Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/101

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Dr. Kidd on the Mineralogy of St. David's.

the crumbing schistus which is here opposed to them, and that consequently in process of time, as this schistus is extended across the island to the eastern shore, the island may eventually be separated into two.

The harbour of Ramsey is a small cove excavated in a mass of black schist, and situated near the southern extremity of the eastern front; advancing from which towards the west, and then ascending the southern beacon from its northern side, you pass over an apparently conglomerate rock made up almost entirely of large pebble shaped masses of white quartz. From the uniformity of colour in this rock, and from its general appearance, a doubt at first sight arises whether it is really a mechanical conglomerate or the result of a peculiar chemical conformation.

On and near the summit of the southern beacon the rock in many places resembles coarse chert, from which it passes into the state of indurated clay containing small crystals of felspar and of dodecahedral quartz, the latter in general very imperfectly defined.

The composition of the rock forming the northern beacon is felspar and hornblende, sometimes assuming nearly a homogeneous appearance, and sometimes, though rarely, inclining to a porphyritic structure.

With the island of Ramsey these notes on the Mineralogy of the neighbourhood of St. David's terminate, in drawing up which it has been my object to avoid as much as possible the language of hypothesis, and to detail the appearances which I met with in terms strictly descriptive: and though I feel strongly persuaded, on grounds which have not been taken up hastily, that all the rocks which I have been describing are essentially allied to each other, and are all of chemical and contemporaneous origin; yet, conceiving