204 Geological Survey of the Territories in 1872. 
Between this point and the great valley along the eastern 
front of the Teton range there lies a heavy body of mountains, 
which appears to be the “main range” of the Rocky Mts. at 
this point, if such a thing ecists. At least, it is a part of the 
highest mass connection between the Wind River and Big Horn 
Mts. on the east, which form the northern termination of what is 
the main range further south, and the range west of the Three 
Forks of the Missouri, which there bears the name of Rocky 
ts, and whose continuation really appears to be the main 
range further north, so far as the best maps indicate. This, of 
course, does not coincide with the water-divide, which curves 
far north above Lake Lewis and far south around the heads of 
the Jefferson. 
After an examination of the sources of the tributaries further 
west, the main Snake was again reached, about twelve miles 
from its source, where it is already a large stream with high 
gravel terraces along its banks, and was followed to its junction 
with Lake Fork, where the main party were in camp. ew 
miles above this point stratified rocks were again found, con- 
sisting of Triassic? red shades and sandstones, followed by a 
nearly white limestone, probably of Carboniferous age. These « 
are at one point crossed by a huge bed of basalt, filling what 
had probably been a stream valley through the older rocks 
before the eruption of the volcanic material from some vent 0 
the Red Mt. range. At the upper edge of this belt of basalt 
there is a small basin of hot springs, once of considerable im- 
portance, but now nearly extinct. Other groups were found 
near the mouth of Lake Fork. 
In descending from Lake Lewis, the Lake Fork was found 
falling rapidly through a narrow cafion, whose nearly vertic 
walls in some places reach the height of 700 or 800 feet, while 
not over 400 feet apart at the top. These are all of dark- 
— volcanic rock. 
This pass probably affords the best line of approach to the 
Yellowstone from the southwest. The average grade from 
Henry’s Fork to the summit is about 54 feet to the mile. 
