12 



formed. The primitive ore was blende, associated generally with more 

 or less pyrites ; the decomposition of the blende produced the Smithson- 

 ite. Contemporaneously, as it appears, with the transformation of blende, 

 water holding some salt, or perhaps several salts, of zinc in solution 

 percolated through the joints, and between the planes of bedding of the 

 limestone underlying the dolomite — chief seat of the Smithsonite — and 

 deposited there, and in the caves formed in the limestone the masses of 

 hydrocarbonates now found there. The proper discussion of the chemical 

 changes by which these minerals have been formed, involves the solu- 

 tion of several chemical problems, such as the action of solutions of 

 bicarbonates upon those of sulphate of zinc, the action of sulphate of pro- 

 toxide of iron upon sulphide of zinc, &c. One of us has already begun 

 the investigation of these problems. "We may therefore defer until its 

 completion any attempt to trace out the successive transformations by 

 which the Smithsonite and hydrocarbonate were formed. 



The occurrence of the bones partially buried in the hydrocarbo- 

 nate of zinc forming the floor of the cavern above described, affords 

 a test by which to determine the exact geological age of the deposits 

 of hydrocarbonate, and consequently of the formation of the greater 

 part of the Smithsonite. This testis the more valuable, because evidence 

 showing the period of geological time to which the deposition of the 

 contents of mineral veins belongs is very rare. There can be no doubt 

 that the deposition of the greater part of the hydrocarbonate was con- 

 temporaneous with the existence of the species of animals to which the 

 bones belonged. It is probable, therefore, that the deposition of that 

 mineral in the cavern began during the pleistocene period, and has con- 

 tinued down to the ;present time. Until an opportunity is afforded of 

 making an accurate examination of all the bones, this conclusion must, 

 however, be looked upon as provisional. 



Effect of the Zinc Solutions on the Fossil Bones. — Before passing to 

 the discussion of the chemical composition of the hydrocarbonate of zinc 

 and the associated silicates, it may be interesting to notice the effect which 

 the solution of a salt of zinc has had upon the composition of the 

 bones. Only a few of the bones found came into our possession, and they 

 were chiefly fragments. Some were wholly enveloped in the white mi- 

 neral, others only partially. Among the latter was a tibia, apparently 

 belonging to some ruminating animal — probably a large-sized deer. 

 This bone had lain on the floor, and was covered from time to time with 

 water holding a salt of zinc in solution, whenever the cave was flooded. 

 On jone side was a partial stalagmitic coating, apparently produced by 

 droppings from the roof. It was beautifully white ; the dense part of the 

 bone adhered strongly to the tongue, like burnt bone ; it was, however, 

 much more fragile, and friable. Even when kept for several days over 

 oil of vitriol, it lost a considerable quantity of water, which appeared to 

 be chemically combined with it. The cancellated tissue of this bone 

 was beautifully preserved. A portion of this tissue was put for three 

 or four days into acetic acid diluted with about twice its weight of 

 water, in order to dissolve out the carbonates which it contained ; this 



