CORRELATION OF PENEPLAINS 125 



these high mountains is deeply dissected ; but from any elevated out- 

 look the even topped summits of the mountains fall into a seemingly 

 unbroken surface, on which the snow-mantled cones of the dominating 

 mountains appear to rest as upon a plain. The practical identity of the 

 peneplain in the two regions is thus strongly implied; but, in addition, 

 it may be noted that the region which lies north of Saint Elias probably 

 likewise exhibits the character of a dissected plateau. The truth of this 

 surmise is indicated in a view looking northward from Saint Elias, which 

 was published as an illustration in the account of the ascent of Saint 

 Elias by Prince Luigi.^ The presence of this high plateau suggests that 

 there is an unbroken continuity of the ancient peneplain on three sides 

 of the Saint Elias group of mountains. 



The immediate comparison of the Chugach and Yukon plateaus is at 

 first suggestive only of the existing difference in the elevation of their 

 surfaces. Along the northern faces of the Saint Elias, Nutzotin, and 

 Alaskan ranges there are abrupt scarps and steps, amounting to several 

 thousand feet, between the supposed equivalents of the Chugach plateau 

 and the surface of the plateau in the Yukon basin. It seems, as will be 

 shown later, that the two features can be regarded as equivalent only by 

 admitting the existence of delimiting faults of very recent date and of 

 large proportions. The description of the Nutzotin range f does, however, 

 furnish a clue of probable significance in this connection, since it makes 

 it possible to suggest that the Yukon plateau and the summit surface of 

 the Nutzotin range are parts of the same peneplain. 



The Nutzotin mountains, which lie north of the Wrangell group, facing 

 the Yukon plateau, are drained by the headwaters of the Tanana river. 

 From the Nabesna river, which is the western of the two main sources 

 of the Tanana, these mountains have a southeasterly course, extending 

 some 250 miles toward the White river, within 20 miles of which the 

 elevation decreases, so that they become a low range of hills. When 

 projected toward the southeast, the trend of the Nutzotin axis coincides 

 with a range lying north of lake Kluane, which probably merges with 

 the Yukon plateau in the vicinity of the Kaskawulsh river, a tributary 

 of the Alsek. 



Antecedent Rivers 



There are several large rivers which take their rise within the region 

 of the inland plateaus of British Columbia and Alaska and flow in deep 

 trenches across the high barrier of the coastal mountains and debouch 



*The ascent of mount Saint Elias, by H. R. H. Prince Luigi Amedeo di Savoia, 1900. 

 fSee Brooks, loc. cit., p. 346. 



XVIII— Bull. Geol. Soc. Am., Vol. 14, 1902 



