Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/473

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463
Dr. Mac Culloch on Quartz Rock.

and of structure which I have detailed, I think that I am justified in considering this rock, like that of Jura, to be a recomposed, and not a purely chemical deposit, being with it equally ill entitled to the name of granular quartz. Its characters would seem to prove that it has originally been a stratified sandstone, which by some of the revolutions of this globe has been both chemically and mechanically altered, consolidated in some places to the apparent loss of its original texture, and so changed in its position as to show but faint indications of its former regularity.

It now remains to enquire into the connexion of this rock with those which accompany it, a part of the subject, and a very important one, on which I must regret that I have so little precise information to offer. On the sea shore at Kylescuagh, and on the shores of Loch Lowie, a very indurated and compact gneiss appears to lie immediately below the quartz rock, but I could not discover their connexion. In the very centre of the district I found hornblende slate, gneiss, mica slate, and syenitic granite, together with numerous veins and detached masses of compact epidote. Here also, unfortunately, I could not trace their connexion. Such is the meagre account I have to render of what it would be of prime importance to ascertain, whether these rocks are every where inferior in position to quartz rock, or whether the older schistose rocks do not here, as in other places, alternate with it. Circumstantial evidence renders the latter probable. In the description of Jura, I have remarked that mica slate does, according to Professor Jameson, lie above the quartz rock, and Williams considers the rock I have described, which he also calls granular quartz, to be, like granite, the rock on which micaceous schist usually rests. Professor Playfair also in his Illustrations, (P. 166,) speaks of a “granitic sandstone in vertical beds,” and mentions its alternation with “micaceous