A Composite Sill at Newton Abbot (Devon)

Abstract

I. Introduction. The sill which is described in this paper forms the summit and part of the northern flank of Knowles Hill, Newton Abbot, 6-inch Ordnance-Survey Map 109, S.E. The hill is bounded on all sides except the western by the alluvium of the Teign and its tributary the Lemon; it forms a prominent hog-back lying in the fork between the two rivers. The base of the hill is formed of Upper Devonian slates, and these are continuous to the west, where, at a distance of about half a mile, another outcrop of dolerite occurs at High week Church. The occurrence of picrite was discovered by Busz, and a short description of the sill and of the presence of original quartz is given in the Geological Survey Memoir on the ‘Geology of Newton Abbot,’ No. 339, 1913. II. Field Relations. The summit of Knowles Hill has been quarried, and a smaller quarry exists by the footpath on the north of the hill, bordering the Teign alluvium. The rocks described are mainly from the upper quarry. The northern slopes of the hill are in pasture, and the exposures are too weathered to admit of a petrographic description of the rocks; on the east, the geological lines have been drawn from very limited exposures, as the area has been completely built over. The sill is intrusive into Upper Devonian slates; its lower boundary is indicated by the fact that the floor of the quarry is in slates, the whole of the sill