198 ROCHESTER ACADEMY OF SCIENCE. 



thickness and of considerable surface relief." The esker knobs 

 would result from a temporary halt in the ice recession. "Crooked 

 re-entrants or shifting stream mouths would result in crooked 

 ridges. Where there was one re-entrant, or one stream, there would 

 be one ridge formed ; where the ice edge was badly broken up and 

 streams ran through all the cracks, the result would be a kame area 

 drawn out into an intricate series of ridges, rather than a single 

 ridge. Converging cracks would result in converging ridges, 

 diverging cracks in diverging ridges, and crossing and recrossing 

 cracks in intricate reticulated ridges. Where the ice edge retreated 

 uphill, the ridges would be extended uphill. Where the ice receded 

 across valleys and divides, the esker would be made to follow a 

 course across a surface of high relief. The rougher the region, the 

 more likely the presence of cracks in the edge of the ice, which 

 explains the greater abundance of eskers in rough than in smooth 

 regions" (111). 



Hershey regards the "plains," areas of "special development" 

 in esker courses, as formed at the terminus of the ice when it has 

 remained stationary for some time (48). It is also suggested that 

 they may be due to the overlapping of several individual deposits. 

 He further states that esker deposits are not generally overriden but 

 exhibit some evidence of ice push. 



Objections. (1) Many eskers and most of the New York 

 eskers do not show an uneven crestline but rather a uniform crest. 

 To produce this condition by this method of origin it would seem 

 essential that the recession of the ice front be very regular, and that 

 the volume and velocity and load of the esker making streams 

 remain constant, a series of conditions that would not be likely to 

 obtain along the borders of receding ice sheets. 



(2) An interval in the course of an esker should be repre- 

 sented by a ridge, or at least by gravels, elsewhere, which is not the 

 case usually. 



(3) Many eskers have till on their surfaces, a fact difficvilt to 

 explain if the esker was built at the edge and not beneath the ice. 

 The presence of large boulders on the surface encounters a similar 

 difficulty in explanation under this idea. 



