1 82 M. L. FULLER 



facing, such as characterizes Hving glaciers. It was apparently con- 

 ceived by the writers named that, as the face drew back to the north, 

 a line of glacial lakelets came into existence at the heads of the 

 northward-leading valleys. These, as the ice retreated, were con- 

 sidered to have grown in size and to have coalesced until the Sud- 

 bury, Charles, and Neponset lakes, and possibly also Lake Bouve, 

 became united into a single lake many miles in width and length, 

 and of considerable area. 



The studies of the present writer in Lake Neponset have led to 

 the conclusion that the ice in that region, instead of retreating with 

 a definite and somewhat regular front, had become absolutely stag- 

 nant before the history of the lake began, and that its disappear- 

 ance was characterized by marked irregularities along lobes, deep 

 re-entrants and detached blocks being the rule rather than the excep- 

 tion. Moreover, the marginal distribution of the deposits makes it 

 seem probable, if not certain, that there was no general body of 

 water such as was postulated for the Sudbury- Charles-Neponset 

 stage, or even for the simple Neponset stage itself, but that the depos- 

 its, generally considered as marking the lake level or levels, were 

 laid down in a series of small and more or less independent lakelets 

 existing along the margins of the residual valley lobes or about 

 entirely detached masses of ice. 



In urging the improbability of the existence of large lakes with 

 definite levels in this region during the earlier stages, however, the 

 writer does not wish to be considered as denying the existence of 

 considerable bodies of water in the lower portions of the valleys 

 during the closing stages of the lakes when the ice-lobes and blocks 

 had practically disappeared. In the following discussion of Lake 

 Neponset the terms "lake" and "bay" are used to designate those 

 portions of the basin of the Neponset River and its tributaries in 

 which glacial sediments were laid down in standing water irrespec- 

 tive of time, elevation, or of the character of the water bodies in 

 which the deposition took place. 



Stoughton Bay is simply a portion of the Neponset basin, lying 

 in the vicinity of the town of the same name. In this bay the con- 

 ditions which the writer believes to have characterized the ice-retreat 

 in the region under discussion are recorded very definitely in the 



