[12] It would be plausible to assume that the ice melted much more rapidly than is generally supposed. Charles Darwin, in his "Naturalist's Voyage around the World," p. 245, states that "during one very dry and long summer, all the snow disappeared from Aconcagua, although it attains the prodigious height of twenty-three thousand feet. It is probable that much of the snow at these great heights is evaporated, rather than thawed." [13] "Principles of Geology," vol. ii, pp. 567-569. [14] Buchner, p. 118 [15] "Pre-Historic Times," p. 362. [16] "Antiquity of Man," p. 97; "Pre-Historic Times," p. 315. [17] The "Science Record" for 1874, p. 501, in speaking of these implements says, "At the very lowest estimate, the flint weapons were made half a million years ago." [18] "Antiquity of Man," p. 98. "Pre-Historic Times," p. 317. [19] "Antiquity of Man," p. 338; Buchner, 27. [20] "Antiquity of Man," p. 510; Buchner, p. 27. [21] Buchner, pp. 118, 306. [22] Buchner, p. 239. [23] "Principles," vol. ii, p. 566. [24] "Antiquity of Man," p. 63. [25] It has been estimated by the British Association that it requires twenty thousand years to produce a foot of stalagmite.--_Science Record._ 1874, p. 601. [26] "Principles," vol. ii, p. 527. [27] "Man's Place in Nature," p. 146. [28] "Pre-Historic Times," p. 337. [29] "Antiquity of Man," p. 80. [30] "Man's Place in Nature," p. 143. [31] "Antiquity of Man," p. 80. [32] Buchner, p. 263. [33] _Ibid._ p. 262. [34] "Man's Place in Nature," p. 158. [35] Buchner, p. 241. [36] Buchner, p. 240. [37] _Ibid._ p. 241. [38] "Man's Place in Nature," p. 164. [39] Buchner, p. 116. [40] "Antiquity of Man," p. 84. [41] _Ibid._, p. 53. [42] "Antiquity of Man," p. 84. [43] Buchner, p. 54. [44] Buchner, p. 242. [45] Denton's "Our Planet," p. 270. [46] Buchner, p. 265. [47] _Ibid._, p. 54. [48] _Ibid._, p. 242. [49] "Pre-Historic Times," p. 422. [50] _Ibid._, p. 423. [51] Wallace's "Natural Selection, p. 322." [52] Buchner, pp. 34, 252. [53] Buchner, p. 242. [54] Buchner, p. 31; "Pre-Historic Times," p. 420. [55] Buchner, p. 33; "Pre-Historic Times," p. 421. [56] Denton's "Our Planet," p. 270; "American Phrenological Journal, Feb." 1874.