THE NORTHERN PACIFIC ROUTE. 95 
controlled directly by the altitude but by the greater precipitation 
on the mountain slopes than on the plains below them. 
Along the new grade many exposures of the Livingston formation 
can be seen in the deep cuts. It consists of chocolate-colored shale 
and sandstone of a lighter shade but still showing a brownish tinge, 
which is due to the fragments of voleanic matter of which it is com- 
posed. The beds are somewhat wrinkled and disturbed but generally 
dip to the right, away from the mountain, at an angle of about 20°.* 
About half a mile beyond milepost 121, in a deep cut, two dikes 
of igneous rock are exposed cutting directly across the bedded sand- 
stone and shale. In places where such dikes have cut through coal 
beds, or have taken the form of a sheet or sill below the coal, as illus- 
trated in figure 15, the heat of the molten rock has changed the 
coal, the resultant material depending upon the conditions attending 
Figure 15.—Dike cutting coal bed and sill intruded in a position to affect the quality of the coal. 
the intrusion. If air is present, the coal will burn out completely; 
if only a moderate amount of air is available, natural coke will be 
formed; and if little or no air is present, the coal will be baked into 
anthracite. Anthracite produced in this manner occurs in Colorado, 
New Mexico, and Washington. 
After a long climb the summit is reached at Muir, a station at the 
east end of the Bozeman tunnel, which has a length of 3,610 feet. 
The summit of the pass is only a few hundred feet 
yiute. above the level of the railway. Beyond the tunnel 
Elevation 5,806feet. the Hagle sandstone, which was seen back of Billings 
and again obscurely at Livingston, carries coal beds 
which have been prospected and mined at various places west of 
Livingston. As a general rule the coal crops out along the base of 
places the formation is only 100 feet thick, 
but about Livingston the sandstone with 
i ing shale beds is about 
1 As the rocks dip away from the moun- 
tains, as shown in figure 13 (p. 89), lower 
formations than those exposed in the rail- 
way cuts appear toward the south. These 
lower rocks include the coal-bearing 
formation which crops out in a continuous 
band from Livingston across the summit 
to Chestnut. This formation overlies the 
Colorado shale and is about equivalent to 
ee oe NG ge Inent 
in the rim rock back of Billings. In most 
ts accompanying 
1,000 feet thick. 
Formerly the Cokedale mine, one of the 
most productive in the State, was in oper- 
ation about 7 miles west of Livingston and 
coke was manufactured from part of the 
coal, but the mine has been abandoned 
for a number of years and the railway 
spur leading to it has been removed. 
