56 FIELD MUSEUM OF NATURAL HISTORY 
were nearly all abandoned at the time of the discovery of gold 
in California and have never regained their earlier importance. 
The series of Mexican ores includes representative speci- 
mens of ore from all the gold and silver mining states of that 
Republic, accompanied, in the case of the more important dis- 
tricts, by specimens of the country rock. The collection is es- 
pecially 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. 
The series of ores representing South America is composed 
chiefly of specimens from Colombia, Ecuador, Brazil, and Vene- 
zuela. The collection of Colombian ores is especially complete 
and includes typical specimens of ores, gangues and rocks from 
practically all the mining districts of that country. This region 
was 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. 
The collections representing the ores of Australia consist 
principally of silver-lead and silver-copper ores. Many of the 
specimens are too large for the serial cases, and should be sought 
in the large center cases and pedestals. 
The series of ores from Great Britain consists of lead-silver 
ores and gold ores. The lead-silver ores illustrate well some of 
the common associations of galena. Galena is commonly asso- 
ciated with pyrite, but 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, illus- 
:;rates another common associate of galena in the English mines, 
as do also the specimens of calcite and galena. Some of these 
ores, as for example that of Snail Beach, are from mines formerly 
worked by the Romans. Note the general absence of “carbon- 
ates,” and the fresh, undecomposed appearance of the specimens. 
This is also true of the Spanish and German ores. Carbonate 
and disintegrated ores occur near the surface where air and at- 
mospheric waters have acted and formed them from the sul- 
phides. These mines having been long worked, most of the 
superficial ores have been removed, so that now only the sulphide 
ores occurring at great depths are mined. 
Gold ores from Great Britain are represented by specimens 
from a single Welsh mine. This series from the New Morgan 
