[1] The Earth. Johnson’s Encyclopædia. See also statement of Murray in Smithsonian An. Rept., 1899, p. 312. Reprint from Brit. A. A. S., Dover meeting, 1899, and Scot. Geog. Mag., Vol. XV, 1899, p. 511.

[2] Its specific gravity as a whole is about 5.57, and the specific gravity of its outer portion is about 2.7.

[3] For an excellent study of the erosion, transportation, and sedimentation performed by the atmosphere, see Udden, Jour. of Geol., Vol. II, pp. 318–331. See also Pop. Sci. Mo., September, 1896.

[4] The Eruption of Krakatoa. Committee of the Royal Society, 1888.

[5] A brief account of the influence of the dust on sunsets is found in Davis’s Elementary Meteorology, pp. 85 and 119.

[6] Science, New Ser., Vol. IV, p. 816, 1896.

[7] Von Richtofen. “China.”

[8] Sketcherley and Kingsmill. Quar. Jour. Geol. Soc., Vol. LI, 1895, pp. 238–254.

[9] Chamberlin. Jour. of Geol., Vol. V, p. 795.

[10] A thoroughgoing study of the Formation of Sand Dunes (by V. Cornish) is to be found in the Geog. Jour., Vol. IX, 1897, pp. 278–309.

[11] Blanford. Geology of India, 2d ed., p. 455 et seq.

[12] Cornish, loc. cit.

[13] Cornish, loc. cit., p. 294.

[14] Diller states (17th Ann. Rept., U. S. Geol. Surv., Pt. I, p. 450) that on the coast of Oregon the slope of dunes is sometimes 40°.

[15] From folio preface, U. S. Geol. Surv.

[16] Credner. Elemente der Geologie, 6th ed., p. 271.

[17] Merrill. Rocks, Rock Weathering, and Soils, p. 295.

[18] Cowles. The Ecological Relations of the Vegetation of the Sand Dunes of Lake Michigan. Botanical Gazette, Vol. XXVII, 1899. An excellent study of the relations of sand dunes and vegetation.

[19] For example, in the Big Horn Mountains of Wyoming.

[20] It should be noted that it is the change of temperature of the rock surface, not the change of temperature of the air above it, which is to be considered. Many data concerning temperature changes are to be found in Bartholomew’s Atlas of Meteorology.

[21] Buckley. Wisconsin Survey, Bull. IV, 1899, pp. 81–3.

[22] Livingstone has reported that the temperature of rock surfaces in Africa sometimes reaches 137° Fahr. during the day, and cools sufficiently at night to split off blocks of 200 lbs. weight.

[23] Buckley. Surv. of Wis., Bull. IV, pp. 19, 20.

[24] For an excellent discussion of erosion in dry regions see Walther’s Die Denudation in der Wüste.

[25] On the assumption that condensation takes place at an average elevation of 3000 feet, it has been estimated that the force necessary to evaporate and diffuse the moisture which falls as rain and snow would be equivalent to 300,000,000,000 horse-power constantly in operation. (Strachey, Lectures on Geography, p. 145.)

[26] McGee. Bull. Geol. Soc. Am., Vol. VIII, pp. 87–112.

[27] For a discussion of convex and concave erosion slopes see Bain, Geol. Surv. of Ia., Vol. VI, p. 449.

[28] Great rivers, like the Mississippi, cut their channels somewhat below sea-level, but probably not by an amount exceeding the depth of the stream itself (see p. 79).

[29] Davis. Jour. of Geol., Vol. X, p. 87.

[30] Ibid., p. 77 et seq.

[31] In regions where canyons are common, the term is often applied to all valleys.

[32] Humphreys and Abbot. Physics and Hydraulics of the Mississippi River.

[33] From Russell’s Rivers of North America, p. 78.

[34] Alkaline carbonates considered as sodium carbonates.

[35] Carbonic acid by difference.

[36] Babb. Science, Vol. XXI, p. 343. 1893.

[37] Quoted by Mason. Water-supply, p. 204.

[38] Sot. Geog. Mag., Vol. III, p. 76. 1887.

[39] Acids and bases combined according to the principles indicated by Bunsen.

[40] Chemical Geology, Vol. I, pp. 76, 77, English ed., 1854.

[41] Allgemeine und chemische Geologie, Vol. I, pp. 456, 457. 1879.

[42] Russell. Rivers of North America, p. 79.

[43] For disastrous floods of the lower Mississippi, see Johnson, Bull. Geol. Soc. Am., Vol. II, pp. 20–25. For effect of precipitation and forests on floods, see Russell’s Meteorology, pp. 198–217, and Vermeule, Report on Water Supply, Geol. Surv. of N. J.

[44] An excellent discussion of this subject is given by Gilbert in The Henry Mountains, pp. 99 et seq., and more briefly in the Am. Jour. Sci., Vol. XII, p. 85 et seq. 1876.

[45] Jour. of Geol., Vol. IV, p. 718. An excellent summary of the principles of Rock Weathering.

[46] Russell. Rivers of North America, p. 17.

[47] W. G. Thompson. Nature, Vol. I, p. 555, 1870. The Matapediac River, N. B. Cited by Russell in Rivers of North America, p. 25.

[48] Dutton. Tertiary History of the Grand Canyon District, Mono. II, U. S. Geological Survey.

[49] The terms rapids, falls, and cataracts are rather loosely used. Many moderate rapids are incorrectly called falls. The “Falls of the Ohio” is an example. The term cataract is often applied to very steep rapids or falls.

[50] Gilbert, article on Niagara Falls, in Physiography of the United States.

[51] Gilbert. Am. Jour. Sci., Vol. XII. p. 99, 1876.

[52] For a brief account of this fall see Gilbert in Physiography of the United States.

[53] Gilbert. Science, Vol. VIII, p. 205, 1886.

[54] See Campbell, Jour. Geol., Vol. IV, pp. 567, 657.

[55] Russell. Rivers of North America, p. 280. The influence of joints on drainage is further discussed by Hobbs, Jour. Geol., Vol. IX, p. 469.

[56] See Willis. The Northern Appalachians, in Physiography of the United States.

[57] This process of adjustment has been well described by Davis in The Rivers and Valleys of Pennsylvania, Natl. Geog. Mag., Vol. I, p. 211 et seq.

[58] This sort of adjustment may be called topographic adjustment. A tributary is in topographic adjustment when its gradient is harmonious with that of its main.

[59] Davis. The Seine, the Meuse and the Moselle. Nat’l Geog. Mag., Vol. VII, pp. 181–202, and 228–238. An article which throws much light on the behavior of rivers.

[60] Another view has been advocated by Tarr, Am. Geol. Vol. XXI, pp. 351–370.

[61] Campbell. Bull. Geol. Soc. of Am., Vol. XIV, p. 277.

[62] Willis. Physiography of the United States. The Northern Appalachians.

[62a] Willis. Physiography of the United States. The Northern Appalachians.

[63] For excellent accounts of the rivers of the Appalachian Mountains see Davis, Rivers of Northern New Jersey, Nat’l Geog. Mag., Vol. II, pp. 81–110; and Rivers of Pennsylvania, op. cit., pp. 183–253; Willis, The Northern Appalachians, Physiography of the United States, pp. 169–202; Hayes, the Southern Appalachians, op. cit., pp. 305–336; Hayes and Campbell, The Geomorphology of the Southern Appalachians, Nat’l Geog. Mag., Vol. VI, pp. 63–126, and Hayes, Physiography of the Chattanooga District, 19th Ann. Rep. U. S. Geol. Surv., Pt. II, pp. 1–58.

[64] This is the case at Davis and Lone Star. Capt Howell, Miss. Riv. Commission.

[65] Russell. Rivers of North America, p. 279.

[66] Russell. Rivers of North America, p. 279.

[67] Hayes. Physiography of the Chattanooga District, 19th Ann. Rep., U. S. Geol. Surv., Pt. II, pp. 9–58. See, also, Hayes and Campbell, Geomorphology of the Southern Appalachians, Nat’l Geog. Mag., Vol. VI, pp. 63–126.

[68] Figs. 165–168 are based on reports of Hayes, and Hayes and Campbell, already referred to. Drawn by E. S. Bastin.

[69] A question might be raised in this case as to what should be called the source. A spring issues from beneath the surface and flows away in a stream. The stream is said to begin where the water appears at the surface, though in some cases the water of the spring was a subsurface stream before it reached the surface. Water escaping from beneath a glacier as a stream may likewise be considered a spring at the point of its issue.

[70] Davis. Science, Vol. X, p. 142, 1887.

[71] L. C. Johnson. Bull. Geol. Soc. Am., Vol. II, pp. 20–25, 1891.

[72] Jefferson. Nat’l Geog. Mag., Vol. XIII, pp. 373–84.

[73] According to map published by the Mississippi River Commission in 1887.

[74] Russell. Rivers of North America, p. 114.

[75] Gilbert. Am. Jour. Sci., Vol. XXVII, 1884, pp. 427–34.

[76] Cooley. Rept. U. S. Engineers for 1879–80, Pt. II, pp. 1060 and 1071.

[77] Gerber. Cited by Todd. Bull. 158, U. S. Geol. Surv., pp. 150, 151.

[78] Chamberlin. Jour. of Geol., Vol. X, pp. 747–754.

[79] For an excellent discussion of deltas, see Gilbert, Fifth Ann. Rept. U. S. Geol. Surv., pp 104–8. Also Lake Bonneville, Monograph I, U. S. Geol. Surv. (same article).

[80] Davis. Physical Geography, p. 294.

[81] Humphreys and Abbot. Physics and Hydraulics of the Mississippi River.

[82] Corthell. Nat’l Geog. Mag., Vol. VIII, p. 351, 1897.

[83] Russell. Rivers of North America, p. 132.

[84] Prestwich. Chemical and Physical Geology, Vol. I, p. 85.

[85] Geike. Text-book of Geology, 3d ed., p. 402.

[86] Medlicott and Blanford, Geology of India. Chap. XVII; Medlicott, Records of the Geological Survey of India, 1881; Oldham, Geology of India, 2d ed., Chap. XVII; and Ferguson, Q. J. G. S., Vol. XIX, pp. 321–54. The extent of this and other deltas is variously stated, probably because it is difficult to determine the exact position of its head and borders.

[87] Dana. Manual of Geology, 4th ed., p. 198.

[88] Salisbury and Kümmel. Lake Passaic. Ann. Rept. of the State Geologist of New Jersey, 1893, and Jour. of Geol., Vol. III. p. 533.

[89] Gilbert. Lake Bonneville, Mono. I, U. S. Geol. Surv.

[90] For discussions of terraces see Gilbert’s Henry Mountains, p. 126; Davis’ River Terraces in New England, Bull. of the Mus. of Comp. Zool., Geol. Series, Vol. V, pp. 282–346; and Dodge, Proc. Boston Soc. of Nat. Hist., Vol. XXVI, pp. 257–73.

[91] Davis, Bull. Mus. Comp. Zool., Geol. Ser., Vol. V.

[92] This point has recently been emphasized by Davis, loc. cit., pp. 282–346.

[93] Murray. Scot. Geog. Mag., Vol. III, p. 70, 1887.

[94] Hoskins. 16th Ann. Rept., U. S. Geol. Surv., p. 853.

[95] Van Hise. Principles of North American Pre-Cambrian Geology, 16th Ann. Rept., U. S. Geol. Surv.

[96] For a full discussion of this subject see King, 19th Ann. Rept., U. S. Geol. Surv., Pt. II, and Slichter, Water Supply and Irrigation, Paper No. 67, U. S. Geol. Surv.

[97] For tables see Buckley, Building and Ornamental Stones, Bull. IV, Wis. Surv., and Merrill, Stones for Building and Decoration, and various Survey Reports.

[98] It is probable that the porosity decreases in more than an arithmetic ratio, both because the deeper rocks are not of porous kinds, and because of the pressure which tends to close openings.

[99] Slichter (op. cit., p. 15) estimates that the ground-water is sufficient in amount to cover the earth’s surface to a depth of 3000 to 3500 feet. Earlier estimates gave still higher figures (see Delesse, Bull. Soc. Geol., France, Second Series, Vol. XIX, 1861–62, p. 64).

[100] Geikie. Text-book of Geology, 3d ed., p. 367.

[101] Ibid., p. 378.

[102] Prestwich, Q. J. Geol. Soc., Vol. XXVIII, p. lxvii.

[103] Reade. Liverpool Geol. Soc., 1876 and 1884.

[104] This is not true in the case of minerals, such as lime carbonate, dissolved under the influence of gases in solution in the water.

[105] Weed. The Formation of Hot Springs Deposits. Excursion to the Rocky Mountains. Compte Rendu. Fifth Session of the International Geological Congress, p. 360, and Ninth Ann. Rept. U. S. Geol. Surv., pp. 613–76. Also B. M. Davis, Science, Vol. VI, pp. 145–57, 1897.

[106] For a racy and interesting account of caverns see Shaler’s Aspects of the Earth.

[107] Russell has emphasized this point in 20th Ann. U. S. Geol. Surv., Pt. II, pp. 193–202, and Cross, 21st Ann. U. S. Geol. Surv., Part II, pp. 129–150.

[108] Gooch and Whitfield. Bull. 47, U. S. Geol. Surv.

[109] Copied from Russell, Mono., XI. U. S. Geol. Surv., p. 176.

[110] Correction for specific gravity only approximate, as specific gravity was not given in original analyses.

[111] As carbonates.

[112] As carbonate.

[113] As oxide.

[114] As carbonate.

[115] As sodium chloride.

[116] As fluoride of calcium.

[117] Oxygen added to SiO₂ to form SiO₃ of Na₂SiO₃.

[118] Liters of gas thrown off per liter of water.

[119] Weed. Ninth Ann. Rept. U. S. Geol. Surv., pp. 613–76, and Am. Jour. Sci., Vol. XXXVII, 1889, pp. 351–59.

[120] Geikie. Geological Sketches, pp. 206–38. Hayden. Amer. Jour. Sci., Vol. III, 1872, pp. 105–15 and 161–76.

[121] Chamberlin. Geol. of Wis., Vol. I, pp. 689–97, and Fifth Ann. Rept., U. S. Geol. Surv., pp. 131–73. The former a brief, and the latter an elaborate, exposition of the principles involved.

[122] Russell. Nat’l Geog. Mag., Vol. III, pp. 127 and 181.

[123] For an account of experiments illustrating the mobility of ice see Aitkin, Am. Jour. Sci., Vols. V, p. 303, and XXXIV, p. 149, and Nature, Vol. XXXIX, p. 203.

[124] Jour. of Geol., Vol. III, p. 888.

[125] The following list includes many of the more available articles and treatises on existing glaciers; others are referred to in the following pages.

Alaskan glaciers: Reid, (1) Nat. Geog. Mag., Vol. IV, pp. 19–55; (2) Sixteenth Ann. Rept., U. S. Geol. Surv., Part I, pp. 421–461. Russell, (1) Nat. Geog. Mag., Vol. III, pp. 176–188; (2) Jour. of Geol., Vol. I, pp. 219–245.

Glaciers in the United States: Russell, (1) Fifth Ann. Rept., U. S. Geol. Surv., pp. 309–355; (2) Eighteenth Ann. Rept., U. S. Geol. Surv., Part II, pp. 379–409; (3) Glaciers of North America.

Greenland glaciers: Chamberlin, Jour. of Geol., Vol. II, pp. 768–788; Vol. III, pp. 61–69, 198–218, 469–480, 565–582, 668–681, and 833–843; Vol. IV, pp. 582–592. Salisbury, Jour. of Geol., Vol. III, pp. 875–902, and Vol. IV, pp. 769–810.

Glaciers in general: Shaler and Davis, Illustrations of the Earth’s Surface; Forbes, Norway and its Glaciers, and Theory of Glaciers; Heim, Handbuch der Gletscherkunde.

[126] Reid. Natl. Geog. Mag., Vol. IV, p. 44.

[127] Rink’s Greenland.

[128] Reid. Variations of Glaciers. Jour. of Geol., Vols. III, p. 278; V, p. 378; VI, p. 473; VII, p. 217; VIII, p. 154; IX, p. 250, and X, p. 313.

[129] For example, in the Middle Blase Dale glacier, Island of Disco, Jour. of Geol., Vol. II, p. 784, and in the Bowdoin glacier (Fig. 242).

[130] Centimeter-gramme-second system. The rate of conductivity has not been very accurately determined.