The Geology of the Fairbourne-Llwyngwril District, Merioneth

Abstract

I. Introduction This paper deals with that part of western Merioneth which lies between the village of Arthog and the town of Towyn. The area is included in a rectangle, the longer side of which runs north-east and south-west and is 8 miles long; the shorter side has a length of 3 miles. The western and northern boundaries are formed by Cardigan Bay and by the estuary of the River Mawddach. On the southern side, the area is bounded by the alluvium of the River Dysynni, and the south-eastern margin is the old Roman road which runs from Llanegryn to Dolgelley. The region is comprised within the Ordnance Survey 6-inch map, quarter-sheets Merioneth 36 S.W. & S.E., 40 S.E., 41 N.W., N.E., & S.W., 45 N.E., and 46 N.W., and within the Geological Survey 1-inch map, Sheet 59 N.E. (Old Series). The topography of the district to be described is in marked contrast to that of the country adjoining it on the north-east, which includes the range of Cader Idris and its foot-hills. Sharp, craggy ridges are absent, the hills having smooth, rounded outlines and grassy slopes. The even contours are largely due to a mantle of glacial drift which smooths out pre-glacial irregularities and in many places conceals the solid geology. The greater part of the area is upland country of low agricultural value, woodland being absent and the general aspect monotonous and bare. The maximum elevation, on Pen-y-garn, is 1500 feet above O.D. The main lowland region lies