520 THE GLACIAL LAKE AGASSIZ. 



general the same from })reglacial time, through the Ice age, to the present, 

 with only changes of slope, commonly small in any limited tract, which, in 

 long distances, allowed great upheavals and depressions. The elevation of 

 the central part of glaciated areas, with downward slopes on all sides, 

 favored the outward ilow of the ice-sheets and their erosion and transpor- 

 tation of the drift. But mountains and hills jutted upwai'd in ridges and 

 peaks within the moving ice-sheets, as they now stand forth in bold relief 

 above the lowlands; and the ice, with its inclosed drift, was pushed around 

 and over them, some portions being deflected on either side, and usually a 

 larger part being carried upward across their tops. 



EPEIROGENIC MOVEMENTS INDEPENDENT OF GLACIATION OFTEN COMBINED V/ITH 

 OTHERS DUE TO THE ICE WEIGHT AND TO ITS REMOVAL. 



The foregoing review of the Pleistocene epeirogenic movements of 

 various parts of the world shows that many of them have affected coun- 

 tries which never were glaciated. In these areas they have been mostly 

 or Avholly without any demonstrable relationship to glaciation. Again, in 

 countries which have become ice-covered, we learn from fjords and sub- 

 merged river valleys that great epeirogenic elevation of the land preceded 

 the accumulation of the ice-sheets. These movements also were evidently 

 independent of glaciation, not being caused by it, though, on the other 

 hand, the writer believes that they were the cause of the ice accumulation 

 and of its resulting drift deposits. The more extended epeirogenic move- 

 ments of the earth within the Pleistocene period have i)robably arisen from 

 the relationship of the earth's crust and interior, and in areas of suffi- 

 ciently high latitudes, and in mountain districts, they have here and there 

 produced ejjochs of glaciation. 



While so widespread earth movements not due to glaciation have been 

 taking place throughout this period, it is evident that some of them would 

 probably be in progress in glaciated countries at the same time with the ice 

 accumulation and after the depai'ture of the ice-sheets, being combined in 

 their effects with other crustal movements due to the weighting of the crust 

 by the ice-load, and to its relief by the ice-melting. Thus, for example, 

 while we may refer the rise of the greater part of North America from the 



