The geology of the Silurian rocks west and south of the Carneddau Range, Radnorshire

Abstract

Summary An account is given of the geological succession from the Upper Llandovery to the lower part of the Lower Ludlow. The former group is developed in two distinct facies—an eastern facies of calcareous sandstones with Pentamerus oblongus , and a western facies of green mudstones and dark shales containing Monograptus crenulatus and other graptolites. The Wenlock rocks are dark graptolitic shales which have been divided into two sub-groups. They include the six graptolite zones erected by Dr. G. L. Elles in 1900. The Lower Ludlow rocks consist of shales with Monograptus nilssoni . In the Upper Wenlock and above the M. nilssoni shales there are important developments of slumped mudstones which have been mapped in detail. The area is a shallow syncline traversed by a series of powerful faults ranging mainly in the direction of the strike. Some of them behave as block faults. One fault appears to be a tear which has shifted earlier faults. Cleavage is sporadically developed.