Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/96

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

divided by the river Alun; the mouth of the river emptying itself into this harbour.

The rocks constituting the rising ground on the left bank of the mouth of this river appear to be a compound of felspar or quartz, or both, with hornblende: the predominating colour is brownish white, arising from the great proportion of the two first mentioned component parts.

On the right bank of the mouth of the river the strata are distinctly schistose, and very various in their appearance. Within the distance of two feet the rock assumes the following characters.

Brick red slate, nearly siliceous.

Brownish purple slate, with streaks of green.

Red slate, with an incrustation between some of the laminæ resembling blackish green scaly chlorite.

Greenish grey compact sandstone.

Stratified sandy slate, partly greenish grey, partly purple.

Traces of steatite and serpentine occur in the rocks of this neighbourhood.

Rock in the Close of the Cathedral.

The cathedral is situated in a part of the narrow valley through which the river Alun winds from the north east; the descent to its eastern and south eastern extremity is steep, and is formed by a rock which might be called a small grained green-stone porphyry, in a high state of disintegration.

The general colour of this rock varies between a brownish white or yellow, and a very obscurely greenish brown: where most compact it has nearly a homogeneous appearance, and would by many be described as a soft compact felspar; but commonly it is in a very loose state of aggregation.