Sheeps Tor is one of Dartmoor's more imposing tors, and is made from solid granite with four separate tor outcrops on top. Two of these are named, Sheeps Tor and Maiden Tor, with the other two unnamed. The slopes are covered with granite clitter, which are boulders ranging in size that have been eroded from the main tor outcrop.
Amongst these craggy granite outcrops lies a naturally occurring cave that throughout history has been shrouded in much mystery and superstition. This is reflected in the names that this cave has been given over the years; Piskie’s Cave, Piskie’s Hole, Piskie’s Grott, Piskie’s House and Elford’s Cave. The first four mention Piskies, which is a reference to the Dartmoor pixies that was penned by William Crossing in his book "Tales of the Dartmoor Pixies". The last name refers to another legend, less mystical than the others, that during the civil war John Elford, Lord of the Manor of Longstone, took shelter to hide from the parliamentarian forces sent after him. It is thanks to these myths and legends that has meant that this cave has been named on the Ordinance Survey Maps as "Piskie's Cave" for over a 120 years.
The geology of the area, as it clear from all of the boulders strewn around Sheeps Tor, is Granite. This makes up the tor itself, as well as the walls of the cave that this EarthCache is made from. From Crossing's description of the cave it is clearly tight and difficult to get into, but well worth the effort once inside. Nearby lies another smaller cave, waypoint 1, with a sign inside saying Pixie Paul's Cave.
There are a number of different types of caves based on their location, geology and processes that have created them. These include Solution Cave, Primary Cave, Sea or Littoral Cave, Corrasional or Erosional Cave, Glacial Cave, Fracture Cave and Talus Caves.
Solution Cave
Solution Caves are the most common type of cave in England and normally occur in areas where the geology is soluble (able to easily dissolve in water) such as limestones and chalks. As the rocks dissolve due to the waters natural acidity cracks appear and over thousands of years caves start to form along these cracks as they are widened.
Primary Cave
Primary Caves are not formed through processes of erosion instead they are created at the same time as the surrounding rocks. These most commonly in volcanic rocks where molten lava/magma has flowed through some already cooled rocks without solidifying, leaving behind an opening which becomes a cave.
Sea or Littoral Caves
Sea Caves, as their names suggests, are formed by the sea and as such are most commonly found along coastlines. Littoral is a more precise word used for these caves formed along the coastline, as the "Littoral Zone" is that where a body of water meets land. Sea Caves are normally created by water eroding faults in the rock, through hydraulic action (water causing increased pressure). However, there are examples where other types of caves, such as Solution Caves, have been flooded by the sea after their creation, effectively making them Sea Caves.
Corrasional or Erosional Caves
Corrasional or Erosional Caves are formed entirely from erosion by flowing streams carrying rocks and other particles. They can occur in any geology, even hard ones, such as granite. Generally they follow weaknesses and faults within the bedrock.
Glacial Caves
Glacial Caves are formed by the resulting erosion by flowing ice and water from within and under glaciers. Due to the weight of the ice above usually collapse the cave soon after creation.
Fracture Cave
Fracture Caves are formed when a more soluble, or weak, underneath a more resistant layer. As the weaker layer erodes the layer above fractures and collapses creating blocks of stones that can create an uneven cave system.
Talus Cave
Talus Caves are formed when large boulders fall into a random heap and the gaps between them form an uneven cave system. They are commonly found at the base of cliffs where the blocks have fallen from. They tend to create unstable systems as they are normally subject to further rockfalls and landslides.
The posted coordinates are a good location to see the square rock that indicates the location of the cave. It is also a good location to see the surrounding area and get an indication of how the cave has formed. From there head straight to the final waypoint.
To log this EarthCache go to the posted coordinates and the cave location and send me a message or email answering these following questions
1) Look at the cave itself and the surrounding area and describe how you think the cave was formed.
2) Once inside look at the roof of the cave and count how many cracks you can see.
3) Describe the appearance and make up of the cave walls.
4) Estimate the height of the tallest part of the cave.
5) Based on your observations of the interior and exterior of the cave and the surrounding area, what type of cave do you think Piskie's Cave is?.
6) On the right hand cave wall there is some graffiti carved by TR. What is the date underneath?