Geology
The Vale of Clwyd is a sedimentary basin which takes the form of a half-graben whose eastern margin is marked by the Vale of Clwyd Fault. Like the Cheshire Basin further to its east, it is mostly floored by thick deposits of Permian and Triassic sandstone. Around St Asaph, late Carboniferous, Coal Measures mudstones and sandstones occur. The area was overrun by ice during the ice ages whose legacy is a covering of glacial till across the area and a swarm of drumlins along the western edge of the vale. Alluvium is encountered across the floodplains of the River Clwyd and its tributaries.
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