76 
Case 7 , Rear.— Silver ores, Utah and Nevada. Hereare in- 
cluded specimens from the mines of the celebrated Comstock lode 
The specimens from Utah illustrate an unusual occurrence 
They are from the Silver Reef, and consist of sandstone impreg- 
nated with argentite and cerargyrite. In one specimen these min- 
erals may be seen replacing organic remains. 
Case 9.— Silver ores, Mexico and New Granada. 
Case lO.— Silver ores, Guatemala and New South Wales. 
Cases 11, 12, 13 and 14, Bear.— Silver-lead ores, Col- 
orado. These ores are especially abundant in Colorado. They 
occur in two forms: the sulphide ores, in which the silver is chiefly 
contained in galena, and the “carbonate” ore, a mixture of cerus- 
site and anglesite. This “ carbonate ” ore comes from the decom- 
position of the sulphide ore. Pyrite often accompanies the galena 
in the sulphide ore, as is well shown in the series from the A. Y. 
and Minnie Mine. 
Cases 14 Front, 15 Bear, and 16 Bear.— Silver-lead 
ore, New Mexico. The principal ores of this class come from the 
Magdalena Mountains. They run very low in silver, averaging 
only about 8 oz. per ton, and the percentage of lead is also low. 
Here may be seen specimens of the “sand carbonate” ore, which 
crumbles to powder when handled. 
Cases F, G, and H. — Collections illustrating the concentra- 
tion and smelting of gold, silver and lead ores. The processes are 
very complicated and varied, so that they can be illustrated here 
only in a general way. 
Case 15, Front.— Lead Ores. 
Type specimens of lead-bearing minerals. These are— 
galena, 86 per cent, lead, the most abundant lead mineral and 
fundamental lead ore; and the following minerals formed from it 
by oxidation: Cerussite, 77 per cent, lead, and anglesite , 68 per 
cent lead. 
There are other minerals which contain lead, but they are not 
of sufficient abundance to be important as ores. The case contains 
also lead ores from Illinois, Wisconsin, and Missouri. These con- 
tain very little silver, and are mined for lead only. On the 
lower shelves are silver-lead ores from Utah, Arizona and Wash- 
ington. 
