59 
It is especially interesting as showing the association of the 
ores with eruptive rocks such as are characteristic of most of the 
richest silver deposits of the world. 
Cases 11 and 12 Rear. — Silver ores, Nevada. These include 
the ores of the famous Comstock lode. 
Cases 12, Front, 14 and 15, Rear.— Silver-lead ores, Colo- 
rado. These ores are especially abundant in Colorado. They oc- 
cur 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. 
Case 13. — Silver-lead ores, Leadville, Colorado. 
Case 15, Front. — Lead ores. 
Type specimens of lead-bearing minerals. These are — galena^ 
86 per cent, lead, the most abundant lead mineral and funda- 
mental 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 sufflcient abundance to be important as ores. The case con- 
tains also lead ores from Illinois, Wisconsin, and Missouri. These 
contain very little silver, and are mined for lead only. On the 
lower shelves are silver-lead ores from Utah, Arizona and Wash- 
ington. 
Case 16, Front. — Silver-lead ores, Mexico. Note the collec-' 
tion of carbonate ore from Minas Viejas, Villaldma, as showing 
how widely ores of this class may vary in appearance. 
Case 17, Front, — Silver-lead ores, British Columbia. The 
localities represented lie just north of the State of Washington, 
between the Cascade and Rocky Mountains, at the latitude of 
Vancouver Island. 
Case 18, Front, — Lead ores. Great Britain. The specimens 
illustrate well some of the common associations of galena. While 
in the Colorado ores the galena is commonly associated with pyrite, 
here we find it mixed with blende, a zinc ore which is very 
troublesome to the lead smelters. Specimens from the Welsh 
mines which contain much blende are marked “Poor Ground.” A 
good specimen of fluorite shown here, illustrates another common 
