174 I. C. Russell — Expedition to' Mount St. Elias. 



are preserved. The dip of the strata is northeastward, and has 

 exerted a decided influence on the Aveathering of the mountain 

 crests. As the opportunities for examining; this formation were 

 unsatis factor}^, a detailed account of it will not now be attempted. 



Geological Structure. 



The abnormal thickness of the Yakutat series, due to crushing 

 and overthrust, has been referred to, as has also the superposi- 

 tion of the St. Elias schist upon rock sapposed to belong to the 

 Yakutat system. 



The plane of contact between the sandstone and the overlying 

 schist of the St. Elias range dips northeastward at an angle of 

 about 15°, corresponding, as nearly as can be determined, with 

 the dip of the strata in the sandstone itself All of the observa- 

 tions made in this connection indicate that the schist has been 

 overthrust upon the sandstones. After this took place the great 

 faults to which the range owes its present relief were formed. 



Al)Out Mount Cook, however, and in the elevated plateau east 

 of Yakutat bay, the conditions are different from those observed 

 along the base of the St. Elias range. The only displacements 

 known in the Yakutat system south and east of Pinnacle pass is 

 the great fault which presumably exists where the rocks of the 

 foothills disappear beneath the gravel and glaciers of the Pied- 

 mont region, the faults referred to belonging to the same series 

 as those which determine the southern and southwestern borders 

 of the St. Elias range and many £)f the foothills south of the main 

 escarpment. Besides the great faults Avhich trend from St. Elias 

 toward the northeast and northwest, there are several cross-faults, 

 one of which determines the position of the Seward glacier 

 through a portion of its course, while another marks out the 

 path of the Agassiz glacier ; and two others may be recognized 

 just east of the summit of St. Elias, which have dropj^ed por- 

 tions of the eastern end of the orographic block forming the 

 crowning peak of the range. 



The southern face of Mount St. Elias is a farjlt-scarp. The 

 mountain itself is formed by the upturned edge of a faulted 

 block in which the stratification is inclined northeastward. As 

 has just been mentioned, the mountain stands at the intersection 

 of two lines of displacement, one trending in a northeasterly and 

 the other in a northwesterly direction. Tlie one trending north- 



