THE REVOLUTIONS OF THE CRUST OF THE EARTH. 303 



ohaptp:r III. 



THE FLUID ENVELOPE OF THE EARTH. 



The formatiou of the crust of the earth is controlled by two powerful 

 agents, one of which is known to us as the force of central heat, and the 

 other has for its domain the atmosphere and the sea, and for principal 

 motive-power solar heat and its unequal distribution at the surface of 

 the globe. Such is the present state of the earth, but these conditions 

 have not always been the same, for the influence of the solar heat is 

 relatively recent, while for a long time the atmosphere was affected only 

 by terrestrial heat, of which it was the medium. When the influence of 

 this heat reached almost its limit, most of the vapors contained in the 

 atmosphere were precipitated, and from the first droi) of water which 

 fell upon the still burning surface of the earth to the first ray of sun- 

 light which shone upon the ocean in the full majesty of its power is the 

 period when the geologist must look for the greatest manifestation of 

 the plutonian forces upon the crust of the globe. It is also at this epoch 

 that the formation of most of the rocks occurred, which for a long time 

 have been considered of eruptive character. Farther consideration of 

 the necessarily greater activity of the atmosphere and of the sea at this 

 early stage of the world's history, and of the composition of these rocks, 

 "will give us some light as to their character. 



The temperature of the atmosphere at the time of the precipitation 

 of the first waters was still considerable, for to the heat proceeding from 

 the radiation of the earth was added the heat resulting from the con- 

 densation of the aqueous vapors. Kow most bodies are more readily 

 dissolved in warm water than in cold, and the same must have been the 

 case on a grand scale when the sea was at an elevated temperature, 

 and uniformly covered the face of the globe. This dissolving action 

 extended to the silica and to the various silicates which form the base of 

 the granite rocks. The first sea acted upon the crust of the earth by its 

 excessive turbulence, by the rapid movement of its waters promoted by 

 the continual oscillation of the crust itself, still very thin, and by the 

 impulsion of a dense atmosphere in which the enormous evaporation 

 and the condensation of the water gave rise to electrical discharges, to 

 storms and whirlwinds, which are not possible under present conditions. 

 Nothing could resist the destructive impetuosity of these waters which, 

 breaking and overleaping all obstacles, became necessarily so over- 

 charged with materials held in suspension, as to form at last only a 

 thick muddy paste. Want of liquidity for a time arrested the move- 

 ment of this mud, but as new waters were precipitated, equally agitated 

 by the causes mentioned, it followed that in many cases this mud was 

 taken up again and deposited anew. However, the impetuosity of 

 these elements began at last to diminish, and in intervals of repose 

 the stratified sediments were disposited. 



