the moor like a ring is an area called the metamorphic aureole where the encircling rocks have been changed in composition by the intense heat of the igneous intrusion. (I shall be writing briefly below about the ancient tinners of Dartmoor and other mining activities. Suffice to say, at this stage, that most metallic ores are associated with plutonic rocks or areas of metamorphosis.)
On the margin of such granite masses as Dartmoor, superheated water or gases forced their way into the cracks and deposited layers of crystalline minerals including the ores of metallic minerals. The way this process led to the present position of the various areas of minerals is very complicated. Put in simple terms, the mineral-bearing fluids and gases started deep down in the granite mass and as they were forced up to the surface the minerals crystallised in the order of their crystallisation temperatures. So obviously minerals with the high crystallisation temperature became solid near the hot granite and the others followed in order as the temperature decreased towards the surface. However, the erosion mentioned earlier has resulted in the mineral deposits on and around Dartmoor, shown in the mineral digram on the previous page.
Simplified mineral diagram
This period of mineral deposition probably took place 190 million years ago but the process might well have been spread over as long a period as 115 million years.
A final word must be written about the tors (Celtic twr, a tower) of Dartmoor. They are after all its most distinctive feature, sometimes described as ‘cyclopean masonry’. It has even been suggested that they were put up by the Druids! They are, of course, residual features left after both chemical and mechanical weathering has taken place. Controversy surrounds their origins and which of the two methods of weathering is the most important.
(i) Chemical weathering is the actual rotting of the rock itself and depends on the composition of the crystals in the rock and how they react within themselves.
(ii) Mechanical weathering is straightforward erosion by water, frost, freezing and heat.
But however they reached their present state, they are fascinating features that are fun to explore and scramble on, each one being different from the next.
Surrounding many of the tors are large areas of rocks lying scattered over the slopes leading up to the tors. These rocks are called clitters and were broken off the main mass of the rotten tors as they became exposed, by water freezing in the cracks and joints and finally pushing them off onto the slopes around.
Finally I refer you once again to the geology books if you want to follow up more details about the tors and the formation of Dartmoor.
Vegetation
Dartmoor usually conjures up thoughts of mists and quaking bogs; Great Grimpen Mire of The Hound of the Baskervilles. A lot of the moor is indeed bogland and while there are a few areas, usually very small pockets, where a horse or a bullock could sink in, and I presume human beings, there are no bottomless pits like quicksands covering large areas of moorland. After rain a lot of Dartmoor makes for wet walking and you have the extraordinary situation of bogs on the top of the moorland – not just by the streams and in river valleys. This is the blanket bog found in areas of eighty inches of rain in a year. Here grow bog asphodel and tormental with sphagnums, also a little heather with sages.
Peat made up of fibrous dead roots forms in areas where the angle of the ground is less than 15 degrees and again where there is abundant rainfall. Then you find areas of valley bogs; marshlands with reeds and the sources of streams and rivers. Here also is found sphagnum as well as cotton grasses, pale butterwort, bog asphodel, sundews and bog violet. The wet areas of moorland that are not blanket bog have got cotton grass, ling and bell heather and purple moor grass.
On the drier moor it is heather and in other areas whortleberry that thrive. Bracken grows in profusion also on the lower slopes of the drier moors and after swaling or burning the heather, bracken will colonise large areas.
On the high moor itself the three ancient woodlands of Wistman's Wood, Black Tor Beare and Piles Copse are fascinating. They are all three found on the west-facing clitter slopes and the trees are mainly stunted oak, never more than 3–5m (10–16ft) high, with a few mountain ash. On the floor of these woodlands, on or among the rocks, are mosses, ferns, wood rushes, lichens, liverworts and whortleberries, while epiphytics festoon the branches of the trees themselves. Even the barren granite tors have mosses and liverworts in the deep crevices and lichens on the rock faces.
Finally there are the delightful wooden stream and river valleys that run down from the granite moorland. The vegetation in them is often profuse: golden saxifrage and sphagnum, stonecrop, daffodil, wild garlic and St John's wort.
Fauna
I mentioned briefly a few of the creatures you can see on Dartmoor: buzzards, red grouse, foxes and skylarks. If you are lucky you might also come across badgers at dusk or the shy, almost extinct otter by the rippling streams and rivers. Stoats, weasels and the ferocious mink that has now colonised certain areas having escaped or been let loose from mink farms, can all be discovered. Rabbits still breed and live in profusion in spite of myxamatosis. The harmless grass snake and the not so harmless adder basks on the warm rocks in summer, as do lizards.
Gorse
Red Campion
Kestrels with pulsating wings hang on the air and the sparrow hawk also hunts the moor. Ravens, carrion crows and rooks are all inhabitants of the margins of Dartmoor. The crows and ravens are hated by farmers at lambing time when they are quick to see the weak, helpless lambs and move in for the kill. On the higher moor the wheatear starts to arrive in March from Africa, to breed here; in Victorian times these small birds were considered a delicacy on many dinner tables.
By the rivers, the dipper, that remarkable little black and white bird that seems to fly underwater and builds its nest on overhanging rocks just above flood level, darts about with low flitting flight. You will often disturb an old grey heron fishing in the streams and rivers and off he will go with long, languid flaps of his great wings.
Early purple orchid with bluebells
Primroses
The moorland streams themselves are the homes of the brown trout and salmon and the beautiful salmon trout called peel in Devon.
Finally black slugs will appear on moist, damp days and probably the Dartmoor midges. A vast number of insects are found including honey bees, dragonflies and spiders while butterflies and caterpillars, including the Emperor Moth, catch the eye with their bright colours.
Man has grazed his animals on Dartmoor from the time of the Bronze Age and herds of cattle still roam certain areas, while large flocks of sheep, including the Scottish black-face that has done so much damage to the whortleberries, are found almost everywhere.
But it is the ponies that most people associate with Dartmoor. They are called ‘wild ponies’ but they are all owned, in fact, by the farmers who have commoner's grazing rights and if you look closely you will see that they have brand marks on them. They are rounded up twice a year but the
