Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/121

 Rh Bodmin, Indian Queen, Redruth, Camborne, Tregonin-hill near Marazion, St. Burien, and Sennen.

The central and highest part of the chain is granite, which extends into a narrow mountain plain at the north eastern extremity, and as it approaches the south-west gradually contracts into a ridge, and is flanked on the right and left by grauwacke. The outline of the range is not altogether continuous, several of the rounded Summits which compose is are separated by small vallies or ravines of various depths. Thus, the Tamar, which flows to the eastward of Dartmoor forest, seems quite to detach that mountain plain from the billy country to the west of Launceston; but it is easy to see, that such a separation does not exist in reality, Brown-Willy, the most elevated point of the whole chain, being in the parallel which passes directly through the middle of Dartmoor forest. The whole chain may be said to be formed of downs, and to be in some places interrupted, but no where entirely broken off. I have little doubt, that in the lower parts of the country, where the granite appears to be wanting, it would be found under the rocks, which I believe cover it, whatever these may be, if wells sufficiently deep were sunk in those places.

The water-shed of the chain is to the north and south, and both sides have nearly the same degree of inclination: the waters on the one side run into the British, and on the other into the Bristol Channel. The whole range has a gradual slope towards the west, but on the east the terminations are rather abrupt. The greatest breadth of the chain, is a little to the east of the middle point in its longitudinal extent. On the west it contracts into a narrow tongue of land, which is almost entirely granitic. The highest part of the