[7] "Pre-Historic Times," p. 418.
[8] "Manual of Geology," p. 590.
[9] "Antiquity of Man," pp. 282, 285.
[10] "Pre-Historic Times," p. 417.
[11] Principles of Geology, vol. i. p. 285; "Pre-Historic Times," p. 411.
Mr. Croll believes that, owing to variations in the eccentricity of the earth's orbit "cold periods regularly recur every ten or fifteen thousand years; but that at much longer intervals the cold, owing to certain contingencies, is extremely severe, and lasts for a great length of time; and the last great glacial period occurred about two hundred and forty thousand years ago, and endured with slight alterations of climate for about one hundred and sixty thousand years."—Darwin's Origin of Species, p. 343.
[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.