The Peak District National Park

The Peak District was the first region in the UK to be designated as a National Park. It is not entirely in Derbyshire so some of the geology of the surrounding counties is included. It is essentially an upland region, forming the southern part of the Pennines. The highest point in the Peak District is on Kinder Scout - 636 m, which is a shade over 2000 feet above mean sea level. There are many hills over 500 m and large areas of the limestone sector are between 250 and 400 metres of altitude.

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 3000 m.

The rolling pastureland of the Limestone plateau 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 Peak District mineralisation.

Further Information - Peak District Geology

This is just a taster of the geology of the area. The British Geological Survey site is worth a visit - it is searchable and there are quite a few pages about  Peak District geology. The OS 1:25000 maps of the White Peak and  Dark Peak are perfect for getting you to the various localities. The OU Geology East Midlands branch (web site here) may be of interest if you live within striking distance of Nottingham particularly for hands-on experience.

Goran Bogicevic's fantastic site is stuffed full of links to general sites about geology and is worth a visit. There are links to sites that suit all levels of geologist from interested amateurs to professionals.

Geological Blocks

Setting the scene

The geological southern boundary of the Peak District is along the Ashbourne parallel. Here, the Carboniferous rocks disappear under the Triassic. They 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, so it seems the landscape developed in Permo-Triassic times and was re-excavated in modern times. The western boundary of the Peak District can be regarded as the Red Rock fault. The eastern boundary is more or less the longitude of Chesterfield.

Peak District geology was influenced by the presence of St. George’s Land (later the Wales-Brabant ridge) also a land mass to the north. A major ocean trough lay to the south of Britain, created by the collision of two of the Earth’s plates. This would later be responsible for the folding and faulting of the rocks of the UK.

The collision gave rise to the Variscan (Armenian) orogeny which continued throughout the Devonian and Carboniferous systems. It was during this orogeny that the Derbyshire dome and the Goyt syncline were formed.

Peak District Geological Faulting

The Variscan Orogeny caused the rocks of the Peak District to be folded N-S into a broad anticline. All of the rocks show faulting in places, as evidenced by the presence of slickenslides. A good example is between Crow Chin and Cleft Buttress at Stanage Edge. The slickenslides can be seen on the rocks to the left hand side of the gully, looking upwards. The anticline has subsidiary folds on the limbs such as the Goyt Syncline and Todd Brook Anticline.

Many faults have been affected by mineralisation giving rise to veins and rakes (vertical mineral veins). Joints in the limestone have also been mineralised. The joints are fissures created in the still consolidating rocks as overlying sediments were eroded. The removal of sedimnts reduced the load and therefore the pressure.

A number of the faults and folds affect all of the Peak District rocks and must therefore be later. These are not aligned and thought to have been caused by movements of the basement rocks. The basement is thought to be made up of a complex system of blocks of older rocks. As these moved under pressure, the overlying rocks were therefore disturbed.

It has been suggested that the Derbyshire dome would have been around 3000m above the sea level of the time. Currently the high point lies on the Kinder Scout plateau at 636m.

St George's Land

St. George’s Land persisted throughout the Lower Carboniferous. It gave rise to a shallow shelf sea of varying depth in the region of Derbyshire. You can see the edge of shelf deposits at Castleton and in the Hartington/Earl Sterndale area. When you look at these areas, you see the topography of the sea floor as it existed at that time. Winnats Pass is believed to be a channel in an apron reef, re-excavated by melt water during the last Ice Age.

Sedimentation

Rainfall was low and the nearest significant land mass was well to the north. As a result, there was little sediment washed into the sea. The water was therefore very clear meaning conditions were ideal for the formation of limestone.

There was a deep basin to the north of the shelf at Castleton. This was filled during the upper Carboniferous with shales and coarse sandstones of deltaic origin. There are occasional marine bands in the deltaic sediments and also some turbidites, showing the front of the delta was not stabilised. These sediments were derived from a mountain range to the north.

The basin was subsiding at about the same rate as sedimentation was occurring. This subsidence was caused by the plate boundary to the south of the UK. Some of the shallow water limestones show weathering surfaces.

Fossils

The sea contained the usual variety of life associated with UK Carboniferous limestone such as brachiopods, corals and crinoids. 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. Occasional plant fossils can be spotted in the millstone grit.

Evidence from fossils shows that the UK was placed close to the equator during Carboniferous times - no seasonal growth is seen. This is further backed up by palaeomagnetic evidence, placing the UK no more than 30 degrees north or south of the equator at most.

Many of the fossils in the Peak District are broken up, therefore showing a relatively high energy environment overall. This damage to the fossils could have been a result of storm damage or strong currents transporting the remains from where the original organisms died. There are a few localities where undamaged, well preserved fossils occur.

Mud Mounds and Volcanoes

In several areas, the fauna created large reefs, for example those seen as Chrome Hill and Parkhouse Hill near Glutton Bridge (Longnor). There is more about the geology of reef limestones in the Peak District and geology of the Castleton area here.

The reef limestones of the Peak District lack the characteristics of modern reefs and are best described as ‘Mud Mounds’. These mounds were held together by (cyano)bacterial or algal activity. Where they are located on areas where the sea bed was flat, they are referred to as reef knolls e.g. High Tor at Matlock Bath, but where they occur at the edge of the shelf, they are called apron reefs e.g. the Castleton area.

There was some vulcanism in the Peak District during the Lower Carboniferous. This gave rise to basalts and tuffs, interbedded with limestones. Some of these flows can be seen at Tideswell dale (where spheroidal weathering is seen in a small quarry). Other localities include the high ground to the north of Matlock Bath and also in the Castleton area, notably Cave Dale and Calton Hill.

Near Calton Hill, mantle material has been identified in a volcanic vent. This is characteristic of areas where the crust is under tension and has been thinned. The lava of Calton Hill was quarried for a number of years in the first half of the 20th century.

Basement rocks of the Peak District

The basement rocks are not exposed anywhere in the Peak District but have been located in boreholes. There are 3 of these, Eyam, Woo Dale and Caldon Low. The Eyam borehole hit Ordovician rocks at a depth of about 1800 metres. Woo Dale near Buxton reached volcanic rocks of an uncertain age at about 270 metres. Caldon Low encountered rocks of probable Devonian age at a depth of about 350 metres.

The dominating factor in the geological development of the Peak District was St. George's Land. This was a large ridge of land extending across the UK, influencing more than just the Peak District geology.

Post Carboniferous Peak District Geology

The Peak District was similar the Bahamas banks today with a sea floor of varying depth with shelf areas. This was created by movements in the northern shelf of the E-W land mass, St. George’s Land. Mud mounds formed on the shelf areas, now seen as reef knolls. At the edges of the shelf, apron reefs formed, as seen at Castleton.

The dip of the Castleton reefs is an actual dip, shown by the partial infilling of brachiopod fossils (geopetal infill). This type of infill acts like a spirit level therefore we are seeing the reefs as theye were at the time of deposition. In the deeper off-shelf regions, the limestones are darker. This is because their deposition was accompanied by the deposition of mud as well.

In some places, chert nodules have formed within the limestone, for example Intake quarry near Middleton Top. It is more resistant to weathering and at Intake, provides climbers with interesting holds. Chert is a form of quartz (silica - silicon dioxide) with no crystalline structure. It is formed where diatoms and radiolarians (microscopic creatures) have died and been concentrated as a siliceous ooze. The equivalent in chalk is flint, whose different properties made it suitable for making tools in the stone ages.

Diagenesis of Peak District Limestone

Some of the limestone has been altered to the dolomitic form in several areas of the plateau. Normal limestone is mainly predominantly the chemical calcium carbonate. Diagenesis alters this to calcium magnesium carbonate to form dolomitic limestone. This is well seen at Harboro Rocks near Ashbourne. The colour is more buff than normal limestone with the presence of more rounded pockets. This type of limestone is also weaker.

The Derbyshire Dome

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, as evidenced by an 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 therefore the limestone is referred to as the 'Derbyshire Dome'.

Where the plateau has been dissected by rivers and streams, you can see horizontal bedding planes. 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. In places, weathered surfaces can be obseved showing that erosion took place.

At the end of the last Ice Age, the Peak District rivers were swollen by melt water from glaciers. They 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. In places, erosion has been severe enough to lead to the formation of caves.

Peak District Reefs

As already mentioned, the lagoon that gave rise to the limestone plateau was ringed by reefs or mud mounds. These are generally more resistant to erosion and give rise to characteristically steep and sharp peaked hills. In Dovedale, there are Thorpe Cloud, Bunster Hill, the Twelve Apostles and Tissington Spires. In the nearby Manifold valley, Beeston Tor and Ecton Hill plus Thor's Cave. 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.

Geological evolution

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. These were comparable to those of the present day Mississippi delta of the southern USA.

The finer particles travelled further, thus making the clear seas of the Peak District cloudy. These fine  particles gradually settled out to form shales. They are most famously found in the Mam Tor area near Castleton. Shales are soft and unstable and landslips caused by movement of the shale have destroyed the main road near Castleton. It was repaired a few times but eventually the authorities gave up. 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.

Shale to Sand

The period of shale deposition did not last for long, geologically speaking. During the later stages of the Carboniferous, the sea level fell in relation to the land thus some rocks were eroded. In deeper water areas deposition continued without a break. The Upper and Lower Carboniferous boundary is marked by a marine band with goniatites, shales  and impure limestones can be observed either side of this. Later, flooding brought a resumption of sedimentation over most of the Peak District but the rocks were of a very different nature to before. No more limestones are seen, instead there were just muds and sand.

The rivers from the north rapidly extended their deltas to the south, filling the seas with particles of sand and occasionally pebbles. Life was no longer possible in this environment for the original fauna of the Lower Carboniferous. Vegetation 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 formed during this period provides much of the quality climbing venues of the Peak District..

As the deltas built out further, creating 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 during which the great Yorkshire, Derbyshire and Nottinghamshire coalfield was formed.

The end of the Carboniferous

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 the broad fold of the Derbyshire Dome.

Once rocks are exposed to the ravages 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 has therefore been completely removed to reveal the oldest rocks of the Peak - the limestone.

Glaciation in the Peak District

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 now 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 to the east of Bleaklow. It has been suggested that the latter is the largest in Britain, but whether that is true 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.

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.

This information is given freely but if you have found it helpful, please show your appreciation by leaving a donation using the button below (securely via PayPal using a credit card).

Mysterious Geology

The geology of the Peak District after the end of the Carboniferous is difficult to unravel. That's because any rocks that were formed have been completely removed. There are outcrops of Permo-Triassic age that lie close to the boundaries of the area e.g. the Churnet valley. This therefore offers the possibility that they may have extended over at least parts of the Peak District.

These deposits may have infilled the late Carboniferous topography and were removed in an ice age. Some of the current limestone topography is almost certainly re-excavated earlier features, e.g Castleton, Chrome Hill, Thorpe Cloud. This idea would also go some way to explaining the the wind sculpted shapes in the Dark Peak.  They could easily have been created when conditions were very different to today.

Dolomites and Desert

The dolomitisation of the limestones at Harboro Rocks has not been satisfactorily explained. The main UK areas with dolomitic limestone are, guess what, Permo-Triassic age. It is therefore possible that the limestones at Harboro were altered as a result of general Permo-Triassic conditions. Now there’s an idea for your postgrad studies ... please let me know what you find out!

Further evidence comes from the presence of clays in the Trent valley, derived from Permo-Triassic marls. This is a very soft rock and could easily have been scraped to the valley by the action of an ice sheet.  Some Peak District rocks show a significant reddening e.g. the Roaches. Rocks that are weathered under arid conditions tend to be reddened. This would fit in with the bigger picture of the formation of the supercontinent of Pangaea.

The north of St George’s Land silted up because of the Upper Carboniferous delta. The seas to the south were destroyed by plate tectonic action therefore the area became landlocked. Much closer to the equator than now, arid conditions would have resulted. Also, the crustal movements changed from tensional to compressional, creating the folds of the Derbyshire Dome. This lead to erosional conditions.

Recent sedimentation

There is no evidence whatsoever to indicate if Cretaceous or Jurassic sediments were ever deposited. Deposits from the Miocene-Pliocene boundary have been found (and exploited) in the Brassington region. Rivers deposited sands into pre-existing solution and subsidence hollows. The Peak District was at the very southern limit of the last glaciation (the Devensian) and this has left behind glacial drift in the form of boulder clay plus meltwater sands and gravels. The most recent deposits are the soils, acidic over the gritstone areas and alkaline over the limestones. The peat of the Dark Peak may have been triggered by the large scale clearance of the forests during the Bronze Age.

Glaciation in the Peak District

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 now enjoy.

Caves and caverns 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".  There are indeed several caverns in the area but not all are natural! The largest of the natural ones is Peak Cavern, also known as the 'Devil's Arse'.

Freeze-Thaw conditions gave rise to landslips like Mam Tor, Lud's Church near the Roaches and Alport Castles to the east of Bleaklow. It has been suggested that the latter is the largest in Britain, but whether that is true 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.

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.

This information is given freely but if you have found it helpful, please show your appreciation by leaving a donation using the button below (securely via PayPal using a credit card).