Notes on the Geology of the District West of Caermarthen

Abstract

In a paper published in the Society's Journal in the year 1885 a complex synclinal of Lower Palaeozoic rocks occurring in the neighbourhood of Haverfordwest was described. Owing to the occurrence of a fault at the northern side of that synclinal, no strata of Arenig age were noticed in the paper, the oldest Ordovician beds referred to being the Didymograptus Murchisoni -shales below the Llandeilo Limestone in the neighbourhood of Narberth, at the south-eastern end of the synclinal. It seemed important, therefore, to work the strata lying east of Narberth in order to try and discover Arenig Beds in the district between that town and Caermarthen. This was accordingly done in some of the vacations between 1886 and 1890, and a complex anticlinal was discovered lying north-east of the Haverfordwest synclinal, having its oldest beds exposed north of Whitland. The accompanying map shows the general distribution of the beds in this anticlinal, no attempt being made to trace accurate boundary-lines ; but two approximate boundaries are drawn at the top of the Tetragraptus -beds (to be presently described) and along the line of outcrop of the Llandeilo Limestone respectively, in order to show the general distribution of the strata and the nature and direction of the anticlinal. The beds may be described, in ascending order, as follows :— 1. Tetragraptus-beds.—These beds consist of alternating conglomerates, shales, and grits, seen at Talfan, :pen-parc-uchaf, and probably near Whitland Abbey, all places lying generally north of Whitland. The shales have yielded graptolites, kindly determined by