92 ICE RECESSION IN NEW ENGLAND 



an analysis of the graphs for the recognition of short 

 periods, and the study of long cycles cannot be 

 made without more data, some problems and con- 

 ditions may be pointed out in order to encourage 

 the collecting of more material. 



T 5 



Recognizable Cycles 



The period of n years, or the sun-spot cycle, 

 together with its multiples, seems to play a promi- 

 nent role in the clay sedimentation. In the growth 

 of trees the same cycles are predominant, as 

 Douglass (1919, p. 99) has shown. He has determined 

 periods of 11 -3- 2 (5 to 6), 11, 2 X 11 (21 to 24), 

 3 X 11 (32 to 35), and 3 X 3 X 11 (100 to 105) 

 years, as well as of 2 years. 



The lines of recession as drawn on Plate VI do 

 not pretend to give an accurate picture of the vary- 

 ing rate of ice retreat; for that a much more 

 detailed study is necessary. It is likely that the 

 rate varied a good deal more than the map suggests. 

 In the Berkshires, Taylor (1903) has mapped a 

 series of recessional moraines, the most conspicuous 

 of which are reproduced on Plate VI. As Taylor 

 points out, they must represent short periodical 

 halts in the ice retreat. Because of their wide spac- 

 ing they cannot be winter moraines, i.e. moraines 

 pushed together by a slight readvance of the ice 

 edge during the winter after a summer of consider- 

 able recession, but record periods of some length. 

 On the map an attempt has been made to connect 

 two moraines with two positions of the ice edge. 

 Unfortunately, these latter are not accurately 

 fixed. Assuming that the connections are correct, 

 Taylor's morainic line No. 2 should correspond to 

 the ice edge position 4800, and his line No. 11 

 to that of 5300. Accordingly, there should be nine 



