4 8 ICE RECESSION IN NEW ENGLAND 



When measurements of the same series were at hand from 

 distant or differently situated parts of the same lake or from 

 separate valleys, separate normal curves were worked out for 

 each district or valley. 



The curve was drawn so that it marked the actual thickness 

 of the varves, except when these were too thick. The distance 

 between the vertical lines was 5 millimeters. In the plates the 

 curve has been reduced one-half. The figures yi % %, etc., 

 indicate the actual scale of each part of the graph. In order to 

 promote continued geochronological studies, the American 

 Geographical Society is willing to make, at cost, photostat copies 

 on the original scale of the normal curve for anyone working on 

 the subject. 



Explanation of Symbols on Plates I-V 



In the normal curve the large-sized figures at the arrows 

 indicate the number of measurements used in constructing the 

 curve, and the small-sized figures give the respective localities. 

 Small-sized figures in parentheses indicate profiles used for 

 control of the number of the varves but not otherwise. The 

 arrows show to what part of the curve the figures refer. 



No Connection As Yet With Absolute Time 



This normal curve is not connected with the chronology of 

 our time, and the time elapsed since the ice sheet disappeared 

 from New England cannot even be estimated with any claim of 

 accuracy. The connections which De Geer (192 1, p. 70) supposed 

 he had made between localities 76 and 78 and the Swedish time 

 seal e cannot be right, both because these profiles are not charac- 

 teristic (cf. p. 32) and because the ice retreat in the respective 

 zones in New England and Sweden was very different. The 

 series given in De Geer's curve, at locality 76, are 7227 to 7297 

 and 7338 (?) to 7368 (?), and, at locality 78, 7159 to 7266 (?). 

 These horizons essentially correspond to a halt and readvance 

 of the ice edge, while the horizons in Sweden with which thev 



