392 ARRAN. GEOLOGY. SECONDARY STRATA. 



respect to others of these strata there is more difficulty ; 

 nor can it be positively determined from the limited ap- 

 pearances here visible, whether, like the former, they are 

 merely variations in the character of the leading beds, 

 or disjointed and limited portions of those secondary 

 rocks which in other situations follow the red sandstone 

 in a regular order of superposition. If all the established 

 successions of strata were equally regular every where, 

 this difficulty would not exist; but as many of them 

 are occasionally absent, or irregular in their proportions, 

 we must, in cases like this, where small and insulated 

 tracts alone are the subject of investigation, unavoidably 

 remain in doubt ; unless we can deduce from the com- 

 parison of relative positions, that which is not obvious 

 to simple inspection. I allude here principally to the 

 white calcareous sandstones and the red caicareo-argil- 

 laceous beds that contain entrochi; the true connexions 

 of which are not completely evident in the places where 

 they occur. Some of the limestones appear to be subor- 

 dinate, or accidental concretionary deposits in the red 

 sandstone ; similar beds occurring in Bute and in other 

 places on the skirts of the Highland mountains. Those beds 

 which contain terebratulae have by some been considered 

 analogous to that which has been in England called moun- 

 tain limestone ; a supposition which, if proved, would show 

 that Arran presented one set of strata at least in a regular 

 order of superposition to the red sandstone. Should 

 this be considered the fact, the white sandstone which 

 follows the limestone would also be a third and distinct 

 deposit; this stratum, where it occurs, appearing to be 

 the last and uppermost in the island. In the same way, 

 the large mass of white sandstone in contact with the 

 red, would also be esteemed a portion of the same depo- 

 sit ; the limestone having disappeared, as occasionally 

 happens among stratified rocks, by the gradual extenu- 

 ation of the beds, and thus suffering it to come into 

 immediate contact with the lower red one. Thus -also 



