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Bolton lies in a valley created by the River Croal running from west to east. There is a high proportion of 'foreign' rocks mixed in with the sandstone and grit, and there are thin streaks of coal.
An examination of the strata from Doffcocker Colliery taken around 1880 showed black shales, beneath which was 15 centimetres (6 inches) of coal, 2 metres (7 feet) of fire clay and shale, 50 centimetres (18 inches) of coal, 10 metres (36 feet) of hard gannister rock with stigmaria.
During the Ice Age, the valley in which Bolton is situated was cut, leaving a lot of boulder clay in the area, to depths of over 30 metres (100 feet), and a lot of gravel and sand to the south of the district. The northern land is over 250 metres (750 feet) high, sloping southwards into the Croal valley to 150 metres (500 feet) to between 50-100 metres (90 - 300 feet).
The Moors were formed during the Carboniferous period, hence the coal seams, interlaced with sandstone and shale.
The area is largely seismically stable, the odd tremors felt usually centre out in the Irish Sea or south towards the Potteries in Stafford. Obviously some subsidence occurs in the area due to the old mineworkings.
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