Northern England district - Solway Lowlands and the Vale of Eden

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Sherwood Sandstone at Ousby in the Vale of Eden, Cumbria. P902240.

This area comprises lowlands to the south of the Solway Firth, along with the valley of the River Eden. Penrith and Carlisle lie within this area.

Sedimentary bedrock

The gently rolling lowlands that border the Solway Firth are underlain by up to 500m of reddish brown Mercia Mudstones containing thin beds of mineral salts, which formed as extensive coastal mudflats and lake deposits. These are overlain west of Carlisle by grey mudstones laid down around 180 million years ago; which represent the youngest sedimentary bedrock in the region.

As in the southern Lake District, these mudstones overlie the Sherwood Sandstone. Together this package of rocks extends to depths of about 200 m north-east of Maryport, to nearly 800 m west of Carlisle, and just over 1300 m at Silloth. At greater depth lie older, Carboniferous sediments up to 2 km thick, including Coal Measures in a concealed extension of the coalfield of west Cumbria described above.

In the Vale of Eden two units of sandstone separated by mudstone form the uppermost part of the sedimentary bedrock. These units are inclined eastwards, with the base of the lower sandstone descending to about 650 m below the surface adjacent to the edge of the north Pennine Hills. The upper sandstone unit is the Sherwood Sandstone (Plate P902240). The mudstone beneath contains layers of gypsum and other mineral salts which have been extracted in the past for use in the chemical industry and for the manufacture of glass, cement and plasterboard. Both sandstone units are locally significant aquifers in this area. Beneath the lower sandstone unit are older mudstone and sandstone containing thin beds of limestone, and these in turn overlie the Carboniferous Limestone.

Basement rocks

The basement rocks of the adjoining Lake District do not occur at the surface in this area, but are present at depth. The basement rocks descend eastwards beneath the Vale of Eden to lie at about 2 km depth adjacent to the north Pennine Hills. By contrast, the top of the basement beneath the Solway Lowlands lies much deeper at about 8 km.