172 Dr. Mac Culloch's Supplement to the 



yielding to the action of the elements. I remarked formerly that 

 these strata, however separated in position, were analogous to the 

 white sandstone which occurs at Portree and elsewhere in the 

 north-eastern portion of Sky, and is accompanied by limestone, 

 shale, and coal. Having then but little acquaintance with that 

 part of the island, the description of these strata was avowedly left 

 imperfect, and it is now necessary to supply the deficiency. 



As I remarked not long ago that a description of the neighbouring 

 islands was requisite to throw light on the obscure connection of 

 the red sandstone with the limestones of Strath and of Sligachan, 

 so I may here repeat that the history of the uppermost strata of 

 Sky, which I now propose to sketch, would be materially elu- 

 cidated by that of Rasay. But as the description of this island 

 would be here inadmissible, I can only say generally, that the 

 deficiencies of connection which occur in Sky, and which compel 

 me on many occasions to have recourse to inference and analogy, 

 are in a great measure supplied by the structure of that island, 

 which, while it is more continuous and accessible, is at the same 

 time such as to leave no doubt respecting the identity of strata 

 separated at present by a narrow arm of the sea. 



It has been seen that as the gryphite limestone immediately fol- 

 lows the red sandstone, so it is succeeded by the calcareous white 

 and grey sandstone of Strathaird. The same succession may be 

 traced in a more circuitous manner by comparing the strata of 

 Sligachan, Scalpa, and Rasay. But it is apparent on considering 

 the map of Sky, that the portion of these uppermost strata which 

 occupies the district of Trotternish is separated from the gryphite 

 limestone by an interval, partly the result of the direction of the 

 shores, and partly produced by the intervening mass of trap and 

 6yenite. There is no actual contact of the two to be seen, but the 



