FOREST TEEES OF THE PACIFIC SLOPE. 



259 



Liard River, here crossing to interior plateau west of Rockies. Throughout Mackenzie 

 River Valley northward from Great Slave Lake, reaching its northern limit at Great 



FlG. 113. — Betula alaskana: a, fruiting twig;-6, seed, natural six.- and enlarged three 



times : <■. cone scale, twice natural size. 



Bear Lake and at the mouth of the river (abonl lat. 68 30') West of Rockies, probably 



extending southward in British Columbia only to Stikine River; little, however, is 



