Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/50

 fall myself. This is confirmed by its texture as well as its colour, both of them resembling those which are supposed to be characteristic of primary limestones. In these respects indeed it possesses an exact resemblance to the limestones which we find in various parts of Scotland associated with schist, gneiss, and granite, of which I have recorded examples in different places. From this, as I have already hinted, we ought to receive with distrust any attempt to distinguish the primary and secondary limestones by internal characters, nay even by their external forms, since in the respect also the limestone of Strath bears a perfect resemblance to the primitive limestones already alluded to. The texture of this stone is almost every where compact, with a fracture finely granular in the surface, and varying between the splintery and conchoidal. It is generally brittle, a character rare in the stratified limestones, and in many places even breaks with the violence and cleanness of siliceous schist. In its chemical composition it is generally pure; but where in contact with the syenite or the trap veins, becomes overloaded not only with silica but with magnesia and argil also. In such situations it often contains veins and nodules of greenish transparent serpentine, and adopts a variety of colours, a circumstance in which it also resembles most exactly those limestones which in Glen Tilt are found in contact with granite, or at Balahulish, and in Tirey and Iona with mica slate and gneiss. The predominant colour is grey, varying from nearly white through all shades of dove colour to a dark blue grey, sometimes beautifully striped, and mottled or veined; in many situations it is of a pure snow white, forming a perfect variety of statuary marble, which I shall have occasion to describe more particularly hereafter, and affording as yet perhaps a solitary instance of this variety of limestone occurring among secondary strata. When I say a solitary instance, I