Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/177

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alternate with the limestone strata on the Broadford side, and in the inferior solidity and thickness of the calcareous beds; while at the same time the harder schist, which divides them on the south-western shore, is absent, the one appearing to be a substitute for the other. The shale is a mixture of black clay, sand, and mica, thickly and imperfectly fissile, and the sandstone which is of different colours, but generally brownish, contains much clay and calcareous earth, the organic remains being found in each of these beds just as they are in the limestone.

The interruptions, to which I have here alluded, that prevent us from tracing the limestone over the hills that bound the southern side of Strath, arise partly from the boggy and covered nature of the ground, and partly from the intrusion of a hill of syenite, which extends far from the portion formerly noticed, towards Broadford, and which can in many places be distinctly traced overlying the limestone, shale, or sandstone, as either of these happens to be present at the point where the contact is exposed. There is no satisfactory evidence to be procured here of that change from the stratified to the unstratified limestone which I have described in the original paper, since there is no situation where the contact of the two can be precisely traced. Yet there is even here sufficient evidence to give rise to such a suspicion, and more than enough to confirm the observations formerly recorded, and to justify the conclusions deduced from them. To enter into further details on this subject would now be superfluous, as the feebler evidence is of little value where the stronger has preceded. I shall only add, that beds of ordinary quartz are in one place found regularly interstratified with the marble limestone, as if the power which had converted the common limestone into this one, had also changed the sandstone into quartz: and that many gradations by