DESCRIPTION OF GLACIER 535 



lures. They form almost straight lines, and individual ones may be 

 four miles in length. They rise symmetrically to a height of more 

 than 50 feet, with tops barely wide enough to support a footpath. The 

 steep slopes are determined by the angle of repose of the gravel and 

 boulders composing them. The base of the landward slope usually rests 

 on the solid rock or talus slopes of the valley wall, while the glacier 

 slope rests on ice or on other glacial debris, a hundred yards or so from 

 the ice. Their tops are in many places several feet above the level of 

 the glacier, so that a longitudinal valley separates them from the ice. 

 The origin of these long, symmetrical, A-shaped moraines at first 

 seemed puzzling; later they were observed in the making. At a high, 

 steep-sloping edge of the glacier, debris was sliding down from the melt- 

 ing top. Accumulation had proceeded until it spread along the base 

 of the glacier and lapped up on its side, like a talus slope at the base of 

 a cliff, for a height of about 45 feet. The continuation of this process 

 would result in a flanking mantle of debris parallel to the edge of the 

 glacier and lapping well up on the side of the ice. Eventually, as melt= 

 ing of the side of the glacier continued, the ice would recede from the 

 glacial talus slope, which then would fall over toward the glacier side 

 and rest at the angle of repose, forming a symmetrical A-shaped moraine 

 separated from the glacier. Further melting of the top of the glacier- 

 would result in the top of the moraine standing above the level of the top 

 of the ice. 



OVERRIDING 



On the west side of Kennecott Glacier is a large embayment into the 

 ice, which obviously at one time was occupied by a pond into which 

 mud-laden water was discharged. Later the pond was drained. At 

 the time of observation the material within the embayment was dis- 

 tinctly stratified with unsorted, coarse material at the bottom, overlain 

 by about four inches of fine gravel, and with about two feet of stratified 

 glacial silt on top. Subsequent movement of the glacier from north 

 to south brought the north wall of the embayment over a part of the 

 stratified silt, and when observed by the writer large boulders and till 

 were sliding from the melting wall of ice down on top of the stratified 

 silt. The boulders and till had accumulated to an average thickness 

 of about five feet over an acre of the stratified silt, thereby producing 

 a local unconformity. In a tunnel, driven for the purpose of drainage, 

 through the ice of a projecting lobe separating two such embayments, 

 at Kennecott, a similar condition was observed. In several other em- 

 bayments, at present, occupied by ponds of thick muddy water, the 



