Several depositional basins stretched east-west across south-west England during the Devonian and Carboniferous periods and, over millions of years, each acquired a mix of sand, mud and silt which would eventually become the sandstones, mudstones and siltstones of Devon and Cornwall .
This series of sedimentary basins were subject to broadly north-south compression during the course of the Variscan orogeny leading to the complexly folded and faulted geology which characterises the area today.
Tavy Formation) outcrops is of Frasnian to Famennian age and consists of greenish-grey and black slates representing an outer shelf facies.
The grey Givetian (Famennian – Eifelian) age Chercombe Bridge Limestone Formation (393-383mya) outcrops at Buckfastleigh and also along the boundary of the park to the northeast between Ashburton and Goodstone.
The Cornubian batholith was intruded into the midst of the folded and faulted sedimentary sequence during the early part of the Permian period, around 280 million years ago.
Within the Dartmoor outcrop as a whole there are numerous isolated pockets of finer granite, particularly in the area north of Burrator Reservoir and in the valley of the Dart below Dartmeet.
Geological evidence such as the occurrence of fragments of volcanic rocks geochemically associated with the batholith, found redeposited in the Crediton Trough suggests that the pluton had been ‘unroofed’ by the later Permian period.
It consists of late Palaeogene age (Eocene to Oligocene) clays, silts and sands with some lignites, some several hundred metres thick in total[5] The tors of Dartmoor are amongst its most celebrated features.
Narrow strips of alluvium i.e. accumulations of clay, silt, sand and gravel, occur along the valley floors of most Dartmoor streams and rivers.
Whitelady Waterfall and the Devil’s Cauldron are amongst the natural features in the deep gorge cut here by the River Lyd through the mudstones of the Lydford Formation.
[12] In the northeast is Becky Falls which is a private attraction where the Becka Brook drops steeply off the edge of granite into a gorge cut in Crackington Formation rocks to enter the Bovey valley.
[13] Further south on the park's boundary are several caves developed in the limestone outcrop at Buckfastleigh, including Bakers Pit, and managed both for bat conservation and for public trips.