THE NORTHERN PACIFIC ROUTE. 
Garrison was named in honor of William Lloyd Garrison. 
115 
Here the 
railway line through Butte unites with the original line of the North- 
Garrison. 
Elevation 4,344 feet. 
St. Paul 1,180 miles. 
ern Pacific through Helena. 
is much narrower than it is above that place, the 
cliff on the west being composed of a volcanic rock 
The valley at Garrison 
(andesite) and that on the east of sandstone, shale, 
and beds of volcanic tuff 1 of Upper Cretaceous age. 
[The itinerary west of Garrison is continued on page 127.] 
The present condition and possible mode 
first formed, this valley was a great struc- 
tural depression in the hard rocks, as rep- 
resented by AB. In that basin sediment 
accumulated in Miocene time until the 
= was filled, as shown in the dia- 
gram. e place where Garrison now 
stands was then near the middle of the 
basin, and probably only soft lake sedi- 
ments showed at the surface from Durant 
to Drummond 
Drummond 
9 
am 
i 
es t 
FIGURE 24.—Sections along Northern Pacific Railway between Duran 
map or by a view seen some commanding 
summit on the valley 
On account of the defoemstion of the old 
material lai 
1 Tuff is a rock composed of fragments 
of lava, as a rule more or less distinctly 
bedded. These fragments may have been 
blown from a volcanic vent and may have 
settled down on dry land or in water. 
Even if deposited on land, the material 
t and Drummond, Mont., showing 
ble mode of formation of Deer Lodge Valley. 
At some later stage the floor of the 
basin was upraised midway between these 
two ends (see C'D), so that the lake beds 
Were exposed to erosion. The soft, inco- 
herent lake sediments were soon washed 
away, and the stream trenched the under- 
lying Cretaceous rocks to a depth of sev- 
eral hundred feet. The upraising of the 
middle part of the trough left a convener 
at either end, and at the present tim 
these structural depressions are asked 
by broad valleys, such as can be seen at 
Deer Lodge and at Drummond. The 
Presence of a broad valley connecting 
these two marked depressions can be 
realized only by a study of a contoured 
may be so fine and loose as to be rapidly 
of lava many fe unded 
masses that ae solidified as “they iow 
Some tuffs include abe aa 
bombs 
the erosion of 
eI erupted lavas. 
