2i8 PHYSIOGRAPHY. [chap. 



crust, except those of rain and rivers, and of the sea ; then, 

 as has been pointed out in Chap. XL, the ultimate result of 

 their action would be the reduction of the solid land to a 

 submarine plain. The waters covering this plain would be 

 more or less completely saturated with the soluble materials 

 extracted from the denuded rocks. Denudation, therefore, 

 on the whole, not only diminishes the quantity of dry land, 

 but also lessens the proportion of the solid to the fluid con- 

 stituents of the globe. 



The tendency of the forces of upheaval is in the opposite 

 direction, though the source of the work done is still largely 

 derived from water. The fused rocks in the depths of the 

 earth, which are vomited forth by volcanoes, are forced to the 

 surface by steam power, and then take on the solid form. 

 There is a transference of matter fromlovver to higher levels, 

 accompanied by an increase of the solid at the expense of 

 the fluid constituents of the globe. Whether the proportion 

 of dry land is, or is not, increased by volcanic action depends 

 upon the locality of the vent, and the amount of matter 

 thrown out from it. If the vent opens on dry land, the 

 erupted matters will necessarily increase the mass of dry 

 land ; while, if it break out beneath the sea, they may reach 

 the surface, or not, according to their mass and the form 

 they assume. 



Supposing that no agents were at work upon the earth's 

 crust except volcanoes — with concomitant movements of ele- 

 vation and depression — the quantity of water in the ocean 

 would remain substantially unaltered ; but, the proportion of 

 the surface of the earth occupied by dry land to the area 

 covered by water, might be almost indefinitely increased or 

 diminished. It is conceivable, for example, that the whole 

 ocean, which, at present, occupies about three-fifths of the 

 surface of the earth, might come to be contained in a few 



