378 The American Geologist. December. 1903. 
In the western part of the county is found a portion of the 
Yellowstone coal field, which lies south and west of Big Tim- 
ber. . 
Carbon County. 
In the eastern and south-central parts of this county are 
found some very productive coal beds. The eastern portion is 
covered with the Clarks Fork field, which yields a good grade 
of semi-bituminous coal, and at Gebo and Bridger, a large 
amount of this material has been taken out. This same field 
extends southward into Wyoming, and there is known as the 
Big Horn Basin field. 
The south-central beds embrace the Rocky Fork field, and 
yield a semi-bituminous coal or a good grade of lignite. The 
mine most productive in this field is the one at Red Lodge, the 
county seat of Carbon county, located on a spur of the North- 
ern Pacific Ry. This is probably a lower Tertiary formation. 
Yellowstone County. 
Yellowstone county lias the Clarks Fork field all along the 
northern part and the Bull Mountain field in the northeastern 
part. This portion of the Clarks Fork field in this county 
yields but very little coal. The formation is Laramie and the 
variety of coal is lignite. The fuel found in the Bull Moun- 
tain field is a post-Laramie formation or probably Eocene, and 
yields the best grade of all of the lignite fields in the state. 
Thus far the county is not very productive although the 
fanners and ranchers get a good fuel for the mere digging. 
Custer County. 
This county is one of the richest in the state in the produc- 
tion of lignite. Miles City, its county seat, is literally sur- 
rounded with this natural fuel. Several mines were visited 
near this place and all were in a flourishing condition. One of 
the best mines is owned by the Electric Light company and is 
about three miles from town. The coal seam is forty-five feet 
from the surface and three feet ten inches thick. It is capped 
by a slate colored leaf-bearing clay and underlain by a thin 
layer of "bone" and then fire clay. This mine supplies all the 
fuel for the Elecric Light plant of the city, and many use it 
entirely for domestic purposes, especially in the furnaces. 
