Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/186

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strewed on the shore proves that this substance also exists somewhere in the cliffs; doubtless under the same circumstances which I formerly described at Duntulm. I must add that the specimens sometimes contain shells, and that, resembling basalt in appearance and texture, they confirm the truth of those suspicions respecting the asserted existence of organic substances in that rock, which it is here sufficient to have mentioned.

Together with these detached blocks of siliceous schist are found similar fragments of a cherry substance, extremely hard and brittle, and breaking into acute conchoidal fragments, but possessing an earthy aspect. Its colours vary from greyish white to dark smoke grey, and I may add that its degrees of induration are also various. Occasionally, portions of the siliceous schist are attached to it, the separation being marked by well defined planes, and, from the contrast of colour, very conspicuous. If there were any doubt that this chert was originally a portion of the lias indurated by the same process that has converted the shale into siliceous schist, it would be removed by the fact that on the western shore of this district. the two substances are found in situ, associated in the same manner and in various states of transition from common lias and shale to chert and siliceous schist.

The last portions of limestone to be seen on this shore occur at the island of Fladda, occupying a very low position, and at length disappearing gradually below the trap, which beyond this point forms the whole coast as far as Duntulm, constituting also the islands of Trodda and Fladdahuna, as well as the various picturesque rocks which are scattered to the north of the point of Hunish. This bed of limestone abounds in organic remains, but so condensed together, and so broken, as to present no specimens capable of being ascertained: they resemble fragments of some sort of cockle and of anomiæ, or perhaps ostreæ.