s 
BT. JOHN.] GROS VENTRE BASIN—CRETACEOUS. 22K 
a distance of 5 miles or more along the Gros Ventre, or from the upper 
main forks to the valley of a considerable south tributary that skirts 
the foot of the Carboniferous plated mountain ridge which here forms 
the northernmost culminating crest of the range. The exposures are 
well displayed but for occasional interruptions in the continuity of their 
visible outcrops in the terrace bluff along the southeast side of the stream. 
The rocks involved in the flexures are of Cretaceous age, according to 
the specific identity of the few fossils here obtained, as kindly determined 
by Dr. White. The northeast-facing mountain slope to the west of the 
before-mentioned Gros Ventre south tributary is heavily plated by the 
Jura-Trias, the outlying lower slopes in places showing low ridges of 
light-buff deposits, which are presumably referable to the Cretaceous. 
The strata are again exposed in the east side of the valley, and thence 
to the main forks of the Gros Ventre they are exhibited in a well-defined - 
synclinal and anticlinal fold, the axial trend of which is in a direction a 
few degrees east of south and west of north, changing farther east to 
about southeast-northwest. A diagram of the geological section here 
alluded to is given in an accompanying plate, the horizontal distances 
being rough approximations, in explanation of which is appended the 
following description: 
Section along Gros Ventre River. 
No. 1-4. The formations, Carboniferous to Cretaceous, inclusive, that 
rise up on the northeast flank of the Gros Ventre Range have been al- 
ready mentioned. The outer border of the Cretaceous, No. 4, at the 
mountain foot is concealed by morainal deposits, No. 5, and alluvial ma- 
terials in the valley. It may be that in this space the Cretaceous strata 
have been eroded over the site of a low fold corresponding to a previously 
mentioned broad low arch in the “red beds” immediately outlying the 
foot of the range to the northeast of Gros Ventre Peak. 
No. 6. Gray, indurated argillaceous beds and drab clays, and soft gray 
sandstone, with thin seams of cannel-like coal. Dip northeastward. 
No. 7. Gray, argillo-calcareous, indurated beds, gray sandstones and 
drab clays, with obscure plant-remains, and thin layers of lignite. Dip 
20°, about HE. 30° N. 
No. 8. Space, showing only obscure rock exposures of similar charac- 
ter to above and following. . 
No. 9. Indurated drab shales and drab and brown clays, and gray 
sandstone, underlaid by a thick deposit of heavy-bedded, gray, buff: 
weathered, soft sandstone. In the overlying drab shales, which also 
form a heavy deposit, at one place a thirty-inch bed of coal was observed, 
below which other thinner seams were seen, the outerop crumbling on 
exposure to the weather; dip 55°, about W. 10° 8. Overlying the coal, 
a small ovate leaf with crenate margins occurs in a drab indurated ar- 
gillaceous bed, together with comminuted vegetable remains, the sand- 
stone also affording what appear to have been large stems of trees, but 
very imperfectly preserved. 
No. 10. Gray sandstone, dip little south of west at an angle of about 
60°. This is probably identical with the sandstone next mentioned 
below, having arched over a sharp anticlinal fold, the axis of which has 
been eroded or otherwise concealed at this point. 
No. 11. Half a mile or thereabout below the main forks of the Gros 
Ventre, a heavy deposit of gray and bufi-gray, coarse-grained, heavy and 
thin-bedded sandstone appears in the bluffs along the left side of the 
stream, and lower down underlaid by dark or brown drab clays showing 
