264 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
plains of the Sudbury valley, twenty miles west of Boston. My pur- 
pose was to investigate the grouping of sand plains in a single drain- 
age basin, with greater accuracy in the determination of levels than had 
hitherto been attempted. The chief result of the work, as will be seen, 
was the discovery that the sand plains of this district do not conform to 
the horizontal step scheme of grouping used by Crosby and others for the 
hboring extinct lakes Nashua, Charles, and Bouvé; but that they 
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Boston 
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Ficure 1. 
Sketch map of eastern Massachusetts showing location of Lake Sudbury. 
seem rather to record a postglacial tilt, by which their original relations 
of level have been upset. 
I shall first review the conditions under which temporary glacial 
lakes might form, and the probable history they would undergo ; passing 
then to these physiographic features which mark extinct ice-front lakes, 
especially sand plains, I shall consider the horizontal step scheme of ar- 
