cSO 
ores of Colorado pass by insensible gradation into silver-lead ores, 
so that these two classes should be studied in connection. Note the 
great variety of the Leadville ores. On the upper shelf of Case 8 
there is a small quartz vein in which many particles of native silver 
may be seen. 
Cases 9 and lO.— Silver ores, Mexico. 
This collection includes examples of both the ores and the 
rocks in which they occur of the important mining districts in 
Northern Mexico. 
It is especially interesting as showing the association of the 
ores with eruptive rocks characteristic of most of the richest sil- 
ver deposits of the world. 
Case 11 .— Silver ores, Guatemala. Vein rock of quartz and 
barite; country rock of schist and volcanic material. 
Cases 12 and 14.— Silver-lead ores, Colorado. 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 cerussite and 
anglesite. This “ carbonate ” ore comes from the decomposition 
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 ores, Leadville, Colorado. 
Cases 15 and 16, Rear.- Silver-lead ore. New Mexico. 
The principal ores of this class come from the Magdalena Moun- 
tains. 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 pow- 
der when handled. 
^'ase 16. 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. 
