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. 
