2i6 PHYSIOGRAPHY. [CH. xill. 



to the ocean, and back again from the ocean to the river in 

 the form of rain. In hke manner, the sohd land is con- 

 stantly being carried, piece by piece, into the sea. Here 

 most of it is spread out upon the ocean floor, forming de- 

 posits which will some day be raised as dry land ; and will 

 then be once more attacked by the water, as soon as it rises 

 above sea-level. The solid earth is, therefore, subject to a 

 cycle of changes not less complete than that exhibited by 

 the circulation of the waters. 



