AMERICAN GEOLOGISTS AND NATURALISTS. 37 



somewhat obscure, although there has been good reason to beheve, 

 that most of them had their origin from the trap rocks, but whether 

 from true veins or from the mass of the rock itself, was not known. 

 He said that after examining the country with care, he was enabled 

 to state, that without doubt a very considerable portion of them had 

 their origin from what may be regarded as true veins. 



Those which were regarded as true veins, were uniformly noticed 

 to originate in the trap rock, but they were frequently traced across 

 the superimposed sedimentary rocks, to and including the red sand- 

 stone. The direction of the veins across the upper rocks most fre- 

 quently corresponds to the dip of those rocks. 



Dykes of trap, traversing the conglomerate and sandstone, were 

 stated to be of frequent occurrence ; but these dykes very rarely 

 cut across the strata of the upper rocks, or in other words, they 

 mostly occupy places corresponding to the lines of stratification, for 

 which reason the veins referred to cut across the dykes at very 

 high angles. 



-So far as we are enabled to judge from the examinations which 

 have been made, those veins originating in the outer range of trap 

 hills are the only ones in the district deserving the name of metallif- 

 erous veins. Not only do the separate veins vary from a mere line 

 to several feet in thickness, but those traversing the several rocks 

 above the trap, are usually very much expanded in their passage 

 across the upper rocks. 



By far the most important minerals contained in these veins are 

 the several ores of copper. The metal occurs in a native form 

 associated with the gray and red oxides, carbonate and silicafe, 

 together with several mixed compounds. Sulphuret of copper is 

 exceedingly rare, and pyritous copper has not been found in Avhat 

 was regarded as a true vein, though this last named m.ineral, asso- 

 ciated with the sulphuret and carbonate of lead, was noticed in small 

 ramifying veins, in what may perhaps be regarded as a distant por- 

 tion of the range under consideration. Native silver was very 

 rarely seen in the form of specks and strings associated with the 

 native copper. 



Most of the ores of copper occur in the greenstone, amygdaloid 

 and lower portions of the conglomerate, or at points in near proxim- 

 ity to the dykes before referred to, and they are most abundant at, 

 or near to the junction of the trap and conglomerate, or in imme- 

 diate vicinity of the dykes, thus following the general laws respect- 

 ing the deposits of the metallic minerals. 



As the veins recede from the trap, the place of the copper is fre- 

 quently supplied by the silicious oxide and carbonate of zinc, 

 together with calcareous spar, which latter usually fills the entire 

 vein in its passage across the sandstone. 



The veinstone in those portions of the vein most rich in the ores 

 of copper is chiefly quartz, and this is frequently filled with minute 

 specks and filaments of the native metal. 



