Ch. IX.] 



VEINS IN PRIMARY ROCKS. 



177 



case they are intimately connected with the quartz of the vein, 

 just as described in the two last chapters as happening at the 

 junction of granite and slate. The substance of the vein is 

 not uniform, but the pure quartz is intermixed in patches, 

 stripes, or veins, with the quartzose varieties of the adjacent 

 rocks, sometimes the one and sometimes the other prevailing 

 in quantity. 



The part of the vein marked A is entirely situated in slate, 

 and is about a hundred feet from Cape Cornwall : its size 

 and direction is distinctly defined, though quartz does not 

 here, as at c, form the greater part of the mass. 



Fig. 15. 



Part of Little Bounds Lode at A. 



Here the quartz forms an irregular band on either side, 

 between which the vein is composed of variously formed 

 stripes or veins, some of quartz, but the greater part of the 

 same kind of quartzose schist, which bounds the vein on either 

 side, partaking, however, more of quartz, into which it con- 

 tinually passes by the most gradual transitions. The slate 

 adjoining the vein is, as at c, very ferruginous, and forms, as 

 it were, walls of two or three feet in thickness, which accom- 

 pany the vein throughout its course ; and might therefore be 

 considered as forming part of the vein as well as the central 

 quartzose part. On either hand this ferruginous slate gradu- 

 ates, at many points, both into the slate and the vein, though, 



N 



