BIOLOGICAL RECONNOISSANCE AT FLATHEAD LAKE. 137 



The plains of the Mission valley have a much rougher and more irreg- 

 ular surface clue to the moraines and other glacial debris deposited over 

 much of the valley. The long hill extending diagonally across the valley 

 diectly 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 

 XXXIII. Small glaciers undoubtedly flowed from the Mission mountains 

 along its entire length but these deposits must have come from a veiy 

 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 large 

 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 Poison 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 3.5 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 



