718 G. SHERBURNE ROGERS 
in color. The areas in which these beds are exposed are gently 
rolling prairies, or less commonly hills, with bare slopes. Directly 
across the river from Terry the yellow beds of the Fort Union 
formation are underlain by the Lance formation, of which only 
about 150 feet are exposed. This formation resembles the Fort 
Union in every way, except that there are perhaps more beds 
which are light gray in color instead of yellow. The contact be- 
tween the two formations is marked by a coal bed (known as bed 
U) which is persistent through the eastern part of the field. 
At a point about five miles west of Terry, however, the strata for 
200 feet above coal bed U are dark gray in color and strikingly 
dissimilar to both the yellow Fort Union and the Lance (see Fig. 1). 
This dark gray member is composed of very irregularly deposited 
masses of shale with occasional arkose sandstones. Except for the 
numerous irregular and discontinuous layers of hard ferruginous 
concretions, and for a few fairly hard and generally massive sand- 
stones, the beds are always soft and practically incoherent. The 
outcrop of this member, which traverses in a broad belt the entire 
field west of this locality, is characterized by the formation of bad- 
lands so rough in many places as to be almost impassable. This 
land is given over largely to grazing purposes, and even in the 
comparatively level creek bottoms it is very poor for agricultural 
purposes. The general sterility of this member, its tendency to 
form badlands, and its decidedly dark gray color all combine there- 
fore to make it easily identifiable in the field. 
For the reasons given below this mass of dark shale is believed to 
represent the Lebo shale member of the Fort Union formation. 
The Lebo was first described on Lebo creek in the vicinity of the 
Crazy Mountains,‘ about 175 miles west of the Little Sheep Moun- 
tain field. It is there interpreted as an outfingering of the Living- 
ston formation,? which is composed of andesitic material, both 
detrital and tuffaceous, and which covers considerable areas west 
and south of the Crazy Mountains. This intercalated fan extends 
1R. W. Stone and W. R. Calvert, ‘‘Stratigraphic Relations of the Livingston 
Formation of Montana,” Econ. Geology, V, No. 6, September, 1910, p. 752 ff. 
2See W. H. Weed, “‘The Laramie and the Overlying Livingston Formation in 
Montana,” Bull. U.S. Geol. Survey, No. 105, 1893. 
