198 BULLETIN I'XIVERSITY OF MONTANA 



foaming river of wondrous beauty, untouched by man's intervention, with 

 only a trail along the bank and an occasional Indian path to the water's 

 edge for fishing purposes. The lake is about thirty miles long. At its 

 widest portion it is perhaps seventeen to nineteen miles. For the greater 

 portion the width is no more than eight or ten miles. 



Two rivers enter Flathead lake. Flathead river flows into the north- 

 ern end near the center. Swan or Bigfork river flows into the northeast 

 corner, past the site of the laboratory. See Fig. 4. Flathead is much 

 the larger of the two, has a much larger drainage area, and carries into 

 the lake much more sediment. The delta made by the river extends into 

 the lake for more than a mile. Beyond this the lake drops off abruptly 

 to deep water. 



The preceding brief statements give the skeleton of the region to be 

 covered in the work of the future, of which the present lecture is the 

 smallest part. Let us consider briefly the agencies that have been 

 at work in remodelling the surface, with the results as revealed by a 

 rather superficial study. 



When the mountain ranges were first upheaved their faces were ab- 

 rupt and perpendicular. The valleys were deep and angular troughs 

 between the ranges, rather than level valleys. It is believed that Flat- 

 head lake and the valleys to the north and south were formed by a slip 

 in the faulting process, by which the western portion fell, leaving the 

 mountain ranges as an. abrupt border for a comparatively level plain. 

 Evidence for this may be seen in the numerous photographs taken in the 

 two ranges, which show plainly the stratification of the rocks, their slope 

 and dip, and the configuration of the mountain range. 



Immediately after this upheaval various agencies began the work of 

 tearing down the ranges, and fashioning them and the valleys into their 

 present forms. The agencies at work have been the wind and air, water, 

 frost and ice, and the vegetation. Vegetation, as also animals, was 

 absent at first, and came gradually, after the disintegration had been 

 sufficient to afford a foothold. 



The process of disintegration has continued from the first to the 

 present, and continues now. It will continue until the entire mountain 

 ranges are levelled. The rocks were alternately hot and cold, wet and 

 dry. The small crevices were filled with snow and ice, which made them 

 larger. Larger and larger they became, until pieces, large and small, 

 tumbled from the face of the cliffs. Disintegration was slow or fast 

 according to the nature of the rock. The smaller portions were washed 

 down into the troughs between ranges, filling them up. While the larger 

 channels between ranges were filling up the smaller gorges and ravines 

 at right angles to these and between peaks were being ploughed deeper 

 and smoother by the melting snows from above. The summits were 

 being penetrated by the percolating waters, and the entire mass in some 

 cases rent in pieces by the expanding ice. In some cases the faces of the 

 cliffs fell away until the entire mountain tops fell, leaving the present 

 summits a mass of boulders^ still being slowly worn away by the wind 

 and water. This is evidently the case with McDonald peak of the Mission 

 range, as may be seen by the photographs taken at the western summit. 



