732 THE JOURNAL OF GEOLOGY. 



all of Holland and part of Belgium. In Germany it extended to the Erz 

 and Carpathian Mountains. It reached its southernmost extension in the 

 valley of the Dneiper, somewhat below latitude 50 . A further point 

 of interest is the representation of an independent ice sheet of con- 

 siderable extent in northeastern Russia and the adjacent parts of 

 Asia, about the Timan and Ural Mountains. The ice sheet which 'cen- 

 tred here is mapped as extending westward until it came in contact 

 with the ice sheet which spread eastward from Scandinavia. This 

 subordinate ice sheet had an area about as great as that of France. 

 According to the map, the edge of the ice during this epoch was 

 markedly lobate, especially to the eastward. Expression is also given 

 to the idea that some of the mountain ridges well within the area of 

 the mer de glace exerted, even at the time of maximum glaciation, a 

 considerable influence on the direction of ice movement. The 

 mountains of Great Britain, of Ireland, and of Eastern Scandinavia are 

 represented as having never been so deeply covered with ice but that 

 they continued to exert an influence upon the direction of its move- 

 ment. They served as local centres of glaciation while the ice sheet was 

 developing, and as such would seem never to have altogether lost 

 their identity. 



During the next glacial epoch (the third) ice again covered all of 

 Scotland, but failed to override the southern extremity of Ireland. It 

 left a considerable part of Wales uncovered, and encroached upon the 

 borders of England only at the north, northwest, and northeast. On 

 the continent, the ice failed to reach its earlier limit. Hamburg, Ber- 

 lin, and Warsaw lie near the limit of its advance, and there was no 

 independent ice sheet in the region of the Urals. The Scandinavian 

 and British ice sheets were again confluent. During the fourth 

 epoch, glacier-ice in Britain was largely confined to the mountain 

 valleys of Scotland, though the valley glaciers sometimes came down 

 so as to coalesce on the low lands, making somewhat extensive " dis- 

 trict" or piedmont glaciers. On the continent, the ice covered the 

 eastern half of Denmark, and reached southward to the Baltic ridge. 

 It failed to cover all the southern part of Sweden, and did not 

 encroach far upon Russian soil. The British and Scandinavian 

 ice sheets were not confluent. During the fifth and sixth epochs, the 

 development of ice was still more restricted, the glaciers of the last 

 being less extensive than those of the fifth. 



What is the basis on which the subdivision of the glacial period is 



