118 GUIDEBOOK OF THE WESTERN UNITED STATES. 
tions as with a mantle, but in the vicinity of Clarkston the Madison 
limestone is exposed, dipping to the northwest. “At milepost 181 
begins a long hillside cut in the upper part of this limestone, but as 
the beds trend in nearly the same direction as the track not much of 
the formation can be seen. The cut continues to milepost 183, where 
the valley opens out. On the right the hard formations are covered 
by clay deposited in the old lake, but on the left the Madison lime- 
stone swings across the river and makes a bluff more than 100 feet 
high above the St. Paul road. Before reaching Lombard the river 
makes a sharp bend to the left (north) and enters a box canyon! in 
the Madison limestone. (See Pl. XVIII.) The height of the walls 
FIGURE 27.—Fold and fault in the rocks near Lombard, Mont. 
of this canyon is about 300 feet, but it decreases downstream, owing 
to the fact that rocks dip in that direction. 
At Lombard the St. Paul line crosses the Northern Pacific and turns 
to the east up Sixteen Mile Creek, crossing the divide to the head of 
Musselshell River. Beyond Lombard the thick beds 
Lombard. of the Madison limestone descend rapidly and pass 
ites feet. below water level about a mile from the station. The 
St. Paul 1,07 miles. Quadrant formation does likewise, and at milepost 
186 attempts have been made to open a mine on a 
coal bed either in this formation or in the overlying Kootenai for- 
mation, but the coal is badly crushed and dirty and the project has 
been abandoned. 
A short distance beyond the coal mine there is a fault that brings 
the coal-bearing rocks into contact with the Belt series, which con- 
sists of red and green shale and argillite, very much broken and dis- 
turbed. (See fig. 27.) The Belt rocks form the surface along the 
river for about 3 miles, including the large bend which the river 
makes to the left. At milepost 189 the railway crosses this fault again 
and an igneous mass that was intruded along the fault. The road 
then enters the Quadrant formation, the lower part of which is gen- 
erally characterized by very brilliant red limestone and clay. This 
color is well shown on the right as the train rounds a sharp bend of 
: The term box canyon is applied in many parts of the West to a narrow canyon 
having vertical or nearly vertical walls. 
