714 



GRANITE IN VEINS. 



[Ch. XXXIII. 



It is here remarked, that the schist and granite, as they approach, 

 seem to exercise a reciprocal influence on each other, for both un- 

 dergo a modification of mineral character. The granite, still remain- 

 ing unstratified, becomes charged with green particles; and the 

 talcose gneiss assumes a granitiform structure without losing its strati- 

 fication.* 



Professor Keilhau drew my attention to several localities in the 

 country near Christiania, where the mineral character of gneiss ap- 

 pears to have been affected by a granite of much newer origin, for 

 some distance from the point of contact. The gneiss, without losing 

 its laminated structure, seems to have become charged with a larger 

 quantity of felspar, and that of a redder color, than the felspar usu- 

 ally belonging to the gneiss of Norway. 



Granite, syenite, and those porphyries which have a granitiform 

 structure, in short all plutonic rocks, are frequently observed to con- 

 tain metals, at or near their junction with stratified formations. On 

 the other hand, the veins which traverse stratified rocks are, as a 

 general law, more metalliferous near such junctions than in other 

 positions. Hence it has been inferred that these metals may have 

 been spread in a gaseous form through' the fused mass, and that the 

 contact of another rock, in a different state of temperature, or some- 

 times the existence of rents in other rocks in the vicinity, may have 

 caused the sublimation of the metals.f 



There are many instances, as at Markerud, near Christiania, in Nor- 

 way, where the strike of the beds has not been deranged throughout 

 a large area by the intrusion of granite, both in large masses and in 

 veins. This fact is considered by some geologists to militate against 

 the theory of the forcible injection of granite in a fluid state. But 

 it may be stated in reply, that ramifying dikes of trap also, which 

 almost all now admit to have been once fluid, pass through the same 

 fossiliferous strata, near Christiania, without deranging their strike or 



di P .j 



Fig. T46. 



General view of junction of granite and schist of the Valorsine. (L. A. Necker.) 



* Necker, Sur la Val de Yalorsine, Mem. de la Soc. de Phys. de Geneve, 1828 

 I visited, in 1832, the spot referred to in fig. T45. 

 f Necker, Proceedings of Geol. Soc, No. 26, p. 392. 

 X See Keilhau' s Gaea Norvegica ; Christiania, 1838. 



