Ch. XXXIV.] CARBONIFEROUS AND SILURIAN PERIODS. 



581 



also penetrated by granite veins, and plutonic dikes, called " elvans."* 

 The granite of Cornwall is probably of the same date, and, therefore, 

 as. modern as the Carboniferous strata, if not much 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. Von 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. 5*72.) 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, ap- 

 pearing as if they would pass under it in mass, as it a, fig. 700, and 

 then again on the opposite side of the same mountain, as at b, 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 overlying masses, as is 

 so commonly the case with trappean formations.f 



Fig. 700. 



Silurian. 



Silurian Strata. 



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

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

 of gneiss ; and the relations of the plutonic rock and the gneiss at their 

 junction, are full of interest when we duly consider the wide difference of 

 epoch which must have separated their origin. 



The length of this interval of time is attested by the following facts : — 

 The fossiliferous, or Silurian beds, rest . unconformably upon the trun- 

 cated edges of the gneiss, the inclined strata of which had been 

 denuded before the sedimentary beds were superimposed (see fig. 

 701). The signs of denudation are twofold; first, the surface of the 



Fig. 701. 



Gneiss. Granite. Gneiss, 



Granite sending veins into Silurian strata and Gneiss, — Christiania, Norway. 



* Proceed. Geol. Soc. vol. ii. p. 562, and Trans. 2d ser. vol. v. p. 686. 

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

 this country. 



