36 ON THE STUDY OF 



trap, of beds of rock salt of various degrees of 

 thickness, of coal formations, and of the chalk 

 deposits to a very considerable depth and extent; 

 all of very useful tendency, particularly the 

 articles coal, limestone, rock salt, and chalk. And 

 as it is in this class of rocks that the remains of 

 the more perfect animals, are to be met with; 

 where, from the agency of subterranean fire, 

 those conical mountains have been forced up 

 which have been denominated volcanoes ; and in 

 which, from a similar operation (as it has been 

 supposed), basaltic rocks of very curious forma- 

 tion and of peculiarly chemical properties have 

 been produced ; so this class of rocks cannot but 

 be highly interesting to the geologist and to the 

 philosopher, as well as practically so to every 

 description of persons, to whom the contents of 

 the earth become a matter of consideration. 



Over the whole of these rocks, and covering 

 the general surface of the earth, we meet with the 

 last deposit or formation, which, from being pro- 

 duced by the agency of water, has been denomi- 

 nated alluvial. It is composed of substances too 

 familiar to us all to need illustration ; namely, 

 clay, gravel, sand, loose stones of various kinds, 

 the different species of loams, and in some places 

 of peat moss. Some of these substances in flat 

 situations extend to a considerable depth from 

 the surface; and frequently contain fossil remains 

 of very large animals perfect in all their parts 



