OUTLINES OF GEOLOGY. 



93 



Applying these principles to the mountains of the United 

 States, it may be inferred : 



That the lower ramifications of the Atlantic chain, from 

 the island of New- York to Georgia, were raised at a date 

 anterior to the deposit of any sedimentary rocks ; 



That the Atlantic ridge itself is posterior to the transition 

 limestone, and probably to the red sandstone of New-Jersey, 

 which is much disturbed in its neighbourhood ; 



That the other ridges of the Apalachian group are subse- 

 quent to the coal measures. 



199. We have used the term elevation" in speaking of the 

 origin of mountains. It is however obvious, that the appear- 

 ances they present may have arisen as well : from the falling 

 in of the adjacent strata ; from the formation of great faults, 

 in the strata of which they are themselves composed ; by the 

 twisting and bending of their own strata, in consequence of a 

 contraction of the dimensions of the globe, as from the pro- 

 trusion of an igneous rock, through a level part of the crust 

 of the earth. In examining mountains, all these different 

 methods of formation are distinctly visible, and, in addition, 

 some ridges of no great elevation are wholly composed of 

 overlying masses. 



200. In examining this theory in connection with the facts, 

 it appears : that the greatest range of mountains on the sur- 

 face of the globe, is of the most recent origin, and that its 

 elevation has been followed by a period of repose probably 

 longer than any which preceded it ; that, as we proceed 

 back in the earth's geological history, the convulsions appear 

 to diminish in extent, while the periods of their recur- 

 rence become more and more frequent. As we have no right 

 to conclude that the revolutions of the globe are at an end, 

 it is to be inferred, that the present quiescent state is to be 

 terminated by a convulsion of still greater violence, and 

 which may cover the whole existing face of the continents 



