GARVH ISLAND. GEOLOGY. 509 



direction, and dipping to the south-east in an angle of 

 about fifteen degrees. In this latter circumstance it differs 

 from the sandstone, which here dips to the north-west, 

 although the direction of both is the same. Its relative 

 position to the gneiss cannot be traced in this place, as 

 the two rocks are separated in such a manner as to prevent 

 an examination of their contact ; nor is it very convenient 

 to examine in the other parts of Diurness bay. It will 

 hereafter, however, be seen that this defect is supplied 

 by another calcareous tract of similar character situated in 

 Loch Eribol, where the connexions admit of a free exa- 

 mination. 



In colour, this limestone varies between different shades 

 of grey, from a very light ash colour, to a leaden, and 

 to a purplish tint. It is of a very fine texture arid com- 

 pact smooth fracture, sometimes approaching to the flat 

 conchoidal. Interspersed among the ordinary beds are 

 large concretions of pink and white carbonate of lime, 

 which, when intermixed with the ordinary limestone, pro- 

 duce ornamental marbles. I could not detect any organic 

 remains among these strata, although it will be seen that 

 they exist in that portion of the same rock which occurs 

 in Loch Eribol. But in the grey basis there are often 

 found red vermicular stains, while the surfaces present 

 on weathering, a variety of singular forms ; both of these 

 seeming to indicate that such remains originally entered 

 into the composition of the rock ; obscured here by 

 posterior changes, as they appear to have been in Sky, 

 and in the Isle of Man. The vermicular forms in par- 

 ticular are very similar to many that occur in the well- 

 known marble of Babicomb, which are doubtless of 

 organic origin. I need not point out the probable causes 

 of these changes, as they are discussed elsewhere, but 

 shall proceed to elucidate the geological history of this 

 island by a sketch of the calcareous tracts of Diurness and 

 of Loch Eribol. 



With the exception of the peninsula of Farout head, the 



