113 



igneous fluidity ; and, from the circumstance that the walls of 

 the vein are encrusted with Laumonite, it would appear that the 

 spar vein itself is of igneous origin. Many other instances of a 

 similar kind indicate that the calcareous spar veins, which tra- 

 verse the conglomerate and sandstone rocks, are true veins of 

 igneous origin. 



At Copper Harbor, the green rock, formerly mistaken for 

 carbonate of copper, but which Dr. J. ascertained to be a hydrous 

 silicate of the oxide of copper, or chrysocoUa, has been explored, 

 and it has led to the discovery of a very remarkable vein of the 

 black oxide, and black and brown silicates of copper, from which 

 a considerable quantity of ore has been taken, and has been 

 wrought into sulphate of copper, at the Roxbury Laboratory. 



This vein is, however, quite uncertain ; for the ore widens into 

 flattened ellipsoidal masses, and then thins out and disappears, 

 while the dead rock or calcareous spar takes its place. It is 

 said that black sulphuret of copper has been found, at some 

 depth, in this vein ; but he had seen no specimens of it. The 

 miners had penetrated, to the depth of forty or fifty feet, in dead 

 vein, but had extracted much rich ore within twenty feet of the 

 surface, where a drift had been excavated for its removal. This 

 vein is from eight inches to one foot wide where the black oxide 

 is obtained, but is quite irregular. 



Dr. J. would suggest that the chrysocolla was, originally, a 

 gelatinous mass, like silica, separated from minerals by acids, 

 and that, when the rock cooled this jelly, the hydrous silicate 

 was deposited, while, in its more heated interior, the brown and 

 black silicates were deposited. He would suggest, also, that the 

 black oxide might have been precipitated, from the hot siliceous 

 solution, by the action of hot limewater, which might have been 

 abundantly produced in the vein during its formation. It is easy 

 to imitate this operation in the laboratory of the chemist ; and 

 there is no reason why it may not have been one of nature's 

 great chemical operations. 



Trap rocks occur very near this vein, and, perhaps, underlie 

 the conglomerate for some distance around. To them is attri- 

 buted the heat which permeated this vein ; and the alkalies, 

 which produced analcime instead of laumonite, in the lower 

 portions of the lode, may have originated from the subjacent 

 igneous rock. 



