MOKAINES AND TERRACES 197 



Terminal moraines were recognized in a few places, but they scarcely 

 formed as conspicuous features as one would have been inclined to ex- 

 pect. From lake Aishihik northward for about 12 miles in the bottom 

 of the valley is a terminal moraine area, represented in places by irreg- 

 ular hills of boulders, which was formed at the foot of the Aishihik lobe 

 of the great ice-sheet when it had reached its extreme northern limit. 

 The low stony hills east of the Hoochi lakes represent another moraine, 

 while the stony hills at the mouth of the west branch of Nordenskiold 

 river are clearly raorainic in character ; but they also show many signs 

 of water action, and merge into the extensive pitted plain or terrace which 

 extends along the banks of the Lewis river from the mouth of the Nor- 

 denskiold to Rink rapids. 



TERRACES 



The classes. — The terraces occurring in this region are of two kinds, 

 namely, stream terraces and lake terraces. 



Stream terraces. — Stream terraces have chiefly been formed by torrential 

 rivers, loaded with detritus, flowing from the feet of the glaciers, and are 

 most conspicuous in the larger valleys beyond the limits of the glaciated 

 area, as, for instance, in the valleys of Lewis and Nisling rivers ; but as the 

 glaciers diminished in size and their fronts retired up the valleys, gravels 

 and sands were deiDOsited in the bottoms of the valleys which had pre- 

 viously been occupied by the ice, and thus terraces were formed on the 

 low lands in the region which had been covered with glaciers. 



Lake terraces. — Lake terraces are confined exclusively to the glaciated 

 area, none having been recognized beyond the northern limits to which 

 the vast ice-sheets of the Glacial period extended. They usually consist of 

 fine sand, silt, or rock flour, which is often of whitish color and commonly 

 has the appearance of the finer material carried down into bodies of quiet 

 water by glacial streams. These terraces sometimes extend 2,000 feet or 

 more up the sides of the mountains, especially in wider parts of some of 

 the great valleys which traverse the country. Such terraces are beauti- 

 fully shown on the sides of the mountains around lake Dezedeash. 

 There can be no doubt that the outlets to the valley were filled with ice, 

 and that the deep lake which existed here, around the shores of which 

 the terraces of white silt were formed, was in part walled in by the fronts 

 of glaciers. 



Similar terraces were seen in many other places, and often several 

 would descend in regular series, until it was difficult to distinguish the 

 lowest fr'om the higher and finer of the stream terraces. It is confidently 

 believed, however, that all the white silt terraces in that portion of the 

 Yukon district examined were formed in ice-dammed lakes and furnish 



