ELEVATION OF GRANITE. 



67 



it. If we date the age of granite from the period of the elevation of 

 granite mountains, we must admit that some granite mountains are 

 comparatively recent, for they have been elevated since the deposi- 

 tion of the secondary strata. In my Travels in the Tarentaise, &;c. 

 published in 1823, I have shown this to be the case with the gran- 

 ite of the Bernese and Savoy Alps. In the third edition of the pres- 

 ent work in 1828, I have also shown, by a description and sections, 

 that the elevation of the granite of Savoy is more recent than that 

 of the central part of England. M. Elie de Beaumont has, since, 

 adopted the same views, and has extended them to other mountain 

 ranges. Prof. Sedgwick and Mr. Murchison have further proved, 

 that a great part of the Tyrolean and Bavarian Alps was elevated 

 since the deposition of tertiary strata ; for these strata are lifted up 

 with them to the height of several thousand feet. 



Here, however, we must also admit that the material which form- 

 ed granite is more ancient than the strata that rest upon it. 



Whether granite ever formed at one time the stony pavement ot 

 the whole globe, or whether it was elevated in a solid state bodily^ 

 or whether different parts of the surface were fused at different 

 epochs are legitimate objects of geological enquiry, and may perhaps 

 admit of a satisfactory solution by extended series of observations. 

 In whatever state granite forms, or has formed, the ancient crust of 

 the globe, it has been, since, pierced through, by ancient and re- 

 cent igneous rocks. Thus, porphyry cuts through, and in some parts 

 covers granite, on the west side of Scodand from Inverary to Ben 

 Nevis. Volcanic rocks, and streams of lava, of a recent geological 

 epoch, pierce through and have poured over the granite of Auvergne, 

 and a large part of central France. 



Some of the currents of lava appear as fresh as the recent cur- 

 rents from Etna or Vesuvius. In other parts of Auvergne, the gra- 

 nite appears to have been acted upon by subterranean fire in situ, 

 and in some mountains, as in the Puy de Chopine near Riom, gran- 

 ite and volcanic rocks are intermixed, one part being true granite and 

 the other volcanic porphyry (trachyte.)"^ 



These volcanoes have long been dormant ; and the only remain- 

 ing proofs of the existence of subterranean fires under that district, 

 are the hot springs that rise in the vicinity of the ancient volcanoes. 

 According to Humboldt, in the Canary Islands, as well as in the An- 

 des of Quito, in Greece, and various parts of the world, subterra- 

 nean fires have pierced through the primary rocks ; and he adduces 

 the great number of warm springs which he has seen issuing from 

 granite, gneiss and mica-slate, as a proof of this opinion. Indeed, 

 in the Andes, numerous volcanoes are in present activity, from Cape 

 Horn, to Mexico, and it is probable that those mountains owe their 



* See Travels ai the Tarentaise and Auvergne," vol. il p. 367. 



