On the Evidence of Glacial Action in South Brecknockshire and East Glamorganshire

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Abstract
Introduction Evidences of glacial action seem to have been very little studied hitherto in this part of South Wales. Professor Ramsay, in the fifth edition of his ‘Physical Geology and Geography of Great Britain,’ merely mentions the occurrence of ice-scratched erratics all along the low ground of Glamorganshire north of the Bristol Channel, between Cardiff and Bridgend, and says that Boulder-clay is common her and there all over South Wales. Mr. A. Tylor has described glacial markings on the surface-rock at Hirwain Common, near Myrthyr Tydfil. No one, however, so far as the author is aware, has as yet attempted to work out the problems of these glacial phenomena in a connected manner. And yet few parts of Great Britain offer equal facilities of such a study. This is chiefly owing to the great development in South Wales of rocks so favourable to retaining marks of glaciation as the Millstone Grit and Pennant Rock, and to the fact that the length of their area is more or less transverse to the direction of glaciation. The Millstone Grit, cropping out to the north of the South-Welsh coalfield, runs east and west, without interruption, except at Caermathen Bay, from 1 1/2 mile S.W. of Abergavenny, in Monmouthshire, to within 2 miles of St. Bride's Bay, in Pembrokeshire. This band of Millstone Grit, 76 miles long, and from 1/4 mile to 2 miles in breadth, probably shows glacial markings at intervals throughout the greater part of its length. In Brecknockshire, even where it must have been

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