Geological Survey of the Territories in 1872. 199 
of Henry’s Fork, and followed the general course of that stream 
to its source in Henry’s Lake. The central portion of the val- 
ley is constantly floored with basalt, which was finally traced to 
it3 source in Sawtelle’s Peak, which stands on the south side of 
Henry's Lake. The crater of this ancient voleano is still from 
1200 to 1500 feet deep, about a half mile wide and something 
less than a mile and a halflong. The range running west from 
this point appears to consist of volcanic rocks ; and probably a 
row of similar craters will be found along its summit. 
The foot-hills and mountains along the east side of the val- 
ley of Henry’s Fork, after we pass the northern termination of 
the Tetons proper, consist of porphyries and obsidian-sand- 
stones, until we reach the very head of the valley, a little north 
of east from Henry’s Lake, where the same series of limestones 
and quartzites that we saw at the Tetons again appears in the 
divide between the waters of the Snake and those of the Madi- 
son; but, instead of the conformity before observed, the Que- 
bec Group limestones apparently le unconformably over the 
upturned edges of the Potsdam quartzites. Beneath these, 
metamorphic rocks form the face of the ridge to the westward 
and northward. The ridge west of the lake is mainly composed 
of metamorphic limestones with quartz bands, which are sup- 
ag to be of Carboniferous age. These include a sixty foot 
ed of trap, standing conformably between the upturned layers 
of the limestone. 
The divide toward the Madison rises into a rather lofty range, 
whose height was not ascertained, but which must reach at least 
a thousand feet above the average level of the plateau of vol- 
canie rocks which fills the broad depression toward the Tetons. 
In crossing here to the waters of the Missouri, one has the choice 
of three easy passes, all level enough for a horse to cross witha 
buggy, at fall trot, and only one of them at all obstructed by 
timber. Henry’s Lake was found to have an elevation of 6492 
feet; from its southwestern side, Red Rock Pass crosses to the 
head of Beaver Head Fork of the Jefferson, at an elevation of 
7271 feet; from its northern extremity, Reynold’s Pass leads to 
: the lower Madison, with an elevation of 6911 feet ; Tyghee Pass, 
with an elevation of 7068 feet, led our party eastward into the 
basin of the Upper Madison. 
e upper cafion of the Madison shows some grand scenery 
saw the first of the boiling springs which are so abundant in 
this region; and, in a few miles more, the Lower Ge. 
of the Fire-hole Fork was reached, at about 3.00 P. M., of 
August 14th. Dr. Hayden's party had arrived at this appointed 
