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. 
No. 82. 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... -+-seeesseeeeeeeee 6.701 
Carbonate of lime+-.+.-eseeeees teseree 53.998 
Carbonate of magnesia. -++-+++.sseeerees 35.059 
Carbonate of irons +++ esseeeseeereeeas 2.253 
Carbonate of Zince ses es erecceecerenes 1.978 
POEASS AE oa) Sa) Bi pin aie ONS Sa sioay eters tee ee 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. -.-- stew ereceseeeeces 10,985 
Iron, alumina, and trace of manganese-- 1.482 
