The Geology of the District between Abereiddy and Abercastle (Pembrokeshire)

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Abstract
I. Introduction. The area with, which this paper is mainly concerned is a strip of country about 5 miles long, bordering on the north-western coast of Pembrokeshire. The eastern end of this strip is about 6 miles south-west of Fishguard, while its western end lies some 4 miles north-east of St. David's. The country is represented on the 6-inch Ordnance Survey Maps, Pembrokeshire Sheets 8 S.W. & S.E., 15 N.W. & N.E., and comes within Sheet 40 (Old Series) of the 1-inch Geological Survey Map. The district is one of low relief, lying as it does for the greater part between the 100- and the 300-foot contour-lines. The ground rarely falls below the former level, and accordingly the very irregular coast-line is largely formed by precipitous cliffs. The valleys are broad, and choked with Drift or alluvium; and, as the watershed (the average elevation of which is between 300 and 400 feet) lies only about 2 miles south of the coast, the few north-ward-flowing streams have very short courses and little or no erosive power. The streams are hence almost lost in boggy ground. The surface configuration has no very direct bearing on the geological structure, while inland exposures are poor and none too plentiful. The district is several miles distant from the nearest railway. The population is scanty, and the only industry, apart from farming, is that connected with the diabase- or ‘granite’-quarries at Porth Gain, where there is a small harbour, the only one now used on this