KI.] 



THE SEA AND ITS WORK. 



169 



d)kes, of rock standing out in bold relief when the neigh- 

 bouring softer rocks have been eaten away. The oldest, 

 and, as a rule, the hardest rocks of Britain are developed in 

 the western and northern parts of the island, and hence the 

 sea acts with less effect upon them than upon the softer 

 rocks in the east and south of England. Even cursory 

 inspection of a map of England and Wales serves to show 

 how the flowing outlines of the chalk coasts of Norfolk, 



Fig. 43. — The Needles, Isle of Wight. 



Lincolnshire, and Yorkshire, contrast with the sharp outlines 

 and bold headlands formed by the old rocks of western 

 Cornwall, Pembrokeshire, and Carnarvonshire. 



In the estuary of the Thames, the rocks are comparatively 

 soft, consisting for the most part of sands, clays and chalk. 

 Within the Thames Basin, then, there should be no difficulty 

 in obtaining evidence of marine waste. Thus Sir C. I.yell 



