Page:A book of the west; being an introduction to Devon and Cornwall.djvu/206

158 means the rain did not drive through, although they did not employ mortar; and the ancient tenement houses on the moor are dry as snufif. 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.