Geology of Exeter and its environs

A 225 km² area around Exeter, described in this report, extends from the villages of Brampford Speke and Whimple in the north to Aylesbeare, Exminster and Woodbury in the south. It is underlain by Carboniferous, Permian, and Triassic solid formations and by a variety of Quaternary superficial deposits. The Namurian Crackington Formation comprises mainly tightly folded shales with subordinate sandstone interbeds. The Permian rocks consist of a lower, predominantly: breccia, sequence (Whipton Formation, Teignmouth Breccia, Monkerton Member) that thins and disappears northwards against a possibly fault-controlled ridge of Crackington Formation; the breccias are overlain by sandstones and mudstones (Dawlish Sandstone and Aylesbeare Mudstone). Volcanic rocks occur at the base of the Permian sequence and possibly within the Dawlish Sandstone. The latter splits into five alternating sandstone and mudstone members when traced northwards from Exeter into the Crediton Trough (an area of thick Permian sediments). The Aylesbeare Mudstone is divisible south of Aylesbeare into two members, the lower containing impersistent sandstones. It is overlain by the basal Triassic gravels (Budleigh Salterton Pebble Beds) which are in turn succeeded by the Otter Sandstone.