II. The coraIlian rocks of Oxford, Berks and North Wilts

Abstract

The rocks described in this paper strike roughly E. N. E.-W. S. W., from Wheatley, near Oxford, to the neighbourhood of Wootton Bassett and Tockenham in Wiltshire, a distance of about forty miles. They are mapped on the Old Series 1-inch Geological Survey Maps, sheets 13 and 34, and those portions east of Kingston Bagpuize also on the New Series 1-inch Oxford Special Sheet. The extreme south-westerly portions have also been recently re-mapped by the Survey on the new Marlborough sheet. This strip of rocks, of which the average breadth is about two and a half miles, varying from five miles to nothing, has resisted subaerial denudation to a greater extent than the Oxford and Kimeridge Clays below and above it. In consequence it forms a conspicuous ridge, roughly parallel to the Chalk escarpment, dividing the Vale of the White Horse (in its broadest sense) into the valley of the Isis on the north and the valley of the Ock on the south. Near Wootton Bassett is the water-parting between the Bristol Avon and the Thames, of which the Isis is the upper portion, above Abingdon, the point of confluence with the Ock. All the formations within this area have an apparent dip to the north-east.