276 THE HISTORY OF 



more capable of resistance, that process must have become 

 more confined to particular localities, and have extended its 

 violently disturbing action over smaller portions of the 

 earth's surface. In many places, merely vesicular elevations 

 were formed, which rose up out of the water, and oftentimes, 

 when the contents consisted of air, sooner or later sank 

 down again. 



How often such phenomena may have been repeated on 

 a great scale, we know not. Many geologists assume, from 

 the conditions observed in our present systems of rocks, 

 that 12 to 24 such elevations may have taken place, but 

 the assumption is only valid for the products at present 

 lying before us, since no one can give us an indication how 

 many entire systems of rocks may have existed in earlier 

 times, and again have been totally destroyed or sunk down 

 to the bottom of the ocean. With that consolidation of 

 the incandescent fluid mass, in which perhaps the oxygen 

 of the atmosphere so far bore a share, that it became united 

 with the metals of lime, silica, potash, soda and the rest, 

 into the oxygen-compounds or oxides, of which the existing 

 rock systems are composed: with that immediate forma- 

 tion of rocks out of the cooling and solidifying mass, I say, 

 there came another process, of no less important influence. 

 As soon as the first solid masses of stone became elevated 

 into the air, forces were also already active to destroy them 

 again, forces which we for the most part still see, although 

 perhaps with less violence, restlessly labouring to destroy 

 and level mountain chains. The alternation of heating and 

 cooling caused the masses of stone to split up ; into the 

 cracks penetrated water saturated with carbonic acid, 

 decomposing the previously formed chemical compounds, 

 and loosening in this way the internal cohesion of the rocks, 

 which became broken up and finally reduced to dust. In 



