RECESSIONAL ICE BORDERS IN BERKSHIRE, MASS. 337 



deposits. The body of the great terrace upon which this moraine 

 rests is composed of limestone. 



3. Lateral moraines of ice-tongues. — This class is probably- 

 much more extensive, measured along the sinuous length of ice- 

 borders, than all the others put together. But, with a few marked 

 exceptions, it is extremely difificult to recognize with certainty. 

 It is also extremely whimsical in its occurrence. In many situa- 

 tions where one would expect to find it there is no sign of it, 

 while in other places it may be splendidly developed where one 

 would not expect it. 



The principal difificulty in recognizing this type of moraine 

 with certainty is its lack of distinctive characters. The place 

 and manner of its occurrence and its association with other 

 border features are the principal guides to its recognition. As 

 would be expected, lateral moraines generally occur o.n hillsides 

 or the sides of valleys, and often where they are steep. In sur- 

 face expression and in composition they appear to differ in no 

 important respect from the relatively smooth and featureless 

 stony till of the ground moraine. Sometimes low knolls of 

 coarser composition, and frequently small kames with more or 

 less gravel and sand, are associated with their upper edges, but 

 seldom enter into their composition as an important quantity. 

 Sometimes the mass of drift composing them forms a thick bank 

 — ten or twenty feet, or even more — and their recognition is 

 easy. But oftener it is thin, and their recognition is then dififi- 

 cult or impossible. They are most easily recognized when 

 associated with strong border drainage. Where such a moraine 

 is banked up on a valley side and a river of some volume flowed 

 along the side of the tongue, the bed of the stream puts a very 

 sharp upper limit to the heavier belt of drift, which is then 

 readily recognized as a siibmarginal deposit of the ice. Usually, 

 too, the hillside above the river bed is bare or only thinly coated 

 with drift. Occasionally these moraines are distinct where 

 border drainage was absent or too slight for recognition, their 

 upper limit being determined as before by a line dividing a heavy 

 bank of drift below from a thinly coated surface above. Where 

 border drainage was very strong, a ridge of coarse detritus was 



