BIOLOGICAL RECONNOISSANCE AT FLATHEAD LAKE. 1387 
The plains of the Mission valley have a much rougher and more irreg- 
ular surface due to the moraines and other glacial debris deposited over 
much of the valley. The long hill extending diagonally across the valley 
directly at the foot of the lake is clearly glacial drift as shown by the 
irreguarly distributed clay, boulders, rounded pebbles, etc. The form of 
this suggests that it may be classed as a drumlin. 
Along the eastern side of the valley are seen many rounded knolls 
enclosing small marshes and ponds which are all clearly of morainal 
origin. The small ponds found scattered over the entire valley which 
contain water most of the summer are probably formed by the depressions: 
in the surface due to glacial deposits. These are plainly shown in Plate 
XXXII. Small glaciers undoubtedly flowed from the Mission mountains 
along its entire length but these deposits must have come from a very 
much larger glacier, probably from one which came down from the north 
throughout the whole valley. 
The lake in its higher elevations probably had its outlet in a western 
direction as shown by the old stream course to the westward of the larga 
bay behind the large islands. A stream course near the town of Dayton 
leading southwestward down the valley of the Little Bitter Root is very 
plainly discernible. 
When the lake reached its present level it found its outlet across 
the lake beds alluded to above, and through the moraines down its pres- 
ent course, the Pend d’Oreille river. This is plainly shown by the high 
cliffs of clay and other sediments that still retain their perpendicular 
sides along the canyon of this river. The increased head of the water 
in the lake above and the canyon cut below furnished the tools for the 
outflow to cut its canyon rapidly and the beautiful Pend d’Oreille rapids 
near the lake at Polson are the result. (These rapids are shown in 
Plate XLV.) 
Flathead lake now forms but one element in the drainage system 
of the upper valley and the territory beyond the Mission and Kootenai 
ranges. The entire drainage from this section of the state flows into the 
lake through two rivers, viz., the Swan and Flathead rivers. The latter 
is made up of three large rivers known severally as the North, South and 
Middle Forks. These three streams by their confluence above Kalispell 
form the Flathead river. This river is very interesting in itself as from 
its fall and other characteristics it shows itself to be but an arm of the 
lake. When the lake receded to near its present level, the drainage 
from the north and northeast flowed across the sediments cutting an ir- 
regular channel, meandering across the plains until sufficient fall of the 
lake level was reached to allow it to cut enough channel to hold the 
stream. At present it winds its circuitous path across the plains and 
has a total length of about 35 miles while the distance as measured in a 
straight line from the forks above is but 15 miles. In general its width 
is from 300 to 800 feet, and its depth is in some places 75 feet. On ac- 
count of the sluggish nature of the current of this river the erosion of 
the banks is slight except on the sharp curves, while the deposition in 
the bottom of the river and at its mouth is very rapid. 
The northern end of the lake into which all of the drainage is poured 
