A. Daubrge. 151-234. Paris, | Sur 1'origine des terrains crystallins primitifs. Par M. Levy. Bui. Soc. Geol. de France, XVI, 1U2-113. Paris, 1887. ? On the metamorphosis of dolorite into hornblende schist. By J. J. H. Teall. Quar. Jour. Geol. Soc., XLI, 133-145; confirmed by John Home, Nature, Sept. 19, 1901, p. 277 278 METAMORPHISM. / METAMORPHOSED ROCKS. . .] All schists,* gneisses, some quartzites, slates, serpentines. Why mountains often have sediments metamorphosed. They are regions of movements, strains, slipping, etc. Why exposed. By erosion. They are often old rocks. They are commonly deep-seated rocks. GENERAL CONCLUSIONS REGARDING METAMORPHISM. 1. Metamorphism is the change of internal form, or structure, of either igneous or sedimentary rocks. 2. The date of the metamorphism is necessarily later than that of the making of the rocks. 3. Metamorphism is produced by a. Heat. b. Pressure. c. Chemical changes aided by water and alkalis. 4. Metamorphism may be local (contact) or regional (widespread). 5. It may occur in alternate beds of a series. 6. It may affect beds either vertically or laterally. 7. Regional metamorphism is a wider extension and greater development of local metamorphism . 8. Metamorphism does not necessarily introduce new chemical elements, but may be only a rearrangement of those already present. 9. Metamorphism is seldom uniform throughout a wide area, but is often more intense here, and less so there. 10. The nature of the changes depends on o. Character of rocks affected. b. Nature and intensity of metamorphosing agencies. 11. Metamorphic rocks may be either old or new. Metaraorphism is therefore no test of the age of rocks. 12. However, all the oldest sedimentary rocks are metamorphosed, and metamorphism. is generally more widespread as we go down in the geologic series. 13. Metamorphism is most common in regions of great thickness of strata. 14. The most common forms of metamorphic rocks are: gneisses, schists, slates, some quartzites, some marbles, and some serpentines. 15. Metamorphism more frequently takes place at great depth below the surface. The metamorphic rocks now exposed have, for the most part, been uncovered by erosion. * The origin of glaucophane schists. Am. Naturalist, May 1901, XXXV, 427. 279 280 ROCK CHANGES. REPLACEMENT. Of woody fiber by silica. (See Plate XIV.) Of shells, corals, etc., by silica. PSEUDOMORPHISM.* Dehydration, or loss of water. DoLOMITIZATION.t A replacement of some of the lime carbonate of limestones by magnesia. Fig. 84. Vertical section in a quarry at Kilkenny, Ireland, showing both dolomite and unaltered limestone. (Prestwich.) HYDRATION. Anhydrite forms gypsum by taking up water. i Peridotite altered to serpentine. WEATHERING. Changes of rocks upon exposure. || These changes are mostly in the direction of disintegration and decomposition, but i i j Fig 85 Horizontal section in sometimes exposure produces hardening, t he Kilkenny quarry, showing and it may even change sandstones into the hardest kind of quartzite.H A part of the limestone (shaded) altered to dolo- mite. (Prestwich.) * Physical geology. By A. H. Green. 81-82. London, 1882. t Hall and Sardensen. Bui. Geol. Soc. Am., 1894, VI, 193-198. Klement and Hogbom. Am. Jour. Sci., May 1895, CXLIX, 426-427. Robert Bell. Bui. Geol. Soc. Am., 1894, VI, 297-308. T. C. Hopkins. Ann. rep. Geol. Surv. Arkansas for 1890, IV, 35-39. Little Rock, 1893. I Manganese; -its uses, ores and deposits. By R. A. F. Penrose, Jr. 534-536. Little Rock, I Merrill.' Geol. Mag., Aug. 1899, pp. 354-358. Holland. Geol. Mag., 1899, pp. 30-31; 540-547. || Wads worth. Proc. Boston Soc. Nat. Hist., 1884, XXII, 202-203. Branner. Cretaceous and Tertiary geology of Brazil. Trans. Am. Phil. Soc., 1889, XVI, 419-421. Hayes. , Bui. Geol. Soc. Am., 1897, VIII, 218. Call. The geology of Crowley's ridge. Ann. rep. Geol. Surv. Arkansas for 1889, II, 99- 101. Little Rock, 1891. 281 282 SPRINGS. Underground Water in Its Relations to Geologic Structure. SPRINGS. The waters of springs are meteoric waters (rain or enow) that have fallen on the earth, soaked into the ground, and are emerging naturally.* Their emergency is caused by gravity, guided by the rocks. Accumulations of water occur in rocks having room for water ; that is, in porous rocks. The porosity is due to rock struc- ture, and may be caused 1. By spaces between coarse materials. The coarser the materials the more the space. Hence, water from con- glomerates and coarse sandstones. 2. By joints or cracks in rocks. In shales, and other com- pact rocks, it flows through the joints. 3. By openings caused by so- lution and removal of Fig " 86. Diagram showing in black the open spaces between spheres of uniform size. rock. As in the caverns of limestone regions. Note the size of springs in limestone regions. 4. By dolomitization which causes a shrinking of the rocks. Water goes where it can flow most easily. Emergence depends on gravity and on geologic structure, or the bedding of the rocks. It may be caused by 1. Fissures. 2. Faults. 3. Folds. 4. Impervious strata stopping the downward passage of the water through overlying porous strata.t " The knobstone of southern Indiana is so compact that water can not pass readily through it, and springs are by no means common in that * Subterranean waters. By Chas. Morris. Jour. Franklin Inst., 1901, CLI, 182-194. On the percolation of rainfall, see The water supply of England and Wales. By C. E. de Ranee, 8-22. London, 1882. Les eaux souterraines a l'6poque actuelle. Par A. Daubree. 2 vols. Paris, 1887. The principles and conditions of the movement of ground water. By F. H. King and C. S. Schlichter. 19th ann. rep. U. S. Geol. Surv., pt. II. Some principles controlling the deposition of ores. By C. R. VanHise. Jour. Geol., Nov. and DPC. 1900, VITI, 730-770. t T. C. Hopkins. Ann rep. Geol. Surv. Arkansas for 1890, IV, 345-346. 1893. Am. Geol., 1894, XIV, 365-368. 283 284 SPRINGS. formation. At the top of the formation, however, the line of parting between the limestones which do permit the . . . circulation of water and the underlying impervious sandstone is a natural spring horizon. Along this line of parting springs are very common, and . . . they are to be found in almost every small side ravine." * Silurian. Fig. 87. A region of nearly horizontal rocks, showing the emergence of springs in the ravines and along the same stratum. ' J. F. Newsom. Proc. Ind. Acad. Sci., 1897, p. 256. 285 286 WELLS. COMMON WELLS. Wells tap rocks holding accumulated, or accumulating, underground waters. Waters accumulate in any openings in rock or soil. 1. Spaces in coarse sediments, gravels, sands. 2. Alluvial lands (owing to position). 3. Pockets in glacial drift.* TJie uncertainty of water in the drift is due to the irregularity of the bed- ding of glacial materials. Why the waters of wells differ even when near each other. Fig. 88. Section in the chalk region of southwest Arkansas, showing why the waters of some of the wells are hard while others are soft. Why wells are sometimes found in mountain tops. 1. Porosity of containing bed, and a confining bed below. 2. Synclinal structure of mountain. Structural features always important. See cases above mentioned. Synclinal trough south of Stanford University. Why water is abundant on College Terrace, but not to be had in the foothills immediately south of the Quadrangle. Case of horizontal well in vertical beds. Where to bore in special cases. ARTESIAN WELLS.t Artesian wells are those from which the water flows. It has accumulated under special structural conditions. '* Water resources of Indiana and Ohio. By Frank Leverett. 18th ann. rep. U. S. Geol. Surv., pt. IV, 419-559. Washington, 1897. t The requisite and qualifying conditions of artesian wells. By T. C. Chamberlin. 5th ann. rep. U. S. Geol. Surv., 125-173. Washington, 1885. Artesian waters of a portion of the Dakotas. By N. H. Darton. 17th ann. rep. U. S. Geol. Surv., pt. II, 1-92. Washington, 1896 New developments in well-boring and irrigation in eastern South Dakota. By N. H. Darton. 18th ann. rep. U. S. Geol. Surv., pt. IV, 561-615. Washington, 1897. Artesian wells upon the great plains being the report of a geological commission, etc. Department of Agriculture. Washington, 1882. 287 288 WELLS. Wide areas are usually involved. Essential conditions for artesian wells are 1. Water-bearing stratum (to hold the water). Must be of coarse or porous material. 2. A confining stratum (to keep it in). Usually fine silts, especially clays. 3. Head or elevated source (to force it out at the opening). 4. Rainfall at the outcrop of the water-bearing stratum (to furnish supply). Origin of the artesian waters of Wisconsin, Dakota, etc. Origin of the Santa Clara county artesian waters. Importance of determining elevations. Help of railway levels to tie to. Massive igneous rocks and granites have water in cracks and joints only. The uncertainty of finding water in them due to the irregularity of joints. Increase of the flow of wells.* Periodic fluctuations in the discharges of artesian wells are probably due to variations of barometric pressure. The ebbing and flowing of wells are attributed to tidal influence ;t this is shown by their correspondence to be the case in some instances. Periodic discharges may also be caused by syphon action when the shape of the water-way is favorable. * Outbursts of springs in time of drouth. By W. E. Abbott. Jour, and Proc. Roy. Soc. N. S. Wales, 1897, XXXI, 201-206. t H. G. Madan. Quar. Jour. Geol. Soc., Aug. 1898, LIV, 301-307. J. F. Knightly. Geol. Mag., July 1898, p. 333. 289 290 PALEONTOLOGY. PART III. HISTORICAL GEOLOGY, OR PALEONTOLOGY. The Order of Events and Life as Recorded in the Rocks. Historical Geology treats of the order and ages of the rocks i. e., the his- tory of the earth as shown by the rocks and their fossil contents. The history of the earth must be learned 1. By deductions from the known laws of matter. 2. By the study of the operation of these laws as shown by the rocks. The laws of matter teach us that 1. Stratified rocks are laid down in water (except seolian and some plant accumulations) in approximately horizontal beds. 2. The oldest beds were laid down first and at the bottom, the newest ones last and on the top. 3. The disturbance of the horizontality and continuity of these beds, and their metamorphism, must have taken place since their deposition. 4. If a locality is above water during a given time, no sedimentary beds can be deposited thereon during that period. 5. Inasmuch as the earth's crust is liable to elevation and depression, deposition of sediments at a given place is liable to be interrupted, and we may not expect to find a continuous and uninterrupted deposition at all places, or perhaps at any one place. 6. The rocks preserve in themselves many evidences of the conditions pre- vailing, and of the geography, when and where they were laid down. 7. The fossils found in a given bed of sediments are the remains of plants or animals that lived when the beds were being deposited. (Except in cases of fragments derived from older beds.) 8. The periods of the first appearance and changes in the characters of faunas and floras will be indicated, or suggested, by the remains of animals and plants preserved as fossils. * Geological biology. By Henry Shaler Williams. New York, 1895. Text-book of comparative geology. By E. Kayser. Translated by P. Lake. London, 291 292 FOSSILS. 9. In many places the sedimentary rocks have all been removed by erosion, and the history of the place as originally preserved in those rocks has been entirely obliterated. It is thus evident that the earth's history, where not obliterated by erosion and metamorphism, is to be found both in the nature and condition of the rocks, and in the character of the fossils. 10. The geological record, therefore, is at best an imperfect one.* WHAT Is SHOWN BY THE KINDS OF ROCKS. . They are sedimentary, organic, chemical deposits, or igneous. Changes making variation of rocks often affected life, and thus the fossil contents of the rocks. WHAT THE PRESENT CONDITIONS OF THE ROCKS SHOW. 1. By metamorphism, that they have been affected by metamorphosing conditions. 2. By faulting, that they have been under tension or pressure. 3. By folding, that they have been squeezed. 4. By dikes, that molten rocks have broken through them. 5. By unconformities, that land conditions, admitting denudation, have intervened. Fossils and Their Uses.t Fossils are the remains or traces of plants or animals imbedded in the rocks. They are often called petrifactions, though they are not always petri- fied. The word " fossil " was formerly applied to minerals, but it is no longer so used. WHAT DIFFERENT KINDS OF FOSSILS SHOW. Salt-water forms show salt-water conditions. Brackish-water forms indicate brackish-water conditions. Fresh-water forms indicate fresh-water conditions. Deep-water forms show deep water. Shallow-water forms show shallow water. Cold-water forms show cold water. Warm-water forms show warm water. Swamp life indicates conditions of swamps. * Darwin's Origin of species. Chap. X. New York, 1870. Lyell's Principles of geology. Chap. XIV. New York, 1889. Darwinism. By A. R. Wallace. Chap. XIII. London and New York, 1889. t Notes on the siliciflcation of fossils. By T. S. Hunt. Canadian Naturalist, 2d ser., I, 46-50. Montreal, 1864. Fossils, their nature and interpretation. Geological biology. By Henry Shaler Wil- liams. 78-110. New York, 1895. The process of fossilization. 48th ann. rep. N. Y. State Museum, II, 211-215. Albany, 1895. Fossils and fossilization. By L. P. Gratacap. Am. Naturalist, Nov. 1896, 912; Dec. 1896, XXX, 993-1003; Jan. 1897, XXXI, 16. 294 FOSSILS. Plants may have been washed down in fresh water. Trees and big stumps show land conditions. Life peculiar to cold climate, indicating cold. Life peculiar to warm climate, indicating warmth. Changed conditions produce variation of faunas and floras. These conditions limit the range of animals and plants on earth, and hence physical changes produced different conditions favorable to different forms of life. In these changes many forms were crowded out and exterminated. MARINE DEPOSITS. Littoral. Deep-water. Abysmal. Animals and plants having hard parts often have them preserved. Examples: bones of fishes, whales, crabs, corals, shells. Animals and plants without hard parts are seldom preserved as fossils. Examples : jelly-fishes, slugs, soft algae. No remains are preserved save when the conditions are favorable. LAND DEPOSITS. Land animals and land plants decay for the most part, unless they fall in water or mud, or are washed to the sea and buried by sediments. In lakes ; peat-bogs ; river mouths. Things preserved in mud or clay. Bones, skeletons, teeth, scales of fishes. Impressions of plants, trunks, bark, and leaves; rain-prints, ripple-marks. Wings of insects. Birds, bird-tracks. Cave deposits ; mammals. Fossils may, therefore, be 1. Mold or impression of the outside parts of animal or plant. 2. Cast of the inside. 3. The thing itself, or its hard parts, preserved. Fossil skin and hair found in Siberia and in Patagonia.* 4. The form of the thing itself replaced by some mineral. Examples: silicification of wood, shells, etc. These are petrifactions. Relative values of fossils. Conditions of preservation better under the sea than on land. Hence marine forms are more abundant as fossils than land forms, and more important. Some kinds of fossils, such as protozoa, sponges, and lingulas are found in rocks of all ages. Others are very limited in geologic distribution. * Bui. Soc. G6ol. de France, 1900, XXVIII, 808. 295 296 THE GEOLOGIC COLUMN. Land organisms have small chance of preservation. A body was found in a copper mine in Chile that had evidently lain there since 1600 A. D., preserved by dryness and by " impregnation of the tissues by copper salts."* Highly developed and specialized mammals are of limited range. The Geologic Column. All divisions are more or less artificial, for periods often grade insensibly into each other. What is meant by " the geologic column." The piling up of rocks upon each other. The thickness of the beds varies greatly at different places. Attempts to divide the column according to 1. Lithologic characters.^ Limestones, sandstones, clays; are contemporaneous and inter- grade. Sedimentary and igneous rocks contemporaneous. All occur from the bottom to the top. 2. Color. " Old Red " and " New Red " abandoned. Color is of little importance; the same ones may occur anywhere in the column. 3. Mineral contents, such as coal in the Carboniferous. But all coal is not in the Carboniferous. Minerals are often introduced as veins in rocks of any age. 4. Order in which the rocks are found. This order is not everywhere the same. Sometimes the newest rocks rest on the oldest ; sometimes on the very new ones. Difficulties of chronologic division increased by overturning, metamorphism, faulting, erosion, and interruptions in the deposition of the beds. CORRELATION OF BEDS IN SEPARATE REGIONS. What is meant by correlation. In making geologic divisions it is necessary that the beds at one place shall be correlated with those of another, or their equivalents determined. This can sometimes, but not always, be done by tracing the beds from one locality to another. Precautions necessary in making correlations. 1. That the rocks are not overturned. This is possible in regions of sharp folds and steep dips, but it is not a common occurrence. Overturns are decidedly exceptional. * J. A. W. Murdoch. Eng. and Min. Jour., May 11, 1901, p. 587. t Individuals of stratigraphic classification. By Bailey Willis. Jour. Geol., Oct. -Nov. 1901, IX, 557-569. 297 298 CORRELATION. 2. That they are not faulted. This is common in some tilted regions. May occur in horizontal strata bringing similar beds opposite each other. 3. Look out for unconformities. 4. But conforming beds may not be continuous deposits, and interven- ing ones may be omitted. Color, texture, and mineralogic composition of bed can only be used within short distances. Use of fossils in the correlation of rocks.* Beginnings of paleontology by William Smith. Life on the globe has been changing from ^.he first.* Each period has had its own forms. This progress has involved constantly closer proximity to existing forms. Hence, identity of fossils shows that the beds containing them have approximately the same age. In every country fossils show the same general order of succession. Why identity is only approximate. 1. Slow change of life at one place. 2. Spread of life-forms over the globe from one point. 3. Life-zones due to climatic differences. 4. Life-zones due to depth and character of water. Use of fossils in the study of geographic changes. Former connection of America with Asia. Fossils as evidences of climatic changes. Conditions of coral growth and the distribution of fossil corals. Fossil palms found in cold climates. Uses of the knowledge of fossils in mining geology. In looking for coal, or other rock deposit or mineral, known to be at certain horizons. Lead and zinc in the Ozark mountains in Silurian rocks below Carbon- iferous. Detection of faults. Detection of overturns. Detection of geologic breaks. Location of coal beds in folded areas. The coal beds about Magazine mountain and Mt. Nebo, Arkansas ; the Bernice basin in Pennsylvania. Stratigraphy will do the same, but it can not always be worked out over large areas. Examples : Pennsylvania, Illinois, east Tennessee, and Alabama coals. * The discrimination of time-values in geology. By H. S. Williams. Jour. Geol., Oct.- Nov. 1901, IX, 570-585. The use of fossils in determinine the age of geologic terranes. By H. S. Williams. Proc. Am. Assn. Adv. Sci., 1889, vol. 37, p. 206. 299 Fig. 89. Section across a fault in the Ozark Mountains. The sandstones at S are let down until they appear to be continuous with the older ones below the Calciferous strata. 300 SUBDIVISIONS OF THE GEOLOGIC COLUiMN. Characteristic Life Period Man Psycho- zoic Recent Kainezoic Pleistocene Terrace Champlain Glacial Tertiary SSel Neocene Eocene Cretaceous Upper Lower Reptiles 1 Jurassic Middle Lower Triassic Upper Middle Lower Acrogens Amphibians Carboniferous Permian Coal Measures Lower Carboniferous Fishes Devonian Catskill Chemung Hamilton Corniferous Oriskany o f Silurian S or g 1 Upper Silurian Lower Helderberg Salina Niagara Invertebrates } Ordovician OQ or L Lower Silurian Trenton Canadian Cambrian Potsdam Belt* Georgian t Algonkian Keweenawan Huronian Archsea a Archaean Laurentian By C. D. Walcott. * Pre-Cambrian fossiliferous formations 1899, X, 199-244. t Van Hise placed the Algonkian as a separate formation betw Paleozoic. Bui. Geol. Soc. Am., Apr. the Archaean and 301 302 ARCHAEAN PERIOD. AECH^AN PERIOD. Sometimes called Azoic and Agnotozoic. Archaean time may be divided into three periods, or eras. 1. Era of the molten globe.* 2. Era of the cooling crust: condensed vapors covered the earth with waters. If any part of the crust remained above water, erosion began. 3. Temperature lowered to a point admitting the simplest forms of vegetation. This was the beginning of life on the earth. The rocks formed during Archaean time are the lowest ones accessible to us, and underlie all others. Evidences of life in Archaean rocks. No fossils are found in Archaean rocks, but it seems reasonable to sup- pose that life began during Archaean time, for the following reasons : 1. Evidences of life are abundant in the next higher rocks the Belt and the Cambrian ; it is, therefore, reasonable to suppose that life had its beginning somewhat earlier. 2. Limestones (marbles) in the Archaean; probably of organic origin. 3. Iron ores abundant in Archaean ; accumulated through the agency of organisms and organic acids in bogs, lakes, and meadows. t 4. Graphite and plumbago in Archaean rocks believed to be derived from plants. { 5. Apatite is a phosphatic rock. Other forms of phosphate rocks are of organic origin, and the apatite deposits abundant in Archaean rocks are probably metamorphosed forms. 6. Presumptive evidence. The existence of animals in the Belt and the Cambrian. Animals live on plants ; plants must have existed first ; animals of the Belt must have had Belt plants, and those probably had Archaean ancestors. The plants could live in very hot waters. Distribution of Archxan rocks in North America. Economic deposits of the Archsean. Iron ores of the Adirondacks in New York. Iron ores of the Lake Superior region. Graphite. Apatite of Canada. Marble beds. Granites for building-stones. * Lord Kelvin on the origin of granite. By A. R. Hunt. Nature, Feb. 22, 1900, L.XI, 391. t Phillips' Ore deposits. 2d ed. 35-43. London, 1896. j On the graphite of the Laurentian of Canada. By J. W. Dawson. Canadian Naturalist, new series, V, pp. 13-20. Montreal, 1870. 303 304 PALEOZOIC PERIOD. PALEOZOIC PERIOD. Nature of the paleozoic rocks. Mostly marine sediments. Some fresh-water and land deposits. Life of the paleozoic times. Chiefly marine invertebrates, and Cryptogamic plants (ferns, club-mosses, horse-tails). Paleozoic rocks are divided (beginning below) into: Belt, Cambrian, Ordo- vician (or Lower Silurian), Silurian (or Upper Silurian), Devonian, and Carboniferous. . Belt. The word " Belt ' ' is from the Belt mountains of Montana, where the rocks of this series occur. Until recently the Cambrian rocks were considered to be the lowest and oldest containing recognizable fossils, but in 1898 Dr. C. D. Walcott announced the discovery of the Belt series* in Montana. The series of sedimentary beds is about 12,000 feet thick, and is unconform- ably below the Cambrian. It is composed of several distinct formations. The remains of crustaceans and annelid trails occur 7,000 feet below the unconformity. Cambrian. The word derived from "Cambria," the ancient name of Wales, where these rocks were first studied. Fossils. No plants certainly known ; by inference, they must have existed, to supply food to the abundant animal life. Animals include, principally: sponges, hydrozoa (graptolites), worms, echinoderms, trilobites, gasteropods, pelycypods, and brachio- pods. Ordovician (or Lower Silurian). Name derived from " Ordovici," an ancient tribe of Wales, where these rocks occur. The name " Silurian " from "Silures," also an ancient tribe of Wales. Fossils. The fossils of the Ordovician show marked advance in life. Some forms, as graptolites and trilobites, culminated and began to de- cline during this period. * Pre-Cambrian fossiliferous formations. By C. D. Walcott. Bui. Geol. Soc. Am., April 1899, X, 199-244. 305 306 PALEOZOIC PERIOD. Corals rather abundant. Centipedes, the first known land animals. Bivalves and gasteropoda increase greatly in size and number. Cephalopoda appeared in the Cambrian, but are abundant in the Ordo- vician. Economic products. Lead ore of the Galena limestone of Wisconsin, Iowa, and Illinois. Petroleum and gas from the Trenton limestone of Ohio and Indiana. Relation of the " Trenton rock " to these products. Marbles of Vermont, Massachusetts, New York, and Tennessee. Fig. 90. Section showing the geologic structure in the oil and gas fields of Ohio. (Orton.) Silurian (or Upper Silurian). Silurian rocks in North America are thicker along the Appalachian moun- tains, and thin out toward the west. An inland sea with its eastern margin near the eastern border of the conti- nent.* Fossils. Scorpions and insects. Some plants, but not abundant. Sharks among the earliest vertebrates. Crinoids increased in numbers. Bryozoa and brachiopods continue abundant. Pteropods smaller and less abundant. Graptolites and trilobites less abundant. Climate. The nature of the fossils suggests warm or temperate seas. The occurence of extensive salt beds in New York and Canada shows that salt water must have been concentrated there. Probably arid at that time. * For the Silurian areas and shores, see Stuart Weller, in Chicago Acad. Sci., Bui. IV, part I, p. 16. June, 1900. 307 308 PALEOZOIC PERIOD. Economic products. Clinton red fossil iron ore along Appalachian mountains from New York to Alabama. Joliet building-stone of Illinois. The brines and rock-salt of New York and Canada from the Salina, or salt group, of the Silurian. Gypsum accompanies the salt, used as fertilizer or "land plaster." Hydraulic cement, the " Rosendale," made near Rondout, N. Y. Devonian.* Name from county Devon, in England. Distribution of Devonian rocks in North America. Geographic interpretation of this distribution. The rocks are sandstones, or shales, in New York and the Appalach- ians, but limestones in Ohio and Illinois. Thins out westward. Fossils. Brachiopods the most abundant fossils. Corals very large and abundant; reef forming. Vegetation very abundant. Fishes remarkable for numbers and size. Some Ohio fishes 18 feet long, 6 feet across head, and 3 feet through. Graptolites and cystids nearly extinct. First amphibians. t Economic products. Oil and gas of Pennsylvania and New York. Flagstones. Phosphates of Tennessee and Arkansas. Hydraulic limestones at Louisville, Ky. Carboniferous. Name from the coal it contains. The principal divisions are Permian, Coal Measures, Lower Carboniferous. LOWER CARBONIFEROUS. Beginning at the base the rocks of the Lower Carboniferous are mostly limestones, and contain marine fossils. The area of these rocks must, therefore, have been covered by the sea at the time of their deposition. Distribution of Lower Carboniferous rocks in North America. * Bui. no. 80, U. S. Geol. Surv. Devonian and Carboniferous. By H. S. Williams. Wash- ington, 1891. t O. C. Marsh. Am. Jour. Sei., Nov. 1896, CLII, 374. 309 310 PALEOZOIC PERIOD. Fossils. Crinoids very abundant; some rocks almost made up of the broken stems. Corals and brachiopods abundant. Bryozoa; Archimedes. Some amphibians. Trilobites decline. Economic products. Salt brines, Michigan. Marble of Tennessee and Arkansas. Building-stones of Indiana.* COAL MEASURES, OR CARBONIFEROUS PROPER. Rocks are conglomerates, sandstones, shales, and coal. These rocks have a total thickness of 16,000 feet in Nova Scotia; 23,780 feet in Arkansas. No definite order of arrangement over the whole area, but locally the order is constant. Examples : Pottsville conglomerate and Mauch Chunk red shale in Pennsylvania. Extent of the Coal Measures in North America. The abundance of coal, and of fossil plants, show that the land was covered by extensive marshes for long periods. The occurence of marine fossils, interstratified with coal beds, shows that the land occasionally sank beneath the sea. The carbon in the coal is derived from the atmosphere. Atmosphere not necessarily heavily charged. t Carbon from rocks constantly renewing it. Fossils. Plants are most abundant ; well preserved in the clays underlying the coal beds. Ferns, club-mosses, pines. Insects abundant ; cockroaches, neuropters. Spiders. Amphibians. Economic products. Coal most important. Beds vary from thin laminae up to 60 feet at Pottsville, Pa. Anthracite, bituminous, cannel. Iron ores. Fire-clays associated with coal. * Hopkins and Siebenthal. 21st ann. rep. Geol. Surv. of Indiana. Indianapolis, 1896. t Microscopical light in geological darkness. By E. W. Claypole. Trans. Am Micro- scopical Soc., 1897. President's address. 311 312 MESOZOIC PERIOD. PERMIAN. Named from the province of Perm, Russia. The division between the Carboniferous and Permian is not strongly marked in North America. Distribution of the rocks in North America. Retreat and shallowing of the Carboniferous seas. The existence of beds of salt in southwest Kansas shows that an arm of the sea was there cut off and dried up. The structure and distribution of the rocks show that there were great geographic changes in North America at the end of the Permian. Fossils. Crinoids much less abundant than in the Carboniferous. The few trilobites of the Permian disappear at the end of this period. First appearance of reptiles. Economic products. Gypsum and salt in Kansas. MESOZOIC PERIOD. The mediaeval period of the earth's history. The precise measurement of the length of the periods is not possible. The Mesozoic is divided into Triassic, Jurassic, and Cretaceous. Triassic.* Name derived from the German rocks, which consist of three marked sub- divisions. In England the climate is believed to have been arid and much of the country a desert.t In North America the Triassic beds are marine on the Pacific coast, fresh and salt lake deposits in the Rocky mountain region, and marine on the Atlantic coast. Distribution of the rocks. Red sandstones of Massachusetts. Connecticut, New Jersey, Pennsylvania, Maryland, Virginia, and North Carolina. Some coal beds in Virginia and North Carolina. Fossils. The fossils of the interior basin show the waters to have been fresh- water lakes. Those of the Pacific coast are marine. * Bui. 85, U. S. Geol. Surv. By I. C. Russell. Washington, 1892. t Nature, Oct. 19, 1899, p. 610. 313 314 MESOZOIC PERIOD. Cystids and blastoids had disappeared. Brachiopods had greatly declined. Pelycypods much more abundant than before. Cephalopoda greatly increased in numbers. Amphibia reached their greatest importance. Reptiles much more abundant. First appearance of mammals. Economic products. Gypsum and salt of the interior basin in Kansas. Coal beds of Virginia. Brownstone, so extensively used in eastern cities for buildings. Potomac marble of the Capitol columns at Washington. Jurassic. The name from the Jura mountains in Switzerland, which are of these rocks. No Jurassic rocks known in eastern North America. A mediterranean sea, or salt lake, in the Rocky mountains and Great Basin region. Marine deposits of California and Oregon. Fossils. Cephalopods culminate in the Jurassic. Reptiles were very abundant ; some of them winged ; many of enor- mous size. Earliest birds known ; toothed birds. Economic products. The gold veins of the Pacific slope are largely in Jurassic slates. These veins are not Jurassic in age, but were formed subsequently. Cretaceous. Name from Latin creta, chalk. The chalk deposits of England belong here. Distribution of Cretaceous rocks in North America. The geographic changes of the lower Mississippi valley, that preceded the deposition of the Cretaceous beds. Contraction of the seas. Some of the interior beds were deposited in fresh water; those of the coasts are marine. Fossils. The change among plants is most marked. Appearance of dicotyledonous plants, with representatives of oaks, maples, elms, etc. First palms known. Bony fishes very abundant. Crocodiles, mammals; some of the birds had teeth. 315 316 CENOZOIC PERIOD. Economic products. Greensand marls and potters' clays of New Jersey. Chalk deposits of Arkansas and Texas. Gypsum beds of Iowa.* Coal deposits of Puget Sound, Colorado, Utah, Wyoming, Montana, and New Mexico. In Colorado these coals are changed to anthracite. Auriferous conglomerates in northern California. CENOZOIC PERIOD. The Cenozoic rocks are known as Tertiary, and Quaternary, or Pleistocene. Mammals became the most important animals. Tertiary. Origin of the name: Paleozoic rocks formerly known as Primary; Meso- zoic as Secondary ; later ones as Tertiary. Name retained, though not used in its original sense. Divisions of the Tertiary: Eocene, Miocene, Pliocene. t 50% to 90% are Pliocene. Of living shells ] 30% are Miocene. ( 5% to 10% are Eocene. Distribution of the seas on the Atlantic and Pacific coasts; the interior basins. Fresh-water Pliocene beds of the Santa Clara valley resting on marine beds. The crustal movements of the Pacific coast. Warm climate of Tertiary times is indicated by plant remains as far north as Greenland. It has been suggested that the warm climate may have been due to the excess of carbon dioxide in the air.t Fossils. The Tertiary is known as the Era of Mammals; but the Tertiary mammals are all extinct. Some gigantic. Horses. Insects, beetles, butterflies. Conifers, palms. Birds abundant. It is thought that man began his existence in Tertiary times. (See refer- ences under Psychozoic.) * Gypsum deposits of Iowa. By C. R. Keyes. Iowa Geol. Surv., Ill, pp. 259-304. Des Moines, 1895. t Chamberlin. Jour. Geol., Sept.-Oct. 1898, VI, 618. 317 318 PSYCHOZOIC PERIOD. Economic products. Auriferous gravels of the Sierras. Diatomaceous earths of California and of Richmond, Va. Phosphate rocks of Florida and of South Carolina. Lignite of Arkansas, Texas, Mississippi, California, and Alaska. Iron ores. Petroleum in California. Greensand marls and potters' clay of the South. PSYCHOZOIC PERIOD. Pleistocene, or Quaternary. Man appeared during this period, or possibly even earlier.* Association with extinct mammals. The period was chiefly characterized by glaciers that covered a large part of northern Europe and the northern part of North America. Climate not necessarily very much colder; decrease of 5 in Europe would bring the glaciers of the Alps down to Geneva. Centers of distribution of ice. Area covered at the greatest development of the ice. (See Fig. 24, p. 92.) Evidences of glaciation ; direction of movements. Thickness of the ice. Withdrawal of the ice. Evidences of interglacial epochs. The Wabash drainage; Mohawk valley drainage; St. Lawrence drainage. Lake Agassiz and its history. Evidences of elevation and depression. Effect of glaciation on the topography. Effect of glaciation on man. Extinct gigantic mammals. t * On the Pithecanthropus erectus. By O. C. Marsh. Am. Jour. Sci., Feb. 1895, CXLJX, 144-147; June 1896, CLI, 476-482. t Mammoth and mastodon remains about Hudson Bay. By R. Bell. Bui. Geol. Soc. Am., 1898, IX, 369-390. 319 320 PSYCHOZOIC PERIOD. PRIMITIVE MAN.* Man probably originated in the tropics, where the climate is not severe, where fruits, nuts, and berries are to be found all the year round; and on the seashore, where fish, mollusks, and crustaceans may be had at all times for food. Deductions from zoology concerning man's character and appearance are matters of inference. Geologic evidences found in the rocks consist of 1. Works preserved. 2. Skeletal remains preserved. Nature of evidence of preserved foot-prints. On Carboniferous rocks on the Ohio river. On limestone at St. Louis, Mo.t At Pottsville, Pa.J On lava in Central America. HOMAN RELICS. It is to be expected that the oldest traces of man are in the form of re- mains, for the earliest men probably had no works of art. Character of the relics. 1. Flint implements: arrow-heads, knives, spears, chips. Rejects. Cactie forms. Specialized forms. Methods of manufacture. || Quarries.1I 2. Stone axes, pestles, mortars. 3. Carvings on bones and rocks. 4. Bone and shell implements and ornaments. Needles and fish-hooks. 5. Pottery. 6. Stone structures. 7. Human bones. * The geological evidences of the antiquity of man. By Sir Charles Lyell. 3d ed., Lon- don, 1863. 2d Am. ed., Philadelphia, 1863. The origin of civilization and the primitive condition of man. By Sir John Lubbock. New York, 1871. Relation of primitive peoples to environment, illustrated by American examples. By J. W. Powell. Smithsonian report for 1895, pp. 625-637. Washington, 1897. Influence of environment upon human industries or arts. By Otis T. Mason. Smith- sonian report for 1895, pp. 639-665. Preadamites, or a demonstration of the existence of men before Adam. By A. Winchell. 5th ed. Chicago, 1890. the t Owen. \ On the Primitive man in the Somme valley. By W. Upham. Am. Geol., Dec. 1898, XXII, 350- 362. (Bibliography for France.) en. Am. Jour. Sci., 1842, XLIII, 14-32. the fossil foot-marks in the red sandstone of Pottsville, Pa. By Isaac Lea. Trans. Am. Phil. Soc., new ser., X, 307-318. Philadelphia, 1853. I Distribution of stone implements in the tide-water country. By W. H. Holmes. Am. Anthropologist, Jan. 1893, VI, 1-15. Wilson. Proc. A. A. A. Sci., vol. 47, p. 464. {Am. Anthropologist, 1895, VIII, 307. Indian jasper mines in the Lehigh hills. By H. C. Mercer. Am. Anthropologist, Jan. 1894, VII, 80-92. Flint implements from the Nile valley. Nature, April 19, 1900, LXI, 597. Haworth. Geol. Mag., Aug. 1901, VIII, 337-344; Jan. 1902, IX, 16-27. 321 322 PSYCHOZOIC PERIOD. Where these relics are found. 1. In caverns. Engis skull and bones, found beneath stalagmitic crust in cave near Liege, Belgium, associated with those of extinct animals. Neanderthal skull, in cave near Diisseldorf ; probably exceptional in character. In southwest France in cave with drawings of mammoth, etc. 2. In peat-bogs. Preservative action of the peat. 3. In river and lake beds. Draining of Haarlem lake 40 years ago; relics were found. The Calaveras skull in the auriferous gravels of California.* A human skull said to have been found under the lava cap of Table Mountain. Many human relics are reported from the auriferous gravels of California. 4. In the glacial drift and loess. In Europe man preceded the glacial epoch. t Evidence of his relations to the glacial epoch in North America is as yet somewhat doubtful.* 5. Shell heaps. Mounds of waste or kitchen-midden. Sites of ancient settlements. Castro mound ; similar heaps abundant in the Santa Clara valley and on the coast. 6. Burial mounds or cemeteries. Marajo burial mounds at the mouth of the Amazon, and the pot- tery from them. The ornaments developed by primitive man. Generalization. All the facts in our possession go to show that primitive man was a savage, and that his development in civilization and the arts has been a gradual one. * The auriferous gravels of the Sierra Nevada of California. By J. D. Whitney. 258-288. Cambridge, 1880,-McGee. Science, Jan. 20, 1899, IX, 104,-Blake. Jour. Geol., VII, 631-637. Hanks. San Francisco, 1901. t Man in relation to the glacial period. By Dr. H. Hicks. Nature, Feb. 24, 1898, LVII, t Holmes. Jour. Geol., 1893, I, 15-37, 147. Several papers in Proc. Am. Assn. Adv. Sci., 1897, XL VI, 344-390. Am. Anthropologist, N. S., I, 107-121, 614-645. Smithsonian report. for 1899, pp. 419-472. Wilson. Ann. rep. Smithsonian Inst., 1896, pp. 349-664. 328 324 GEOLOGIC TIME. Length of Geologic Time.* Difficulty of stating geologic time in years. Rate of the recession of waterfalls. Age attributed to the Falls of St. Anthony, Minnesota. Method of computation. t Efforts to compute the age of the Niagara gorge. t Uncertain elements in the computation. Varying thickness of the beds. Different heights of the falls. Different amounts and varying character of the water. Rate of weathering of cliffs. Rate of erosion and deposition. Rate of erosion over the Mississippi basin is 1 foot for 6,000 years. Ganges " " " 2,358 " Hoang-Ho " " " 1,464 " Rhone " " " 1,526 " Danube " " " 6,846 " Po " " " 729 " Mean rate of the six " " 3,000 " Ratio of sea-bottom to land is 145 to 52, or say 2.8 times as much water as land. The deposition of one foot of sediment would require 8,652 years. The whole of the sedimentary beds since Archaean would, at this rate, require 130 millions of years.|| Rate of cooling.^ Calculated from the rate of cooling rock, the age of the earth is esti- mated at 24 millions of years. geologic time. By H. L. Fairchild. Proc. Rochester Acad. Sci., 1894, Some geological evidence regarding the age of the earth. By J. G. Goodchild. Proc. Roy. Phys. Soc. Edin., 1896. XIII, 259-308. Geological biology. By H. S. Williams. 55-65. New York, 1895. Kelvin. Philosophical Mag., Jan. 1899, XLVH, 68-90. Am. Jour. Sci., Feb. 1899, pp. 160- 165. Science, May 12, 1899, p. 665. Chamberlin. Science, IX, 889-901; X, 11-18. Hunt. Geol. Mag., Mar. 1901, VIII, 125-128. Joly. Sci. Trans. Roy. Dublin Soc., 1899, VII, 44. Geol. Mag., Aug. 1901, pp. 344-350. Fisher. Geol. Mag., Mar. 1900, pp. 124-132. I Notes on subaerial erosion in the Isle of Skye. By Alfred Barker. Geol. Mag., Nov. 1899, pp. 485-491. t N. H. Winchell. The geology of Minnesota. II, 313-341. St. Paul, 1888. \ Niagara Falls and their history. By G. K. Gilbert. Physiography of the United States. 203-236. New York, 1897. (Brief bibliography.) | Nature, 1895, LI, 533-607. \ The age of the earth. By Clarence King. Am. Jour. Sci., 1893, CXLV, 1-20. On the age of the earth. Nature, Jan. 3, 1895, LI, 224-227, 438-440. Das Alter der Welt. Von S. Wellisch. Wien, 1899. Geikie. Science, Oct. 13, 1899, X, 513-527. Gilbert. Nature, July 19, 1900, pp. 275-278. Proc. Am. Assn. Adv. Sci., XLIX, 1-19. Joly. Geol. Mag., May 1900, VII, 220-225. Ackroyd. Geol. Mag . , Dec. 1901, VIII, 558-559. Very. Am. Jour. Sci., Mar. 1902, CLXIII, 185-196. e length of II, 263-266. 325 326 GEOLOGIC TIME. Rate of growth of corals and limestones. Estimates from the rate of deposition of limestones, etc., lead Mr. Goodchild to estimate the age of the earth since the beginning of Cambrian time at 704 millions of years. The estimates of the age of the earth since it was in a molten condition, stated in years, vary all the way from 3 million to 2,400 million years. " Time is as long as space is broad." 327 328 PHYSIOGRAPHY. PART IV. PHYSIOGRAPHY, OR TOPOGRAPHIC GEOLOGY.* Topographic Geology treats of the surface features of the earth in their relations to geology. Topographic forms are produced by constructive, destructive, and modifying agencies acting upon the rocks of the earth's crust. The forms may be classed as 1. The major relief, or the continental masses and ocean basins. 2. The minor relief, or the details of the topography. THE MAJOR RELIEF. The broad continental and oceanic features of the earth are due to vertical movements of large areas. These movements are very gradual. Theories of the causes of mass movements. 1. Loading and unloading. The theory of isostacy.t Adjustments must be slow.J * The physiography of the United States. By Powell, Shaler, Russell, etc. New York, 1897. Physiographic types. By Henry Gannett. Folio I, Physiography. Topographic Atlas of the United States. Washington, 1898. Penck gives a genetic classification of topographic forms on pages 14-17 of Die Geomor- phologie als genetische Wissenschaft. Sixth International Geographical Congress. London, 1895. See also the classification of geographic forms by genesis. By W. J. McGee. Nat. Geog. Mag., 1888, 1, 27-36. Earth sculpture, or the origin of land forms. By James Geikie. New York, 1898. Nature, Dec. 27, 1901, pp. 207-208. The physiography of Allegany county (Maryland). By Cleveland Abbe, Jr. Md. Geol. Surv. Allegany county, 27-55. Baltimore, 1900. The Appalachia region. By Bailey Willis. Md. Geol. Surv., vol. IV, pt. I, Nov. 1900, pp. 23-93. (Bibliography, p. 93.) Elementary physical geography. By W. M. Davis. Boston, 1902. An introduction to physical geography. By G. K. Gilbert and A. P. Brigham. New York, 1902. t For references and discussion, see Earth movements. By C. R. Van Hise. Trans. Wis. Acad. Sol., 1898, XI, 469-475. On some of the greater problems of physical geology. By C. E. Dutton. Bui. Phil. Soc. Wash., XI, 51-64. Washington, 1889. The great valley of California, a criticism of the theory of isostacy. By F. L. Ransome. Bui. Dept. Geol., Univ. Cal., I, 371-428. Berkeley, 1896. Wallace's Malay archipelago. 9, foot-note. London and New York, 1894. U. S. Coast Survey, 1894, pt. II, pp. 51-55. Washington, 1895. Dawson. Quar. Jour. Geol. Soc., 1888, XLIV, 815. Nature, July 16, 1896, LIV, 256. An hypothesis to account for the movements in the crust of the earth. By J. W. Powell. Jour. Geol., VI, 1-9. Chicago, 1898. Gilbert. Bui. Phil. Soc., XIII, 61-75. Washington, 1895. Bui. Geol. Soc. Am., 1893, IV, 179-190. t Coleman. Geol. Mag., Feb. 1902, p. 61. 330 THE MAJOR RELIEF. 2. Unequal contraction of the globe. Theory of the early cooling of the plateaus. Deeper cooling along depressions. Theory of differences of materials. Daubrde's experiments with rubber.* 3. Early tidal action. Tendency for early folds to be permanent. Ocean Basins. Relations of ocean basins to the life of the glohe.t Relations to land areas. Modification. By deposition 1. Of mechanical sediments. { 2. Of organic sediments. 3. Of eruptive materials. By elevation and depression. Probable instability of continents and ocean basins. Suggested by faunal migrations. Suggested by elevation of marine sediments, which is as great as the depths of the oceans. Mountains.il The great masses of mountain systems are due to deformation or differen- tial elevation, while the details of mountain sculpture are produced chiefly by erosion. Types of mountains. 1. Mountain chains. 2. Isolated peaks. Geikie's classification.^ 1. Original, or tectonic, mountains. Accumulations : volcanic ejectamenta, moraines, sands. Deformations : folds, faults, laccolites. 2. Subsequent, or relict, mountains. Those left by denudation. * Daubree. Geologic experimentale. 585. t J. P. Smith. Jour. Geol., 1895, III, 384-495. t Milne. Lon. Geog. Jour., 1897, X, 259-289. I References in Geikie's Text-book of geology. 3d ed., 1070. New York, 1893. Gilbert. Bui. Geol. Soc. Am., 1893, IV, 187. La question de la permanence ou de I'instabilite' des grandes depressions oc^aniques. Par F. Prien. Annales de Geographic, III, 173-182. Paris, 1893-94. II Die Hochgebirge der Erde. Von Robert von Lendenfeld. Freibunr, 1899. \ Mountains. Ey James Geikie. Scottish Geog. Mag., Sep. 1901, XVII, 449-459. 331 332 ' THE MINOR RELIEF. MOUNTAIN CHAINS. Theories of the origin of mountain chains.* 1. Arching of the rocks. (Deformation.)t 2. Rise of isogeotherms through sediments. 3. Outflows of lava. a. Due to relief of pressure by arching. b. Due to relief by tensile movements. The fusion point is lowered in both cases. 4. Permanency of folds, however produced. 5. Faults. Location of faults of California with reference to the Sierras and Coast ranges.* (See Plate XXV.) ISOLATED PEAKS. 1. Culminating points in mountain chains. 2. Constructed by volcanic ejectamenta. San Francisco mountains ; Flagstaff, Arizona. Jorullo, Mexico, made in a night (1,692 feet). 3. Mountains or peaks left by circumdenudation. Enchanted mesa and the buttes of that type. (See also page 48 and Plate XXIV.) MINOR RELIEF. Relief forms may be built up by construction, may be produced by some modification or superinduced structure, or they may be the results of destructive agencies acting upon land masses. The agencies may, therefore, be classed as constructive, modifying and de- structive. * The origin of mountain ranges. By T. Mellard Reade. London, 1886. Orographic geology, or the origin and structure of mountains. By G. L. Vose. Boston, 1866. Etudes des alignements. Par M. de Chancourtois. Congres Internal, de Geologic, 1878, pp. 43-52. plan of th The plan of the earth and its causes. By J. W. Gregory. Am. Geol., Feb. 1901, XXVII, 100-119; Mar. 190], pp. 134-147. Theory of the origin of mountain ranges. By J. Le Conte. Jour. Geol., 1893, I, 543-573. The tetrahedral earth and zone of the intercontinental seas. By B. K. Emerson. Bui. Geol. Soc. Am., 1900, XI, 61-106. t Willis. 13th ann. rep. U. S. Geol. Surv., pt. II, 249. t The great Sierra Nevada fault scarp. By H. W. Fairbanks. Pop. Sci. Monthly, Mar. 1898, LII, 609-621. I Voyage de Humboldt et Bonpland. Atlas pittoresque. 242-244. Paris, 1810. Plate XXV. Photograph of Dr. Drake's relief map of the State of California, showing the northwest-southeast axes of the valleys, partly due to faulting. 333 334 THE MINOR RELIEF. I. Constructive Agencies and the Forms They Produce.* Subaqueous forms. Widespread deposits. Deltas. (See page 52.) Bars. (See page 74.) Barrier beaches. (See page 76.) Spits. (See page 74.) Emergent forms . Transformation of deltas, bars,t barriers, and spits into dry land.* Case of Interlaken; Gulf of California. A delta on a rising shore. Silting up of fjords. Example: Oceanside, Cal- ifornia. Silting up of lakes; salt marshes and fresh- water marshes. Formation of storm beaches; coral islands. Subaerial forms. ^Eolian deposits. Volcanic ejectamenta. Cinder cones. Near Flagstaff, Arizo- na ; in San Bernar- dino county, Cal. Lava cones. Examples : Shasta ; Marysville buttes. Laccolitic mountains. || Lava sheets. Example : Wyoming, Idaho, etc. Calcareous and siliceous deposits formed by certain springs and streams. Alluvial cones. * The topography of Florida. By N. S. Shaler. Bui. Mus. Comp. Zool., XVI. Cambridge, 1890. t On the forms of certain deltas. Daly. Science, June 14, 1901, XIII, 952-954. t An interesting case, partly attributable to elevation and partly to emergence from delta accumulations, is that of the Isthmus of Suez filled in as a part of the Nile delta, and separating Asia from Africa. See Hull's Survey of western Palestine, 72. Beitriige zur Morphologie der Flachkiisten. Inaug. Diss. von Karl Weule. Weimar, 1891. Shore-line topography By F. P. Gulliver. Proc. Am. Acad. Arts and Sci., Jan. 1899, XXXIV, 151-258. I Fresh-water morasses of the United States. By N. S. Shaler. 10th ann rep. U. S. Geol. Surv., 261-339. Washington, 1890. The dikes of Holland. By G. H. Mathes. Nat. Geog. Mag., June 1901, XII, 219-234. || Geology of the Henry mountains. By G. K. Gilbert. The laccolitic mountain groups of Colorado, Utah, and Arizona. By W. Cross. 14th ann. rep. U. S. Geol. Surv. 157-241. Washington, 1895. Fig. 91. Sketch map showing the submerged and choked up valleys near Oceanside, California. 335 THE MINOR RELIEF. Folding. Faulting.* II. Deformation, or Modifying Agencies. III. Destructive Agencies. I. Atmosphere, by means of 1. Atmospheric moisture. 2. Winds. 3. Changes of temperature. II. Water in form of 1. Rain. 2. Springs. 3. Streams. 4. Waves. 5. Glaciers. 6. Tidal currents, t THE FORMS PRODUCED BY DESTRUCTIVE AGENCIES, AND THE FACTORS DE- TERMINING THEM. The forms produced by destructive agencies, other things being equal, depend upon several controlling factors, which may act alone or in combination.* CONTROLLING FACTORS. I. The character and alternation of the rocks. Erosion avoids the hard and seeks the softer rocks. Harder sandstones resist, and make ridges. Softer shales and clays yield, and make valleys. Soluble limestones are carried off in solution, leaving caves and sink-holes. In regions of alternate hard and soft beds, the topog- raphy is controlled more or less, according to cir- cumstances, by the difference in the resisting powers of the rocks. * Origin and structure of the Basin ranges. By J. E. Spurr. Bui. Geol. Soc. Am., 1901, The ranges of the Great Basin. By W. M. Davis. Science, Sept. 20, 1901, XIV, 457. Physiographic evidence of faulting. By W. M. Davis. Science, Sept. 20, 1901, XIV, 458- t Tidal erosion in the Bay of Fundy. By G. F. Matthew. Canadian Naturalist, new ser., 1881, IX, 368-373. J: Denudation with reference to ... configuration, etc. By A.' B. Wynne. Geol. Mag., IV, 3-10. London, 1867. Fig. 92. A smooth surface of alternate hard and soft (shaded) strata standing on end. Fig. 93. The same as Fig. 92 after being sub- jected to denudation. The streams follow the soft beds. 337 5 THE MINOR RELIEF. Influence of the varying character of sediments on the continuity of ridges and valleys. Origin of " pulpit rocks," "chimney rocks," "table rocks," "bottle rock."* (See Fig. 98.) Exceptional character of the Tepee buttes.t Fig. 94. Profile of bench-and-bluff topography yielded by alter- nate hard and soft beds. Fig. 95. A bluff of homogeneous soft with a single bed of hard rock. (Harris.) Fig. 96. Bench-and-bluff topography in a region of horizontal beds. (Simonds.) II. The geologic structure or position of the beds. Influence of the slope of the beds on the character of the topography. Topography of horizontal beds. Bench and bluff topography. (See Figs. 96 and 97.) Grand canon of the Colorado. Mountains and hills of circumdenudation.t Enchanted mesa. (See Plate XXIV.) Fig. 87. Diagram representing a section across an anticline, and showing the influence of the fold upon the topography. * Excellent illustrations by Gould in Trans. Kansas Acad. Soi , XVII, plates IX X XI Topeka, 1901. t Tepee buttes. By Gilbert and Gulliver. Bui. Geol. Soc. Am., 1895, VI, 333-342. t The Enchanted Mesa. By F. W. Hodge. Nat. Geog. Mag., VIII, 273-284. Washington, 339 Fig. 98. A " pulpit rock," left by the removal of the adjacent horizontal strata. (Hopkins.) 340 THE MINOR RELIEF. Fig. 99. Sketch map showing the relation of folded and denuded beds of rock to topography. (Means.) Topography of folded beds.* Arkansas, t Colorado. Seashore topography varying with the position of the beds in relation to the waves. Topography of eruptive dikes.* Influence of dip on the lateral movements of streams. (See page 354.) III. Jointing or fracturing of the rocks. Influence of lines of weakness produced by joints and other breaks. Zig-zags of Cheddar gorge. H IV. The slope, of the land surface. The transporting power of a stream varies with the sixth power of the velocity. Velocity is determined by the slope. It follows that the rate of cutting is determined by the slope. Influence of settling basins on the work of streams. Examples : Great Lakes and the St. Lawrence. * Manual of coal and its topography. By J. P. Lesley. Philadelphia, 1856. Some illustrations of the influence of geological structure on topography. By Benjamin Smith Lyman. Jour. Franklin Inst., May 1898, CXLV, 355-360. t Physiographic geology of western Arkansas. By Arthur Winslow. Bui. Geol. Soc. Am., 1891, II. 225-242. 1 Spanish Peak folio, U. S. Geol. Surv., no. 71. I Dutton's High plateaus of Utah. Plate VII, 253; plate X, 280. Washington, 1880. Daubre'e's Geologic experimentale. 300-374. Paris, 1879. Erosion forms in Harney Peak district, South Dakota. By E. O. Hovey. Bui. Geol. Soc. Am., 1899, XI, 581-582. | Callaway. Geol. Mag., Feb. 1902, IX, 67-69. 341 342 THE MINOR RELIEF. Fig. 100. The " hogbacks " at Morrison, Colorado. The Rocky Mountain range is on the right and the rocks dip eastward away from it. V. Climatic conditions. Minor topographic features mostly carved by water. Regions without water subject to little or no change from this cause. Blown sands of arid regions. Origin of "hog- wallows."* Effect of frost and moisture on rocks easily disintegrated. Example : " Knobstone " of Indiana has gentle slopes facing south- ward. Deserts.t VI. Interruptions in development. The process of topographic development may be hastened, retarded, or entirely changed, by 1. Landslides damming up streams and shifting divides. 2. Faults across streams producing falls, cataracts, or lakes. Examples: American valley, Calaveras valley, Sierra valley. 3. Lava flows damming streams, and diverting the old, or imposing a new drainage. * Turner. 17th ann. rep. U. S. Geol. Surv., part I, 681-684. Washington, 1896. J. Walther. Die denudation in der Wiiste. 377. Leipzig, 1891. Hog-wallows, or prairie mounds. By J. Le Conte. Nature, Apr. 19, 1877, XV, 530-531. Across the Vatna Jokull. By W. L. Watts. 76. The hillocks, or mound formations, of San Diego, California. By G. W. Barnes. Am. Nat., Sept. 1879, XIII, 565-571. t Lapparent. Annales de Geographic, V, 1-14. Paris, 1895-96. 344 THE MINOR RELIEF. 4. Glaciation filling old depressions, scooping out basins, and com- pelling a new drainage.* Moraines damming water in valleys. Donner lake. Seattle lake. Kettle moraine region of Wisconsin and Minnesota. 5. Depression carrying the region beneath the sea. The origin of fjords and harbors.t VII. The primitive drainage. Sinking of land beneath the sea, and the deposition of new beds upon the old topography. When such areas are re-elevated the drainage of the new surface is determined by general slope and local accidents. Cutting their channels downward, the streams reach and uncover the buried topography. The channels are already determined, however. Such drainage is said to be superimposed. In the main, it is often quite independent of the geologic structure in which it ultimately flows. There is a tendency, however, for such drainage to come more and more under the influence of the geology. VIII. The length of time the region is exposed to erosion. Erosion attacks all land surfaces. It follows that the longer these surfaces are exposed to erosion, the more they are eroded. Topography of any area, therefore, changes constantly. Cfl B S C ^ J Fig. 101. Diagrams illustrating the structures shown by the wearing down of an overturned anticline. (Ashley.) * Glacial origin of certain lakes of Switzerland. By A. C. Ramsay. Quar. Jour. Geol. Soc., 1862, XVIII, 185-204. Physical geology and geography of Great Britain. By Sir A. C. Ramsay. 8th ed., 264- 275. London, 1894. Glacial erosion. By W. M. Davis. Proc. Boston Soc. Nat. Hist., XXII, 19-58. Boston, 1884. t The geological history of harbors. By N. S. Shaler. 13th ann. rep. U. S. Geol. Surv., part II, 93-209. Washington, 1893 Topographisch-geologische Studien in Fjordgebieten. Von Otto Nordenskjold. Bui. Geol. Inst., Univ. Upsala, 1899, IV, 157-226. Upsala, 1900. On the physical history of the Norwegian fjords. By E. Hull. Geol Mag., Dec. 1901, VIII, 555-558. 345 346 VALLEYS. Waterfalls are new topographic features, and must disappear in time. In general, there is a tendency to smooth down irregularities, and to reduce all to a common low level. Peneplains or base-levels of erosion.* The geographical cycle.t IX. The nature and working methods of the eroding agency. Erosion is done mostly by water and ice in motion. Erosion done by water tends to cut deep, narrow gullies and gorges on the land, and to undercut sea and lake shores, and to spread out silts over flood-plains and sea-bottoms. Erosion by ice tends to round off small surface irregularities, while its load is left in the form of moraines. Erosion in arid regions by isolation and deflation 4 Valleys. General forms. 1. V-shaped and inverted-A-shaped. 2. U-shaped. 3. With gently sloping sides. VALLEY-FORMING AGENCIES. 1. Erosion. Most of our narrow valleys, canons, gulches, gorges, ravines, etc., have been made by this agency. These are mostly steep-sided. Examples : Yosemite, Tuolumne, Colorado. The U-shape of valleys often attributed to ice action. || 2. Folding. Example : Lackawanna-Wyoming. 3. Faulting.^ Examples: northern California and Oregon Coast ranges and their paral 1 el valley s . (See Plate XXV . ) Valleys are not always washed out along fault-lines. 4. Building up the sides. Such valleys lie between volcanic mountains. Examples: central France; Hawaii. Construction by moraines. Seattle and Tacoma maps. * Tarr. Am. Geol., June 1898. Daly. Am. Nat., Feb. 1899, XXXIII, 127-138. Davis. Am. Geol., Apr. 1899, XXIII, 207-239. - Jour. Geol., 1902, X, 77-111. Shaler. Bui. Geol. Soc. Am., 1899, X, 263-276. t Davis. International Congress of Geography. Berlin, 1900. t Earth sculpture. By James Geikie. 250-265. New York, 1898. I The Pleistocene geology of the ... Yosemite Valley. By H. W. Turner. Proc. Gal. Acad. Sci., 3d ser., I, 261-321. San Francisco, 1900. II Die Hochketten des nordamerikanischen Felsengebirges u. der Sierra Nevada. Von Dr. E. Deckert. Sonder-Abdr. a. d. Zeitsch. der Gesells. f. Erdkunde zu Berlin, Mar. 1901, XXXVI, 162. \ Valleys and their relations to fissures, fractures and faults. By G. H. Kinahan. Lon- don, 1875. The rift valleys of eastern Sinai. By W. F. Hume. Geol. Mag., 1901, VIII, 198-200. 347 348 Fig. 103. The glaciated narrow canon of the Tuolumne river west of Poopenaut valley, Sierra Nevada Mountains. (Turner.) Fig. 103. Profile of the glaciated gorge between the Camp Bird mine and Ouray, Colorado. (Purdue.) 349 Fig. 104. Profile of the Animas canon below Silverton, Colorado. This gorge was filled with ice during the glacial epoch. (Maofarlane.) H-J- Fig. 105. Profile of the V-shaped Animas canon two miles below Silverton, Colorado. (Macfarlane.) 350 LAKES. AGENCIES MODIFYING VALLEYS. I. Ice erosion and moraines. Examples: Yosemite, Lackawanna. II. Filling in when dammed up. Examples: Calaveras, American, Sierra. Lakes.* Lake basins originate in some of the following ways : 1. Scooping out of basins by glaciers. t 2. Damming back the waters by a. Landslides. t b. Existing glaciers. v c. Moraines left across valleys. Lake Chelan in northern Washington is 50 miles long, and from a half to one mile wide, 1,400 feet deep in the mid- dle, is dammed at its lower end by a moraine. || Moraine-dammed lakes in Norway. if d. Igneous outflows across the drainage. Nicaragua.** Tahoe.tt e. Faults rising across the drainage. /. Shore accumulations, or cordon littoral.tt g. Sand-dunes. * Les lacs de Jura. Par Ant. Magnin. Ann. de G6og., 1894, III, 213-226. Lakes of North America. By I. C. Russell. Boston, 1895. The English lakes. By H. R. Mill. Geog. Jour., July-Aug. 1895. Present and extinct lakes of Nevada. By I. C. Russell. Physiography of the United States, 101-136. New York, 1897. Jour. Geol., 1896, IV, 647-648. An account of the researches relating to the Great Lakes. By J. W. Spencer. Am. Geol., Feb. 1898, XXI, 110-123. The formation and deformation of Minnesota lakes. By C. W. Hall. Science, 1893, XXI, 314. Les lacs francais. Par Andre Delebecque. Paris, 1898. The scientific study of scenery. By J. E. Marr. 158-202. London, 1900. t On the origin ... of the basins of the Great Lakes. By J. S. Newberry. Proc. Am Phil. Soc., 1882, XX, 91-101. Spencer. Quar. Jour. Geol. Soc., 1890, XLVI, 523-533. Bonney. Geol. Mag., Jan. 1898, pp. 15-20. Parkinson. Geol. Mag., Mar. 1901, VIII, 97-101. Winchell. Bui. Geol. Soc. Am., 1901, XII, 109-128. 1 Topographic features due to landslides. By I. C. Russell. Pop. Sci. Monthly, Aug. The landslip at Gohnah, India. Nature, July 5, 1894, L, 231-234, 428, 501. 2 Russell. 13th ann. rep. U. S. Geol. Surv., pt. II, 76-80. || Henry Gannett. Nat. Geog. Mag., Oct. 1898, IX, 417-428. H Monckton. Geol. Mag., Dec. 1899, pp. 533-540. ** Geology of Nicaragua canal route. By C. W. Hayes. Bui. Geol. Soc. Am., X, 340. ft Lindgren. Folio 39, U. S. Geol Surv., 1897. Jour. Geol., 1896, IV, 895. n Les lacs francais. Par Andre Delebecque. Plates XVII, XVIII, XIX, 280-284. Paris, 351 352 STREAMS. 3. Cutting off of basins by silting up. Examples: Saltonlake;* Interlaken, Switzerland ; Vale of Kash- mir.f 4. Shifting of streams. Ox-bows of the Mississippi river. 5. Orographic movements. fi. Depressions caused by solution of rocks. Sink-holes and ponds of limestone regions of Tennessee, Kentucky, etc. 7. Extinct craters. Crater Lake, Oregon.* West side of Mt. Hood. Generalization: lakes are temporary features, and are constantly being formed and obliterated. Streams and Their Changes.^ The age of streams. Newer than the beds over which they flow. Importance of initial conditions. Consequent streams. Streams whose positions are determined by the slope of a new surface. Subsequent development depends chiefly upon the geology. Regions of horizontal rocks. Regions of folded rocks. Influence of rock joints. || Shifting of channels due to dip. (See Figs. 106 and 107.) Shifting of channels due to choking by debris. If * Sal ton Lake. By E. B. Preston, llth ann. rep. State Mineralogist of Cal., 387-393. Sacramento, 1897. t Climbing and exploration in the Karakorum-Himalayas. By W. M. Conway. 37. New York, 1894. t Crater Lake, Oregon. By J. S. Diller. Nat. Geog. Mag., VIII, 33-48. Smithsonian rep. for 1897, pp. 369-379. Science, Feb. 7, 1902, pp. 203-211. Mazama. I, 139-393. Crater Lake number. Portland, Or., 1897. On the physical features of the Valley of the Colorado. Part II, 147-214, of The explora- tion of the Colorado River of the West. By J. W. Powell. Washington, 1875. The rivers of northern New Jersey. By W. M Davis. Nat. Geog. Mag., II, 81-110. Wash- ington, 1890. The rivers and valleys of Pennsylvania. By W. M. Davis. Nat. Geog. Mag., I, 183-253. Washington, 1889. Lecons de geographic physique. Par A. de Lapparent. 109-130. Paris, 1896. Drainage modifications and their interpretation. By M. R. Campbell. Jour. Geol., 1896, How rivers work. The physical geography of New Jersey. By R. D. Salisbury. 70-82. Trenton, 1898. Rivers and river valleys. Aspects of the earth. By N. S. Shaler. 143-196. New York, River adjustments in North Carolina. By W. J. Weaver. Jour. Elisha Mitchell Sci Soc., 1896, pp. 13-24. Rivers of North America. By I. C. Russell. New York, 1898. I The river system of Connecticut. By W. H. Hobbs. Jour. Geol., Sept.-Oct. 1901, IX, H Davis. Bui. Mus. Comp. Zool., XXXVIII, Geol. series, V, 135. Cambridge, 1901. 353 354 Fig. 106.-A smooth surf ace of hard and soft (shaded) inclined beds. Fig. 107. The same as Fig. 106 after being subjected to erosion. The streams follow the soft strata. Fig. 108. A region of folded bed streams follo Superimposed streams. Superimposed streams have cut down from initial conditions that were developed regardless of the present structure. Example : southArkansas. Antecedent streams. Antecedent streams are those that hold and cut their way through obstacles rising across their courses. New cycles of erosion are brought about by interruptions of a system of drainage. The winding of upland streams. Superimposed ; developed drainage.* The winding of lowland streams. Stream capture. TERRACES, t Terraces may be produced by 1. The cutting of waves along a shore. i 2. The cutting of a meandering stream. Why the highest terraces are the oldest. Why stream terraces are often in pairs. 3. The differential resistance (to eros- ion) of horizontal beds (rock ter- races). 4. Streams truncating alluvial cones. Examples: in New Mexico and Arizona. 5. Faults producing step-like terraces. 6. Chemical or organic deposits, such as marls or spring deposits. || * A. Winslow. Science, 1893, XXIII, 312. C. F. Marbut. Am. Geol., Feb. 1898, XXI, 86-90. t Geographical development of alluvial terraces. By R. E. Dodge. Proc. Boston Soc. Nat. Hist,, 1895, XXVI, 257-273. Ohio terraces. Am. Geol., 1896, XVIII, 227. Russell. Am. Geol., Dec. 1898, XXII, 362. H. H. Smith. Brazil, the Amazon, and the coast. 631-632. New York, 1897. I Raised shore-lines on Cape Maysi, Cuba. By O. H. Hershey. Science, Aug. 12, 1898, VIII, 179-180. Hill. Nat. Geog. Mag., IX, 242. A. Agassiz. Nat. Geog. Mag., IX, 200, 208; Bui. Mus. Comp. Zool., XXVI, 4-5, 109-113, 116-117, 120, 130. Cambridge, 1894. The topographic features of lake shores. By G. K. Gilbert. 5th ann. rep. U. S. Geol. Surv., 69-123. Washington, 1885. \ Shaler. Am. Jour. Sci., Mar. 1887, p. 210. Gulliver. Bui. Geol. Soc. Am., Jan. 1900, X, 492-495. | The origin of travertine falls. Science, Aug. 2, 1901, XIV, 181-185. with the ing the soft and avoid- the hard ones. Fig. 109. A meandering upland stream cutting homogeneous rocks and becoming more and more crooked. 355 356 TOPOGRAPHY. ISLANDS. (] T-V . t - ( When the sea encroaches on the land, leaving I resisting points. , ! < Sediments deposited by tides, currents and Islands of < Construction 3 gtreams I Emergence Igneous; orographic movements. V Submergence Subsidence leaves isolated peaks as islands. Effects of Topography upon Civilization.* Relations of topography to 1. Political boundaries. 2. Harbors and marine industries. t 3. Location of cities and manufactures.* 4. Art. Scenery. 5. Agriculture. 6. Literature.il TOPOGRAPHIC MODELS OR RELIEF MAPS. IT Uses. Methods of construction. Materials of the originals. Materials used for the finished map. The question of the vertical scale. * Nature and man in America. By N. S. Shaler. New York, 1891. t The geological history of harbors. By N. S. Shaler. 13th ann. rep. U. S. Geol. Surv., part II, 93-209. Washington, 1893. 1 McGee. Am. Jour. Sci., 1890, CXL, 16. \ The scenery of Switzerland and the causes to which it is due. By Sir John Lubbock. New York, 1896. Tauchnitz edition, Leipzig, 1897. The scenery of England. By Lord Avebury. New York, 1902. The scenery of Scotland viewed in connection with its physical geology. By A. Geikie. London, 1865. 2d ed., London and New York, 1887. 3d ed., London, 1901. Landscape geology: a plea for the study of geology by landscape painters. By Hugh Miller. Edinburg and London, 1891. The scientific study of scenery. By J. E. Marr. London, 1900. I Types of scenery and their influence on literature. By Sir Archibald Geikie. London, 1898. H Topographical and geological modeling. By O. B. Hardin. Trans. Am. Inst. Min. Eng., X, 264-267. The construction of maps in relief. By John H. and E. B. Hardin. Trans. Am. Inst. Min. Eng., XVI, 279-301. Topographic models. By Cosmos Mendeleff. Nat. Geog. Mag., I, 254-268. Washington, Relief maps. By Marcus Baker. Bui. Phil. Soc. Wash., XII, 349-368. Washington, 1894. 357 359 360 361 362 INDEX. INDEX. Abrasion, 40. Acid rocks, 222. Acids, effect of, 114, 180. Acrogens, age of, 300. yEolian rocks, 18. Age of the earth, 324. of faults, 268. of topography, 344. Agencies, 10. Agriculture, influence of glacia- tion on, 104. Algge, 184, 196. Alkali, 26. Alkaline lakes, 130. Alluvial soils, 26. Alteration of rocks, 272-280. Alternation of rock beds, 218. Amphibians, age of, 300. Andesite, 222. Animals, distributed by wind, 14. hasten rock decay, 180. man's influence on, 206. rocks made by, 196. Anthracite, 186, 188. Anticlines, 254-256. Ants, 182. Aqueous agencies, 36, 54. Archaean, 302. Arches, natural, 122. Architecture and glaciation, 100, 104. Arenaceous deposits, 212. Argillaceous deposits, 212. Aridity, 126. Artesian wells, 286. Ashes, volcanic, 144, 146. Asphaltum, 186. Atmospheric agencies, 12, 20, 32. Axes of folds, 252. Bamboos protect land, 184. Banks, submarine, 70. Bars, 52, 74. Basalt, 222-224. Basaltic columns, 234. Base-level, 50, 346. Basic rocks, 222. Beach cusps, 72. Beaches, 70. barrier, 76. Bedded deposits, 232. Bedding, 214. Belt series, 304. Bench and bluff topography, 338. Bitter lakes, 130. Bituminous coal, 188. Blow-holes, 58. Blowing caves, 120. Borax lakes, 130. Bore, 62. Boring mollusks, 172, 182. "Bottle rocks, "338. Boulder-clay, 94. Boulders, glacial, 88, 92. of decomposition, 22. origin of, 40, 62. Breccia, 212. Bryozoa, 202. Building-stones, 302, 308, 310, 314. Buried valleys, 174, 334. Buttes, origin of, 332, 338. Marysville, 152. 363 Calcareous deposits, animal, 196. deposits, plant, 196. Cambrian, 304. Canons, 48. Carbon dioxide in air, 192. in wood, coal, etc., 186. Carbonaceous deposits, 184. Carbonic acid in water, 114. Carboniferous, 308. Caves, 64, 118. Cenozoic period, 316-318. Chalk, 202, 212. Change of level, 170; see Elevation. of temperature, 20. Chemical agencies, 114-134. deposition, 122. erosion, 114-122. Chert, 202. Chimney rocks, 338. Cinders, volcanic, 44, 212, 224. Circumdenudation, 332, 338. Cities buried, 210. Civilization and topography, 356. Clay, boulder, 94. carried in water, 40, 44. causing landslips, 38. origin of, 116, 134. potters', 316. same as slate, 212. Cleavage, 240. Cliff dwellings, 120. Climate, 32, 56. Coal, anthracite, 186, 188. area of, 190. bituminous, 186, 188. measures, 310. origin of, 192. Column, geologic, 300. Concentric staining, 246. Concretions, 242. Cone-in-cone, 246. Conformity, 216. Conglomerate, 178. Consequent streams, 352. Constructive work of seas, 68. agents, 184, 196, 334. Contact metamorphism, 274. Cooling of eruptives, 148, 220, 222. Copper in drift, 98. Coquina, 202. Coral reef, fossil, 200. reefs, 196-202. Corals, 174. Corrasion, 42. Correlation, 296. Country rock, 234. Cracks, 226-228. Crater lake, 352. Craters, 142. Creep, 256. Cretaceous, 314. Crevasses, 86. Crevices, 226-228. Crystallization, 274. Currents, ocean, 56. stream, 44. tidal, 68. transporting power, 44. Cusps, 72. "Cut-offs, "40. Cuyahoga, 98. Cycle, geographic, 354. Data of geology, 6. Date of glaciation, 106. Death Gulch, 142. Decay of rocks, 22, 116. Decomposition, boulders of, 22. Deformation, 336. Dehydration, 280. Deltas, 52, 76. Deluge, 168. Denudation, 38, 50. Deposition, chemical, 122. by glaciers, 90. by streams, 50. by wind, 16. in seas, 68. rate of, 324. Deposits, calcareous, 196. by man, 210. carbonaceous, 184. 364 INDEX. Deposits, ferruginous, 194. nitrogenous, 194. organic, 184. phosphatic, 204. plant, 184. siliceous, 194. spring, 122. sulphurous, 194. Depression, 174, 248. Depth of borings, 138. of seas, 54. Devonian, 308. Diamonds, 192. Diatoms, 194. Dikes, 152, 224. sandstone, 238. Dip, 256. Discharge of streams, 46. Disintegration, 20-24. Displacement of rocks, 248, 266. Distribution of plants, 14. of animals, 14. of volcanoes, 150. Dolomitization, 280. Dormant volcanoes, 152. Drainage, affected by glaciation, 102. primitive, 344. Drift, 86, 92. Driftless area, 94. Drift-timber, 192. Dunes, 16, 210. checked, 184. Dust-storms, 12. Dynamical geology, 10. Earth, interior of, 136. pillars, 34. Earthquakes, 162-170. Efflorescence, 26-30 Elevation and temperature, 82. and depression, 170. evidences of, 170-174. Emergent forms, 248-334. Enchanted mesa, 338. Eocene, 316. Epicentrum, 164. Erosion, chemical, 116. general, 38. glacial, 90. rate of, 46, 324. stream, 38. valleys of, 346. wave, 66. wind, 14. Erratics, 88, 92. Eruptions, volcanic, 140. Eruptive rocks, see Igneous. Evaporation, 26. Exfoliation, 22, 246. Expansion of rocks, 22. Extermination, 208. Extinct volcanoes, 152. False bedding, 216. Faults, 178, 262-271. by earthquakes, 166. normal, 262. reversed, 264. shear, 266. valleys formed by, 346. Faunas, influence of glaciation on, 102. influence of oceans on, 56, 330. Feldspar, 116. Ferruginous deposits, 194. " Finger lakes," 104. Fishes, age of, 300. Fissures by earthquakes, 166. Fjords, 176. Flagstone cleavage, 240. Flint, 202. Floating stones, 46. Flocculation, 78. Floe-ice, 112. Flood-plains, 50. Flow, laws of, 44. Focus of earthquake, 164. Folds, 248, 252. forming valleys, 346. Footprints, 218. Foot-wall, 234. INDEX. 365 Foraminifera, 202. Forests, man's influence on, 206. protection by, 184. Fossils, defined, 292. uses of, 292. Freezing, 24. Fret-work, 26-28. Frost, 24. Fulgurite, 246. Fusion of rocks, 138. Gangue, 234. Gas, 306, 308. volcanic, 142, 144. Geodes, 226, 242. Geologic column, 300. Geology, 6. Geysers, 158-162. Glacial epoch, 94-110. epoch, causes, 108, 110. epoch, date of, 106. soils, 104. streams, 90. Glaciation in North America, 94, 104. influence of, 100-104. Glaciers, 82-112. advance and retreat of, 92. erosion by, 90. movements of, 84. origin of, 82. theories of, 106. work of, 90. Gletscher-milch, 90. Gneiss, 222. Gold, placer, 234. Gorges, 48. Grand cafion, 48. Granites, 222, 302. Graphite, 192, 302. Gravel, 212. Gravity faults, 262. Guano, 204. Gulf stream, 32, 56. Gullies, 40. Gypsum and salt, origin of, 128. Gypsum, bedded, 232. cleavage, 240. occurrence of, 308, 312. Hail, 34. Hanging-wall, 234. Harbors, 74, 334. Hardening of rocks, 218. Hills, anticlinal, synclinal, 262. Historical geology, 290. Hog-wallows, 20. Horse, 234. Hot springs, 162. springs deposits, 162. waters, 132. Human records, 174. relics, 320. Humic acids, 114. Hydration, 280. Ice, 82-112. Icebergs, 112. theory, 106. Ice-cap, 96. Ice caves, 120. Igneous agencies, 136. rocks, 156, 220. Inclusions, 144. Insects, burrowing, 182. distributed, 208. Interior of the earth, 136-140. Intrusions, 222. Invertebrates, age of, 300. Iron ores, 302, 310, 318. "Iron pots," 242. Iron-sands, 226. Islands, 356. Isoclinal ridges, 262-264. Isostacy, 248, 328. Jasper, 198, 212. Joints, 168, 234, 340. Jura mountains, 94, 314. Jurassic, 314. Kaolin, 116, 134. Kettle-holes, 92. 366 INDEX. Laccolites, 154, 224. Laccolitic mountains, 334. Lakes, 52, 350. alkaline, 130. aqueous agencies in, 52-54. bitter, 130. borax, 130. fresh-water, 52. geologic work of, 52. postglacial, 104. salt, 124-130. Laminae, 216. Landslides, 36, 168. Lapilli, 144. Lava, 148. ancient, 152. caves in, 120. cones, 146. sheets, 222. Lead, 306. Lenticular beds, 21f>. Levees, natural, 50. Lignite, composition of, 186. changes of, 188. occurrence, 318. origin of, 188. Limestone, caves in, 118. changes of, 212. origin of, 202. Lithodomus holes, 172, 182. Lobate glaciers, 98. Local metamorphism, 274. Lode, 226. Loess, 104. puppets, 242. Lower Silurian, 304. Major relief, 328. Mammals, age of, 300. Man as a geologic agent, 204. Manganese polish, see Chemical Deposition. Man, primitive, 320. epoch of, 300. and the glacial epoch, 108. influence on animals, 206. Man's influence on forests, 206. plants, 204. land, 208. Mangroves protect land, 184. Marble, occurrence, 302, 306. origin of, 212. Marl, 196. Marmarosis, 274. Mechanical aqueous agencies, 36- 80. Mesozoic, 312-316. Metamorphism, 272-278. local or contact, 274. regional, 276. Mineral veins, 224-234. Mining, influence of glaciation on, 104. placer, 234. risks of, 232. Minor relief, 332. Miocene, 316. Models, 356. Mollusks, boring, 172, 182. Monocline, 256. Moraines, 86, 92. Mountain chains, 332. laccolitic, 334. Mountains, 330. of circumdenudation, 332. Mud streams, see Landslips. Mud volcanoes, 150. Needle-ice, 24. Niagara, 102, 106. Nitric acid in rain, 114. Nitrogenous deposits, 194. Normal faults, 262. Obsidian, 148. Ocean basins, 330. currents, 32. effects of, 56. depth, 54. temperatures, 54. Oceans, mechanical work of, 54. Oil, origin of, 186. 367 Oil, occurrence of, 306, 308. Psychozoic period, 318. Oolites, 246. " Pulpit rocks," 338. Ooze, 212. Pumice, 144. Orbicular granite, 246. Ordovician, 304. Quartzite, 212. Ores, origin of, 226-230. Quaternary, 318. Organic acids, 114. agencies, 180-204. Rain, 36. Outcrop, 252. Rain-prints, 218. Overloading, 52. Red Sea, 126. Overturn, 258-262. Reefs, coral, 196-202. " Ox-bows," 40, 50. stone, 124, 220. Oxygen in wood and coal, 186. Regelation theory, 86. Regional metamorphism, 276. Paleontology, 290-322. Relief, topographic, 328. Paleozoic period, 304-312. maps, 356. Peaks, volcanic, 144. Replacement, 280. isolated, 330. Reptiles, age of, 300. Peat, 186. Residuary products, 134. Peat-bog, bursting of, 186. soils, 24. Pebbles, 40, 42. Retreat of ice, 98. Peneplain, 50, 346. Reversed faults, 264. Permian, 312. Ripple-marks, 216. Petrified wood, 194. Rivers, 352. Petroleum, 186, 306, 308. Roads, relation to glaciation, 104. Pholad borings, 172, 182. Roches moutonn6es, 92. Phospbate deposits, 204. Roots of plants, 180. Physiography, 328-356. Pisolites, 246. Saddle reefs, 248. Placer deposits, 234. St. Anthony's falls, 106. Plants distributed by wind, 14. Salt, 128. man's influence upon, 204. lakes, 124. hasten rock decay, 180. occurrence of, 308, 310. preservative work of, 184. Salton lake, 128. Plant deposits, 184. Sand grains, 44. Pleistocene, 318. grains, abrasion by, 14, 40. glaciation, 94. Sand-dunes, 16. Pliocene, 300, 316. Sandstone, 212. Plutonic rocks, 222. seolian, 18, 212. Polishing by ice, 88. dikes, 238. Pororoca, see Bore. reefs, 124, 220. Porosity of rocks, 282. Sand-storms, 12. Pot-holes, 40, 42, 104. Scenery, 356. Primitive man, 320. Schistosity, 240. Protective agents, 184. Schists, 278. Pseudomorphs, 280. Sea-caves, 64. INDEX. Seas and oceans, 54-80. mechanical work of, 58. Sea-urchins, 180. Sedimentary rocks, 212-220. Sediments, 50, 70. Seismograph, 166. Seismology, 162. Serpulje, 202. Shale, 212. Shear faults, 266. Shingle, 212. Shore forms, 66. Shrinkage, 226. Siliceous deposits by animals, 202. deposits by plants, 194. Silicified wood, 194. Silurian, 306. Sink-holes, 120. Slate, 212. Slaty cleavage, 240. Slickensides, 268. Snow, 82. Snow-line, 82. Soda, 130. Soil, cultivation by man, 210. from volcanic rocks, 156. glacial, 104. origin of, 24. Solution, chemical, 114. Sounds by earthquakes, 166. South American glaciation, 106. Spheroidal weathering, 22. Spits, 52, 74. Sponges, 184, 202. Spray, 62. Springs, 282. deposits, 122. hot, 162. Stalactites, 122. Stalagmites, 122. Stone reefs, 124, 220. Storm beaches, 72. Stratified rocks, 212. Stratum, defined, 214. Streams and their changes, 352. glacial, 90. Streams, matter in, 46. work of, 38. Striae, 88. Strike, 256. Structural features, 234. geology, 212-288. Stumps, 174; see Wood. Stylolite, 246. Subaqueous forms, 334. Subaerial forms, 334. Subglacial streams, 90. Subjective phenomena, 8. Submarine banks, 76. volcanoes, 148. Submerged valleys, 174. Subsidence of coral reefs, 174. Sulphurous deposits, 194. Sun-cracks, 218. Syncline, 254-256. Table rocks, 338. Talus, 26. Temperature, changes of, 20. effect of changes, 20-24, 34. decreases with elevation, 82. increases downward, 138. of seas, 54. Tepee buttes, 338. Terraces, 354. Tertiary, 316. Text-books, 4. Thickness of glacial ice, 98. of sediments, 176. Thrust faults, 264. Tidal waves, 62. Tides, 56. effect of wind on, 56. Till, 94. Tilting of rocks, 252. Timber, drift-, 192. Time, geologic, 324. Tin, 234. Topographic geology, 262, 328-356. Topography and glaciation, 102. and civilization, 356. Trachyte, 222. INDEX. Transportation, laws of, 44. by glaciers, 90. by seas and ocean, 68. by streams, 44. by wind, 12. marine, 68. Trap, 222. Travertine, 122. Trenton gravels, 108. Trenton rocks, 300, 306. Triassic, 312. Tripolite, 194. Tufa, 122. Tuff, 154, 224. Tumbleweed, 14. Unconformity, 21(5. Underground waters, 282. Undertow, 68. UnionidEe, 102. Unstratified rocks, 220. Valleys, 48, 346. Vegetation, influence of glaciation on, 102. Veins, 224. Velocity and transportation, 44. Volcanic ashes, 12, 144. eruptions, 140. gases, 142. rocks, 148. Volcanoes, 140-156. active, 140. distribution of, 150. Volcanoes, dormant, 152. mud, 150. submarine, 148. Wabash drainage, 102. Water, 32, 36. and life, 34. solvent power, 114. transporting power, 44. underground, 132. Waterfalls, origin of, 48. recession of, 324. , Water-hyacinth, 184. Water-level affected by wind, 30. Waves, 30, 58, 68. earthquake, 168. extraordinary, 62. tidal, 68. work of, 58. Wearing by wind, 14. Weathering, 280. Wells, 286. artesian, 286. Wind, effect on water-level, 30. effect on ocean currents, 32. transporting by, 12. wearing by, 14. bedding, 18. Wood, petrified, 194. Worms, 182. Wrinkles, 252. Yosemite Valley, 100. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles This book is DUE on the last date stamped below. NOV 2 3 NOV 7 1958 JUN 4 1965 Form L9-100m-9,'52(A3105)444 The RAFPH D. RKED LIBRARY UC SOUTHERN REGIONAL LIBRARY ''' "i 'i I',', ,';"'',',: A 000838442 2 V