87 
THE NORTHERN PACIFIC ROUTE, 
See 90,000 gallons of water an hour at a temperature of 148° 
eS 
Slee Springdale the river through a narrow gorge known 
as McAdows Canyon. In this canyon the rocks, which are well 
exposed, show many wrinkles or minor folds that were undoubtedly 
formed by the upheaval of the great Absaroka Range, on the south. 
The mountain range is high and rugged, indicating a youthful stage 
in its development, for if the range were old it would have been worn 
down by erosion and its rugged features would have been smoothed 
and rounded off. Another proof that the Absaroka Range has been 
recently formed is found in the fact that the rocks along its flanks 
have been wrinkled and upturned by the same forces as those that 
folded and raised the mountain rocks into their present positions. 
From this it is evident that the mountains must have been formed 
since the deposition of the youngest of the plains rocks, and as the 
Fort Union formation, which is early Tertiary, is involved in the fold- 
= the mountains must have been formed in middle or late Tertiary 
Gx the right (north) near milepost 103 a near-by view may be 
obtained of the Sheep Cliffs, which, as seen from the train, are very 
prominent. They are the result of an intrusion of molten lava 
between beds of sedimentary rocks, probably from some of the dikes 
hard and resists = akscas much more 
successfully than the diorite. These 
baked rocks form a zone nearly a mile 
wide around the core. Through this zone 
and beyond it the rocks have been cut 
and hardened by a countless number of 
dikes that radiate from the central mass 
in all directions. Here and there the 
molten matter has found an outlet be- 
of igneous rock that was forced in molten 
condition into the soft shale and sand- 
great mass of 
~ soft sedimentary beds, the surface 
t have been above the present top 
at ne mountains. J. P. Iddings, who has 
given the most study to is comustata 
mass, says that it is not at all certain that 
the molten material ever poured over or 
even reached the surface. It is exposed 
view now because the beds that once 
covered it have Laphnetgt been washed 
away by rain and stre 
The stock is 4 sail ee and 6 miles 
long. It consists of a very coarse 
diorite which disintegrates rapidly when 
to the weather. In this con- 
dition it is easily eroded, and the slopes 
are very steep, as can be seen from the 
train. The present mountains are made 
up not only of the igneous reck, but also 
of the shale and sandstone into which it 
was forced. These rocks were heated so 
SS oe 
a porcelain-like mass that is very 
tween the beds of sandstone, resulting in 
great sheets or sills of the hardened lava. 
These are very dense and serve as pro- 
tecting caps to the softer strata beneath. 
The forcing of so much material between 
the layers of the sedimentary rocks has 
raised them up around the stock until 
they dip from it in all directions 
Nearly the last stage in the evolution of 
ciers during th 
were so small that they did not even 
coalesce and form an ice cap, but each 
little glacier scoured out the valley in 
which it lay and built a moraine at its 
cuter end, where it came down nearly to 
the level of the bench land 
