584 Metalliferous Veins. pabt n. 



. \ : . 



or more tliin veins or strings running in a different- 

 direction, intersect a poor ' veta real : ' it is unanimously 

 believed that at such points of intersection (cruceros), 

 the quantity of metal is much greater than that con- 

 tained in other parts of the intersecting veins. In some 

 cruceros or points of intersection, the metals extend 

 even beyond the walls of the main, broad, stony vein. 

 It is said that the greater the angle of intersection, the 

 greater the produce ; and that nearly parallel strings 

 attract each other ; in the Uspallata range, I observed 

 that numerous thin auri-ferruginous veins repeatedly 

 ran into knots, and then branched out again. I have 

 already described the remarkable manner in which rocks 

 of the Uspallata range are indurated and blackened (as 

 if by a blast of gunpowder) to a considerable distance 

 from the metallic veins. 



Finally, I may observe, that the presence of metallic 

 veins seems obviously connected with the presence of 

 intrusive rocks, and with the degree of metamorphic 

 action which the different districts of Chile have 

 undergone. 1 Such metamorphosed areas are generally 

 accompanied by numerous dikes and injected masses 

 of andesite and various porphyries : I have in several 

 places traced the metalliferous veins from the in- 

 trusive masses into the encasing strata. Knowing 

 that the porphyritic conglomerate formation consists of 

 alternate streams of submarine lavas and of the debris 

 of anciently erupted rocks, and that the strata of the 

 upper gypseous formation sometimes include submarine 

 lavas, and are composed of tuffs, mudstones, and mineral 

 substances, probably due to volcanic exhalations, — the 

 richness of these strata is highly remarkable when com- 



1 Sir E. Murcbison and his fellow travellers have given some 

 striking facts on this subject in their account of the Ural Mountains. 

 * Geolog. Proc' vol. iii. p. 748. 



