130 A. C. SPENCER — PACIFIC MOUNTAIN SYSTEM 



until in the vicinity of Lynn canal it attains an altitude of over 7,000 

 feet, as represented by the summits in the Coast range, which is also the 

 elevation of the adjacent portion of the Saint Elias range. In this region, 

 then, the supposed displacement is reduced to zero, but toward the south- 

 east the fault may be continued with the downthrow on the opposite 

 or coastward side. In support of this belief is the conception that the 

 Saint Elias range becomes partially submerged in this direction, and to 

 the southeast of Cross sound and Icy strait is represented by the islands 

 of the Alexander archipelago.'^ f 



The localization of differential movement along such a fault line is not 

 unknown in other regions, and a similar hypothesis is held by Russell to 

 account for certain phenomena observed upon the opposite side of the 

 Saint Elias range. J 



Localized deformation in the form of a flexure along the inland side 

 of the Coast range in British Columbia is strongl}^ suggested by the 

 physiographic relations which have been pointed out, and it is believed 

 that as a working hj^pothesis this explanation of the existing relations 

 between the Pacific mountains and the plateau of the interior is worthy 

 of careful consideration. 



The attitude of the Yukon plateau to the northern face of the Nutzotin 

 range is very similar to the relation which it presents against the Saint 

 Elias scarp, and may be referred to the same hypothetical origin. If 

 the suggested causes for the observed physiography of this region are 

 corroborated by future workers, it may be found that the zone of differ- 

 ential movement marked by the inland side of the Coast range is con- 

 tinued northwestward to coincide with the line of movement which 

 forms the northeastern face of the Nutzotin range ; also that the Nutzotin 

 mountains are related to the western continuation of the Saint Elias 

 range as the Coast range is to their southeastern portion. In this case 

 the great break northeast of the Saint Elias range passes between the 



* Alfred H. Brooks : A reconnaissance from Pyramid Harbor to Eagle City, Alaska. Twenty-first 

 Ann. Rept. U. S. Geol. Survey, pt. ii, 1900, p. 345. 



fThe chain of islands which lies off the mainland of British Columbia and southeastern Alaska 

 comprises Vancouver island, the Queen Charlotte group, and the islands of the Alexander archi- 

 pelago. These islands have been described as constituting a range of partially submerged moun- 

 tains distinct from the Coast range. From the standpoint of the geographer, this suggestion is not 

 unnatural, since the larger islands lie in the same general trend andare separated from the main- 

 land by a continuous waterway. However, the available data concerning the geologj' of the islands 

 seem to warrant the belief that the significant features of internal structure in them and in the 

 Coast range adjacent are entirelj' comparable and of equivalent age, and therefore that the two 

 lines of relief were not formed, as has been supposed, by distinct orogenic movements. It is con- 

 sidered probable that future study of the features of this province is more likely to show that the 

 "inside passage," as a separating depression between the mountains of the mainland and the 

 island heights, has been the result of erosion rather than the effect of crustal adjustments. 



1 1. C. Russell : Expedition to mount Saint Elias. Nat. Geog. Mag., vol, iii, 1892. 



