STRATIGRAPHIC POSITION OF JUDITH RIVER FORMATION 543 
valley long before Fullerton is reached and at the latter place form 
the bluffs on both sides of Judith River in typical exposures con- 
taining characteristic fossils. The entire thickness does not show 
at Fullerton but there is here an exposure of at least 4oo feet. The 
total thickness is probably from 600 to goo feet. Immediately 
below the Judith River beds which form the summit of the bluffs 
and the surface of the bench reaching to the eastward, there are 
from 50 to roo feet of sandstone with Halymenites major and the 
following invertebrate fossils: Avicula nebrascana E. & S., Tancredia 
americana M.&H., Lunatia subcrassa M. & H., Tellina equilateralis 
M.&H., and Mactra sp. These are identified by Dr. Stanton 
and referred by him to the Claggett, but it seems to me they are 
undoubtedly of Fox Hills age, the beds containing them resting 
on Pierre shales and being immediately followed above by the 
Judith River beds. The basal layers of the latter series contain 
Ostrea subtrigonalis and other brackish-water forms. The contact 
between the two formations as seen from the west side of the 
valley is somewhat irregular, suggesting the unconformity which 
elsewhere marks the upper limit of the Fox Hills and the base of 
the Lance formation. Up to this point no faults occur nor is there 
any evidence of folding nor of overturn. The section is normal 
and complete, unless a stratigraphic break exists corresponding 
to the paleontological hiatus at the top of the Fox Hills, the sequence 
from the Kootenai up through the Colorado and Montana into the 
Judith River formation being perfect except for the paleontologic 
and possibly stratigraphic hiatus at the base of the latter. 
A short distance below Fullerton the first of three well-marked 
faults that occur south of Judith Landing crosses Judith River, 
The direction of this fault is nearly east and west and the dip of the 
beds thrown down is quite steep (about 20°) toward the northwest. 
This outcrop, mainly of Fox Hills sandstone and a smaller part of 
Judith River beds, is underlain by Pierre shales; and above the 
faulted beds are Pierre shales capped by Fox Hills sandstones 
(containing invertebrates and Halymenites major) which underlie 
the undisturbed Judith River beds which have a very slight inclina- 
tion to the north or northwest. The lower slopes of the hill back 
to the faulted beds is composed of Pierre shales capped with Fox 
