ESKERS IN THE VICINITY OF ROCHESTER, NEW YORK. 201 



deep canyons cut back from the ice front. These may have been ice 

 floored or again cut entirely through the ice sheet with bottoms on 

 the terrane beneath. In these ice-walled channels deposition of the 

 esker gravels took place, the materials being derived from the sur- 

 face of the ice, from the basal and englacial debris, and from the 

 stream's floor. 



Objections. The greatest objection to the theory is the disre- 

 gard that the normal esker manifests for the topography. The ap- 

 pearance of an esker first on one side of a valley then on the other, 

 the courses of eskers up long gentle slopes, could only be explained 

 tmder this idea by the canyons being ice floored and sloping upward 

 from the edge of the ice. In this case the theory meets the same 

 objections as the superglacial hypothesis. 



Conclusion. An occasional esker may have been deposited in 

 an ice canyon, but the majority of eskers have arisen in other ways. 

 Tarr has stated that "it is by no means impossible that in favorable 

 situations, rapidly moving, heavily laden marginal streams may have 

 flowed in valleys or tunnels cut in the ice, making deposits which, 

 on the melting of the ice, took the esker form" (107). 



Other views. Eskers may have arisen in other ways. Wright 

 has described the formation of an esker ridge of the Muir glacier 

 as follows : "The formation of kames, and of the knobs and kettle 

 holes characteristic both of kames and terminal moraines, is illus- 

 trated in various places about the mouth of the Muir glacier, but 

 especially near the southwest corner just above the shoulder of the 

 mountain where the last lateral branch comes in from the west. 

 This branch is retreating, and has already begun to separate from 

 the main glacier at its lower side, where the subglacial stream pass- 

 ing the buried forest emerges. Here a vast amount of water-worn 

 debris covers the ice extending up the glacier in the line of motion 

 for a long distance. It is evident from the situation, that when the 

 ice stream was a little fuller than now, and the subglacial stream 

 emerged considerably farther down, a great mass of debris was 

 spread out on the ice at an elevation considerably above the bottom. 

 Now that the front is retreating, this subglacial stream occupies a 

 long tunnel, 25 or 30 feet high, in a stratum of ice that is overlaid 

 to a depth in some places, of 15 or 20 feet of water-worn glacial 



