ESKERS IN THE VICINITY OF ROCHESTER, NEW YORK. 173 



chaotic, with cross-bedding common, the cross-bedding planes 

 dipping toward the side or toward the lee end of the esker. The 

 beds may dip from 5° to 60° or more. 



There is a tendency toward an anticlinal arched arrangement of 

 the beds, a feature exhibited in most eskers to a notable degree when 

 viewed in cross-section. The layers may be curved, twisted, or dis- 

 torted markedly. The beds not only tend to dip outward from the 

 center toward the sides, giving the anticlinal appearance, but they 

 are also inclined in the direction of the trend of the esker, they dip 

 away from the point of origin toward the place of termination of the 

 ridge or segment. A single bed may be of fine material, adjacent 

 beds of very coarse material, and vice versa. The larger materials 

 may show an imbricated arrangement observable often among the 

 stones and coarse shingle of streams and rivers. 



One part of a ridge may show good stratification, another part 

 poor, obscure stratification. A few eskers exhibit no stratification, 

 they have a "pell-mell" structure, as it has been described, a confused 

 arrangement of materials all of which are rounded. An esker may 

 exhibit stratification in one part of its course, and a "pell-mell" 

 structure in another part. "Pell-mell" structure is characteristic of 

 those eskers especially that are more irregular and hummocky in 

 external form. 



In the broad "plains" characteristic of many esker courses the 

 strata are nearly horizontal, or gently dipping toward the southern 

 termination of the esker. 



Slopes. The lateral slopes of eskers are as steep as the mate- 

 rials will lie, being the angle of rest for the material of which the 

 esker is composed. This slope varies from 25° to 35° from the hori- 

 zontal. In cross-section the narrow crest and steep slopes give the 

 appearance of an isosceles triangle, with the cross-sections in any 

 section of a ridge tending to uniformity. The steepness of the slope 

 is an indication of the character of the esker material, the steeper 

 slopes indicating coarser material. Often where the high knolls, 

 characteristic of many esker crests, appear, the declivity is very pro- 

 nounced, and where the cols appear the angle of slope is somewhat 

 less. Sometimes the slopes of both the cols and the knolls remain 

 the same, the width of the base changing so as to maintain the usual 

 degree of slope. 



