Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/181

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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 subsequent 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 on 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 correspondence of the same complicated schistose structure, that structure being even more apparent in the softer rocks, as more readily