172 ALASKA GLACIERS 



ance of levels represents their sum or difference. While 

 the question thus raised is not susceptible at present of 

 a complete answer, it is nevertheless possible to make 

 some progress in that direction. 



In studying the Alexander Archipelago, which adjoins 

 the Fairweather coast on the southeast, no evidence was 

 found of a high sea-level in association with the greatest 

 Pleistocene glaciers; but it seemed probable, on the con- 

 trary, that the mid-Pleistocene sea-level was considerably 

 lower than the modern sea-level. Beyond the St. Elias 

 Mountains, in the opposite direction, lies the district of 

 Prince William Sound, and the Pleistocene history of that 

 region appears to resemble closely that of the Alexander 

 Archipelago. The Pleistocene history of the Fairweather- 

 St. Elias coast thus appears to be exceptional and to be con- 

 trasted with the histories of neighboring coasts on both 

 sides. This contrast is associated with a contrast in gen- 

 eral geologic history, as revealed in the physiography. 

 The district of the Alexander Archipelago is genetically 

 a plateau, from which mountains and valleys have been 

 developed by erosion. The district about Prince William 

 Sound has been found by Schrader and Spencer 1 to have 

 the same character and history. In each case a region of 

 complex structure was reduced to a condition of low 

 peneplain by long-continued erosion and then uplifted 

 bodily though somewhat unequally. The original altitude 

 of one plateau ranged from 3,000 to 7,000 feet, that of the 

 other averaged 6,000 feet. The intervening tract has 

 been lifted to a much greater height, so that its culminat- 

 ing peaks have altitudes of 15,000 to 19,000 feet, and it is 

 probable that crustal deformation here produced mountain 

 ranges directly, instead of creating a plateau from which 

 they were developed by erosion. 



1 Geology and Mineral Resources of a portion of the Copper River district, 

 Alaska. U. S. Geol. Survey, pp. 62-76, 1901. 



