50 FIELD MUSEUM OF NATURAL HISTORY 
to be found in actual trial by assay. The above observations do 
not apply, however, to the lead ores, which are readily recognized 
by one having acquaintance with the lead-bearing minerals. 
If the visitor enters from the West Dome and passes around 
Hall 72 to the left, the gold, silver and lead collections may be 
inspected in the cases along the walls in a geographical order 
This order begins with northwestern North America, passes east- 
ward through Canada, then south along the Appalachians and 
then westward through the Mississippi Valley to the Cordilleras, 
completing the series of ores of Canada and the United States 
The ores of Mexico then follow, then those of South America, 
Africa, Australia and Europe. The gold, silver and lead ores 
are displayed together in this series and often are even intimately 
mixed in the individual specimens as may be seen from the 
numerous cases in which the labels read “gold-silver ore’’ or 
“silver-lead ore” or even “gold-silver-lead ore.” 
The wall case nearest the entrance to the West Dome con- 
tains a series of specimens showing typical associations of gold 
with other minerals, as they are found in mining. A similar 
series of silver-bearing minerals presents examples of those 
minerals which contain silver as an essential constituent and 
those minerals commonly closely associated with silver in the 
mines. A third series illustrates the lead-bearing minerals and 
the more ordinary types of the association of these lead con- 
taining minerals with others in the lead ores. Below these 
synoptic series is a group of auriferous quartzes representing 
the ores of three widely separated regions of Alaska. The next 
section of this case is occupied by Canadian ores of which 
there are two series. One consists principally of silver-lead 
ores from the Kootenai and adjacent districts of British Col- 
umbia; the other includes the ores of the Height of Land in 
Ontario. The more prominent of these are the silver ores of 
Cobalt with their associated arsenic and cobalt minerals and 
the gold quartz ores of Porcupine. The third section of this 
case contains a series of ores of the Appalachian Mountains. 
These include the gold ores which were first exploited in the 
United States. With the gold ores are examples of lead ores 
some of which have been exploited from colonial times to the 
present day. 
The next case, which is the first upon the south wall, con- 
