Ch. XXXIII.] 



GRANITE IN VEINS. 



569 



Fig. 692 is a sketch of a group of granite veins in Cornwall, given 

 by Messrs. Von Oeynhausen and Von Dechen* The main body of the 



Fig. 693. 



Granite veins passing through hornblende slate, Carnsilver Cove, Cornwall. 



granite here is of a porphyritic appearance, with large crystals of fel- 

 spar • but in the veins it is fine grained, and without these large crystals. 

 The general height of the veins is from 16 to 20 feet, but some are much 

 higher. 



In the Valorsine, a valley not far from Mont Blanc in Switzerland, an 

 ordinary granite, consisting of felspar, quartz, and mica, sends forth veins 

 into a talcose gneiss (or stratified protogine), and in some places lateral 

 ramifications are thrown off from the principal veins at right angles (see 

 fig. 693), the veins, especially the minute ones, being finer grained than 

 the granite in mass. 



Kg. 693. 



Veins of granite in talcose gneiss. (L. A Necker.) 



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

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

 modification of mineral character. The granite, still remaining unstra- 

 tified, becomes charged with green particles; and the talcose gneiss 

 assumes a granitiform structure without losing its stratification."!* 



* Phil. Mag. and Annals, No. 27, new series, March, 1829. 

 ■j- Necker, sur de Val. de Valorsine, Mem. de la Soc. de Phys. de Geneve, 1828. 

 I visited, in 1832, the spot referred to in fig. 693. 



