Pennines and adjoining areas - Peak District and Pennine Hills
This area comprises the Pennines between Blackburn and Lancaster in the west, and Richmond, Leeds-Bradford in the east, and also incorporating, in the southern part, the Peak District extending to Derby (Figure P902241). The rocks of this area have generally given rise to poor acidic soils that are not suitable for crops and have resulted in predominantly livestock-based farming.
Sedimentary bedrock
In the Peak District and Pennine Hills, the bedrock is formed by sedimentary layers that can be divided between:
- an upper sandstone and mudstone unit (Plate P005589), referred to as the Millstone Grit and an underlying mudstone unit and potential hydrocarbons resource, the Craven Group, that is present beneath much of the Pennine Hills, from north of Derby and Leek (Staffordshire), to Harrogate and Catterick (North Yorkshire) and south of Preston to Lancaster (Lancashire); and
- a lower limestone unit, commonly known as Carboniferous Limestone (Plate P005589), that is present at surface in the Yorkshire Dales and Derbyshire Peak District.
In some places the layers are steeply tilted and folded, in response to ancient episodes of earth movements. Some of the sandstone and limestone layers within this bedrock are minor aquifers, meaning that they can provide minor amounts of water for local public supply.
Very thick accumulations of sediment within this area were deposited in deep basins in some parts of the area; in others uplifted areas of basement rocks occur, bounded by geological faults, leading to much thinner sediments. In parts of Lancashire and Yorkshire the Millstone Grit, Craven Group and Carboniferous Limestone are present to depths exceeding 2000 m below ground. Limestone is quarried extensively as a major source of aggregate and for cement manufacture. Historically, ores of lead, zinc and copper were deep-mined in parts of the Peak District, in the Forest of Bowland, and Wensleydale in North Yorkshire. Being soluble, the limestones have been dissolved by rainwater percolating through them to form many caves, dry valleys and sinking streams. Landscapes where drainage is underground through caves in this way are called karst landscapes. Such features are especially well developed in the Yorkshire Dales (Plate P005589) and the White Peak. The limestones form an important aquifer locally, both for water flowing through caves and fissures, which are used for public supply but also for much deeper groundwater flow that feeds the famous springs at Buxton.
Basement rocks
The sedimentary bedrock layers rest on much older basement geology which, although only exposed at surface near Malham in North Yorkshire (Figure P902241), has been proved by some deeper boreholes or interpreted from seismic surveys that were carried out for the exploration of oil and gas. Beneath most of the area, the basement comprises very old sedimentary rocks that are very hard, including slates, sandstones and mudstones and are intensely folded and faulted.
The basement rocks include a large intrusion of molten rock which cooled and solidified to form granite, some 60 by 25 km in extent beneath parts of Wensleydale in the Yorkshire Dales. This granite was indicated by regional gravity surveys and later proved at 500 m below ground surface by a deep borehole. The presence of a second granite beneath the south-eastern parts of the Peak District has also been suggested from the gravity data, but this is so far unproven by drilling.