150 THE CHEMISTBY OF CREATION. 



of this intense heat to the sedimentary strata 

 has been in many cases to produce the most re- 

 markable alterations in their chemical compo- 

 sition, or in the arrangement of their particles. 

 Thus, rocks have been metamorphosed into sub- 

 stances very different to their original constitu- 

 tion. The celebrated Carrara marble, which, 

 from its unsullied purity of composition, has for 

 ages afforded the principal supply of marble to 

 the sculptor and architect, appears to have un- 

 dergone this peculiar change; and beds, repre- 

 senting the original limestone previous to its 

 metamorphosis, have been discovered. It ap- 

 pears to have been melted under high pressure, 

 so as not to have lost its carbonic acid, and 

 afterwards to have cooled dowri and crystal- 

 lised. The common blue slate used for roofing 

 is another instance of a substance altered by the 

 same process. Every volcanic eruption pro- 

 duces, only in a more limited degree, chemical 

 and molecular changes upon the substances with 

 which the heated matter comes in contact. 



But, in addition to the chemical alterations 

 effected by the contact of a heated mass, most 

 important decompositions have taken place, and 

 are still proceeding, from the discharge of va- 

 pours from the interior. Vapours of sulphuric 

 acid passing upwards from the interior have 

 acted upon large masses of lime-rock, and ex- 



