19G J. B. TYRKELL GLACIAL PHENOMENA IN YUKON DISTRICT 



more or less rounded in shape, some of which are striated while the 

 great majority are smooth and without glacial markings. In general 

 character it is very similar to the till which underlies so much of the 

 plains of northwestern Canada between the edge of the Archean nucleus 

 and the Rocky mountains. Similar till was found to underlie the bottoms 

 and sides of most of the valleys everywhere throughout the glaciated 

 area in the Yukon district, having evidently been formed as a ground 

 moraine beneath the great sheets of ice. 



STRIA TION 



Striated rock surfaces were not very often seen, for where the rock is 

 exposed it has usually become rough through weathering, but they were 

 recognized in a few places on the interior plateau, and in every instance 

 they indicated a direction of ice-movement motion from the coast toward 

 the interior or essentially simply a wider extension of the glacial con- 

 ditions which exist in the region at the present time. In this extension 

 toward the interior the ice for the most part followed the great valleys 

 which trench the surface of the country in a general north-and-south 

 direction, and therefore the movement of the ice was generally north- 

 ward. 



Close to the coast the glaciers flowed seaward and filled the many 

 deep valleys which descend from the mountains to the Pacific ocean. 

 In the Skagway valley the White Pass railroad while constructing its 

 line has cut a notch along a rocky hillside which has been beautifully 

 smoothed and scored by such a glacier. 



MORAINES 



Lateral moraines occasionally form conspicuous features along the 

 sides of the mountains, often running as long, narrow lines of boulders 

 or transported material, swaying slightly up and down with the irregu- 

 larities of the surface, and in places running into water-Avorn terraces 

 where some small stream has thrown its load of gravel against the side 

 of the glacier. A very well marked moraine of this character extends 

 along the west side of the valley of Aishihik lake at about 1,500 feet 

 above the water. It is a fairly regular ridge of boulders, along the crest 

 of which, in some places, runs the horse trail from Fort Selkirk south- 

 ward to Pyramid harbor. Above it the surface of the mountain con- 

 sists of a fairly even, regular incline of decomposed rock, while below 

 it is a till-covered slope, often broken into very lumpy, irregular hills. 

 Lateral moraines were also traced down the side of a deep valley north- 

 west of Aishihik lake as well as in some other places. 



