The Conglomerates and Grits of the Bala And Valentian Rocks of the District Between Rhayader (Radnorshire) and Llan-Sawel (Carmarthenshire)

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Abstract
I. Introduction and Historical Survey During the survey of the country between Elan Valley (Radnorshire) and Pumpsaint (Carmarthenshire) (Davies, 1926 & 1928), a collection was made of the grits and of the pebbles from the conglomerates which occur at many horizons in the district. To these have been added further specimens from the country to the north-east, so that the arenaceous deposits between Camlo Hill (Radnorshire) and Llansawel (Carmarthenshire) are described in the following paper. The whole of the sediments dealt with occur in rocks of the graptolitic facies and lie on the north-western side of the Towy anticlinorium, and they range from the upper part of the Bala stage to the lowest part of the Gala stage. Although the largest accumulations of coarse rocks are confined principally to the Upper Bala and the Lower Birkhill stages, arenaceous material occurs locally throughout the whole succession, and it is only the Monograptus convolutus zone that lacks a noteworthy amount of coarse material; even at this horizon, however, grits up to 6 inches in thickness are found in the country near Ystradffin. As the rocks of the area consist predominantly of fine-grained shales and mud-stones, the widespread occurrence in them of arenaceous and conglomeratic deposits gives to these sediments an additional importance. Some of the arenaceous deposits appear at first sight to occur at constant horizons, and therefore to afford data for correlation purposes throughout Central Wales. Closer investigation, however, proves that they cannot be so applied, since they are only local

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