THE NORTHERN PACIFIC ROUTE. 
113 
The town of Warm Springs (see sheet 18, p. 134) is built around a 
group of springs having a temperature of about 150° and affording 
a copious flow of water. 
miles wide and is so flat that much of it is swampy. 
The hills on the right (east), about 500 feet high, 
are composed of light-colored clay and volcanic ash 
Warm Springs. 
Elevation 4,832 feet. 
Population 866.* 
St. Paul 1,153 miles. 
The valley floor is several 
d are remnants of the Tertiary lake beds that 
once filled the valley at least as high as the top of these hills. These 
materials were deposited in a great lake, which occupied this valley 
at the same time that similar lakes occupied the Gallatin and Madi- 
son valleys to the east.t 
1There is no more interesting sub- 
ject in the geology of the mountain 
region of Montana than that of the lake 
beds. They imply conditions which at 
first sight seem to be anomalous—that 
is, extensive bodies of water in a rough 
&: 134), lake beds have been found in 
ractically every valley from the Yel- 
nea, on the east to the Bitterroot on 
Blackfoot River. It therefore seems 
fairly safe to assume that in Tertiary time 
lakes existed in nearly every mountain 
valley in the State. Many of the valleys 
that to-day are separated were doubtless 
connected through the canyons, but in 
such locations the material deposited in 
the lakes has been removed by the swiftly 
tions. Although the distribution of a. 
materials that were laid down in these 
lakes indicates that many of gum were 
connected, a study of the bones of animals 
that lived at the time and were buried in 
the mud and sand of the sake mcionton 
that the la ke-fi 
Met ULIO Leads 
‘ over a long period of time, some of the | 
fossils being of Oligocene, some of Mio- 
cene, and some of Pliocene . It is 
generally supposed, however, that most 
95558°—Bull. 611—15——8 
of the lakes were in existence in the 
Miocene epoch. 
Lakes are abnormal features and have 
no place in the orderly development ofa 
drainage system—that is, when a drainage 
system is established on the land there is 
no tendency in the action of the 
to form lakes, and when such features are 
formed they are the direct result of some 
interference with the work of the streams. 
Most lakes in mountainous are 
due to the action of glaciers, either in 
scouring org rock basins ole a sass ari 
1] 
aa oi 
d fi fi f theice. 
If the old lakes of Montana were due to 
the action of ice, there would remain some 
trace of the glaciers that did the work and 
of the great dams which they must have 
built. Dams formed by landslides or lava 
flows would likewise leave some evidence 
of their existence, and they could not 
have been so extensive as to pond the 
water in all the principal valleys opening 
out on both sides of the ran; 
. The wide extent of the lakes seems at 
once to rule out all local causes, so it is 
necessary to appeal to some cause that 
would have been operative throughout a 
wide region and that would have been 
adequate to produce such results, The 
great regional cause that is fully re id 
tent to pond rivers or produce lake b: 
is movement within the crust of the aah 
whereby one area is raised or depressed 
with relation toanother. To the geologist 
the history of the earth, so far as it has 
