THE NORTHERN PACIFIC ROUTE. 133 
' them, but those that have been found are fresh-water forms, indicat- 
ing that the sediment forming the rocks was deposited in a lake or 
lakes. 
Many of the beds of sandstone are beautifully ripple marked, show- 
ing that the water in which the sand was deposited was so shallow 
that the waves piled up the sand in ripples or ridges. They also show 
cracks, indicating that at times the water receded, allowing the 
material composing the bottom of the lake to dry and crack irregu- 
larly, as mud deposited along a stream to-day will crack when it 
dries. Another indication of shallow water, or of no water at all, 
is the preservation of the prints of raindrops, which, after the millions 
of years that have elapsed since these rocks were mud on the shore 
of some lake, indicate the direction from which the storm came that 
drove along the coast. This may not be of great importance, but it 
illustrates how well nature has preserved the record of events of that 
far-off time, if only we will learn to interpret it. 
The Spokane shale is well exposed in the portals of the tunnel 
between mileposts 94 and 95 and can be seen to good advantage from 
the observation car. From Bonita to Missoula the 
Bonita. walls of the canyon are steep and high but not particu- 
Elevation 3,594 feet. arly rugged. They are composed almost entirely of 
27 myn rt Spokane shale, which supports a much heavier 
growth of pine trees than the other formations. This is particularly 
noticeable on the south side of the canyon, or on the northward facing 
walls. The difference in the vegetation on the two sides is due to the 
difference in the amount of moisture conserved. The northward 
facing slope is not exposed to the direct rays of the sun, and hence the 
moisture in the soil is not readily evaporated and trees thrive better 
than they do on the opposite side. 
Below Clinton the character of the canyon is much the same as it 
is above that place. The hills range from 1,500 to 
Clinton. 2,000 feet in height above the stream, and the 
Elevation 3,490 feet. slopes are everywhere strewn with the débris of the 
St. Paul 1,231 miles. 
red shale of the Spokane. 
Bonner (see sheet 19, p. 144), at the mouth of Blackfoot River, is 
noted for its lumbering industry, being the location 
Bonner. of some large sawmills. The river has been dammed 
Elevation 3,321 feet. elow the mouth of the Blackfoot, affording about 
oe 4,000 horsepower, which is converted into electricity 
and transmitted to Missoula and the towns of the Bitterroot 
Valley. : 
At Bonner the traveler again comes upon the route of Lewis and 
Clark, for on his return trip Lewis ascended Hell Gate Canyon as far 
as this point and then turned to the north up Blackfoot River. Six 
