THE VARIATIONS OF GLACIERS 89 



Mountains, Alaska, and a topographic map of the region; and 

 from it we draw the following information : 



A very important feature of the Wrangell Mountains is the great ice cap 

 that occupies the crest of the range and that has its greatest development in 

 the region around Mount Wrangell. From the periphery of this great feed- 

 ing- ground valley glaciers extend in all directions down the more important 

 drainage lines. 



The Nabesna and the Chisana are by far the largest of these 

 glaciers. The former is about 55 miles long and has an area of 

 about 400 square miles. The latter is 30 miles long with an area 

 of 135 square miles. There are many smaller ice tongues, and 

 even small glaciers independent of the main ice cap. 



The St. Elias Mountains, south of White River, are snow-capped in much 

 the same way as the Wrangell Mountains. Most of the mountain range is 

 unexplored, however, and the extent and area of the ice field is unknown. 

 All the more important tributary valleys to the north are occupied by valley 

 glaciers, the largest and best known of which is the Russell Glacier, at the head 

 of White River. The main lobe of ice in the head of the White Valley is 

 between 6 and 7 miles long and about 2\ miles wide, and most of the ice moves 

 in a northeast direction. A small crescentic lobe, however, moves westward 

 into the head of Skolai Creek. 



Formerly the glaciation was much more extensive, but very 

 little information is available to determine what changes are 

 taking place at present. In 1891 the western terminus of Russell 

 Glacier was a smooth slope, but in 1909 it was a wall of ice from 

 25 to 75 feet high. This certainly indicates an advance of the 

 ice, but at the northeastern terminus the ice passes into the moraine 

 without a clear line of demarkation, indicating a slow, gradual 

 retreat. The Nizana Glacier was formerly crossed by prospectors 

 going to the White River region, but it has become so crevassed 

 as to be practically impassable, which suggests an- advance of 

 the ice. 



