MATERIAL UNIVERSE. 61 



vapor ; and this vapor, for a length of time, 

 would be driven off so rapidly as scarcely to 

 admit of any action upon the oxidized metallic 

 crust. But this vapor would carry off the ca- 

 loric from the surface much more rapidly than 

 before, and soon reduce the temperature so low 

 as to admit the vapor to be absorbed by the 

 oxidized crust. This heated vapor would grad- 

 ually penetrate the pulverulent oxides, and serve 

 to reduce them to powder ; thereby exposing 

 their surfaces to the further action of the accu- 

 mulating waters. Take, for instance, the oxide 

 of calcium, or lime, as it is generally termed, as 

 a specimen. The action of vapor or water upon 

 that substance is too well known to require elu- 

 cidation. But here, another agent in the prepa- 

 ration of the oxidized crust, for future chemical 

 uses, was first allowed to act on it. This agent 

 was carbonic acid gas, which, till that period, 

 had been hovering around the earth, without 

 being allowed to come in contact with it. The 



