152 GEOLOGICAL RECONNOISSANCE 



in ferruginous clay. The most valuable ore is a compact, cellular, sub- 

 crystalline smithsonite, of brownish-white and grayish-white color, surface 

 botryoidal, resembling, in its general appearance, the principal ore from 

 the Koch mine, (analysis No. 5); the cavities are partially filled with clay. 

 The subjoined analysis, No. 8, represents the composition of this ore. 

 The sample has been carefully selected, so as to approach as near as 

 possible to the composition of a fair average-specimen. 



Well developed crystals of smithsonite, abundant in the mines of Law- 

 rence county, appear to be entirely wanting, as are also the thin veins of 

 pearlspar, traversing the dolomite. In their stead, the dolomite is frequently 

 found incrusted with a compact mass of a pale brownish-white, or 

 greenish-white carbonate of zinc, with botryoidal surface, consisting of a 

 succession of concentric layers, the whole deposit having sometimes a 

 thickness of upwards of half an inch. Its hardness is between 4 and 5; 

 streak white; translucent; brittle; fracture splintery; heated in a glass-tube, 

 closed at one end, gives no water, but turns opaque and yellow, after 

 cooling opaque and white; on charcoal before the blowpipe, gives the 

 reactions of oxide of zinc. Its composition is given in No. 9. Interven- 

 ing between this mineral and the dolomite, a thin layer of crystallized 

 quartz, of brownish color, is frequently met with; the quartz in the sub- 

 joined analysis (No. 9), is probably derived from an intermixture of this 

 layer with the carbonate of zinc. 



No. 8. Brownish-white, cellular, smithsonite. 



Composition, dried at 212 deg. F: 



Clay, sand, and silica 7.523 



Oxide of zinc 59.770 



Peroxide of iron, with trace of manganese- • 3.507 



Oxide of cadmium 0.486 



" " lead 0.066 



" " copper trace 



Lime 0.466 



Magnesia trace 



Carbonic acid, water, and loss 28.182 



100.000 

 The air-dried ore lost 1.84 per cent, of moisture at 212 deg. P. 

 59.77 percent, of oxide of zinc are equal to 47.97 per cent, of metallic 

 zinc. 



The iron has been represented as peroxide, because the greater part of 



