Abstract

In southern Britain a line joining the Bristol Channel with the Thames estuary roughly demarcates the areas of Old Red Sandstone deposition to the north and of marine Devonian to the south. Transgressions occasionally carried marine rocks farther north, in the Late Devonian at least as far as Pembrokeshire and Wyboston. Similarly O.R.S. conditions often spread south, in the Siegenian as far as South Devon and Cornwall and in the Middle and Late Devonian as far as North Devon. Many marine facies are represented; in the Middle Devonian, the slates of Cornwall pass into calcareous facies in South Devon. The deeper water facies of the Upper Devonian in South Devon and Cornwall shows “becken” and “schwellen” type deposition.

South of the bounding line the Devonian rocks are involved in intense Armorican fold and thrust systems. The area has been intruded by late Carboniferous granites and a belt of associated mineralization crosses South Devon and Cornwall.