Granite

In south-west England granite gives relatively flat-topped moorland plateaus with frequent rock outcrops, which from time to time form rock blocks called tors. Tors are some 5-10 metres high and are surrounded by weathered materials of all sizes from boulders to sand.On the higher parts of the moorlands there are man areas of standing surface water forming marshes and bogs. The many surface streams have cut deeply into the upland block of Dartmoor to form deep and steep V-shaped valleys, especially where rivers such as the Dart go over the edge of the plateau. Dartmoor has a radial pattern of drainage.

Dramatic coastal scenery occurs where granite and Atlantic breakers meet, as at Land's End. In Scotland the granite peaks in the Grampians and on Goat Fell in Arran are rocky and frost-shattered, although where the land is relatively flat, such as on Rannoch Moor, extensive bogs occur.

Granite is a hard rock, resistant to erosion, which is why it forms areas of high relief inland and cliffs along the coast. It is an impermeable rock, which explains why there is so much surface water. Another reason for the presence of so many bogs is the high precipitation in western upland areas.

The rock which forms tors is that which remains after the surrounding rocks have been weathered and carried away.

Where tors occur, the joints in the granite are wider apart than in the rock around them.

Freeze-thaw weathering can operate more effectively and blocks of rock break off more quickly where the joints are close together, because there are more cracks in the rock for the water to fill.

Each time the water freezes and expands within a joint, more pressure is put on the surrounding rock and the crack widens.

Where there are fewer joints, it takes longer for the blocks of rock to be broken off and the blocks are left upstanding as tors.

On the higher areas, bog, marsh and moorland produce some of the least useful land in the UK. In some places there may be opportunities for water storage. At lower levels there may still be nothing better than poor grazing land suitable only for sheep and cattle (and, on Dartmoor also for ponies). Soils are acidic and infertile; it is only around the edges of the uplands that the pastures improve sufficiently to allow grazing by dairy cattle.

Granite is a fine building stone. Aberdeen is known as 'the granite city' since so much use was made by builders of locally available supplies of stone. It is also often used for headstones in graveyards.

Granite rock is susceptible to attack by chemical weathering and in some places it has decomposed. This has resulted in the feldspar in the granite being converted into clay minerals, such as china clay (kaolin). China clay is best known as the raw material for the pottery and porcelain industries, and much is sent to the Potteries region around Stoke-on-Trent. It is also used in the manufacture of paper and is an ingredient in paint, toothpaste, skin creams and many other products.

• Dartmoor has a high rainfall and is known for its mists and fogs.
• Much of the land is covered by heather.
• The many boggy areas contain a rich variety of plant life.
• The central upland block was enclosed within a National Park in 1951.
• The Park covers almost 100 000 hectares and over 30 000 people live inside it.
• Up to eight million people visit or pass through the Park each year.
• Most of the towns, such as Tavistock, Okehampton and Ashburton, are located around the edges of the central block.
• Places popular with visitors include Buckfast Abbey, Haytor, Becky Falls and Lydford Gorge.
• Some of the remains of old woodlands have been preserved as nature reserves.