OF THE SECONDARY CLASS. 381 



accessible in consequence of the absence of the 

 latter. To repeat these characters, and to mark 

 their insufficiency, singly taken, for the purpose 

 of determining the nature of any member, would 

 be merely to recapitulate that which was already 

 said in the introductory remarks to the primary 

 class, where the nature and extent of these uncer- 

 tainties were stated. It is sufficient merely to 

 observe, that neither the low inclination of the 

 strata, the mineral characters of the species, nor 

 the presence of organic remains, are, separately, 

 capable of establishing a criterion between the 

 two. The student who is foiled in. one quarter, 

 must have recourse to some other : but he can 

 rarely be at a loss in determining their characters 

 from their geological positions ; as the most doubt- 

 ful rocks will generally be found associated in a 

 manner easily investigated, with some other stra- 

 tum of which the character is unquestionable, 

 and, in particular, very often rendered so by the 

 nature and abundance of the organic bodies which 

 it contains. 



In the former remarks on the primary rocks, 

 no detailed reasons were given for chusing the 



