﻿192 EVOLUTION IN THE PAST 



also was completely overspread ; but the ice-sheet here 

 seems to have been formed independently by local glaciers. 

 Over scenes in Germany, where in earlier times palms and 

 cinnamons had flourished, polar bears were roaming. Great 

 indeed had been the change. 

 north The moraines show that the southern extension of the 



America sheet in North America was much greater in the east than 

 in the west ; but more than half the continent was covered 

 with thick ice from the Atlantic to the Pacific. The massive- 

 ness of the ice in some regions was enormous. In parts of 

 North America (and in parts of Scandinavia) the thickness 

 must have been fully 3000 feet. And in regions far beyond 

 the limits of the ice-sheets the cold must have been 

 intense. 



Europe These conditions, varied by occasional relaxations, con- 

 tinued for a long time. At length in Europe, owing chiefly 

 to land subsidences in the more northern latitudes, a steady 

 change towards mild conditions set in. Exposed masses of 

 pushed-on debris now marked the lost frontiers of the icy 

 sway. Traversed rocks reappeared, scratched and polished 

 after long entombment ; and huge glacier-transported boulders 

 were to be seen perched on mountain-tops, hundreds of miles 

 away from their pre-glacial abodes. 

 inter- We now reach in Europe what can only be called an Inter- 



glacial glacial Epoch, for in course of time a second Great Glaciation 

 epoch in took place. Although there were several relaxations of the 



Europe intense cold in North America, it is not at all clear that 

 there was any inter-glacial epoch of importance such as 

 occurred in Europe. 



The gradual melting of the ice, and an abundant rainfall, 

 resulted in great floods, and the removal of vast amounts of 

 surface earth from place to place. New lakes were formed 

 in basins hollowed out by the glaciers ; and in some cases 

 old rivers, finding their former channels blocked by glacial 

 debris, were making their way by new routes to the sea. 



The change of climate in Europe, involving the recession 

 of the ice, was followed naturally by many migrations of 

 life. Polar willows, dwarf birches, hardy forms of saxifrage, 

 and other cold-climate growths were gradually advancing 



