2H4 DISINTEGRATION CHAP. V. 



land. A Luge pile of rock has been planed 

 iiway on one side and not a remnant left. 



Until the last twenty or thirty years, most 

 geologists thought that the waves of the sea 

 were the chief agents in the work of denuda- 

 tion ; but we may now feel sure that air and 

 rain, aided by streams and rivers, are much 

 more powerful agents, that is if we consider 

 the whole area of the land. The long lines of 

 escarpment which stretch across several parts 

 of England were formerly considered to be 

 undoubtedly ancient coast-lines ; but we now 

 know that they stand up above the general 

 surface merely from resisting air, rain and 

 frost better than the adjoining formations. 

 It has rarely been the good fortune of a 

 geologist to bring conviction to the minds of 

 his fellow- workers on a disputed point by a 

 single memoir ; but Mr. Whitaker, of the 

 Geological Survey of England, was so for- 

 tunate when, in 1867, he published his paper 

 " On sub-aerial Denudation, and on Cliffs and 

 Escarpments of the Chalk." * Before this 



* 'Geological Magazine,' October and November, 18G7, vol. 

 iv. pp. 447 and 483. Copious references on the subject are given 

 in this remarkable memoir. 





