6o 
CASE 5, FRONT AND 6 FRONT. — Silver ores. Mexico. 
This collection includes examples of both the ores and the rocks 
in which they occur of the important mining districts in North- 
ern Mexico. 
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. 
CASE 7, FRONT, AND 8, REAR.— Silver-lead ores, New 
Mexico. The principal ores of this class come from the Magda- 
lena Mountains. They run 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. 
CASE 8, FRONT. — Silver-lead ores, Arizona. 
CASE 9. — Silver-lead ores, Leadville, Colorado. These ores 
are similar to those from other Colorado mining districts in the 
iollowing cases : 
CASES 9, 10, 11, 13, 13, AND 14, REAR.— 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. These ores commonly carry gold in 
small quantities and at times the ore is more valuable for its 
gold than for its silver. 
The following cases contain ores from mining districts 
which yield both gold and silver, and which may be called gold- 
silver ores : 
CASE 14, FRONT AND 15, FRONT. — Gold and silver ores, 
Oregon and Washington. 
CASES 16 AND 17.— Gold and silver ores, United States 
•of Colombia. 
These are from the ancient “El Dorado,” or land of gold, 
from which came the first important yield of gold in the New 
World, and of which many wonderful stories were circulated. 
CASE 18, FRONT.— Lead and silver ores. Great Britain. 
The specimens illustrate well some of the common associations 
•of galena. Galena is commonly associated with pyrite, but here 
