A book of the west. Volume 1, Devon

by S. Baring-Gould

The ancients were not such fools as we take them to have been. They did condescend to consider the capabilities and the disadvantages of their building material before employing it. The "old men," when they constructed a wall of granite, always gave it two faces, and filled in with rubble between. By this means the rain did not drive through, although they did not employ mortar; and the ancient tenement houses on the moor are dry as snuff. But the modern architect insists on having the walls built throughout with lime, in courses, and the rain enters by these as by aqueducts. Then, to remedy the evil, the whole face of the house is tarred over or cemented, with what result to the prospect may well be conceived. The granite, though pervious, is so to a very limited extent when compared with limestone, and through a granite country there are no springs that issue from subterranean reservoirs. All the rain that falls on the surface runs off superficially, but not all at once, for on the granite lie enormous beds of peat, the growth and decomposition of moor plants through vast ages. These beds of peat are like sponges; they absorb the rain, retain it, and slowly give it up during the summer. In limestone districts the making of a river goes on within the bowels of the mountain, but in a granite district it takes place on its outside. Remove the beds of turf and peat, and there will be torrents after a shower, and then dry torrent beds.

To north and south of the equator of the moor lie vast tracts of bog in which the rivers are nursed, and without which they could not be. No visitor can realise what Dartmoor really is in the economy of nature as the mother of the Devonshire rivers till he has visited either Cranmere Pool, or the ridge on the south, where are the meres from which spring the Avon, the Erme, the Yealm, and the Plym.

The granite being of unequal hardness, its constituent crystals become separated by the action of the weather into an incoherent gravel, which in Cornwall is called growan. The process may be seen in full activity on any tor. Sometimes water lodges on a slab, and finding a soft spot begins to decompose it; then, when this is the case, the wind swirls the water about, and with it the grit is spun round and round, and this continues the work of disintegration, and finally a rock basin is produced.

Of these rock basins some fine samples exist: that on Caistor Rock has had to be railed round, to prevent sheep from falling in and being drowned. Mis Tor has another, the Devil's Frying-pan. There are plenty of them to be seen in all conditions, from the rude beginning to the complete bowl.

At one time it was supposed that they were Druidical vessels employed for lustration, and archæologists talked long and learnedly concerning them. But what is quite certain is that they were produced by Nature unassisted.

When a hard bed of granite lies on one that is very soft, the latter becomes disintegrated and eaten completely away. The hard bed is left either balanced on one point or more, or else has its centre of gravity so placed as to precipitate it from its position. Plenty of rocks may be seen in all these conditions. If it should chance that a rock remains poised on one point, then possibly a little pressure at one end of the slab will set it in motion. This, then, is known as a logan, or rocking stone, which antiquaries of old pronounced to have been employed by the Druids as oracles, or for purpose of divination. All this was bred out of the phantasy of the antiquaries. There is absolutely not a particle of evidence to show that they were supposed to be mysterious, or were employed in any rites, and it is also absolutely certain that they were formed by the hand of Nature alone.

There are many logan rocks on Dartmoor. One is on Black Tor, near Princetown. It is instructive, as it not only shows the process of weathering which made it what it is, but it has on top of it a rock basin that decants by a lip over the edge of the stone when the latter is made to vibrate.

The "Nutcracker" stone near Amicombe Hill above the West Ockment rolls in a high wind like a boat that is anchored. There were two very fine logans on Staple Tor above Merivale Bridge, but quarrymen wantonly destroyed the whole of one of the steeples, together with the finest logan on Dartmoor that was on it. The other remains. On Rippon Tor is one, another in Lustleigh Cleave.

The felspar dissolved by the rain was carried away, and has been deposited in many places, filling up an ancient lake-bed and forming Bovey Heathfield, coating plains and hills with a deposit white as snow; this is kaolin, and is worked as china clay at Lee Moor and in Shaugh. The water flowing from the works is like milk, and, curiously enough, cows relish it.