ESKERS IN THE VICIXITY OF ROCHESTER, NEW YORK. 169 



Eskers may follow the bottom of a valley ; in the majority of 

 cases however they lie along the sides of the valley and above its 

 bottom. They may cross from one side of the valley to the other, 

 often they trend toward the bordering hills on the one side or the 

 other. If the latter are more than 200 feet high the eskers never 

 leave the valley; if less, after following the valley for some distance 

 they may break across the low divide and wind across areas of con- 

 siderable relief. An esker may divide, one ridge maintaining its 

 position in the axis of the valley, or along the side and above the 

 valley bottom, the other ridge paralleling the first along the opposite 

 side. A single ridge may break up into several ridges that follow 

 along the valley, especially if it is a broad valley. If the valley lies in 

 the general direction of ice movement, eskers will not leave it even 

 if adjoining divides are considerably less than 200 feet in height. 

 They often enter and leave valleys of other trend. They are more 

 strongly developed throughout their courses in the valley than when 

 crossing the neighboring uplands. 



They show discordance in most cases with existing drainage. 

 They may pass through lakes and their courses be traced beneath 

 the water; they may pass from the land surface to beneath the level 

 of the ocean (99). 



They are more common in rough regions than in regions of 

 slight relief, more numerous in ]\Iaine than over the upper Missis- 

 sippi plains. 



Leverett has noted the frequent occurrence of eskers in river- 

 like channels cut into the till sheets (61, 62, 63). These troughs may 

 be almost as narrow as the esker ridge at its base, commonly they 

 are several times as broad, the individual trough may not be occupied 

 by the esker throughout its whole length. 



In Western New York they lie in narrow valleys between the 

 drumlins. Instances have been recorded when they are known to 

 pass over drumlins (125). They are bordered on either side by wet- 

 swampy places. In fact lakes, ponds or swamps bordering eskers 

 on one side or both sides, elongated in the direction of the esker are 

 common features (29, 122). 



Large eskers are apt to be found in large drainage basins, and to 

 be composed of coarser material. 



