Geology
Bedrock geology
The overlying Upper Carboniferous sandstones and shales of the Millstone Grit and the mudstones, shales and sandstones of the Coal Measures form a broad band of outcrop from the coast north of Whitehaven to the north of the Lake District. The lower land around the Solway Firth in north Cumbria, the Carlisle Plain and Vale of Eden are floored by mudstones and sandstones of Permian and Triassic age. These outcrop on the coast in the St Bees area, where they form the well-known red sandstone cliffs._
2.15 The end of the Variscan mountain-building phase resulted in the formation of a new land surface, on which the deposition of sediments began again in the late Devonian or early Carboniferous (354-290 million years ago) following the encroachment of the early Carboniferous sea. In Northern England and southern Scotland, the land over which the sea transgressed comprised a series of blocks and troughs or basins. Greater thicknesses of sediment were deposited in the troughs than over the blocks which tended to remain as relatively stable, shallower, areas throughout the Carboniferous. Much of Cumbria lay over what was then one of these block areas and this influenced deposition during this period._
2.16 Apart from the south-west Cumbrian coast, rocks of Carboniferous age form a broad swathe of outcrop around the older core of the Lake District. The oldest rocks of the area belong to the Carboniferous Limestone Series. These rocks are composed of limestones, sandstones and shales deposited in a shallow marine-estuarine environment, and outcrop in south Cumbria in the Ulverston-Furness area, in a broad lobe between the Kent Estuary, Kirkby Lonsdale and up to Kendal and then in a broad band following the eastern and northern rim of the Lake District from Ravenstonedale, north-westwards to Penrith and then around the north of the Lakes to Cockermouth._
2.17 The Carboniferous Limestone is overlain by the Millstone Grit Series. In this area of England, the differences between the Millstone Grit and the older Carboniferous Limestone are less marked than further south, with sandstone common in the Carboniferous Limestone and limestone present in the Millstone Grit. In Cumbria, the Millstone Grit series consists of a series of limestones, marine shales and sandstones, and the ‘Millstone Grit’ itself, thick coarse-grained sandstones, siltstones and mudstones. These rocks were deposited in the late Carboniferous (approximately 300 million years ago) in a coastal environment where large river deltas were building out into the shallow marine waters. Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swampy land area in which the succeeding Coal Measures were deposited._
2.18 The Lower and Middle Coal Measures outcrop in north-west Cumbria from the coast at Whitehaven to Maryport and then easterly to south-east of Wigton. The rocks of the Coal Measures show a repeated coal, sandstone and mudstone cycle which reflects relative changes in land and sea level. The coals represent the fossilised remains of swamp vegetation which grew as luxuriant forests on the deltas, while the mudstones were deposited under shallow marine conditions. The Lower and Middle Coal Measures contain the workable coals of the West Cumbria Coalfield._
2.16 Apart from the south-west Cumbrian coast, rocks of Carboniferous age form a broad swathe of outcrop around the older core of the Lake District. The oldest rocks of the area belong to the Carboniferous Limestone Series. These rocks are composed of limestones, sandstones and shales deposited in a shallow marine-estuarine environment, and outcrop in south Cumbria in the Ulverston-Furness area, in a broad lobe between the Kent Estuary, Kirkby Lonsdale and up to Kendal and then in a broad band following the eastern and northern rim of the Lake District from Ravenstonedale, north-westwards to Penrith and then around the north of the Lakes to Cockermouth._
2.17 The Carboniferous Limestone is overlain by the Millstone Grit Series. In this area of England, the differences between the Millstone Grit and the older Carboniferous Limestone are less marked than further south, with sandstone common in the Carboniferous Limestone and limestone present in the Millstone Grit. In Cumbria, the Millstone Grit series consists of a series of limestones, marine shales and sandstones, and the ‘Millstone Grit’ itself, thick coarse-grained sandstones, siltstones and mudstones. These rocks were deposited in the late Carboniferous (approximately 300 million years ago) in a coastal environment where large river deltas were building out into the shallow marine waters. Continuing deposition over the millennia led to the further building out of the deltas and the formation of an extensive low-lying, swampy land area in which the succeeding Coal Measures were deposited._
2.18 The Lower and Middle Coal Measures outcrop in north-west Cumbria from the coast at Whitehaven to Maryport and then easterly to south-east of Wigton. The rocks of the Coal Measures show a repeated coal, sandstone and mudstone cycle which reflects relative changes in land and sea level. The coals represent the fossilised remains of swamp vegetation which grew as luxuriant forests on the deltas, while the mudstones were deposited under shallow marine conditions. The Lower and Middle Coal Measures contain the workable coals of the West Cumbria Coalfield._