

CAUSES, STAGES, AND TIME OF THE ICE AGE. 359 



Chandler's investigations, estimates that the place of the pole 

 since the Glacial period, and from even earlier geologic times, has 

 been without greater changes of position than would lie inside 

 the area of a block or square inclosed by the intersecting streets 

 of a city. 



We come now to the wholly terrestrial or geologic theory of 

 the causes of the Ice age, which in terms varying with increasing 

 knowledge has been successively advocated by Lyell, Dana, Le 

 Conte, Wright, and the present writer. According to this ex- 

 planation, the accumulation of the ice sheets was due to uplifts of 

 the land as extensive high plateaus receiving snowfall through- 

 out the year. Geology has received from Gilbert, in his mono- 

 graph on Lake Bonneville for the United States Geological Sur- 

 vey, the terms epeirogeny and epeirogenic (continent-producing), 

 to designate the broad movements of uplift and subsidence which 

 affect the whole or large portions of continental areas or of the 

 oceanic basins. This view, accounting for glaciation by high 

 altitude, may therefore be very properly named the epeirogenic 

 theory. It is adversely criticised by Prof. James Geikie, who calls 

 it " the earth-movement hypothesis." 



So early as 1830 Lyell pointed out the intimate dependence of 

 climate upon the distribution of areas of land and water and 

 upon the altitude of the land. In 1855* Dana, reasoning from the 

 prevalence of fiords in all glaciated regions, and showing that 

 these are valleys eroded by streams during a formerly greater 

 elevation of the land previous to glaciation, and from the marine 

 beds of the St. Lawrence Valley and basin of Lake Champlain 

 belonging to the time immediately following the glaciation, an- 

 nounced that the formation of the drift in North America was 

 attended by three great continental movements : the first upward, 

 during which the ice sheet was accumulated on the land ; the 

 second downward, when the ice sheet was melted away ; and the 

 third, within recent time, a re-elevation, bringing the land to its 

 present height. But with the moderate depth of the fiords and 

 submarine valleys then known, the amount of preglacial eleva- 

 tion which could be thus affirmed was evidently too little to be 

 an adequate cause for the cold and snowy climate producing the 

 ice sheet. The belief that this uplift was three thousand feet or 

 ore, giving sufficiently cool climate, as Prof. T. G. Bonney has 

 shown, to cause the ice accumulation, has been only reached 

 within the past ten years through the discovery, by soundings of 

 the United States Coast Survey, that on both the Atlantic and 

 Pacific coasts of the United States submarine valleys evidently 

 eroded in late Tertiary and Quaternary time reached to profound 

 depths, two thousand to three thousand feet below the present 

 sea level. 



