Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/94

84 of it is here and there altered by the action of the weather, after the manner of ferrilite.

On the coast, a little to the north-east of Penberry, is a slate quarry; worked out of a mass of schist, which forms remarkably bold and nearly perpendicular cliffs, the strata of which are occasionally much contorted. The surfaces of the laminæ of the slate have sometimes an ochry tarnish, and abound with minute particles of mica.

This quarry is situated between St. David's Head on its north, and a beach called the White Sands on its south side. The slate is of nearly a black colour, and is here and there traversed by veins of brownish white compact and indurated clay, containing tarnished cubical crystals of iron pyrites. The slate is employed in roofing; but does not thoroughly resist the action of the weather, perhaps from the effect produced on pyritical matter disseminated through it: wherefore it is customary in all this part of the country to whitewash the roof as well as the walls of their houses.

The laminæ of this slate are sometimes wrinkled or wavy. It contains but faint traces of mica; and sometimes approaches to the character of siliceous schist.

This name is given to a beach of about one-third of a mile in length, which at its northern extremity is separated from St. David's slate quarry, by a low and narrow ridge of rocks projecting into the sea; and is terminated at its southern extremity by high cliffs. Towards the land it is bounded principally by heaps of sand;