512 THE ICE AGE IN NORTH AMERICA. 



in the luminous glacial theory of Croll, but their origin and 

 effectiveness toward causing a glacial climate are here referred 

 to extensive crust oscillations instead of eccentricity of the 

 earth's orbit. The prolonged warm interglacial epoch, or sev- 

 eral such epochs, of which evidence is obtained in the Qua- 

 ternary deposits of Europe and North America, preceded and 

 followed by severe arctic climate and ice-sheets, meet an ade- 

 quate and consistent explanation in the view here taken ; and, 

 indeed, the same reasoning that is presented by Croll in the 

 details of the secondary elements of his theory seems equally 

 applicable if these depend primarily on crustal elevation. 



The principal interglacial epoch in the United States, un- 

 der this view, may well have been several times longer than 

 either the previous or subsequent epochs of glaciation, or than 

 the whole of post-glacial time, as claimed by McGee ; * but it 

 does not follow that an exact parallelism will be found in the 

 glacial history of Europe. Former extension of vast glaciers 

 in the Rocky Mountains and Andes, the Pyrenees and Alps, 

 the Atlas range, the Caucasus, the Himalayas, and elsewhere, 

 far exceeding the glaciers of the present time, may be due to 

 the uplift of these mountains much above their present height, 

 followed by subsidence! with retreat of the ice ; but these os- 

 cillations and resulting alternations of climate were not proba- 

 bly synchronous everywhere. The highest mountain-ranges in 

 four grand divisions of the world — namely, Asia, Europe, and 

 North and South America — were doubtless largely uplifted and 

 plicated, with formation of deep adjoining lakes, during the 

 early part of the Quaternary period. Twice upheavals of the 

 whole district of the Alps seem to have covered the region with 

 great accumulations of ice, which each time may have depressed 

 the area, first to be succeeded by the formation of interglacial 

 deposits with lignite, and during each depression to send down 

 floods, spreading loess along the Rhine, the Rhone, and the 

 Danube.]; After the later epoch of subsidence and glacial re- 



* "American Journal of Science," III, vol. xxxv, pp. 463-466, June, 1888. 

 f A. Geikie's "Text-Book of Geology," second edition, p. 934. 

 X J. Geikie's "Great Ice Age," second edition, chapters xxxiii and xxxiv, 

 and his " Prehistoric Europe," chapters ix and xi. 



