540 



CENOZOIC TIME. 



The excavation of lake basins also has been attributed to glacial 

 action. In the case of many lakes in Alpine regions, the origin is due 

 to the filling of the narrow outlet of a deeply excavated valley, by 

 Drift. But, in some cases, especially when the rocks underneath the 

 glacier were soft and easily abraded, the ice may have gouged deeply 

 into the underlying deposits, and then have had this excavating action 

 stopped by a barrier of harder rock in front ; and thus a lake-basin 

 may have resulted. 



IV. Icebergs. 



While the glacier theory affords the best and fullest explanation of 

 the phenomena, over the general surface of the continents, and en- 

 counters the fewest difficulties, icebergs have aided beyond doubt in 

 producing the results along the borders of the continents, across ocean- 

 channels like the German Ocean and the Baltic, and, before the final 

 disappearance (as explained in the account of the Champlain period), 

 over the region of the Great Lakes of North America. Their effects 

 are well exhibited along the coast of Labrador. 



V. General Observations. 



1. Geography — The Glacial period a period of high-latitude eleva- 

 tion, and hence of deep valley-excavation. — Elevations of land do not 

 leave accessible records like subsidences. Still, there is evidence on 

 this point deserving consideration. 



(1.) The existence of an epoch of unusual cold in the early Qua- 

 ternary, seems to be a natural sequence to the vast amount of eleva- 

 tion and mountain-making that had been going on in the Tertiary 

 over all the continents (p. 525), and for the Eocky Mountain regions, 

 late in the Pliocene Tertiary ; for this upward movement must neces- 

 sarily have resulted in increasingly cold climates over the earth. 



(2.) The occurrence of fiords only in Glacial latitudes is further 

 reason in favor of the supposed elevation ; and of Europe as well as 

 America. They are positive evidence that, in the era when they were 

 made, the land stood above its present level, and high enough above 

 to allow of their having been excavated, to their bottoms, by the flow 

 along them of fresh water, or fresh water and ice — for they are valleys 

 of erosion ; moreover, the fiords on the coast of Maine increase in 

 depth from the southwest to the northeast, showing that the amount 

 of elevation increased in the same direction (Verrill). They may have 

 been begun in earlier periods, and have been partly finished in the 

 Cretaceous and Tertiary ; but the almost precise identity of Glacial 

 and fiord latitudes over the globe make it a reasonable supposition 

 that the Glacial era did the finishing work, through the increased ele- 

 vation of northern lands. 



