178 ROCHESTER ACADEMY OF SCIENCE. 



Some subglacial streams may have formed no deposits in their 

 channels before diversion of their waters, in some cases apparently 

 a low ridge or only a partially completed ridge was formed, again a 

 ridge fully developed may have been formed before the waters were 

 diverted. Such a ridge by clogging the channel and making great 

 "head" necessary to continue the flow may have led to the diversion 

 of the waters. Again the stream may have maintained its course along 

 the crest of the esker until the tunnel became roofless, and even 

 subsequently if the front of the ice was bathed in waters, the pres- 

 ence of which caused the tributary stream to flow sluggishly, thus 

 preventing erosion of the ridge. With the recession of the front of 

 the ice the ridge became a subaqueous embankment. This may have 

 been covered by delta deposits or by a sand plain built into the glacial 

 lake as in the case of the Auburndale esker, jMass. (28 J. It is evi- 

 dent that if the ice possessed vigorous movement tunnels could not 

 exist, or if it was very thick tunnels would be closed by its weight. 



Eskers were doubtlessly formed near the ice edge, within a few 

 miles at most of the receding ice front. The most favorable position 

 for esker development was under the stagnant front of the glacier, or 

 beneath a detached ice block, conditions that were common along the 

 front of the receding ice sheets. "Doubtless also esker development 

 was favored along the margin of valley glaciers, or glacier lobes, 

 when the ice was thin, the motion slight and the volume of water 

 great. It is from such places that glacier torrents issue from living 

 glaciers, and doubtless eskers are forming in some of them, as, for 

 example, in Alaska, where small eskers are found on ground from 

 which the glaciers have receded within a century" (105). 



Such were the conditions under which typical eskers were 

 formed according to the subglacial view. In the argument that fol- 

 lows the attempt is made to explain the peculiarities exhibited by 

 eskers in terms of this hypothesis. Following this argument there is 

 a list of all the objections that have been raised against this manner 

 of esker origin. Most of these objections will be found to have been 

 adequately answered in the argument. 



Argument. The length of many esker systems has been urged 

 as an objection to the subglacial hypothesis, it being maintained that 

 correspondingly long tunnels could not exist beneath a mass of mov- 



