SUCCESSION' AMONG ROCKS. 273 



scntly notice more particularly; but it is incumbent on 

 the inventors to explain its meaning, and, if it has 

 one, to show that it does not form a subterfuge. 



Whatever analogies may subsist between some 

 rocks of the most antient and others of the most recent 

 date, such as between the limestones in both classes, 

 there can be no alternation between these two great 

 divisions, by the very nature of the admission which 

 constitutes this distinction. It remains to see the 

 nature and accuracy of the order in which the secon- 

 dary strata follow each other. 



There are but three distinct and principal rocks in 

 the secondary series, namely, sandstone, shale, and 

 limestone ; although a variety of circumstances, arising 

 from minute changes of character, relative position, or 

 imbedded fossil bodies, give rise, in them, to many 

 different, and often very constant varieties. If these 

 were to be considered merely according to their fun- 

 damental distinctions, the result would be, that they 

 are repeated in every possible kind of disorder, and in 

 endless alternations. But to give the subject every 

 advantage, as well as those to which it is really en- 

 titled, let all the distinctions that have been made be 

 granted, as far at least as these are really constant, 

 and as far as they are not merely dependent on place ; 

 in which latter case, it is plain that the whoie question 

 would be resolved into a petltlo principil. 



Proceeding on this principle, we find that a parti- 

 cular sandstone, frequently red, is the lowest stratum 

 in the secondary series. I have already shown, how- 

 ever, that it is wanting between the gneiss and the 

 coal series of Morven, and between the granite and t , 

 that of Sutherland. It does not exist in certain parts 

 of Sky, and it is also absent in Mull, in Airdriamur- 

 chan, and in other places which I need not enumerate, 

 VOL. i. T 



