93 







To which are sometimes superadded 



Limestone. 

 Argillaceous schist. 

 Gneiss. 

 Knapdale, Nether Lorn. 



Respecting the secondary rocks, it is only ne- 

 cessary to offer some general remarks ; since from 

 their very limited number, as far as essential cha- 

 racters are concerned, they do not admit of the 

 same method of enumeration. 



It has already appeared, that the lowest (red) 

 sandstone does not necessarily succeed to the pri- 

 mary strata. 



Any member of the three leading species of 

 which they consist, namely, sandstone, limestone, 

 and shale, may succeed another in any mode of 

 repetition or alternation. 



It is not however believed that local varieties, 

 such as the oolite among the limestones, or the 

 red marie of England among the sandstones, can 

 have their order inverted, so as to appear above, 

 and also below, any other local rock. But any 

 of the members may be absent ; and thus one 

 rock may, in some places, follow another in im- 



