Clearwater mountains. The firet of these, the Priest River Mountains, 
lie in the extreme northwest, west of the Kootenai River and north 
of the Clark Fork, rising to maximum elevations of 7000 to 7400 feet. 
They are drained by the Priest River, which flows southward from a 
point in British Columbia a few miles north of the Canadian Boundary. 
Most of the bed of this stream within the United States lies below 
3000 feet. Due to stoppage by glacial detritus, it widens perceptibly 
at an elevation of about 2600 feet, forming Priest Lake and Upper 
Priest Lake, connected by a short but very beautiful channel, the 
"Thorofare". At the boundary and a short distance above it are sit- 
uated two small picturesque falls where the river has carved its way 
through @ narrow canyon. This range has been deeply sculptured by 
glaciers and streams and the canyons are narrow, with steep sides. 
Cliff-bordered cirques, talus slopes, and sharp rugged ridges are fre- 
quent, especially on the east side. The rocks of these mounta ins con- 
sist principally of Paleomic metamorphic sedimentary rocks with con- 
siderable intrusions of fissured granite and syenite. The soils re- 
sultant from the disintegration of these rocks and the consequent re- 
tention of surface water may explain in part their luxuriant vegeta- 
tion and the occurence there of not a few species more characteristic 
of the Cascade Mountains. 
In the extreme northeastern corner, north and east of the 
Kootenai Valley, lies a small part of the Purcell Range of northwestern 
Montana and British Columbia. This range is closely allied geological- 
ly to the Cabinet and Coeur d'Alene ranges which lie successively 
