Ch. XXIV.] 
OF MOUNTAIN-CHAINS. 
351 
mountain -chain to the base of another, the beds being vertical 
or inclined in one chain, and horizontal in the other. We 
might then decide with confidence, according to the method 
proposed by M. de Beaumont, on the relative eras when these 
chains had undergone disturbance ; and from one point thus 
securely established, we might proceed to another, until we 
had determined the dates of many neighbouring lines of 
convulsion. 
We fear that the cases are rare where such evidence can be 
obtained ; and, for the most part, we can identify the age 
of strata, not by their continuity and homogeneous mineral 
character, but by organic remains. When by their aid we, 
prove strata to be contemporaneous, we must generally speak 
with great latitude, merely intending that they were deposited 
in the same geological epoch during which certain animals and 
plants flourished. 
