200 REPORT UNITED STATES GEOLOGICAL SURVEY. 
curving up to the west where the chocolate-red beds are seen to form 
part of arch. 
1. Dark rusty-weathered beds, probably gray sandstone, forming jag- 
ged crest of spur, with undulating inclination northeastward. 
m. Soft, ash-drab deposits, apparently upraised into a low arch, but 
not clearly made out at a distance. 
n. Dark rusty-weathered, probably bluish-gray sandstones and argil- 
laceous beds. 
The deposits a, b, of the foregoing section unquestionably, belong to. 
the west flank of the John Day ridge uplift. The lower arch represented 
in the section, on the east flank of which occur the black carbonaceous 
clays, d, may possibly be the northern continuation of the above ridge, 
and which, in the latter event, was not here faulted. The reddish- 
brown ledge, ¢, the sole vestige of the west flank of the fold, strikingly 
resembles the earthy sandstones associated with the before- mentioned 
Ostrea ? shaly beds found in the west foot of the ridge a few miles 
south. Should the identity sought prove well founded, it would appear 
that the John Day ridge here ‘sinks sufficiently to allow the Mesozoics 
to completely mantle the arch. The carbonaceous deposits alluded to 
are the same visited by Professor Bradley, and in his notice he refers to 
the exposure as consisting of “two or three heavy beds of black, calea- 
reous shale and friable clay, with some harder bituminous mud-stones, 
A) COMA; fragments of teeth and bones, probably belonging 
to amphibians.” These “deposits are overlaid by a thick bed of chert, 
probably represented by c of the above section. 
The told represented next above the last described, constitutes the 
axis of the more elevated, rugged portion of the ridge which here closely 
borders the stream, and which is believed to lie to the east of the axial 
trend of the John Day ridge proper. This fold was also mentioned by 
Professor Bradley, who describes it as being of mountainous propor- 
tions, with a nucleus of limestone. Opposite these exposures, as already 
mentioned, quantities of spar-seamed drab limestone and hard reddish 
sandstone débris occur in the steep declivities, but in the absence of 
fossils their age remains in doubt. <A short distance above the latter 
occurrence, however, and opposite this uplift, the trail passes a succes- 
sion of steeply inclined gray, rusty-weathered, thin-bedded sandstones, 
with which are associated fragmentary light chert beds, whose ensemble 
certainly bears close resemblance to horizons in the plant-bearing beds 
east of Station X1, which were compared with the Laramie. The latter 
beds are doubtless the same shown at l, and if their stratigraphical 
identity, as above inferred, be correct, the underlying strata composing 
the axis of the fold may not include deposits of earlier date than the 
Jura. To the north, however, in the more mountainous region occupy- 
ing the bend of the Snake below Jackson’s Basin, and constituting the 
extreme eastern flank of the Snake River Range south of Téton Pass, 
the prevalent rock formations apparently belong to a later or Post-Ju- 
rassic age. The latter quarter, however, was not visited, and the infer- 
ences arrived at are founded upon lithological appearances made out at 
a distance. 
The deposits » appear in more or less interrupted exposures in the 
bluff-bank of the terrace, the evenly leveled-off tilted strata bearing 
the Quaternary deposits which constitute an important element in the 
composition of the terraces that now fill the valley. These strata con- 
tinue as far as the mouth of Hoback River, where ‘good exposures recur 
in the banks of the latter stream, a short distance above the confluence. 
At this locality a thickness of 20 to 30 feet is made up of bluish-gray, thin- 
bedded to shaly, sometimes concretionary, sandstone and fine argillo. are- 
