&CALPA. GEOLOGY. 433 



limestone of Sky, to the sandstone strata which lie on 

 each side of it. 



It has been seen that the calcareous strata, both of 

 Scalpa and Broadford, follow the sandstone of the south- 

 eastern division of Sky with a common dip, and as the 

 limestone of Sky lies on that mass, it is to be presumed 

 that the limestone of Scalpa also bears the same relation 

 to it. But the sandstone which immediately follows the 

 calcareous strata in Scalpa appears to lie above them, since 

 it is higher and has a common dip. And here the evidence 

 of its geological superposition ends, since neither in Sky 

 nor in any of the islands to the south-west is any approxi- 

 mation of the two rocks on the same alignment as these 

 to be discovered. On general principles it is not probable 

 that such an order actually exists, since it would introduce 

 a greater anomaly into geological arrangements than any 

 thing which has yet appeared in the course of these exami- 

 nations. Further, the identity of structure in the eastern 

 and western portions bespeaks a community of nature, 

 which is still more confirmed by the very peculiar cha- 

 racters they both exhibit. The extent occupied by Rum, 

 which in a manner connects these two branches into one, 

 is a further argument in favour of this view. To conclude 

 this reasoning, it is easy to imagine that the limestone 

 ceases at a certain point to be prolonged on its line of 

 direction, and that it thus forms one of those basin-like 

 deposits in the cavity of the inferior strata, of which abun- 

 dant examples are not wanting every where. 



If the preceding view be correct, it will materially eluci- 

 date the structure of Sky, which was left in many points 

 undetermined, till the whole evidence could be collectively 

 stated. Thus the detached portions of sandstone and of 

 limestone at Loch Sligachan, with many of the rocks of 

 Rasay, as well as the upper beds which exist in so scat- 

 tered a manner in the northern parts of Sky, will find their 

 places in an arrangement from which their irregularity had 

 excluded them when considered in an independent view. 



VOL. i. F F 



