RIVER TERRACES AND GLACIAE SERIES 457 



In studying the river terraces between the coast and the Sum- 

 merville basin, I independently arrived at the conclusion that 

 the region of glaciation rose at least 2,000 feet and perhaps nearly 

 3,000 feet relative to the coast line, at approximately the time 

 of the last great glacial stage and that this region is now as high 

 as it has been at any time during the Quaternary era. Thus two 

 distinct lines of argument are mutually corroborative and virtually 

 establish, to my satisfaction, the fact of such an uplift. It is 

 practically certain that the early glaciation of this region occurred 

 under a lower altitude than the present. Therefore, the theory 

 of elevation as directly and solely the cause of glaciation is 

 inadequate. 



I will suggest that there is between the earlier and later drifts 

 in the Mississippi basin a contrast of practically the same 

 character as I have imagined to exist here and perhaps the same 

 explanation may apply. It is well known that there are in con- 

 nection with the Wisconsin drift sheet evidences of greater 

 elevation during that epoch than during preceding glaciations. 

 During the Kansan, lUinoian and lowan stages, the altitude may 

 have been low, the climate very cold and comparatively uniform 

 over broad areas, the ice-fields sluggish and the moraines formed, 

 weak. The cause of the glaciation, as many now think, may 

 have been something quite independent of elevation. During 

 the Wisconsin stage, differential elevation may have temporarily 

 resuscitated the ice-fields, but it also brought them under the 

 influence of higher altitude climatic conditions, they were 

 vigorous, but melted rapidly along the borders, ended abruptly 

 and formed massive moraines. 



As to the prime cause of the past glaciations, I am as yet far 

 from convinced. At present I am most strongly inclined toward 

 the atmosphere-composition-variation theory as defined by 

 Chamberlin, but some of the ideas advanced in this paper hardly 

 support it. My attention has been called to the fact that what 

 I have described as the great characteristic of the glaciers of 

 this region in their last stage, namely, their sensitiveness to sun- 

 light, may have been produced at a lower altitude than the present, 

 by a decrease in the carbon dioxide in the atmosphere, which is 



