Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/79

 excavations made for quarrying that marble. I have always found the marble much indurated and very much coloured at the contact, being at the same time contaminated with silica and other earths; while the syenite itself in the same places appears rotten. Although in a general sense the contact of these two rocks may be said to be visible in various parts of this tract, some accident or other always occurs at the point of meeting, to prevent the real contact from being seen. If it is of small extent it is overgrown with soil and herbage; if it is of great dimensions, there is a chasm intervening which is filled with fragments and rubbish. Thus the contact at Kilbride, which would otherwise prove instructive is overwhelmed and invisible. I was equally unable to find any place on the eastern side where its junction with the upper of the secondary strata could be observed, though it unquestionably takes place near Broadford; the soil is every where a deep peat completely covering the rocky surface. It may probably be found on the shores between Broadford and Scalpa. I know not that there is much to regret in not having seen more of its connections with these strata, since, if, as I believe is undoubted, it has the same relation to them as the trap has, no instruction further than that which we already have can be derived from such knowledge. It will be found indifferently interfering with every one of the strata, and consequently no judgment of priority or posteriority to any can be formed respecting it.

The basis of the syenite is a substance which having been generally received as a felspar, I shall describe as such, although not convinced of a sufficient identity in the composition of these two substances. In its softest state it may be considered as a claystone, since it offers no differences in character, while in a state of somewhat greater induration it becomes a clinkstone, and when more