Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/90

From Wikisource
Jump to navigation Jump to search
This page has been validated.
Dr. Kidd on the Mineralogy of St. David's.

and the general character of them is crystalline: but the felspar rarely if ever occurs in distinct crystals; and even the hornblende, though usually the most accurately defined of the two, is sometimes not discernible from the felspar. Again, though the mass often appears upon the whole to have been of chemical origin, yet at the same time it is, partially, of a structure to the eye decidedly mechanical; and in some instances the character is so extremely equivocal as to leave the judgment in a very difficult state of suspense. The predominating colour of these crystalline rocks is a brownish green.

The two highest of these hills, called Carnllidy and Penberry, are situated to the north of St. David's: they rise less abruptly from the plain than the similar hills of the neighbourhood; and are in a manner connected with each other, and with a third summit not far distant from the last mentioned, by a slightly elevated ridge which passes in a south-westerly direction from one hill to the other; Penberry being at its north-eastern extremity. From the summit of Carnllidy the ground gradually slopes towards the west for a few hundred yards, and then, again rising, forms the promontory called St. David's Head.

The ascent to the two hills above mentioned, both on the north and on the south side, is formed by highly inclined strata of a slaty rock which would be commonly called grau-wacke, a term in the present instance used only for the purpose of general description; and the nearly precipitous cliffs, by which the greater part of the adjoining coast is bounded for some miles, appear to consist principally of the same kind of rock. The massive tabular laminæ of this schist rise abruptly from the sea, with a highly elevated degree of inclination towards the land, over the edge of which they are sometimes folded in the form of a broad mantle, or are occasionally broken into natural arches and caverns; giving to the outline