8 The Geological Structure 



been coated by tbat mineral. Smaller masses occur in a simile 

 relation to the quartz. In one of tbe beds of amygdaloid, are 

 kernels of copper impressed by crystals of zeolite, wliicli had 

 lined the vesicles previously to the deposition of the metal. In one 

 small vein, plates of copper cut across the veinstone of quartz. 

 Such examples indicate deposition of copper after that of the 

 veinstone. In other specimens, delicate arborescent crystals of 

 copper penetrate calc spar crystals in such a manner as to give 

 them a general red color, indicating contemporaneous deposition. 

 Fig. 2 exhibits a magnified view of a thin slice of this cupri- 

 ferous calc-spar, in which the crystalline laminse of copper remind 

 one of the quartz plates in graphic granite, and have evidently m 

 part conformed themselves to the structure of the calc spar. 



Fig. 2. Slice of cupriferous calc spar from LaJce Sup)erior ^ 

 magnified 20 diameters. The fine straight lines indicate the 

 cleavage; the darh lines the laminae and fibres of copper. 



IN'ative silver occurs on the shore in small quantity, in similar 

 dendritic forms, in a vein containing calc spar, zeolites, and frag- 

 ments of trap. The sulphurets of copper occur in precisely the 

 same relations with the native metal. The carbonate is probably 

 a product of oxidation of vitreous copper and native copper near 

 the surface of the rock. 



The whole of the appearances indicate that the deposition of 

 copper belongs to the period of aqueous infiltration, by which the 

 veins and vesicles were filled after the consolidation of the trap ;- 

 and the copper, like the calc spar and zeolites, occurs both in true 

 veins and in the cavities of beds of vesicular trap and tufa. Its 

 deposition must, therefore, be explained, not by igneous causes? 



