53 
the ordinary impurities have upon the usefulness of the sub- 
stance. 
Meerschaum. This is not a clay but is included here on ac- 
count of its use for pipes. 
Other clay-like minerals including allophane and hallo>site. 
HALL 69. 
COALS OF THE UNITED STATES. 
Here one may study the distribution and extent of the coal 
fields of the United States, also the kinds of coal produced by 
each and the available means of transportation. 
On a large plate-glass map in the center of the hall, scale 
ten miles to one inch, the coal fields of the United States as at 
present developed are indicated by areas in black, and the 
principal railroads connecting them are also represented. 
CASES 1-18. — Specimens taken from these different fields, 
the exact locality of each being shown by figures on the labels 
corresponding to those on the map. The order of numbers is the 
same as the alphabetical order of the States. The specimen 
labels show the uses of the coal, the names of the operators of 
the mines, the means of transportation, the markets, and the 
analysis of the specimens. Other data will be given to any one 
desiring to obtain them, on application to the Curator. 
HALL 70. 
COALS AND HYDROCARBONS. 
This hall contains a series of the carbon minerals, beginning 
with the diamond, and passing through graphite, the coals (an- 
thracite, semi-anthracite, semi-bituminous, bituminous and lig- 
n'te) to bitumen and asphalt. 
CASE 1. — Diamonds from Kimberley Mines, South Africa. 
‘'Blue ground” or matrix in which diamonds occur, from De 
Beers mines. Cape Colony, South Africa. Graphite. 
CASE 2. — Asphaltum minerals. Oil shale. 
