720 . 
YX 2775 
2575 
2375 
€_member 
Lebo shal 
ABOVE SEA LEVEL 
LANCE FORMATION 
G. SHERBURNE ROGERS 
Fic. 2.—Diagram showing stratigraphic relations of Lebo shale member of Fort Union formation in Little Sheep Mountain coal 
field. Compiled from sections made along a line running 11 miles northeast from the mouth of Custer Creek (point X) to point Z; thence 
At peint a a detailed section was made which showed the alternation of yellow 
six miles east to a point opposite Terry (pointY). 
and dark-gray strata as indicated. 
last mentioned locality there are 250 
feet of these dark shales between 
coal U and the yellow phase of the 
Fort Union; and on Custer Creek, 
seven miles farther southwest, about 
340 feet. Beyond this there was 
no opportunity for measurement, 
and 20 miles farther west the coal 
which marks the base of the Lebo 
runs out of the district. The Lebo 
is therefore fan-shaped (see Fig. 2), 
of a thickness unknown in the 
western part of the field, but prob- 
ably not greater than 350 or 400 
feet; and reaching its eastern limit 
in this’ area) im) sec. th. 20 seuoee Nee 
R. 51 E., opposite Terry. 
A noticeable structural feature 
of the Lebo member is the very 
irregular character of the beds, 
which change rapidly in a horizontal 
direction. A measured stratigraphic 
section represents the strata in one 
place only; at a distance of 1,000 
feet on either side many of the beds 
change in color and often in texture. 
Scattered throughout the member 
are numerous lenses of a white and 
sandy material; these are commonly 
less than 2,000 feet in length and 
perhaps 60 feet in thickness, and are 
often only 200 feet long and ro or 
20 feet thick. In many cases they 
lie obliquely to the surrounding 
beds (Fig. 3) and are themselves 
strikingly cross-bedded (Fig. 4). 
The latter feature, together with 
