174 ROCHESTER ACADEMY OF SCIENCE. 



The ends of esker ridges and of the individual segments are, 

 Hke the sides, as steep as the materials will lie. In few cases do the 

 ends tend to trail out with a gentle slope and blend with the ground 

 moraine. 



Surface characters. Many eskers preserve a uniform crest line 

 throughout their whole length or a greater part of their length. This 

 is in many instances remarkably level, similar to a railroad grade, 

 however such long stretches are in truth slightly curved. Again the 

 crest may be very uneven, thrown into a series of alternating knobs 

 and depressions. This type of crest may characterize the entire 

 course of the esker. Again eskers may have a uniform crest for 

 part of their length, and an uneven crest characteristic of the remain- 

 ing part. Also the two types may alternate throughout the esker 

 course, each type persisting for some little distance. Knobs above 

 the crest are particularly apt to occur at termini and at ridge inter- 

 sections (88). The knobs vary in height from 3 or 4 feet to 10 or 

 20 feet and rarely may be 50 feet above the general level of the crest. 

 They may be so high and pronounced that the esker resembles a 

 series of kames more or less connected. Where they occur the esker 

 ridge tends to broaden. 



The materials on the surface are of the same nature as the 

 materials of the esker — sand and gravel, with gravel more common 

 by far. While most eskers have no till on their surfaces, yet its 

 occurrence on a part of the surface or over the whole surface of a 

 number of eskers has been noted. Scheffel describes eskers mantled 

 with till to the depth of 5 or 6 feet (88). and Leverett describes a 

 number of eskers from the interior with till present upon their sur- 

 faces (62, 63). 



Boulders with a diameter of several feet may be present upon 

 the surfaces of eskers, their occurrence here however is not com- 

 mon. They may be sparingly distributed over the surface, they may 

 be confined to certain restricted areas, again they may cover the sur- 

 faces. of certain eskers quite profusely (117). 



River silt may bury eskers that lie in valleys, as is the case with 

 the series of eskers of the Connecticut valley. They may be buried 

 by outwash carried out by streams from the front of the receding 

 ice edge (28). Along the coast of Maine marine sediments cover 



