PHYSIOGEAPHIC AND GLACIAL FEATURES 195 



but, as far as 1113^ observations went, they are confined exclusively to 

 those parts of the country which have been more or less completely 

 covered by glaciers during the Pleistocene epoch. Beyond the limits of 

 the glaciated region no lakes were seen. 



Glacial Features 

 extent of the snow and ice 



While the Chilcat mountains are almost buried in snow throughout 

 the year, very little snow is to be seen in summer on this " interior pla- 

 teau," and any small glaciers that do exist are in some of the higher 

 mountains close to the Chilcat range. 



Though the ice-fields of the present day are confined almost entirely 

 to the Chilcat mountains, the ice-fields of the Glacial period Avere much 

 more extensive, for they spread northward as far as Five-fingers rapids 

 on the Lewis river and to a short distance beyond Aishihik lake in the 

 Aishihik valley. The northern limit of glaciation is not by any means 

 an approximately straight line, for it indicates the lengths to which the 

 glaciers filled the valleys rather than the even margin of a great conflu- 

 ent ice-sheet. The higher mountains rose above the level of the ice, just 

 as the)' do at the present time in the Chilcat range, and small glaciers 

 moved clown their sides to join the larger glaciers in the valleys. 



The Chilcat-Alsek valley gives a beautiful idea of the former depth or 

 thickness of the ice. The bottom of the valley is almost flat, and the 

 sides rise in gentle willow-covered slopes for 2,000 feet or more to the 

 foot of the ungraded rocky peaks on either hand. Rock is everywhere 

 exposed above this line, while below it rock exposures are comparatively 

 rare, and the country is underlain by a loose unassorted till, on which 

 willows and dwarf birches grow in dense thickets. As seen from the 

 bottom of the valley, the. upper limit of the willow-covered slope forms 

 a fairly regular line along the sides of the mountains, and indicates ap- 

 proximately the depth to which the ice-sheet filled the valley, a depth 

 which here varied from 2,000 to 3,000 feet. Above this line the higher 

 mountains rise in broken, jagged peaks, while any lower mountains 

 which do not rise above the level of the top of the till have their sum- 

 mits evenly rounded and unbroken. 



THE TILL 



The till which fills the bottom of this valle}', often to depths of 100 

 feet or more, is a mass of unassorted material, in part local and in part 

 derived fi'ora a distance. It contains pebbles and boulders, usuall}' 



