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Geological Field Excursion to the Bideford Area (Geology Section)
Sun. 30 July 2023 at 10:00 am
Leaders: John Mather and Jenny Bennett
Bideford and the surrounding area lie on rocks formed in the latter part of the Carboniferous period, some 326-299 million years ago. Although dominantly sandstones and mudstones, they contain sporadic thin beds of impure coal or “culm” and were named Culm Measures by early geologists. The sediments were deposited in a marine basin, which lay to the south of a landmass situated over what is now south Wales. The oldest beds, called the Crackington Formation, after Crackington Haven on the north Cornish coast, were deposited in a muddy- bottomed sea which was inundated periodically by sediment-laden currents (turbidity currents) forming thin beds of sandstone.
Around Bideford, close to the top of the Crackington Formation, somewhat different rocks occur, which bear similarities to the Coal Measures found in south Wales. These are shallow water mudstones, siltstones and sandstones which are thought to represent deltaic deposits from a river flowing into the basin from the north. Called the Bideford Formation, they date from about 320-315 million years ago and contain beds of culm which have been worked at least since the 17th century. Beds (or seams) of culm, thick enough to be worked commercially, extend in a belt from Greencliff on the coast, through Bideford town and East-the-Water, and probably as far east as Chittlehampton. Two types of culm have been mined, glossy lustrous lumps of anthracite and dull earthy carbon-rich mudstones.
The object of the excursion is to examine the Culm Measures rocks and review the exploitation of seams of culm, mined from the 17th century until closure of the last mine in 1969. Localities visited will include the foreshore at Westward Ho! (Crackington Formation), Greencliff (coal seam and sandstones of the Bideford Formation) and East-the-Water (carbon-rich mudstones in the Bideford Formation). We will also not ignore the magnificent exposures of the raised beach at Westward Ho!
We will assemble at 10am in Westward Ho! and will finish late afternoon in Bideford. Stout shoes and a hard hat are required, as we will be walking over a boulder strewn foreshore at Greencliff, otherwise walking is reasonably flat. Bring a packed lunch and plenty of water.
Please register with the organiser (details below) by 20th July. An administrative charge of £3 per head will be collected on the day. Any queries to Jenny or John at the same email. We’ll send further details to everyone registering.