58 
stance in invisible particles ; gold combined with tellurium in; 
sylvanite, petzite, etc., (teliuride ores); and placer gravels in 
which the gold occurs as particles scattered through gravel and 
sands. A more extensive exhibit of placer gold may be found in* 
Hall 32. 
With each specimen there is a glass tube containing the sub- 
stances which form the mineral in the exact proportions in 
which they occur in the actual ore. 
Many minerals other than those shown here are gold-bear- 
ing, but the gold in them occurs as microscopic inclusions in 
some one or more of the minerals exhibited in this case. 
Gold, silver, lead and copper are so frequently associated in 
the same ores that it is impossible to draw a sharp line between 
the deposits of these metals. Hence it will be observed that in 
the space devoted to gold ores, the specimens frequently carry 
much silver, lead or copper or even all three. This occurrence of 
several metals in one ore deposit will be observed also in the 
space occupied by ores of the other metals mentioned above. 
CASE 1, REAR. — Gold ores. Pacific Coast. These are chiefly 
quartz or quartz and pyrite. They may be distinguished in general 
from ores in this class of other localities by a cleaner appearance^ 
the absence of rust and disintegration, and by the smaller propor- 
tion of pyrite present. 
CASE 2, FRONT. — Gold ores, Colorado. The ores of Crip- 
ple Creek, Col., should receive special attention on account of 
their remarkable richness. Gold, which almost universally occurs- 
free, is in these ores combined with tellurium (a substance re- 
lated to sulphur) in the form of teliuride ore 
CASE 2, REAR. — Gold ores. Black Hills, South Dakota. The 
ores included here are a good example of the great variety of 
gold ores which may occur in a limited area. Compare, for 
example, the ore from the Homestake mine with that from the 
Holy Terror, which again is wholly different from that of the 
Golden Reward mine. In Hall 79 may be. seen ores of yet 
different characters from this region, some carrying tin, others 
tungsten, etc. 
CASE 3, FRONT. — Gold ores, Great Britain. The collec- 
tion from the New Morgan Mine, Dolgelly, Wales, is worthy 
of special attention both on account of its completeness and of 
the character of the ore. The gold is nearly all free, and mudt 
