Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/403

From Wikisource
Jump to navigation Jump to search
This page has been validated.
393
various parts of Scotland.

seems the only very discriminating character. I think it necessary also to mention that the hornblende rock exhibits the two subordinate varieties of hornblende slate and greenstone slate.

Since I have already indulged in some cursory remarks on that sort of nomenclature which tends to mislead, by confounding substances, I may be excused for suggesting a reformation in the terms primitive greenstone and greenstone slate. These consist of mixtures of felspar and hornblende, in the latter case disposed in a laminated form, and in the former without that regular structure. Their title to greenstone, as far as colour is concerned, is still less than that of the varieties of the trap family, as the felspar is (in Scotland at least) always of a red colour. By the use also of the term greenstone, and by the series which is formed of primitive, transition, and flœtz greenstones, the mind is naturally led to look for a geological and natural connection between these rocks. But the primitive greenstones belong to that class in which gneiss and mica slate form the principal features, and which constitute that great system of rocks of which hornblende in its several modifications of hornblende rock, primitive greenstone, hornblende slate, and greenstone slate, is only a subordinate and occasional member. The geological character of the flœtz greenstones, is their independence with respect to the rocks with which they are associated, and their intrusion, if I may so call it, among a regular system of stratified bodies. The transition greenstones are, I conceive, of a character merely arbitrary, and only so called because occupying the same situation with regard to the transition, as the former do with regard to the flœtz rocks.

Thus also, greenstones may be classed among the primitive, where they occupy similar positions among primitive rocks.

But the primitive greenstones to which I now allude, and which

Vol. II.3 d