OKIGIN OF THE PACIFIC MOUNTAINS 129 



conceived to have taken place without local differences in the amount 

 of movement, and it is definitely known that the uplift has not been 

 uniform. The Interior and Yukon plateaus have been raised to a pro- 

 gressivel}^ greater height from northwest to southeast, so that a gentle 

 northwesterly tilt exists throughout the extent of these features. Local 

 warping of the land surface has been reported in the Forty-mile region 

 near the Yukon river, where Goodrich* has made a careful study of the 

 origin of certain stream adjustments which he considers as due to the 

 combined effect of a general northwestward tilting and local arching of 

 the surface; in the upper White and Tanana regions by Brooks, f and 

 in the Cooks inlet region by Mendenhall.J 



Such variations as these have not resulted in the production of topo- 

 graphic features which would be of striking prominence to the casual 

 observer, and even the slope of the summit level of the Coast range 

 toward the Interior plateau in the vicinity of the White and Chilkoot 

 passes, and toward the Yukon plateau in the vicinity of Lynn canal, 

 are features which would not ordinarily be noted except by a trained 

 geographer. The relations of the Yukon plateau to the Saint Elias 

 range, however, are more prominently presented to the eye. 



"Approaching the northern base of the Saint Elias range the plateau character 

 is almost wholly lost, giving way to steep and rugged though not lofty mountains 

 separated by rather wide river valleys. There is, however, no merging of the 

 plateau in to the Saint Elias mountains, but south of a well marked limit the 

 whole character of the topography suffers a complete change. Between the 

 southern limit of the interior plateau and the northern base of the Saint Elias 

 mountains is a depression running parallel with the mountain range and having 

 an altitude of about 4,000 feet." " Southward across this depression was seen the 

 abrupt northern face of the Saint Elias mountains, with many sharp and rugged 

 peaks rising to altitudes of 10,000 to 12,000 feet." 'i 



It is suggested for future corroboration or disproval that this abrupt 

 scarp-like face of the Saint Elias range may be due to displacement along 

 a gi'eat fault b}' which the Saint Elias range has been raised en bloc not less 

 than 7,000 feet in excess of the adjacent portion of the plateau. Following 

 the two features eastward, it is found, as already noted, that the mountain 

 summits decrease in elevation while the plateau surface gradually rises, 



*H. B. Goodrich : "Recent warpings as shown by drainage peculiarities." Report on the geol- 

 ogy of the Yukon gold district, by Josiah Edward Spurr. Eighteenth Ann. Rept. U. 3. Geol. 

 Survey, pt. iii, 1S98, pp. 276-289. 



t Alfred H. Brooks : Reconnaissance in the Tanana and White River basins in 189S. Twentieth 

 Ann. Rept. U. S. Geol. Survey, pt. vii, pp. 448 and 453. 



X W. C. Mendeuhall : Reconnaissance from Resurrection bay to the Tanana river, in 1898. Twen- 

 tieth Ann. Rept. U. S. Geol. Survey, pt. iii, p. 33.3. 



§C. W. Hayes: An expedition througli the Yukon district. Nat. Geog. Mag., vol. iv, 1892, pp. 

 29-130. 



