Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/99

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89
Dr. Kidd on the Mineralogy of St. David's.

Not far from Carvay I met with two insulated masses, one of which, bearing a very close resemblance to the mill-stone grit of Derbyshire, was made up of small particles of white and reddish white semitransparent quartz cemented together by white earthy felspar: the other was also a kind of grit-stone, consisting almost entirely of particles of quartz, occasionally interspersed with specks of white earthy felspar. Though I saw no rock in situ to which these masses could be directly referred, yet as they did not much differ from some of the rocks of this district, excepting in the size of their component particles, and as there was not any ground for supposing they had been brought there by art, they probably belong to the suite already described.

Treginnys.

This is a broad headland, about three miles to the south-west of St. David's. It is frequented by trading vessels on account of a fresh-water spring which rises near the edge of the adjacent cliff's, beneath which is a convenient harbour.

The general character of the rocks in the neighbourhood of Treginnys is of that equivocal nature alluded to in the beginning of these notes: here and there they assume the appearance of a compact earthy felspar of an olive-green colour, and then probably often contain epidote, compact veins and crystals of which I saw in more than one instance. In one place this compact green rock occurs in angular columns horizontally aggregated, and forming a part of the cliffs on the north side of the harbour. The number of the columns is not above eight or ten; their form irregularly pentagonal, and their diameter less than a foot. This was the only

Vol. II.M