30 THEORY OF THE EARTH. 



The fragments of the great mountain ridges are 

 carried down into the valleys ; their finer parti- 

 cles, together with those of the lower hills and 

 plains, are borne to the sea ; alluvial depositions 

 extend the coasts at the expence of the high 

 grounds. These are limited effects, to which ve- 

 getation in general puts a stop, and which, besides, 

 presuppose the existence of mountains, valleys, 

 and plains, in short, all the inequalities of the 

 globe ; and which, therefore, cannot have given 

 rise to these inequalities. The formation of downs 

 is a phenomenon still more limited, both in regard 

 to height and horizontal extent ; and has no rela- 

 tion whatever to that of those enormous masses 

 into the origin of which it is the object of geology 

 to inquire.* 



Depositions formed in Water. 



Although we cannot obtain a precise knowledge 

 of the action exerted by water within its own 

 bosom, it is yet possible to determine its limits to 

 a certain degree. 



Lakes, pools, marshes, and sea-ports, into which 

 rivulets discharge their waters, more especially 

 when these descend from near and steep hills, de- 

 posit large quantities of mud, which would at 

 length fill them up entirely, if care were not taken 

 to clean them out. The sea also throws quanti- 



* Note H. 



