Denudation. 33 



solidated into rock, and afterwards bent and contorted. 

 The strata marked x may perfectly correspond in all 

 respects in their structure and fossils, and in hundreds 



FIG. 7. 



22 i 



1. Synclinal curves. 2. Anticlinal curve, 



of similar cases it is certain that they were once joined 

 as horizontal strata, and afterwards thrown into anti- 

 clinal and synclinal curves. The strata indicated by 

 dotted lines (and all above) have been removed by 

 denudation, and the present surface is the result. 



Chemical action is another agent that promotes waste 

 or denudation. Thus rain water, always charged with 

 carbonic acid, falling on limestone rocks such as the 

 Carboniferous Limestone, or the Chalk, not only wears 

 away part of these rocks by mechanical action, but 

 also dissolves the carbonate of lime and carries it off in 

 solution as a bicarbonate. This fact is often proved by 

 numbers of unworn flints sometimes several feet in 

 thickness scattered on the surface of the table-land 

 of chalk in Wilts and Dorsetshire. The flints now 

 lying loose on the surface once formed interrupted beds 

 often separated by many feet of chalk. The chalk has 

 been dissolved and carried away in solution chiefly by 

 moving water, and the insoluble flints remain. 



Degradation of the rocks of many regions is also 

 powerfully affected by occasional landslips. The waste 

 thus produced is seen on a large scale in many of the 

 Yorkshire valleys, where Carboniferous sandstones and 

 shales are interstratified, and vast shattered ruins of 



D 



