The caves of Devon lie in Devonian limestone which is much older (398-385 million years BP) than the Carboniferous limestone in which most other British caves are formed. Outside of Devon the only other caves in Devonian limestone are Holwell Cavern in the Quantock Hills of Somerset and two minor caves at Cremyll in East Cornwall, near Plymouth.
In Devon there are several blocks of exposed limestone scattered throughout the county, mainly in the south. The main areas are around Plymouth, the Torbay area, Chudleigh Rock and close to the southeast edge of Dartmoor. This latter area consists of a line of Devonian limestone exposed along the valley of the River Dart, near the village of Buckfastleigh and is where the best developed caves are found. Other smaller outcrops exist around the county, including a small outlying formation in North Devon, near Ilfracombe, in which is found Napp’s Cave, containing good aragonite formations. Most of the caves are small in extent. The largest and best known caves are the Baker’s Pit - Reed's Cave System (3.6km), and Pridhamsleigh Cavern (1.1 km), both near Buckfastleigh, along with Afton Red Rift (0.4km), between Newton Abbot and Totnes. Other notable caves in the county include Kent’s Cavern in Torquay, open as a show cave and renown for its finds of bones and evidence of settlement by early man; Bunker’s Hole, which contains many beautiful aragonite fromations; and Joint-Mitnor Cave, which contains the richest deposit of interglacial remains yet discovered in Britain. Many of the Devon caves are important roosting sites for Greater and Lesser Horseshoe bats.
||Aragonite, Bunkers Hole
During the last ice (ending around 10 000 years ago) Devon, along with the rest of southern England faired better than further north and was un-glaciated, although conditions were still very cold, with sub-glacial tundra being present, similar to modern day Siberia. Much of the life eked out a precarious existence or moved to warmer climes via the land bridge that still linked the south eastern part of England to the near continent. It is possible that some organisms survived the Ice Age by living deep underground where the temperature was above freezing, but food would have been a major difficulty. Organisms that survive underground for generations will often have adaptations to help them survive, and will lose some features that are of no benefit e.g. use of eyes. Those that are adapted to life underground become troglobites - cave dwellers that complete their life cycle in the cave and do not exist outside of this environment. These are the most fascinating creatures you will see underground, but they are also part of a delicate ecosystem that is easily disturbed by cavers and man’s activities.
The creatures found in caves can be classified according to how much of their life cycle they spend in the cave and how dependant they are on the cave environment.
Troglophile: can successfully complete its life cycle both in and out of the cave environment.
Troglobite: cannot complete life cycle outside of the cave environment. These have morphological adaptations to the cave environment e.g. blind, longer legs, lower metabolic rate.
Cavernicole: a more general term for a creature that lives in a caves and can complete its life cycle there, but may also live in other dark habitats e.g. soil, under stones, bark.
As many of our troglobites have only been underground since the last Ice Age they have not had time to evolve some of the bizarre adaptations seen abroad, where cave life has been unaffected by such catastrophes for much longer.