57 



the reasons for differing on this point from those 

 geologists who have received it, and who, it 

 must be supposed, have considered it, either a 

 natural or a convenient division, or perhaps 

 both. 



The primary class is distinguished from the 

 secondary by a number of circumstances, obvious, 

 in a greater or less degree, to examination ; con- 

 sisting, in a constant inferiority of position, a 

 prevailing' high angle of elevation in the strata, 

 peculiar mineral qualities, and the rare occur- 

 rence of organic remains. It is also most fre- 

 quently separated from that class by a definite 

 boundary ; which is indicated by a reverse order, 

 or a want of consecutive parallelism in the strata 

 of the two classes at the place of contact, accom- 

 panied by a striking peculiarity in the rock which 

 is found at that boundary, and which is the first 

 and lowest of the secondary strata. The difficul- 

 ties which, in a practical view, occasionally inter- 

 fere with and obscure this arrangement, need not 

 be examined at present, as they are discussed 

 hereafter in the preliminary remarks on these 



