On the Igneous and Associated Sedimentary Rocks of Liangynog (Caermarthenshire)

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Abstract
I. Introduction In the neighbourhood of the village of Llangynog, some 6 miles south-west of the town of Caermarthen, an elevated tract of ground lying between the River Towy on the east and the Cywyn on the west, presents features of especial interest in that it contains several small masses of igneous rocks among the Ordovician sediments. In the re-mapping on the 6-inch scale of the South Wales Coalfield and the ground adjacent thereto, it fell to us to re-examine this district. In memoirs necessarily devoted chiefly to a description of the Coal-field, it is not possible to enter into such detail concerning the petrology and stratigraphy of these older rocks as they seem to deserve. We therefore sought the permission of the Director of the Geological Survey to lay before this Society the following particulars. The district is comprised in the Old Series 1-inch Ordnance-map, Sheet 41; in the New Series 1-inch map, Sheet 229 (Caermarthen), and in the 6-inch maps, Caermarthenshire 38 S.E., 39 S.W., 45 N.E., and 46 N.W. It consists of an elevated plateau, which at Pen-y-Moelfre and Castell Cogan attains an altitude of 546 feet and 426 feet respectively; it is drained in part by several streams which flow southward into the estuaries of the Tâf and the Towy, and in part by streams flowing north-westward into the Cywyn, which itself falls into the Tâf. The south-eastern part of the plateau is occupied by the red marls of the Lower Old Red Sandstone, the base

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