ESKERS IX THE VICINITY OF ROCHESTER, NEW YORK. 189 



(18) More frequent trenching of the ground moraine, and the 

 more frequent occurrence of eskers in troughs in the ground moraine 

 would be expected under this hypothesis. Stone found Httle evidence 

 of subglacial stream work except near the coast in his study of 

 INIaine eskers (101). 



(19) In order to preserve the esker the subglacial stream had 

 to be diverted when the ridge was completed. How was it diverted, 

 and why was no esker formed in the new channel ? Also erosion 

 channels of such streams after their diversion are very rare (21). 



(20) The trend of the subglacial stream demands ice control 

 and a long life, its deposits demand a short and intensely active life, 

 followed by a sudden disappearance from the scene of its labors 

 (21). The two ideas are inconsistent. 



(21) Deltas and outwash plains should show more tributary 

 eskers than thev do. They have not been ice removed, for ice con- 

 tact slopes of the sand plains are intact, there is no evidence of dis- 

 turbance due to ice push. 



(22) Eskers should be well-stratified if subglacial, yet there is 

 found extremely chaotic stratification with ''pell-mell" structure. 



(23) Absence of an adequate supply of material since the ice 

 sheet protected till already deposited from erosion except where the 

 subglacial tunnels were located constitutes an objection. All of the 

 material must come from subglacial stream erosion of till, from 

 debris in the basal portion of the ice and a little englacial and super- 

 glacial material, this must form eskers miles in length and extensive 

 outwash plains. This source seems inadequate entirely. 



( 24) Crevasses are too few after cessation or near the time of 

 cessation of ice movement to afford new subglacial tunnels, and 

 those already existing are too few to accommodate sudden floods 

 formed by melting during the warm summer season, this excess of 

 water must therefore pass oft" in superglacial streams, hence few 

 eskers would be formed subglacially. 



(25) Eskers should tend to show a more uniform cross-section 

 than they do, for with a given thickness and weight of ice any en- 

 largement of tunnel would be precluded by creep of ice inward. 



(26) Under this theory one would expect to find more large 

 boulders on the surfaces of eskers. 



