The Ordovician and Associated Pre-Cambrian Rocks of the Pontesford District, Shropshire

Remapping of the area east of Pontesford hill, Shropshire, western England, has revealed that the Precambrian rocks at Lyd Hole are faulted and that the Ordovician shales form two outcrops separated by faulting rather than a single one. The sheet of so-called rhyolite which has been postulated to occur between the Precambrian and the Pontesford shales is reexamined, but no undisputed exposures have been found. It is suggested that the basal conglomerate of the Pontesford shales contains boulders of rhyolite, of which partial exposure might suggest a rhyolite sheet. If the rhyolite does not exist as a sheet, a hypothetical phase of Ordovician volcanic activity is no longer necessary in the interpretation of the area. The graptolite and shelly faunas (particularly trilobites) of the Pontesford shales are described.