The Tundra and the meager Forests. 1 37 



these areas are wholly msignificant when compared with those 

 which are covered with moss. The black alder, so abundant on 

 the coast, is also very common in the interior, but in a dwarfed 

 form, decreasing in size with increasing altitudes from ten or 

 twelve feet in the valleys to a few inches on the higher parts of 

 the plateau. The upper limit of the spruce forests is reached 

 along the coast at an altitude of about 1,800 feet, but this limit, 

 along with the snow line, gradually ascends toward the interior. 

 The high valleys of the Taku tributaries have considerable spruce 

 timber, although the trees are not close together and the largest 

 are seldom over a foot in diameter. Taku pass, with an altitude 

 of 5,100 feet, is approximately at the timber line and only a few 

 stunted trees manage to exist there. 



Ahklen valley is quite heavily timbered, and some trees 

 eighteen inches in diameter, the largest seen anywhere in the 

 interior, were among the drift from Nisutlin river. 



In the White River basin only the valleys are wooded, the 

 timber extending less than a thousand feet up their sides, while 

 the greater part of the plateau surface is practically treeless. 

 The timber line on the northern side of the St Elias mountains 

 has an altitude of about 4,500 feet. 



The Chittenah and Copper river valleys feel the influence of 

 the coast climate, and their vegetation is consequently much 

 more luxuriant than in the valleys of White River basin. 



Hard Geology. 



Character of the Observations. — Any attempt to solve the many 

 difficult problems connected with the geology of the region trav- 

 ersed would necessitate detailed study of large areas. The op- 

 portunities afforded by a hasty reconnaissance along a single 

 line of travel are obviously inadequate to the solution of these 

 .problems, particularly when the greater part of the geologist's 

 energy is absorbed in overcoming the physical obstacles to his 

 progress and in making even the crudest topographic map to 

 which to refer his observations. 



The most satisfactory information on the hard geology of any 

 portion of this region is contained in Dawson's report, already 

 cited, on the geology of the Yukon district. Dr Dawson had the 

 great advantage of familiarity with similar rocks and geologic 

 problems from previous study in British Columbia. He was also 



