st. JOHN] BULL LAKE FORK CANON. 2AD5 
fect exhibitions of the upper Carboniferous limestones and Permo-Carbo- 
niferous horizon. The small streams, of which there are four in this 
section, cut through the sedimentary ridge down to the Archean core 
of the range, revealing in their narrow gorges sections essentially like 
that last described above. Immediately along the foot of the mountain 
usually occurs a shallow parallel depression, in which the Triassic ‘red 
beds,” and farther out local exhibitions of dark drab and variegated 
Jurassic horizons appear, gently inclined to the northeast. The former 
deposits occupy a belt half a mile toone mile in width, and never ex- 
tend to any height on the mountain flank. Their junction with the sub- 
jacent Permo-Carboniferous is well exposed at several localities, the 
latter beds being charged with the characteristic little Lamellibranchi- 
ate shell, Plewrophorus. But the Jura is much less well exposed in 
this quarter. Indeed, the gentle grassy slopes intervening between the 
streams rarely showing later deposits than the thin coating of drift and 
soil that is spread over their surface, and here and there mesa-like rem- 
nants of the tufa-conglomerates. The main crest of the outer mountain 
ridge is formed of the lower members of the Carboniferous and the Silu- 
rian formations, which rise into elevations between 10,000 and 11,000 
feet above the sea. 
Twenty miles to the southeast of Campbell’s Fork the great sediment- 
ary mountain ridge is again cleft to its base by the cation in which Bull 
Lake Fork flows. The latter stream rises high up under the precipitous 
wall of the great central crest of the range in the neighborhood of Fre- 
mont’s Peak, and flowing east-northeast joins Wind River, 25 to 30 
miles distant from its ultimate source. Of its upper course, or that por- 
tion lying within the elevated rugged Archean area, little can be said 
from actual knowledge of the region. It is not, however, an inaccessi- 
ble region, and to the lithologist and mineralogist it offers an absolutely 
new field of research. Along its lower course it has eroded a broad 
canon-way walled by characteristic cliff exposures of the Paleozoic for- 
mations, which on the south side rise up into heights above 10,800 feet 
actual altitude. At its exit from the mountain the stream flows in a 
narrow valley hemmed in by high bluffs capped by enormous morainal 
accumulations that extend to Wind River, eight miles away. Just be- 
low the debouchure the stream expands into a lake between two and 
three miles in length, its indented shores bordered by sage-covered slopes 
and fringed with cotton-woods and willows. Mr. Clark’s barometrical 
observations give the water-level of Bull Lake an altitude of 5,911 feet 
above the sea. 
The immediate mountain-foot in the debouchure of Bull Lake Fork is 
composed of the upper members of the Carboniferous series. In the 
blufis bordering the stream in its passage across the outlying benched 
area, late continued erosion, fortunately, has swept off the superficial 
materials and barred one of the most complete sections of the Mesozoic 
series to be met with in the northern half of the range. Besides the 
Paleozoic series shown in the lower cafion walls, where their general 
characteristics were hastily glanced over, we here have the Mesozoic 
formations displayed under exceptionally favorable conditions for detail 
stratigraphic study. This whole grand series of geological formations 
from the Primordial up to the upper member of the Cretaceous of the 
region, are here revealed without slightest indication of discordance of 
deposition of more than local significance or such as a stratum of any 
subordinate member may be expected to show. But during the Post- 
Cretaceous time the duration of these conditions was interrupted, and 
the evidence is legibly recorded in the unconformably superimposed 
Cenozoic deposition here met with. 
