222 ROCHESTER ACADEMY OF SCIENCE. 



by connecting ridges may represent formation at the ice front or 

 within a re-entrance into the ice, the point where the kame occurs 

 representing a hah in the withdrawal of the ice front, the connecting 

 ridge representing a time of slow, steady retreat of the ice edge. 

 The high knob described above that is located about a mile from the 

 north end of the esker was probably formed at the ice edge, after the 

 formation and uncovering of the esker south of it and while the por- 

 tion of the esker to the north of it was being built beneath the ice. 

 The numerous kettles that parallel the course of the esker may rep- 

 resent the melting out of ice blocks that lingered adjacent to the sides 

 of the esker, or unequal deposition at the ice front. 



The high elevation occurring at the north end of the esker prob- 

 ably represents deposition at the ice edge or within a broad re- 

 entrance back into the ice by a powerful stream pouring from the ice 

 and carrying a large quantity of material with it. It was this same 

 stream that built the esker extending southward from the elevation, 

 the one just described. The formation of the elevation itself was not 

 begun until after the building of the esker had been completed. Why 

 there should not be an esker continuing northward from this eleva- 

 tion and built beneath the ice at the time the elevation was forming 

 is an interesting question. Apparently all the material was carried 

 out and dropped to make up the large mass of the elevation itself. 



The local character of the materials of these Mendon eskers 

 constitute a strong argument in favor of the subglacial hypothesis. 

 It would seem impossible for this material to have gotten up on top 

 of the ice in such a short distance especially when this ice was ad- 

 vancing over a level plain. 



Further the occurrence of the high knolls in the course of these 

 eskers is antagonistic to the idea of esker origin at the edge of the 

 ice or in re-entrants from the edge ; the knolls themselves represent 

 the deposits forming in these situations, while the eskers stretching 

 northward from them were being deposited in the subglacial streams 

 at the same time the materials were being contributed by these 

 streams to form the knolls. The latter doubtlessly clogged the 

 exits of the tunnels leading to erosion of the roof of the tunnel and 

 deposition in the slacker water in the lower part of the stream. The 



