on the Mountain Cruachan. 135 



pounded porphyries that occur in Glenco and correspond with those 

 which are every where found in veins among the older rocks, being 

 entirely absent in those which lie above the red sandstone. Are we 

 to attribute these diversities to a different era of formation ? Unfor- 

 tunately our knowledge of these rocks is as yet so limited that this 

 question cannot be answered ; but the few remarks which precede 

 may for the present remain as slender contributions towards their 

 history, independently of the local interest they may possess in 

 illustrating the description of Cruachan. 



The next rock of which it is necessary to take a somewhat more 

 extended view, for the purpose of illustrating the structure of this 

 mountain, is the ced sandstone, together with the white calcareous 

 sandstone which res above it. As the former is of frequent occur- 

 rence while the latter is only occasionally present, and as there is no 

 difficulty respecting the consecutive position of these rocks, I shall 

 neglect it in the short notice here to be given. 



It has been shewn that these sandstones occur at the foot of the 

 mountain, occupying a very small space, and that no continuation 

 of them can be traced to the immediate vicinity. But in traversing 

 a larger portion of this tract of Argyleshire a similar phenomenon is 

 found frequently occurring, which, if it diminishes the suprize at 

 first excited by this very limited extent of the secondary strata in the 

 spot above described, adds a much greater interest to the fact, while 

 it naturally leads the geologist to enquire into the circumstances 

 under which so remarkable a dismemberment of these strata has taken 

 place. Their continuity and extent as they occur on the eastern and 

 southern skirts of the highland mountains are too well known to 

 require notice, and they will be found to occupy an extent similarly 

 continuous, as far as geographical circumstances will permit, on the 



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