38 FOREST DISTEIBLTIOX 



indicate that some of the streams at flood may attain more than 

 1000 times their lo\v water volume, but more often the increase 

 is about 20 to 30 fold. 



The tributary valleys of western Montana mostly have a 

 north and south direction and occupy trench-like depressions 

 between high ranges. The valleys are often or even usually 

 narrow, but oecasionaUj- broaden out into numerous inter- 

 mountain basins, as some parts of the Flathead and the upper 

 Blackfoot Valley. Some are the basins of old lakes with the 

 evidence of their ancient shore lines still intact. The positions 

 of the ranges and their alternating valleys in most cases is 

 squarely across the lines of eastward or westward movement. 



