90 FOREST DISTRIBUTION 



importance on the different mountain ranges in this section. 

 Leiberg (32) gives the volume per cent for the different species 

 in the Little Belts as follows : 



Pinus flexiUs - - 8.2 



" albicauU.s , - 009 



" contorta - - - 34.2 



" ponderosa — - - -- -0^ 



Picea Engelmaiinii 11-i 



Pseudotsuga taxifoUa - - - i4-7 



Abies Jasiocarpa - - 1-4 



In addition to the above species it is probable that Juniperus 

 scopidorum and /. communis are likewise present. Isolated as 

 most of the outstanding ranges are, the influence of the climatic 

 conditions are readily felt, so that the lower timber line is fixed 

 at elevations unusually high. In sheltered canyons and valleys, 

 however, many of the species may descend to where they open 

 out upon the plains. 



The Three Porks Section (Xo. 10) is an area 140 miles from 

 east to west and 100 miles in round figures from north to south. 

 The westward direction of the Continental Divide from the vicin- 

 ity of Butte, and its wide curve to the south and thence to the 

 east to Yellowstone Park forms a huge embayment, drained by 

 the three main sources of the ^Missouri, the Gallatin, the iladi- 

 son and -Jefferson rivers, which push their ultimate branches 

 to the high walls of this huge amphitheater. The western por- 

 tion of the basin is known as the Bighole. particularly that part 

 drained by the Bighole River which is the main western branch 

 of the Jefferson. The basin is traversed by several low moun- 

 tain ranges, and in altitude most of its floor lies above 5000 feet. 

 The country is largely prairie and only the highest elevations 

 are forested and these with few species and comparatively meager 

 growth. It is largely glaciated and climatically dry and cold. 



