174 I. C. Russell— 2ft. St. Elias and its Glaciers. 



is probably an extension of the same bed, increases very 

 greatly in thickness toward the west and forms the Samovar, 

 Chaix, and probably the Robinson hills. These hills are 

 formed of sandy shale, filled with both angular and rounded 

 stones and bowlders which represent a great variety of rocks. 

 This terrane is a morainal deposit, and was formed in the ocean 

 from the debris of glaciers which broke off in bergs. In the 

 Chaix hills this deposit is over 4000 feet thick and is com- 

 posed of conformable brown and gray strata, dipping northward 

 at an angle of about ten degrees. 



The topographic form of Chaix hills shows that they have 

 been formed by a monoclinal uplift, of very recent date. 

 Although composed of soft beds, they have not been deeply 

 dissected by erosion. This conclusion as to the recency of the 

 uplift to which they owe their prominence, is fully sustained 

 by the fossils with which some of the beds are charged. All 

 of the shells obtained are of species still living in the adjacent 

 ocean. 



North of the principal outcrops of the Pinnacle system are 

 sandstones and shales that are lithologically undistinguishable 

 from the characteristic rocks of the Yakutat system. These 

 dip under the crystalline rocks forming the Augusta and St. 

 Elias ranges, and form the actual bases of the mountains. 

 From such facts as have been observed, I have ventured the 

 hypothesis that the schists have been overthrust on to the sand- 

 stones and shales, and hence that the uplifting of the mountains 

 is an event of very recent date. This conclusion was reached 

 during the expedition of 1890, and was tested the following 

 year, but without succeeding in fully demonstrating it, or find- 

 ing evidence which would militate strongly against it. It 

 must stand, therefore, as an interesting hypothesis, which awaits 

 additional study. 



The cliffs in which the rocks of the Pinnacle system are ex- 

 posed at Pinnacle pass and in the Samovar, Chaix and Robinson 

 hills, are monoclinal uplifts, due to the elevation of one side — 

 in these cases always the north side — of faults. The Augusta 

 and St. Elias ranges are also monoclinal uplifts. Nothing 

 of the nature of anticlinal or synclinal folds was observed 

 in the region explored. The prevailing and characteristic 

 structure is monoclinal and very similar to the Great Basin 

 type. The ranges including those immediately north of Mt. 

 St. Elias have steep escarpments on one side and a gentle slope 

 corresponding approximately with the dip of the strata, in the 

 opposite direction. The ranges are short and in general trend 

 northeast and southwest. Their steepest slopes are toward the 

 southeast. 



