98 ILLUSTRATIONS OF THE 



add moifture, heat, and perhaps light ; fub- 

 ' fiances which, from their affinities to the ele- 

 ments of mineral bodies, have a power of enter- 

 inr into combination with them, and of thus di- 

 niiniihing the forces by which they are united 

 to one another. By the a£lion of air and moi- 

 iture, the metallic particles, particularly the 

 iron, which enters in fuch abundance into the 



I 



compoiition of almod all foffils, becomes oxy- 

 dated in fuch a degree as to lofe its tenacity ; fo 

 that the texture of the furface is dellroyed, and 



■ ■ 



a part of the body refolved into earth. 



^ 



g^. Some earths, again, fuch as the calcare- 

 ous, are immediately diifolved by water ; and 

 though the quantity fo diifolved be extremely 

 fmall, the operation, by being continually re- 

 newed, produces a How but perpetual corrofion, 

 by which the greatefl: rocks mull in time be fub- 

 dued. The a6lion of water in deftroying hard 



4 



bodies into which it has obtained entrance, is 



F 



iBuch affifted by the viciffitudes of heat and 



F 



Cold, efpecially when the latter extends as far as 

 the point of congelation ; for the water, when 

 frozen, occupies a greater fpace than before, and 



r 



if the body is compa(5l enough to rcfufe room 

 for this expanfion, its parts are torn afunder by 

 a repulfive force a6ling in every diredion. 

 94. Beiides thefe caufes of mineral decompo- 



iition, the action of which we can in fome mea- 



fure 



