Association of American Geologists. 185 



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 sandstone. 

 The direction of the veins across the upper rocks most frequently corres- 

 ponds 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 cor- 

 responding 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 metalliferous veins. Not 

 only do the separate veins vary from a mere line to several feet in thick- 

 ness, 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 grey and red oxides, carbonate and silicate, together with several 

 mixed compounds. Sulphuret of copper is exceedingly rare, and pyritous 

 copper has not been found in what was regarded as a true vein, though 

 this last named mineral, associated with the sulphuret and carbonate of 

 lead, was noticed in small ramifying veins, in what may perhaps be re- 

 garded as a distant portion of the range under consideration. Native sil- 

 ver 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 proximity to 

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

 the junction of the trap and conglomerate, or in immediate vicinity of the 

 dykes, thus following the general laws respecting the deposits of the me- 

 tallic minerals. 



As the veins recede from the trap, the place of the copper is frequently 

 supplied by the silicious oxide and carbonate of zinc, together with calca- 

 reous 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. 



Dr. H. conceives these to be veins of sublimation, or in other words to be 



simple fissures filled from below by the metal in a vaporous state, and that 



all the compounds had their origin from copper in a native form. The 



conglomerate was stated to have been noticed where the cement consisted 



Vol. XLi, No. 1.— April-June, 1841. 24 



