500 TEE ICE AGE IN NORTH AMERICA. 



by concomitant or subsequent movements thus due to defor- 

 mations under strains, by which the elevation attributable to 

 the departure of the ice- sheet may be augmented or partly or 

 wholly counteracted, giving much irregularity to the glacial 

 and post-glacial oscillations of the land. 



Jamieson appears to have been the first, in 1865, to suggest 

 this view, which I receive from him, that the submergence of 

 glaciated lands when they were loaded with ice has been caused 

 directly by this load pressing down the earth's crust upon its 

 fused interior, and that the subsequent re-elevation was a 

 hydrostatic uplifting of the crust by underflow of the inner 

 mass when the ice was melted away.* Two years later Whit- 

 tlesey published a similar opinion. \ In 1868 Shaler referred 

 the subsidence of ice-covered areas to a supposed rise of iso- 

 geothermal lines in the subjacent crust, operating, in conjunc- 

 tion with the ice-sheet, to produce downward flexure ; \ but in 

 1874 and later he regards the depression as due directly to the 

 weight of the ice, and the re-elevation as due to its removal.* 

 The same view is advanced also by Chamberlin to account for 

 the basins of the Laurentian lakes, where he believes a con- 

 siderable part of the glacial depression to have been permanent. || 



*" Quarterly Journal of the Geological Society," vol. xxi, p. 178. Later 

 discussions of this subject by Mr. Jamieson are in the " Geological Magazine," 

 II, vol. ix, pp. 400-407 and 457-466, September and October, 1 882 ; and III, 

 vol. iv, pp. 344-348, August, 1887. In the article last cited, he applies this ex- 

 planation to the changes of the beaches of Lake Agassiz, which up to that time 

 I had attributed mainly to ice attraction. The same principle, however, was 

 brought forward by Herschel in 1836, and had been advocated by Professor 

 James Hall, of New York, in 1859, in attributing to the weight of sediments the 

 long continued subsidence of the areas on which they have been deposited in 

 great thickness. 



■ • f " Proceedings of the American Association for the Advancement of 

 Science," vol. xvi, pp. 92-97. 



\ " Proceedings of the Boston Society of Natural History," vol. xii, pp. 

 128-136. 



* " Proceedings of the Boston Society of Natural History," vol. xvii, pp. 

 288-292; "Memoirs," ibid., vol. ii, pp. 335-340; "American Journal of 

 Science," III, vol. xxxiii, pp. 220, 221, March, 1887; " Scribner's Magazine, " 

 vol. i, p. 259, March, 1887. 



|| " Geology of Wisconsin," vol. i, 1883, p. 290 ; " Proceedings of the Ameri- 

 can Association for the Advancement of Science," vol. xxxii, 1883, p. 212. The 



