428 SCALPA. GEOLOGY. 



neighbouring shores of Sky, that they are higher in geolo- 

 gical position, and are, the upper beds, of a calcareous 

 deposit, of which the lower are to be seen between Broad- 

 ford and Lucy. The breadth of the limestone on the 

 north-eastern side of Sky, as far as any regularity can 

 be traced in it, is therefore limited by the latter point 

 on the one hand and by the shore of Scalpa now described 

 on the other. Here it terminates in the sandstone beds 

 which will be presently described ; and as these belong 

 to the same extended and regular deposit as those of 

 Sky, this place must be supposed the natural termination 

 of that calcareous tract. It was shown that on the 

 neighbouring shore of that island the deficiency of the 

 limestone is caused by the overlying rocks of syenite 

 and trap which cover it; admitting its edge to be seen 

 in some places, while in others, reaching to the water, 

 they conceal it from view as effectually as the sea itself 

 conceals those portions which, from general considerations, 

 and from the examination of the low rocks in the inter- 

 mediate channel, must be concluded to exist from Scalpa 

 through Pabba to the opposed shore of Broadford bay. 

 For the same reason we are unable to trace the north- 

 western edge of this calcareous zone towards Loch Scavig, 

 where it should be found, with the same facility that 

 we trace the south-eastern one to Swishnish ; the syenite 

 mountains intruding far over its edge into Strath, as the 

 description of that district has already shown. I forbore 

 to examine these relations under the article of Sky, 

 because, without the evidence which Scalpa, Pabba, and 

 the smaller isles give, the proofs were imperfect ; but 

 the investigation must be considered as properly apper- 

 taining to the description of that island. 



Where the limestone series of Scalpa ceases to be 

 visible, the land rises suddenly into the hills already 

 mentioned, which in a general view are formed of red 

 sandstone. Gravelly beaches on the shore and vegetation 

 in the hills prevent the actual junction from being seen ; 



