Chap. V. AND DENUDATION. 231 



recrystalllzed, have often been again dis- 

 integrated. Denudation means the removal 

 of such disintegrated matter to a lower level. 

 Of the many striking results due to the 

 modern progress of geology there are hardly 

 any more striking than those which relate to 

 denudation. It was long ago seen that 

 there must have been an immense amount 

 of denudation ; but until the successive forma- 

 tions were carefully mapped and measured, 

 no one fully realised how great was the 

 amount. One of the first and most remark- 

 able memoirs ever published on this subject 

 was that by Eamsay,* who in 1846 showed 

 that in Wales from 9000 to 11,000 feet in 

 thickness of solid rock had been stripped off 

 large tracks of country. Perhaps the plainest 

 evidence of great denudation is afforded by 

 faults or cracks, which extend for many miles 

 across certain districts, with the strata on one 

 side raised even ten thousand feet above the 

 corresponding strata on the opposite side ; and 

 yet there is not a vestige of this gigantic 

 displacement visible on the surface of the 



* " On the denudation of South Wales," &c., ' Memoirs of the 

 Geological Survey of Great Britain,' vol. i., p. 297, 1846. 

 11 



