This EarthCache is one of a series of EarthCaches based on Logan Stones. Others in the series include:-
Logan or Rocking Stones - 'La Roche Tremblante'(GC11389). (Brittany, France)
Helman Tor is a 217ha (536 acre) Nature reserve and County Geological site. It also has the remains of a Neolithic hill settlement which is a Scheduled Ancient Monument. Permission for this EarthCache has been given by the Cornwall Wildlife Trust who own the site.
Tors are towers of delicately balanced rocks and boulders which are found on hilltops mainly on Dartmoor and Bodmin Moor in South West Britain. As geomorphological forms their origin is still the subject of controversy. The term 'tor' is also used to describe similar features occurring in different parts of the country including the gritstone tors of the English Pennines and the granite tors of the Cairngorms and Scottish Islands. The term is now used to describe similar structures around the world.
The formation of the best known and characteristic granite Tors of Dartmoor and Bodmin Moor is not fully understood. It has been suggested that chemical weathering is the main factor in producing these amazing structures whilst other geomorphologists suggest mechanical weathering during the ice age was responsible.
However they were formed, many tors harbour another interesting geological formation, namely rocking or Logan stones, sometimes called Logans. Again the exact formation of these stones is the subject of several theories but it is generally accepted that Logan stones on the Tors of South West Britain were formed through selective weathering (wind, frost and rain) of granite rocks, until a part has become disjoined from the parent-rock and is pivoted upon it. Before the nineteenth century it was believed that the ancient Druids had constructed them and their strangeness has long been thought to give them supernatural associations and made them a focus for witchcraft.
Many other Logan stones around the world were formed as a result of glacial or river deposition. For further reading a good starting point is found at this link. A simple definition of a Logan stone is - a stone which is substantial, permanent, historic and can be rocked (in a see-saw action) easily by a single person
Even the origin of the name “Logan” is not well understood. It may come from the English dialect ‘log’ which means to rock (in some parts of Britain the stones are called logging stones) It is also thought the word may have a link with Danish ‘logre’, to wag the tail, which could suggest a Norse origin. Others have suggested that the name may come from a Cornish use of the verb ‘to log’, used to describe the rocking action of a drunken man.
The coordinates given are for the car park of the Helman Tor Nature Reserve. In order to log this earthcache you must walk along the well-defined path to near the top of the Tor. As you approach the summit you will be confronted with the view as shown in the photograph below.
Your first task is to identify which of the boulders (labelled A-J) is the Logan stone. Next, given that the Trig Point is 209m above sea level, you must estimate the height of the Logan stone above sea level. Then measure the vertical movement of either end of the stone (in cms. please) when it is rocked. Finally, photograph your GPSr (or yourself) on the logan stone or in the area of the stone, in a way that the photograph is not a spoiler for part 1 (see sample photographs). If you are unable to provide a photograph, the co-ordinates taken from the centre of the stone (+/- 0.005’)will be accepted.
Email me using this link or via the profile, with :-
1) The letter denoting the Logan stone,
2) its estimated height above sea level in metres,
3) the vertical movement of either end of the stone, in centimetres (please indicate which end you measured)
New EarthCache guidelines 2010
Under the new guidelines, a photograph can be requested but specific detail in the photograph cannot be required. Consequently your photograph can be just a general photo of the site. However a personal touch such as your GPSr (or yourself/member of your team!) in the photo makes it much more interesting. To log this cache you must still answer the questions relating to the Logan Stone but you may submit the co-ordinates for the ‘Logan Stone’ instead of a photograph, as stated in the notes, but a photograph will eliminate the need for this measurement (and the risk of being outside the +/- .005’ limits) Please log the cache and include your photograph, I will review your answers and if there is any problems I will contact you to agree a course of action.
A final word of warning - it is said that if a woman touches a logan stone nine times at midnight, she will become a witch!!! 
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