ST. JOHN.] HOBACK CANON RIDGE—JOHN DAY RIDGE. 187. 
geologically the same as that on which Station II was located; that is, 
the eastern flank of the synclinal trough, which is here also filled with the 
“red beds,” and probably remnants of the Jura. The eastern verge of 
the synelinal probably lies at least a mile east of the station, where it is 
marked by prominent red pyramidal heights overlooking the high 
morainal benches in the foot of the Gros Ventre Mountains, and which 
here constitute the divide between the upper north affluents of the 
Hoback and the little stream that joins the Snake a mile or so above 
the mouth of Hoback’s River. The heavy upper “ red beds” rest upon 
a series of grayish buff limestones and red drab and chocolate banded 
arenaceous deposits, occurring in heavy alternating beds, with a verti- 
cal exposure of near 1,000 feet in the south side of the cafion north of 
the Hoback. The latter deposits bear marked resemblance, lithologi- 
cally, to the Permo Carboniferous horizon in the Snake River Mountains; 
but in the absence of fossils, none having been noticed in these beds, the 
data is as yet insufficient to establish their identity beyond question. 
As regards the geological character of the outlying strip on the south- 
west flank of the Gros Ventre Mountains, and extending well over to 
the Snake River south of the basin course of the Little Gros Ventre 
Creek, the only data gained was that presented in the view from Station 
If. This mainly discloses the red and gray deposits of the Jura-'Trias, 
from beneath which the Palseozoic formations rise up on the south flank 
of the great Archan spur of the Gros Ventre Mountains, which abruptly 
terminates on the Little Gros Ventre in Jackson’s Basin, to the north- 
west of Station XII. To what extent the strata in this belt have been 
disturbed is not clearly made out. Nor is the contact of the Hoback 
Caton ridge with the southern flank of the Gros Ventre Mountains in 
this quarter better displayed, though the two undoubtedly belong to 
entirely distinct areas of mountain upheaval, as wiil be further noticed 
in another place. 
The Carboniterous series in the Hoback Caiion ridge offers striking 
resemblances to the same series as developed in the Snake River Range 
to the northwest of the Grand Cation; the upper measures consisting 
of gray, buff, and flesh-tinted hard sandstones and red arenaceous de- 
posits, including beds of more or less siliceous and sometimes magne- 
sian limestones. This upper siliceous member is of great thickness (the 
exact measurement in feet would be difficult to determine after so hasty 
exploration), and in the deeper gulches and canon it has contributed im- 
mense quantities of fragmentary materials to the steep taluses. With 
the inferior and perhaps heavier limestone member the whole series 
probably attains a thickness above 3,000 feet in this area. 
JOHN DAY RIDGE. 
West of the Hoback Caiion ridge a nearly parallel mountain ridge 
extends from the southern line of the district, where it is identitied with 
the Green and Snake River water-divide, northwards in a nearly direct 
course a distance of 22 miles, terminating in the angle at the junction 
of the Hoback and Snake Rivers, and which may be distinguished by 
the above appellation. ; 
The belt intervening between the Hoback Cajion and John Day ridges 
is partly drained by the lower south fork of the Hoback, and north of 
the latter stream the area here alluded to merges into the valley of the 
Snake above the Grand Caiion. To the south a high divide separates 
the Hoback drainage from the sources of the East Fork John Day’s River, 
south of which one of the upper tributaries of the main Hoback takes 
