6 FLORA OF THE MONTANA FORMATION. 
vary considerably in character and thickness within short distances, but the fossil- 
iferous and overlying portions of the section maybe described in general terms as a 
series of variable sandstones, clay, and coal beds, exposed in low hills and ridges, 
with a dip of 9 or 10 degrees eastward at the base, but decreasing in the upper por- 
tions to 5 or 6 degrees, which is about the same as the dip of the overlying Wasatch 
beds. 
The section at Black Buttes as thus denned is referred without 
hesitation to the Laramie, aniJ the flora is considered a true Laramie 
flora, as now understood. The flora and invertebrate fauna are prac- 
tically identical with that of the Laramie of Converse County, Wyo- 
ming, 1 a locality in which the geological relations are much plainer 
than at Black Buttes, since the section is continuous from the Fort 
Pierre slates to and perhaps above the Fort Union beds. 
Point of Rocks, Wyoming, 11 miles northwest of Black Buttes, has 
afforded an extensive fossil flora which has, until recently, been 
regarded as a true Laramie flora. The section is somewhat similar to 
that at Black Buttes, having at the base a massive light-colored sand- 
stone about 100 feet in thickness, the presence of which, together with 
the evidence of certain local faulting between the two points, has 
led several geologists to regard them as representing about the same 
horizon. Powell, in his Geology of the Uinta Mountains, page 48, named 
his u Point of Rocks group" from this section, and drew the line sepa- 
rating it from the Bitter Creek group above at the top of the heavy 
sandstone, where the somewhat uneven surface was regarded as repre- 
senting an erosive interval. The base of the Point of Rocks group 
as defined by him is observed about (3 miles west from Point of Rocks 
Station, near where the comparatively narrow valley broadens into 
that of the Salt Hills Valley. The base was placed at the base of the 
massive sandstone, which is quite different lithologically from the 
thinly laminated beds of the summit of the Salt Hills group below. 
The Point of Rocks group of Powell was therefore supposed to corre- 
spond more or less closely with the Laramie, 2 but this has since been 
shown to be an entirely wrong conception. 
The Point of Rocks section had been previously visited and somewhat 
hastily studied by Messrs. Meek and Bannister, of the Hayden survey, 3 
and they would place the coal beds several hundred feet lower than 
those at Black Buttes. The observations of Mr. Stanton and myself 
are abundantly confirmatory of this latter view, for not only did a 
comparative study of the two sections seem to indicate differences, but, 
in addition, we found marine Cretaceous shells above the coal. The 
beds containing this fauna occupy a position near the top of the bluff 
in front of the Point of Rocks Station, and about 260 feet above 
the top of the massive sandstone. The dip of the beds is about 6° 
a little north of east, and almost parallel with a valley that joins that 
1 See Stanton and Knowlton, op. cit., pp. 128-137. 
2 See White, Bull. U. S. Geol. Survey No. 82, p. 156. 
* Ann. Kept. U. S. Geol. and Geog. Surv. Terr., 1872, pp. 529 et seq. 
