174 GEOLOGICAL RECONNOISSANCE 



/ 



ROCKS ASSOCIATED WITH THE ORES OF ZINC 



AND LEAD. 



A careful examination of the rocks in which the ores of zinc and lead 

 occur, and of the substances which are found associated with them in the 

 veins and crevices, will probably throw some light on the origin of these 

 metalliferous deposits, and enable the geologist to form a correct idea of 

 their mode of formation. This was one of the objects we had in view in 

 submitting the below enumerated rocks to chemical analysis. Want of 

 time, however, prevented me from carrying on the investigation to a 

 sufficient extent, and I was obliged to defer to a future period the comple- 

 tion of a sufficient number of analyses to enable us to draw satisfactory 

 conclusions from them. 



f No. 32. Dolomite, which cuts out the ore at the Hoppe mine, Lawrence 

 county. 



A pale yellowish-gray, compact dolomite; fracture subconchoidal; very 

 hard; brittle; powder of a light cream-color. 



Composition, dried at 230 deg. F: 



Insoluble silicates 6.701 



Carbonate of lime » 53.998 



Carbonate of magnesia 35.059 



Carbonate of iron 2.253 



Carbonate of zinc 1.978 



Potassa 0.106 



100.095 

 The air-dried rock lost 0.37 per cent, of moisture at 230 deg. F. 



No. 33. Dolomite, with and below the zinc-deposit at the Koch mine, 

 Lawrence county. 



A dark yellowish-gray dolomite, compact and close-textured; fracture 

 subconchoidal; very brittle; gives out a peculiar bituminous odor when 

 struck with the hammer; powder ash-colored. 



Composition, dried at 250 deg. F: 



Insoluble silicates 10.935 



Iron, alumina, and trace of manganese- • 1.482 



