( 125 ) 



On the Origin of Quartz and Metalliferous Veins. By Pi'o- 

 fessor GuSTAV Bischof, of Bonn. 



(Continued from vol. xxxvilLj p. 353.) 



It is a quite common occurrence to find the rock adjacent 

 to quartz veins more or less impregnated with quartz, or, at 

 all events, altered, v. CEynhausen and v. Dechen,* who 

 had an opportunity of observing a great number of quartz 

 veins or strings in the granite or killas of Cornwall, in ex- 

 posed cliffs on the sea-side, always found the adjacent rock 

 changed. Near Mousehole, this alteration extended for an 

 inch and a half into the granite, giving it a darker yellowish- 

 grey colour, and a harder and quartzy appearance. The 

 quartz strings are about an eighth of an inch thick, widen- 

 ing at some parts to nearly six inches. Near Cligga Point 

 they found a rock very similar to granite, of a light grey 

 colour, having, as its prevailing constituent, quartz crystal- 

 lized, generally very distinctly, in double six-sided pyramids ; 

 mica and felspar, however, only in small quantities, and more 

 frequently schorl. This rock is weathered on the surface, 

 but is harder underneath, and, at a little distance from this 

 spot, makes a transition into the granite. Here, too, the fel- 

 spar appears more frequently, partly fresh, partly decom- 

 posed into porcelain eai'th, and the quartz is less apparent. 

 The quartzose rock has the same relation to granite, as the 

 granite altez'cd by the quartz veins at Mousehole has to 

 the granite there, and this latter rock is actually traversed by 

 frequent quartz strings, which seem to have produced a like 

 alteration. At another place near Cligga Point, there is a 

 perpendicular granite cliff, above 100 feet high, traversed by 

 numberless quartz veins, altering it on both sides. At a 

 third point, the granite presents a most remarkable appear- 

 ance. It is traversed by numberless quartz veins, which 

 have changed it, on either side, into a rock similar to that 

 already described (much quartz, with little mica and felspar, 

 but frequent schorl). These quartz strings arc seldom more 



* Kaxsten's Archiv, 1828, toI, xvii., p. 3. 



