174 ISLAND LIFE 



Now Dr. Croll gives us the following account of the 

 present asj^ect of the surface of a large j^art of the coun- 

 try :— 



''Go where one will in the lowlands of Scotland and he 

 shall hardly find a single acre w^iose upper surface bears 

 the marks of being formed by the denuding agents now in 

 operation. He will observe everywhere mounds and 

 hollows which 'cannot be accounted for by the present 

 agencies at work. ... In regard to the general sur- 

 face of the country the present agencies may be said to be 

 just beginning to carve a new line of features out of the 

 old glacially-formed surface. But so little progress has 

 yet been made, that the kames, gravel-mounds, knolls of 

 boulder clay, &c., still retain in most cases their original 

 form." ^ 



The facts here seem a little inconsistent, and we must 

 suppose that Dr. Croll has somewhat exaggerated the uni- 

 versality and complete preservation of the glaciated sur- 

 face. The amount of average denudation, however, is not 

 a matter of opinion but of measurement ; and its conse- 

 quences can in no way be evaded. They are, moreover, 

 strictly proportionate to the time elapsed ; and if so much 

 of the old surface of the country has certainly been re- 

 modelled or earned into the sea since the last glacial epoch, 

 it becomes evident that any surface-phenomena produced 

 by still earlier glacial epochs mttst have long since entirely 

 disappeared. 



Rise of the Sea-level Connected ^vitli Glacial Epochs, a Cause 

 of Fihrther Denudation. — There is also another powerful 

 agent that must have assisted in the destruction of any 

 such surface deposits or markings. During the last glacial 

 epoch itself there were several oscillations of the land, one 

 at least of considerable extent, during which shell-bearing 

 gravels were deposited on the flanks of the Welsh and 

 Irish mountains, now 1,300 feet above sea-level ; and there 

 is reason to believe that other subsidences of the same area 

 though perhaps of less extent, may have occurred at 

 various times during the Tertiary period. Many wi'iters, 

 as we have seen, connect this subsidence with the glacial 

 ^ Climate and Time in tlieir Geological Relations, p. 341. 



