The Fledinont Plateau and the Mountains. 57 



The lowlands bordering Yakutat bay on the southeast are 

 composed of assorted glacial debris. Much of the country is low 

 and swampy, and is reported to contain numerous lakelets. 

 Northwest of the bay the plateau is higher than toward the 

 southeast, and has a general elevation of about 500 feet at a dis- 

 tance of a mile from the shore ; but the height increases toward 

 the interior, where a general elevation of 1,500 feet is attained 

 over large areas. All of this plateau, excepting a narrow fringe 

 along the shore, is formed by a great glacier, belonging to what 

 is termed in this paper the Piedmont ty]3e. There are many 

 reasons for believing that the plateau southeast of Yakutat bay 

 was at one time covered by a glacier similar to the one now ex- 

 isting on the northwest.* 



The mountains on the northern border of the seaward-stretch- 

 ing table-lands, both southeast and northwest of Yakutat bay, 

 are abrupt and present steep southward-facing bluffs. This 

 escarpment is formed of stratified sandstones and shales, and 

 owes its origin to the upheaval of the rocks along a line of frac- 

 ture. In other words, it is a gigantic fault scarp. The gravel 

 and bowlders forming the plateau extending oceanward have 

 been accumulating on a depressed orographic block (or mass of 

 strata moved as a unit by mountain-making forces), which has 

 undergone some movement in very recent times, as is recorded 

 by a terrace on the fault scarp bordering it. West of Yakutat 

 the geological structure is more complex, and long mountain 

 spurs project into the platform of ice skirting the ocean. Filling 

 the valleys between the mountain spurs, there are many large 

 seaward-flowing glaciers, tributary to the great Peidmont ice- 

 sheet. 



This brief sketch of the geography of Yakutat bay, together 

 with the accompanying outline map of Alaska (plate 2), will, it 

 is hoped, aid in making intelligible the following historical sketch 

 and the narrative of the present expedition. 



* Tills matter will be discussed in part IV of tills paper, where it is also 

 shown tliat Yakutat bay Itself was formerly occupied by glacial ice. 



