The Peak District was the first region in the UK to be designated as a National Park. Read a little about the geology of the area on this page. The rocks are predominantly Carboniferous in age and include examples of coal measures, Millstone Grit, Yoredale series and Carboniferous limestone groups. The overall thickness of the Carboniferous rocks in the Peak District is around 3000m.

This is just a taster of the geology of the area. More detailed information can be found by visiting the Peakscan site (see bottom of page). If you want to find more geological web sites try Goran Bogicevic’s fantastic site. There are links to suit all levels of geologist from interested layman to professionals. I don’t have any links to geological maps but these can help you find the key localities White Peak or Dark Peak (10% discount to users of this site!). If you are interested in finding out more about the geology of the Peak District and of the East midlands - Click here for the Open University Geology East Midlands branch web site.

Please click on the images to see larger versions. If you use them on your own web site please credit our site as the source and add a link to us. Thank you.

Derbyshire Carboniferous limestone

The southern boundary of the Peak District, geologically speaking, is along the Ashbourne parallel, where the Carboniferous rocks disappear under the Triassic. The latter lie unconformably on the eroded Carboniferous beds, which have a slightly different dip. There are some Triassic outliers such as the Churnet Valley and Rudyard Valley. No Permian is seen in these areas so it is thought that the landscape developed in Permo-Triassic times and has been re-excavated in modern times. The western boundary of the Peak District can be regarded as the Red Rock fault whilst the eastern boundary is more or less the longitude of Chesterfield. The dominating factor in the geological development of the Peak District was St. George’s Land, a large ridge of Dry land that extended across the UK - read more here plus a more detailed overview here.

The rocks of the Peak District were laid down about 300 million years ago during the Carboniferous period. At that time, the part of the Earth that would become the Peak District was the bed of a shallow warm sea about 5 - 10 degrees south of the equator. The sea  Peak District fossils - brachiopodcontained a variety of life such as brachiopods, corals and crinoids.  Rainfall was low and the nearest significant land mass was well to the north (Caledonia, the land mass that now forms Scotland) so there was little sediment washed into this sea. The water was therefore very clear - perfect conditions for the formation of limestone. As the plants and animals of this sea died, they became part of the limestone as fossils. Crinoids were particularly abundant in the Peak District Limestone and are sometimes referred to as ‘Derbyshire Screws’ owing to their appearance. In several areas, the fauna created large reefs known as ‘reef knolls’. Good examples of these can be seen now as Chrome Hill and Parkhouse Hill near Glutton Bridge (Longnor). Winnats Pass (Castleton) is thought to be a reef channel in an apron reef that was re-excavated by melt water from the last Ice Age (click here for more about the geology of reef limestones in the Dove Dale and geology of the Castleton areas).

Derbyshire screws - fossil crinoids   Calcite and limestone

The rolling pastureland of the Carboniferous Limestone plateau formed by the clear tropical sea is crisscrossed with the dry stone walls of sheep and dairy farms. The purity and accessibility of the limestone has led to the establishment of some of Europe’s largest quarries. The limestone has been mineralised by volcanic action, giving rise to lead mining in the past. Other minerals such as fluorite, Blue John and barytes have been (and still are) extracted. Click here for information on mineralisation.

Some of the limestone has been altered to the dolomitic form in several areas of the plateau. Normal limestone is mainly made from the chemical calcium carbonate, this is altered to magnesium carbonate in dolomitic limestone. This is well seen at Harboro Rocks near Ashbourne. The photographs below show how the colour is more buff than normal limestone and illustrates the presence of more rounded pockets. This type of limestone is also weaker.

Pocketed dolomitic limestone at Harboro Rocks  Harboro Rocks - dolomitic limestone

The limestone is generally regarded as a plateau although it is technically a broad N-S anticlinorium (anticline with subsidiary folds on the limbs). Older rocks are therefore exposed at the centre of the Peak District. This anticline existed in Triassic times (unconformable boundary). The dip angles of the anticline are seen to change in the northern part of the region - at Buxton W/NW; Castleton - N; Bakewell - E so the limestone is referred to as the ‘Derbyshire Dome’. Where the plateau has been dissected by rivers and streams, you can see the horizontal bedding planes of the region. The limestone plateau of the Peak District has not been tilted or folded a great deal. The bedding planes represent times where sedimentation had stopped for a time and perhaps even erosion took place. Bedding planes in the limestone plateau of the Peak District National ParkAt the end of the last Ice Age, the Peak District rivers would have been swollen by melt water from glaciers. The also contained huge amounts of rock flour and larger pieces of rock. This made them act like liquid sandpaper, enlarging the bedding planes forming ledges in the cliffs that are used by nesting birds, plants and as belay points for climbers. In places, erosion has been severe enough to lead to the formation of caves.

The lagoon that gave rise to the limestone plateau was ringed by reefs. These are generally more resistant to erosion and have given rise to characteristically steep and sharp peaked hills. In Dovedale, there are Thorpe Cloud, Bunster Hill, the Twelve Apostles and Tissington Spires amongst others; in the nearby Manifold valley Beeston Tor and Ecton Hill plus Thor’s Cave and crag; at Matlock bath the spectacular High Tor is a reef and in the area of Castleton there is Winnats Pass, Cave Dale and Peak Cavern.

This tropical sea lasted for about 20 million years or so. The mountains to the north of the Peak District were uplifted by the tremendous forces of plate tectonics. The rivers were steeper and therefore faster flowing and carried more sediment. The heavier particles were deposited at the mouth of the rivers, creating warm swampy deltas (like the Mississippi delta of the southern USA). The finer particles travelled further, making the once clear seas of the Peak District cloudy. These fineWinnats Pass, Castleton, Peak District particles gradually Mam Torsettled out to form the shales of the region. They are most famously found in the Mam Tor area (Castleton is the nearest town). Shales are soft and unstable and landslips caused by movement of the shale have destroyed the main road near Castleton. Traffic now has to use the road through Winnats Pass, a few hundred metres south on the more stable limestone. The rocks around this part of the Peak District belong to the Yoredale series.

Destroyed main road at Castleton 

The period of shale deposition did not last for long, geologically speaking. The rivers from the north rapidly extended their deltas to the south, filling the seas Gritstone from the Peak Districtwith particles of sand and occasionally pebbles. Life was no longer possible in this environment, apart from the vegetation that established itself on the older and more stable delta areas (north and East of the current Peak District). This stage of the development is referred to as ‘Millstone Grit times’. The millstone grit rock formed during this period provide so much of the quality climbing venues of the area together with the wilder walking.

As the deltas built out further, creating even more swamp land, the vegetation became established further south. The plants were predominantly tree ferns and as they died they formed a thick peaty layer. If you look carefully as you walk amongst the rocks of the gritstone edges, you can spot occasional tree fern fossils. These were the ‘Coal Measures’ times when the great Yorkshire, Derbyshire and Nottinghamshire coalfield was formed.

A period of mountain building signalled the end of the Carboniferous period. The Mercian Highlands were formed where Wales, the Midlands and East Anglia now are. The immense pressures caused the rocks to be folded. The rocks of the Peak District were pushed upwards to form a broad fold that is now known as the Derbyshire Dome. Once rocks are exposed to the ravagesCoal measures sandstone from the edges of the Peak District of the weather, they are worn down by erosion. The softer and higher the rocks are, the more rapidly they are eroded. The coal Measures were the last to be deposited and are therefore the softest. They were also on the top of the pile and the folding pushed these up the highest. They eroded rapidly at the centre of the dome to reveal the more resistant Millstone grit. The grit was thinner in the southern areas of the region and so has been completely removed to reveal the oldest rocks of the Peak - the limestone. Glaciation during 2 of the 3 main episodes of the Pleistocene Ice Age (ending about 10,000 years ago) affected the Peak District. Ice and melt water removed material and carved the valleys that visitors to the Peak District so enjoy. The caves and caverns are thought to have been created by glacial melt waters travelling as underground rivers through the limestone. Sir Arthur Conan Doyle suggested, in his story ‘The Terror of Blue John gap’, that the area around Castleton was so hollow that if you hit it with a gigantic hammer, it would “boom like a drum or may even cave in completely”. Freeze-Thaw conditions gave rise to landslips like Mam Tor, Lud’s Church near the Roaches and Alport Castles (click for pictures), to the east of Bleaklow. It has been suggested that the latter is the largest in Britain, whether it is or not, it is certainly the biggest in the Peak District. There are plenty more landslips for the geology enthusiast to spot whilst out and about.

Click here to find out about the volcanoes of the Peak District.

Disclaimer - (probably not needed but here goes anyway!) We can accept no responsibility for your well being if you visit any of the geological sites mentioned on this web site, they are included only as information. You should ensure that the necessary permissions are sought when entering private property and also take appropriate action to ensure your personal safety.

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For more information visit Peakscan - Peak District landscapes: rocks & routes, moors & millstones, timelines & turnpikes.

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