Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/120

 108 Pfyffer are, I believe, the first, who paid attention to this circumstance: Saussure in the mountains of Meillerie and St. Gingouph, in Savoy, Pfyffer in the Alps bordering on Lucerne. The neighbourhood of Plymouth affords an example of it in this part of England.

As the physical structure of the western part of England, from the banks of the Tamar as far as the Lands End, offers little variety in geology, and as the great masses consist of a small number of different rocks, it will, I think, be convenient, to give, at first, a sketch of the chain of mountains which traverses this part of the country, such at least as I conceive it to be. It will be an outline, which may afterwards be more easily filled up by future observations. Besides, as the grauwacke constitutes one of the most essential component parts of this chain of mountains, and as it is susceptible of numberless modifications, it will be better to give, in the first place, some details on the nature of this rock in the different states which it assumes.

The chain of low mountains, which forms the county of Cornwall, extends nearly into the centre of Devonshire, comprehending the elevated and irregular mountain plain, called Dartmoor Forest.

Like all primitive chains, it stretches from N.E. to S.W. or, more correctly, from E.N.E. to W.S.W. extending in this direction from 115 to 118 miles.

Its line of direction is pretty accurately represented by a line passing through the following places, viz. Two Bridges, Launceston,