170 ROCHESTER ACADEMY OF SCIENCE. 



At higher ahitudes eskers are confined to valleys chiefly, thus in 

 Sweden at elevations greater than 300 feet they lie in valleys. 



Relations at teniiiiiatioii. Eskers frequently terminate in kanie 

 areas. They may also end in marine and lacustrine deltas and out- 

 wash plains. The esker ridges widen as they approach these, and 

 merge with them gradually. Their termination may also be very 

 abrupt without regard to the character of the surroundings. This 

 may take place in an uneven bouldery field, or in a morainal sur- 

 face. When eskers terminate in recessional or terminal moraines, 

 they tend to advance toward them at nearly right angles. 



Eskers may split up near their southern termini into several 

 distinct branches or distributaries, like the mouths of a stream in a 

 delta. These distributaries may be connected by cross-ridges giving 

 a decidedly complex, reticulated appearance. 



In case a single ridge has broken up into a number of ridges 

 some distance from its termination the latter ridges are often found 

 to converge and unite just above the termination. Again these 

 diverging ridges may terminate miles from each other in separate 

 deltas, kame areas, fans, etc. 



The burial of the lower ends of esker ridges by lacustrine silts, 

 marine sediments, outwash and delta materials, has been observed 

 repeatedly. 



Association zvith moraines. There is no denying the fact that 

 many eskers, possibly most eskers, are associated with either ter- 

 minal or recessional moraines. Their courses lie north of these 

 moraines in which they terminate. This intimate relationship seems 

 to indicate a close connection in the formation of the two types of 

 glacial deposits. 



Composition. Eskers are composed chiefly of sand and gravel. 

 The sand is coarse for the greater part. Gravel is considerably the 

 more abundant material and may be very coarse. It probably makes 

 up the greater part of most eskers, while some eskers are composed 

 entirely of gravel (38, 99.). Very fine material, such as "rock flour", 

 is absent and clay is rare, and when present occurs only in thin beds. 

 Boulders several feet in diameter may be present, embedded in the 

 sand and gravel, some with a diameter of over 5 feet have been 

 observed (99). The pebbles of the gravel are well rounded, rarely 



