GRANITE SCENERY: A view of Sheepstor in Dartmoor, England.
By
Alan Rogers
Only six weeks ago I just finished reading “The White Rajahs of Sarawak” by Professor Bob Reece of Murdoch University, W. Australia when my sister phoned and invited me for a walk to Sheepstor on SW Dartmoor in Devon. Yes, I immediately took off to explore the Brookes family graves at St. Leonard’s Church only 100 kms from my house. Alas, alack, in my impetuosity, I neglected to bring my camera!
A few weeks later on holiday in Kuching I read two articles in the Borneo Post, one derived from the local SW England newspaper – The Western Morning News –on the final resting place of the Brookes family. The following day, in the Borneo Post, Dato Sri Dr James Masing explained how just before the downturn of the economy in 1997 the Sarawak Government tried to purchase land in that area of SW Dartmoor to promote Sarawak tourism. Had that happened the vicar of this beautifully built granite church in the 1400’s would be rubbing his hands in glee today. Actually the origins of the church date back to 1240 AD when a chapelry was built on that very site.
Rising majestically, above the graves of the First Rajah, James (d.1865), the Second Rajah, Charles (d.1917) and Charles Vyner (d.1963) and other members of the Family Brookes, is Sheepstor – a granite monolith. Interestingly inside St. Leonard’s Church one of the upper leaded light windows displays a Nepenthes Rajah (pitcher plant), a butterfly and a moth as a living memorial to those valiant Sarawakians who lost their lives during the occupation in World War 2. They will always be remembered.
Buried in the shadow of the imposing Sheepstor (altitude 369 metres) the Brookes family rest in peace surrounded by rugged granite scenery in an environment which was once moulded in geological times by a tropical climate almost identical to that which the Brookes family experienced here in Sarawak!
The word “tor” comes from Celtic meaning a hill. As a pure Celt of Cornish and Welsh parentage I was born only 15 kilometres from the castellated, famous granite cliffs of Land’s End. Only 4 kilometres away from my parents’ house I took my five year old son on his first abseil down a granite escarpment tor! Granite scenery has haunted me throughout my life be it in Cornwall, on Dartmoor or at Shap Fell in the Lake District – all in the UK but also on Mt.Kinabalu and at Praslin in the Seychelles in the Indian Ocean.
Granite is a molten plutonic rock intruded into the overlying country rocks at Cornish and Dartmoor as two continental tectonic plates converged. As the molten granite meets the country rocks it bakes those rocks into metamorphic rocks thus changing their form. Various elements at different cooling stages in the molten rock were deposited as ores in the country rock – arsenic, copper, lead, tin and tungsten. The Cornish and Dartmoor tin mining industries continued into the early 20th Century when alluvial deposits of tin were exploited in a more economically viable form in Ipoh.
Granite magma was intruded at both high temperature and pressure and upon cooling it contracted producing vertical cracks or joints. In time the overlying country rocks were eroded and gradually the granite appeared nearer to the surface. Thus the granite mass experienced a reduction in pressure and ltemperatures! It responded by developing pseudo (false) bedding planes or horizontal pressure release joints. However as the granite cooled and crystallized water was released, which attacked the feldspars (brown crystals) to produce kaolin or china clay. Two other minerals in this granite are quartz – white or pink – (SiO2) and mica (black) the crystals of which occur at different sizes according to the rate of cooling.
Returning to Sheepstor, where the granite was injected some 290 million years BP (Before Present time) it was only in early Tertiary times (65 million years BP) that Dartmoor experienced a tropical climate with very high annual rainfall and temperatures and evergreen and semi-evergreen forests almost identical to Sarawak!
Consequently the rainfall percolated down through the soil overlying the country rocks into the granite thereby rotting the granite through its joints and pseudo bedding planes decomposing the quartz crystals into sand and the feldspar and mica crystals into clays.
The chemically rotted rock around the least affected parts of the was washed away by the high annual rainfall or by solifluction (litterally: soil flow) as a result of soil thaw at the end of the Ice Ages 10000 years BP. This exposed (exhumed) the solid granite core stones, which are now precariously balanced on each other. (See Diagram). Thus the granite tors were eventually revealed in the landscape. The processes of exhumation are still highly debateable and will continue to be, as each granite mass is studied in depth. However, Mt. Kinabalu with its ice cap which melted only 3000 years BP and subsequent exposure to freeze-thaw conditions meant that some chemically rotted granite was sludged downslope to reveal small granite boulders parly embedded in clays as on the Pinosuk Plateau in Kinabalu National Park. On the road up to the mountain one can see granite boulders embedded in clays where landslides or excavations have occurred. Its jagged skyline and peaks suggest as some geomorphologists believe that the ice cap protected some of its features.
Sheepstor in SW England never experienced the ice sheets and glaciers that sculpted the Northern areas of the UK and interestingly near Sheepstor remains of Prehistoric animals that migrated south from the advancing ice sheet have been found.
Whatever the continuing debate on the origins of granite scenery Sheepstor and Mt.Kinabalu weekly attract hundreds of hikers/climbers yet the Brookes family are buried in a geological time capsule. I just wonder what Rajah James would have made of Burrator Reservoir (the water supply to the city of Plymouth) in a flooded granite valley near his last residence at Burrator House.
For further information please refer to:
Professor Bob Reece, Murdoch University, Australia. The White Rajahs of Sarawak – A Borneo Dynasty. 2004 Archipelago Press.
htpp:// www.dartmoor-npa.gov.uk/lab-geologylandforms
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