4H RELATION OF MINERAL VEINS TO IGNEOUS ACTION. 



blende. The veinstones are heavy spar, fluor spar, a little quartz, and 

 rarely calc spar. The veins range east and west. To this system 

 Werner boldly referred the veins of Derbyshire, the Harz, and also 

 those of Gisloif in Scania ! 



The fifth consist of native silver, silver glance, and glance cobalt, 

 sometimes with grey copper ore, lead glance rich in silver, fine-grained 

 brown blende, and sparry ironstone. The veinstone is heavy spar in a 

 state of disintegration, and fluor spar. It always occurs in the intersec- 

 tions of the first and fourth systems. Its directions are north and 

 south, and east and west. It sometimes is found even in the middle 

 of the westerly veins. 



The sixth contains native arsenic and light red silver ore ; w r ith a 

 little orpiment, copper nickel, glance cobalt, native silver, lead glance, 

 iron pyrites, and sparry ironstone. The veinstones are heavy spar, 

 green fluor spar, calc spar, and a little brown spar. This system 

 occurs in the intersections of the fourth and fifth systems, or in the 

 middle of veins. 



The seventh is of red ironstone, with a little iron glance, quartz, 

 and heavy spar. Occurs in the upper parts of veins. 



The eighth and newest is of copper pyrites, mountain green, mala- 

 chite, and red and brown iron ochre, with a little quartz and fluor 

 spar. 



Relation of Mineral Veins to the Local Centres of Igneous Action. 



Our investigations lead directly to the inquiry, how far the geogra- 

 phical occurrence of metalliferous veins is connected, as that of rock 

 dykes is known to be, with the evolution of igneous rocks ? 



Evidence on this subject can be obtained in two ways : first, 

 by comparing metalliferous and non-metalliferous districts of old 

 strata in their geographical relation to igneous rocks and convulsions ; 

 secondly, by examining the relation to igneous agency of the locally 

 metalliferous newer strata. 



In Older Rocks. The older rocks are not by any means univer- 

 sally stored with metalliferous veins any more than with dykes. 

 Large tracts in the slate rocks of Devonshire are nearly devoid 

 of metals, but near the granitic masses of Cornwall they are abund- 

 antly supplied with veins. In Wales the slate rocks yield copper and 

 lead chiefly along the western borders of the Principality, where the 

 local centres and axes of elevation are situated. Amid the Cumbrian 

 lakes lead and copper veins adjoin the granitic, hypersthenic, and 

 syenitic axes of Carrock, Skiddaw, High Pike, &c. They occur near 

 the porphyries of Helvellyn and Old Man, but the greater portion of 

 the slates, far removed from the foci of disturbance, are devoid of mineral 

 treasures. 1 



In Scotland metallic veins adjoin the granitic nucleus of Strontian. 



The Mining tracts of the Harz, the Erzgebirge, Hungary, Brit- 

 tany, and other localities are convulsed by disruption and diversified 

 1 See Postlethwaite. 



