Ch. XXXIV.] CARBONIFEROUS AND SILURIAN PERIODS. 725 



passes insensibly into granite. The limestone is changed into granu- 

 lar marble, with a band of serpentine at the junction."* 



Carboniferous Period. — The granite of Dartmoor, in Devonshire, 

 was formerly supposed to be one of the most ancient of the plutonic 

 rocks, but is now ascertained to be posterior in date to the culm- 

 measures of that country, which from their position, and as containing 

 true coal-plants, are regarded by Professor Sedgwick and Sir E. Mar- 

 chison as members of the true carboniferous series. This granite, 

 like the syenitic granite of Christiania, has broken through the strati- 

 fied formations without much chano'ino; their strike. Hence, on the 

 northwest side of Dartmoor, the successive members of the culm- 

 measures abut against the granite, and become metamorphic as they 

 approach. These strata are also penetrated by granite veins, and 

 plutonic dikes, called " elvans." f The granite of Cornwall is probably 

 of the same date, and, therefore, as modern as the Carboniferous 

 strata, if not newer. 



Silurian Period. — It has long been known that the granite near 

 Christiania, in Norway, is of newer origin than the Silurian strata of 

 that region. Yon Buch first announced, in 1813, the discovery of its 

 posteriority in date to limestones containing orthocerata and trilobites. 

 The proofs consist in the penetration of granite veins into the shale 

 and limestone, and the alteration of the strata, for a considerable dis- 

 tance from the point of contact both of these veins and the central 

 mass from which they emanate. (See p. 715.) Von Buch supposed 

 that the plutonic rock alternated with the fossiliferous strata, and that 

 large masses of granite were sometimes incumbent upon the strata; 

 but this idea was erroneous, and arose from the fact that the beds of 

 shale and limestone often dip towards the granite up to the point of 

 contact, appearing as if they would pass under it in mass, as at a, fig. 

 752, and then again on the opposite side of the same mountain, as at 6, 



Silurian. Granite. Silurian strata. 



dip away from the same granite. When the junctions, however, are 

 carefully examined, it is found that the plutonic rock intrudes itself 

 in veins, and nowhere covers the fossiliferous strata in large over- 

 lying masses, as is so commonly the case with trappean formations. J; 



Now this granite, which is more modern than the Silurian strata of 

 Norway, also sends veins in the same country into an ancient forma- 



* Yon Buch, Atmales de Chimie, &c. 



f Proceed. Geol. Soc, vol. ii. p. 562 ; and Trans., Second Series, vol. v. p. 686. 

 % See the Gaea Norvegica and -other works of Keilhau, with whom I examined 

 this country. 



