321 



THEORY OF SUDDEN E1SE OF 



[Ch. VII 



would be the case if they were deposited in seas or lakes f 



mountains have partly formed 



the other sedimentary beds, tilted up, and more or less con- 



mountains 



;am 



points 



even to their highest crests.' * There are, therefore, in and 

 adjacent to each chain, two classes of sedimentary rocks the 

 ancient or inclined beds, and the newer or horizontal. It i 

 evident that the first appearance of the chain itself was an 

 event < intermediate between the period when the beds now 

 upraised were deposited, and the period when the strata were 

 produced horizontally at its feet.' 



A 



Thus 



assum 



*d its present position after the 

 deposition of the strata b, which have undergone great move- 

 ments, and before the deposition of the group c, in which the 

 strata have not suffered derangement. 



If we then discover another chain B, in which we find not 



it 



Fig. 



•r7V"7 



d 



only the formation b, but the group c also, disturbed and 



may 



must 



fi 



the deposition of c, and before that of the group d ; whereas 



1/5 



It is then argued, that in order to ascertain whether other 



mountain ranges are of contemporaneous date with A and B, 



or are referable to distinct periods, we have only to enquire 



* Phil. Mag. and Annals, No. 58. New Scries, p. 242. 









