Mineralogy of Sky. 171 



in which respect it possesses a resemblance to the marble limestone 

 formerly described. But I need not detail those peculiarities of 

 structure which can scarcely be rendered intelligible by words. 

 That which is most remarkable is the large quantity of siliceous 

 matter it contains. This is found dispersed through it in irregular 

 nodules, often scarcely differing from common flint, or rather 

 resembling that variety of chert which in other situations is found 

 in limestones. These nodules are white, grey and mottled, in some 

 places of an obscure pale red, and they are so predominant in a 

 few situations as nearly to exclude altogether the calcareous matter. 



In the original paper I represented the sandstone of Strathaird as 

 a portion of a series superior to the limestone of Strath, and a sub- 

 sequent and more extensive examination of the country enables me 

 to confirm this view. But I may add to it the following remark, 

 which is not unworthy of notice. The trap veins which form so 

 conspicuous a feature pn the eastern side of this promontory are 

 crowded together in the manner already described only along a 

 certain, though by far the greatest, portion of the shore. At the 

 extremity of the promontory they are rare, and are scarcely found 

 on the western side. They appear indeed to be connected with 

 the body of the trap which was described as covering the stratified 

 rocks, and to be ramifications or processes from that mass. On 

 the western side, and at the point of Aird, where they are rare or 

 altogether wanting, the strata consist of a soft white calcareous 

 sandstone, and are nevertheless apparently continuous with the 

 hard ones formerly described as occurring where the trap veins 

 predominate ; while the identity is still further marked by the cor- 

 respondence of the same complicated schistose structure, that struc- 

 ture being even more apparent in the softer rocks, as more readily 



