Geological Papers. 71 



because even now the non-ocean-current-influenced plateau of 

 eastern Turkestan, nearly one-half of which country is north 

 of that city, has an altitude of more than two miles greater 

 than that of the above-mentioned city of Des Moines (Swin- 

 ton's Geography, p. 110) ; yet, though cold, it is not covered 

 by an ice sheet one mile in thickness, 6000 feet being the sup- 

 posed thickness of the ice sheet in the New England and North 

 Central States (Le Conte's Elements of Geology, p. 576), nor 

 by any ice sheet at all in the summer. And furthermore, the 

 plateaus of the Desert of Gobi and Mongolia, which are situ- 

 ated, for the most part, wholly north of said city, and whose 

 altitudes are more than one and one-half miles greater than 

 that city's altitude, are not covered by perpetual ice, though the 

 balmy and moisture-carrying breezes from the Pacific ocean 

 are shut out by the Khingan mountains. Not only that, but 

 there are places in interior Asia, on the same latitude as St. 

 Petersburg, that are over 2000 feet — the supposed elevation of 

 glacial times (Le Conte) — higher than that city, yet perpetual 

 snow does not rest upon them. Another serious objection to 

 the elevation theory is, that now we are having northern eleva- 

 tion of land and southern depression of the same. Neverthe- 

 less, the antarctic ice sheet is at present larger and thicker 

 than the now existing ice cap in the northern hemisphere. 

 (Le Conte's Elements of Geology, p. 613.) Still another serious 

 objection is that, had the arctic plains been elevated and after- 

 wards depressed, as the theory suggests, they would have 

 faulted as has the basin region; but no such faults are to be 

 found. Geological causes alone, therefore, are quite insuffi- 

 cient to explain the causes of the frigid climate of the glacial 

 epoch. To use the words of Mr. T. J. Bonney, "Each attempt 

 to account for the glacial epoch solely by terrestrial causes 

 places us on the horns of some dilemma." (Story of Our 

 Earth, p. 495.) 



To meet the objections to the above theory, Mr. Croll has ad- 

 vanced the theory that the glacial epoch was caused by the 

 combined influence of the precession of the equinoxes and the 

 secular changes in the eccentricity of the earth's orbit. (See 

 Lyell's Principles of Geology, vol. I, p. 275.) 



This condition, says this accepted authority on the subject, 

 would make the northern winter twenty-two days longer and 



