Page:A Treatise on Geology, volume 2.djvu/175

 CHAP. VIII. of the former,—the author gives a section of the country between Valorsine and Servoz, and points out the probable extension of the granite of Valorsine under the Aiguelles Rouges and Mont Breven, composed of protogine, chlorite, and talcose schists, to the immediate vicinity of the mines of Servoz, which are situated in the latter formation. He also refers the reader for further illustration to the metallic deposits of Wanlockhead and the Lead Hills; to the mines of Huelgoet and Poullauen in Brittany; to those of Macagnaga and Allayna at the foot of Mount Rosa; to those of Sardinia, Corsica, and Elba; to the metalliferous veins of the Vosges, Brescina in the Alps, and the Altai chain; all of which occur in districts where unstratified rocks are known to exist.

In reply to the third question,—Do their exist metalliferous deposits entirely disconnected from unstratified rocks?—the author enumerates the mines of the Netherlands, those of quicksilver at Idria, the lead mines of Poggau in the valley of the Mur; Pezay and Macoz in the Tarentaise, and the veins of galena in the mountain limestone of the south-west of England. (See Geological Proceedings, 1832.)

On considering the cases mentioned by Mr. Necker, of metalliferous veins entirely unconnected with great masses of unstratified rocks, we perceive they are not unaccompanied by great dislocations of the strata, such as are usually associated with the appearance of trap rocks at the surface. It is probably not to the "Whin Sill" that the rich and abundant lead mines of the whole district extending from the Tyne to the Aire are due, —for indeed, through all the southern portion of this tract, almost no igneous rock appears,—but to the mighty and continuous disruption of strata caused by disturbance of interior heat, which bounds the mining district. In like manner, the very rich mining tract of Flintshire is unconnected with igneous rocks, but is defined, and is obviously dependent on the great disruption of strata along the eastern side of the vale of Clwydd. The