The Unconformity between the Coal Measures and the Lower Carboniferous Rocks in the Clapton-Clevedon District, Somerset

Abstract

In 1915 I published a short paper in which it was shown that the Coal Measures of the Clapton area on the northern side of the Clifton-Clevedon ridge, Somerset, rested with strong unconformity upon the Carboniferous Limestone and all older rocks. Subsequently Professor S. H. Reynolds, having observed the relations at Court Hill, Clevedon, where the Carboniferous Limestone is clearly thrust over the Coal Measures, saw no reason to differ from the earlier observers, Buckland and Conybeare, the officers of the Geological Survey, and Lloyd Morgan, all of whom regarded the Main Limestone-Coal Measures junction south of Clapton as a faulted one; accordingly, on the map accompanying his paper, Professor Reynolds showed the boundary as a fault as far as the eastern limit of the Coal Measures, even where they transgress from the Main Limestone across the Lower Limestone Shales. At a later date Dr. E. Greenly, in a description of the sections at East Clevedon Gap, about three miles west of Clapton, referred to the unconformity as follows: “Whether, as believed by A. Vaughan and F. Dixey, there be unconformity, the whole of the Visean, with apparently the Lower Coal Measures as well, having been locally removed by inter-Carboniferous erosion, is a question that will not be discussed in this paper. But, independently of that question, there is reason to suspect that the base is cut out, for the lowest visible sandstones on the wooded bluffs are buckling over, as if driven forward on a thrust-plane. Should serious unconformity be eventually proved, this thrust need not be of much tectonic importance. In any case, the plane, whatever its nature, is over-stepped by the Bella-Vista Thrust-plane…”