VALLEYS, AND HOW THEY ARE FORMED 407 



water contained in the 

 stream. So in excavating 

 valleys, rivers wear a\\'ay 

 the banks on alternate sides 

 and give rise to inosculating 

 spurs. 



In the northern parts of 

 our islands we seldom meet 

 with typical valleys of this 

 kind. Their outlines have 

 been modified by events — 

 not far chstant. geologically 

 speaking — when glaciers, 

 nursed and fed by the 

 snows which fell on the 

 high grounds of North 

 Wales, the Lake District 

 and Scotland, moved slowly 

 down into the plains. These 

 glaciers grew to such enor- 

 mous dimensions that the 

 Irish Sea was completely 

 filled, and the ice welled 

 over into the Midlands. 

 Ice from S c a n d i n a \' i a, 

 too, crossed the shallow- 

 North Sea, and not only 

 infringed on the eastern 

 coasts but travelled for 

 many miles into the 

 interior, even as far as 

 Finchley, near London. 



In contrasting the erosive effects of 

 river and glacier we note that a current 



'SOMETIMES THE 



NOT SYMMETRICAL." 





'IN EXCAVATING VALLEYS RIVERS WEAR AWAY THE BANKS O: 

 ALTERNATE SIDES AND GIVE RISE TO INOSCULATING SPURS." 



Church Strelton. 



of water confines its action to the lowest 

 part of the valle}' through which it flows ; 



and unless ex- 

 ceptionally hard 

 rocks intervene, 

 the sides run 

 with an even 

 slope from the 

 crest to the 

 ])lace where the 

 cutting is in 

 progress. 



In any case 

 the gene r a 1 

 effect resolves 

 itself into the 

 characteristic V 

 section men- 

 tioned above. 



On the other 

 hand, a glacier 

 does not con- 

 fine its acti\'i- 

 ties to a narrow. 



