34 FOREST DISTRIBUTIOX 



The third group remains to be eoiisidered. From the Snowy 

 Range across the ^Missouri to the north, about 100 miles from 

 summit to summit, lie the Bearpaw ]Mountains. These are of 

 comparatively low altitude >-et of sufficient elevation to support 

 forest growth. They practically constitute a culmination of the 

 divide between the Milk River and the ^Missouri. They reach 

 an altitude of 6000 feet and with the Sweet Grass Hills and a 

 few other low elevations represent almost the only forested slopes 

 within 100 miles of the main front of the Rockies in a strip 100 

 miles ^\ide below the Canadian Boundary. 



Geologically, of course, the State presents a gi'eat varietv 

 of formations. The eastern half is mainly Upper Cretaceous 

 (with an extensive coal bearing portion) and Early Tertiary. 

 Later Tertiary formations appear in several isolated tracts in 

 the western part, occupying portions of the Flathead, Bitter 

 Root, Blackfoot, Big Hole, and other valleys, alternating in the 

 southwest and center with larger areas of the Paleozoic. The 

 northwestern portion from the Continental Divide to the boun- 

 dary and from the British possessions to the head of the Bitter 

 Root Valley is mainly Proterozoic (Algonkian). The Bitter 

 Root Range and the high mountains of the main divide about 

 Butte and southeast^^'ard through the Absarokas are chiefly 

 granitic, but the northern ranges are sedimentary. Volcanic 

 rocks and lavas form a very small portion of the State. 



The soils derived from these sources are necessarily varied, 

 both locally and regionally. Over much of the eastern part of 

 the State the soil is of that comminuted variety known as loess 

 (18), in many places overlying glacial drift and now supportinsr 

 a typical prairie vegetation, mostly grasses. It is a fertile soil 

 and when broken up and sdwn to grains yields heavy crops. 

 Extensive glaciation characterizes the greater portion of the 

 State and morainic deposits are common (9). Many of these 

 are thinly covered with soil and. wliile fertile enough when pro- 

 vided with water, are usually dry and verv difficult situations 

 for plant life. Deltas at the mouths of canyons, river bottoms of 

 silt, sand or heavy clay, and in varying areas and depths, form, 

 west of the divide, a limited part of the vegetation-bearing laud, 

 composed of transported materials. The slopes which, in the 

 western portion of the State support nearly all the coniferous 



