50 THEORY OF THE EARTH. 



or flat beaches, and protect the, bottoms of the 

 cliffs against farther depredations. 



Such are the ordinary actions of water upon the 

 solid land, which almost entirely consist in reducing 

 it to lower levels, but not indefinitely. The frag- 

 ments of the great mountain ridges are carried 

 down into the valleys, while their finer particles and 

 those of the lower hills and plains are floated to the 

 sea. Alluvial depositions extend the coast at the 

 expense of the interior hills, which last effect is 

 most limited in its extent by means of vegetation. 

 All these changes necessarily suppose the previous 

 existence of mountains, valleys, and plains, and 

 consequently the same causes could not have 

 given rise to these inequalities on the surface of 

 our globe. 



The formation of downs is the most limited of 

 all these phenomena, both in regard to height and 

 horizontal extent, and has no manner of relation 

 whatever to those enormous masses^ the origin 

 of which forms the peculiar object of geological 

 research.* 



13. Of Depositions formed in Water. 



Although we cannot obtain a precise knowledge 

 of the actions exerted by water within its own bo- 

 som, still it may be ascertained in a certain degree. 



* Note EL 



