USEFUL MINERALS. GOLD. 



629 



the containing rocks when in a hard and metamorphosed state. They 

 have been formed and filled in the very act of the contortion and 

 altering of the strata, and are thus of the nature of segregation veins, 

 gradually formed as the spaces containing them were opened out, by 

 a process so slow and gentle that the containing beds were bent 

 without fracture and with but little crushing. The barrel quartz is 

 most instructive as an illustration of this peculiar mode of formation, 

 which must have often occurred in the disturbance and metamorphism 

 of sediments ; though geologists, from the habit of looking exclusively 

 at fissure veins on the one hand, and beds on the other, have often 

 been puzzled by these apparent anomalies which occur in the case of 

 what may be termed contemporaneous veins following the strike of 

 the enclosing beds, and which, while simulating beds, and obviously 

 not filling mere rents or fractures opened in hard rocks, must have 

 been produced by forces acting long after the original deposition of 

 the containing strata. 



Fig. 219. — Section of Vein of ^^ Barrel Quartz," Waverley. 



(a, a) Quartz vein, with contorted slate below and quartzite above. 



The minerals associated with the gold at the Waverley Mines are 

 mispeckel (sulph-arsenide of iron), galena (sulphide of lead), blende 

 (sulphide of zinc), and, more rarely, iron pyrites, copper pyrites, and 

 calcareous spar. The visible gold appears in irregular grains and 

 nuggets, included in and attached to the mispeckel, galena, blende 

 and quartz, in such a manner as to show that it is in all cases either 

 of contemporaneous or later introduction, and it has probably been 

 segregated from the mass of the quartz when the latter was in a soft 

 or pasty condition, or while it was in process of deposition. This 

 view is confirmed by the fact, that those veins and parts of veins, which 

 contain many " sights " or visible portions of gold, are less rich in 



