At the periphery, the remaining exposures of gritstone form what are locally termed "Edges", such as Birchen Edge and Stanage Edge Figure 2 which are manifested as cliffs around the White Peak which are popular with climbers today. Over time these edges will continue their retreat through weathering and erosion. In other parts of the area, the interbedding of shale and gritstone has led to instabilities and resulted in the formation of numerous landslide features including that at Mam Tor which has been active for many years and extends nearly 1 km in length Figure 3.
Tors are an additional landform characteristic of the region although confusingly, Mam Tor is not a tor, this is simply its name. Tors consist of protrusions of bedrock through the surrounding regolith that may rise many metres above the surrounding land Figure 4. Theories as to their origin abound, but they most likely formed in the region when it was within the tropics and subject to deep weathering processes, widening joints in the bedrock, and have since become exposed as the weathered material above has been eroded away.
An alternative theory is that they were produced in periglacial environments with freeze-thaw activity shattering the exposed bedrock material and erosive processes removing the material. In the central White Peak region, the limestone rock and persistently wet conditions have led to the formation of characteristic karst features including sink holes, gorges and caves, formed as water percolates through and enlarges existing rock joints by solution weathering.
Your Account. Figure 1. Show caption. Figure 2. The buildup of ice on the supercontinent reduced the amount of water in the oceans which caused a global drop in sea level.
This change in sea level meant that the Peak District emerged from being underwater and exposed the sediments to erosion and weathering. Much of Britain became coastline rather than being submerged under a sea and rivers became the dominant source of sediment.
During this time, large rivers from continental Scandinavia started depositing fluvial material on top of the limestone. The silt, sand and gravel that was being washed in by the large rivers was compressed and lithified formed rock. This coarse grained sandstone is called millstone grit and this is what makes up the prominent landscape feature at Stanage Edge. It has been used to grind grain in mills for the last years and was exported across Northern Europe until the 18th century.
As sea levels dropped further in ancient Britain, plant matter began to grow in the warm, swampy, coastal regions but the fluctuations in sea level meant that this large quantity of plant matter was frequently submerged and buried by tidal sediment.
These repetitions are called cyclothems and are the source of the coal, found above the millstone grit in the Peak District and surrounding areas. After this deposition, tectonic forces compressed this area of crust and the rocks responded by doming upwards.
This is the result of the forces involved in the final stages of the formation of the supercontinent, Pangea. There was then further uplift and erosion of post-Carboniferous rock strata at the end of the Cretaceous to 66 million years ago. This uplift and subsequent erosion has effectively sliced the top off the dome to reveal a concentric outcrop pattern. At the centre, the grit and shale has been eroded to expose the limestone layers but at the edge where Stanage Edge is located the grit is still intact and forming and escarpment above the limestone.
As with the gritstone escarpments found at Stanage Edge, the sediments found at the mouth of the Ganges and Brahmaputra rivers form vast river deltas of material washed off the nearby mountains. Except here, the sediments are washing off the modern-day Himalayas as opposed to the uplifted regions of Scandinavia that supplied This website uses cookies This website uses cookies to give you the best user experience.
Winnats Pass. Axe Edge Coal mine. Geology About million years ago, the area which is now the Peak District was covered by a warm, clear, shallow sea. Over a long period, millions of years, these creatures lived and Chrome Hill died in this area, gradually laying down a thick bed of calcium deposits from their shells up to a depth of m in places - sometimes these have now been eroded in strange formations like the ancient coral reefs around Chrome Hill.
This did not fill the sea because the seabed gradually sank as the deposits were laid down. This is now the rock which is known as Carboniferous Limestone and this rock lies under the whole of the Peak District.
The sea was also a centre for occasional volcanic activity and at intervals undersea volcanoes would pour out lava across the sea bed, or inject it into the gaps in the beds of compressed fossils. This lava cooled to form layers of basalt known locally as 'toadstone'. Mam Tor from Hope Valley As the sea became more shallow, conditions changed.
From about million years ago, large rivers from adjacent continents to the North began to drain into the sea and deposit silt, which was gradually compressed to form rocks. The first layers of silt were fine and formed rocks now known as shale as can be seen on Mam Tor, but later deposits were very coarse with large lumps of gravel in them and they laid down thick layers of sediment which was hardened to form Millstone Grit, as can be seen on the eastern edges at Stanage, or in the west at Windgather.
These layers eventually covered all the Limestone. Stanage Edge As the sea filled completely, islands of land formed and became richly vegetated, with trees and huge ferns.
However, in this period the land was constantly sinking and rivers were changing their course, so areas of land often would subside and become covered in water again. This laid down a series of layers of alternating shale and vegetable deposits which are now known as the Coal Measures. This whole era of rock formation, which is known as the Carboniferous period, lasted for 65 million years. It was followed by an era when the whole region was subjected to massive earth movements which raised and folded the rocks of the area.
This folding was not even, for the rocks to the West were folded more than those to the East, and even as the folding took place the rocks at the top of the arch were being eroded by the elements. The region was raised in a North-South line which resulted in the dome-like shape of the modern Peak District and the rocks were worn away until even the Limestone beneath was exposed.
At the end of this period the Earth's crust sank in this area and the whole region was covered by sea which deposited a whole range of new rocks over it. Gelena During this period the rock especially the limestone often cracked under the pressures and molten rock magma was forced into the fissures. This was often rich in minerals, such as galena lead sulphide - grey metallic coloured rectangular crystals , fluorspar calcium fluoride - translucent white crystals, sometimes coloured blue or yellow , barytes barium sulphate , calcite a form of calcium carbonate - white crystals and sometimes copper, all of which crystallised as the magma slowly cooled.
The result was the many mineral veins or rakes which are to be found in the limestone areas and which have been mined for lead and other minerals since at least Roman times.
About 63 million years ago at the start of the Caenozoic era, the area was raised again by more massive earth movements and most of the newer rocks which covered the Peak District were gradually removed by erosion.
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