1922] Swarth: Birds and Mammals of the Stikine Region 145 



The Stikine is one of several large rivers of the northwest that 

 break through the Coast Eange at right angles to the lines of those 

 mountains, their valleys thus lying transverse to the main lines of the 

 range. In a published report upon the geology of Alaska, A. H. 

 Brooks (1906) makes the following statement regarding the Copper, 

 Alsek, Taku, and Stikine rivers: "These, together with the other 

 large rivers of British Columbia, seem to traverse the coastal moun- 

 tain barrier along valleys determined by antecedent conditions. Their 

 lower valleys at least have the same direction as before the present 

 coastal mountains were elevated, and the streams maintained their 

 courses across the barrier during the slow uplift" (p. 286). Again: 

 "The valleys of the Stikine and Taku rivers, .... which lie trans- 

 verse to the Coast Range, have probably inherited their courses from 

 a former mature drainage system which was developed on the old 

 peneplain" (loc. cit., p. 287). 



In this connection it is worth while to nbte the appearance of the 

 river valley of the upper Stikine in the Telegraph Creek region. There, 

 and for many miles down stream from that point, the stream is bord- 

 ered by series of terraces, rising step by step to the base of the moun- 

 tains beyond. Viewed from some overlooking height the course of any 

 one of these terraces may be traced for a long distance. It seems 

 obvious that they represent the level of the river valley at different 

 periods of its history. (See fig. B.) 



The evidence of the geologist goes to show that, diverse as the coast 

 region and the interior are, as regards fauna and flora, the two have 

 not been absolutely separated by the Coast Range at all times in the 

 past any more than they are at present. A channel of communication 

 through the mountains has been there continuously from very remote 

 geologic times, save for a period when it must have been blocked by ice. 



Presumably all animal life was swept from both regions when the 

 whole country was glacier-covered. Presumably, too, conditions in the 

 areas on either side of the Coast Range permitted the return of animals 

 and plants from the southward when the mountains between were still 

 mostly ice. Even now the range is glacier-covered over a large portion 

 of its area. The higher peaks and ridges protrude, steep and serrated, 

 far above the ice. From the jagged, unworn appearance of these 

 higher crests they apparently never were covered. The sheet of ice 

 as seen today lies below the summit of the range, and can be traced 

 as a series of hanging glaciers appearing and re-appearing for many 

 miles at about the same level, visible from the river below. In certain 

 canons and valleys, tongues of this glacial covering extend downward 



