Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/100

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

appearance of the kind observed in the neighbourhood of St. David's.

The internal texture of many of the rocks about Treginnys, and in the road between that place and St. David's, resembles that of a very compact mechanical aggregate, the particles of which are however obscurely defined: the predominating colours are green, greenish-white and pale purple: the character of the recent fracture is like that of coarse steatite. A close inspection brings to view numerous crystalline surfaces of semitransparent laminated felspar, and particles of glassy quartz; and it is worth noticing that the felspar and quartz now and then occur in the substance of the imbedded particles as well as in the cementing medium, shewing a probably contemporaneous formation of the whole mass.

Some of the rocks of this neighbourhood approach to serpentine in their general character, and contain veins of indurated steatite.


This is by far the largest of a number of rocky islands lying off the coast of St. David's, and is separated from the main land by a channel of about two or three miles in breadth. The greatest extent of the island is from north to south, and at each extremity in this direction is an elevated summit, or beacon, of considerable height, the general character of each of which is similar to that of the corresponding summits on the main land. The intervening rocks are principally slaty. The western front of each of these two summits projects into the sea far beyond the intermediate space of land; and it appears probable that the bay interposed between the promontories has been cut out by the dashing of the waves against