256 W. N. LOGAN 
The Jurassic limestones contain the following species: Astarte 
meeki,; Belemnites densus; Pleuromya subcompressa; Gryphea cal- 
ceola, var. nebrascensis; and a fragment of an undetermined 
Ammonite. 
This is one of the most northerly areas from which Jura has 
been recorded for Montana. If the formation is present in 
the Bear Paw Mountains which lie to the northwest of this area 
it has not been differentiated. 
Three Forks—The Jura has a thickness in this area of from 
300 to 400 feet. The lower beds rest on a basal quartzite and 
consist of argillaceous limestones which carry characteristic 
Jurassic fossils. The middle and upper beds are more arena- 
ceous than the lower beds and are non-fossiliferous. Under 
such conditions it is very questionable whether they should be 
assigned to the Jura. It is very probable that the thickness of 
the Jura in this area conforms more nearly to that assigned to it 
in other areas of Montana. 
Livingston.2—The Jurassic formation of the Livingston area 
has a thickness estimated at 4oo feet. It consists at the base of 
a massive, cross-bedded, ripple-marked sandstone. This sand- 
stone is overlain by a layer of impure fossiliferous limestone 
containing Pleuromya subcompressa M. ‘The limestone is fol- 
lowed by a bed of arenaceous limestones containing shell frag- 
ments. Since the lower layer is non-fossiliferous it may or may 
not represent a part of the Jura, but there is the possibility of 
an overestimation of thickness here as well as in the Three 
Forks area. 
Although the thicknesses given for the Three Forks and 
Livingston area are not extremely large, yet they are nearly 
double that given for the other Montana areas. But as has been 
pointed out, this lack of harmony may be due to the inclusion 
of beds belonging to other formations. If the faunal relations 
are not carefully worked out in connection with the stratigraphy 
errors are likely to occur either in the direction of the overlying 
t PEALE, U.S. Geol. Surv., Three Forks Folio, 1896. 
2IpDINGS and WEED, U.S. Geol. Surv., Livingston Folio, 1894. 
