ICE-RETREAT IN GLACIAL LAKE NEPONSET 183 



distribution and topographic expression of the deposits; and, as the 

 history of the retreat in this locahty is beheved to be essentially 

 the same as in the other glacial lakes of the region, the bay has, for 

 the purpose of discussion, been selected as a type. 



STOUGHTON BAY AREA AND ITS DEPOSITS. 



Topography and drainage. — In a broad way it may be said that 

 Stoughton Bay occupied a somewhat oval area surrounded by an 

 interrupted belt of hills which, starting northwest of North Stoughton, 

 extends southward about four miles, and then curves first to the 

 west and then to the northwest, finally terminating in the range of 

 hills southwest of Canton. The breadth of this basin is about four 

 miles, and the length a trifle greater. The crests of the hills con- 

 stituting the boundary vary from 200 up to 420 feet in altitude, 

 while the intermediate cols vary from 190 to 250 feet in elevation. 



Notwithstanding these relatively low gaps in the southern rim 

 of the basin, it seems probable that the preglacial drainage, like 

 that of the present period, was by way of the Neponset River to the 

 north. Both the lower level of the rock-floors of the channels and 

 the greater width of the valleys at the northern end of the area bear 

 out this supposition. The possibility of a deflection of the drainage 

 to the southwest through the valley now occupied by Massapoag 

 Pond, has been considered, but although the valley is relatively 

 broad, the frequent projection of rock "islands" through the out- 

 wash drift deposits, with which it is filled, appears to indicate that 

 the rock bottom is much higher than in the present valley at Canton 

 Village. The Canton valley, however, is not a broad one, the rock 

 outcropping at relatively short distances from the stream on both 

 sides, and probably underlying it at no great depth. The high 

 elevation of the bottom of this channel, as compared with the low 

 elevation, which probably characterizes the near-by Neponset valley 

 bottom, would appear to indicate, either that the former is not the 

 main preglacial drainage channel, or that the Neponset valley has 

 been materially deepened by glacial erosion. The latter appears 

 to be the more probable. In fact, the drainage and topography of 

 even the bed-rock areas of this portion of Massachusetts show very 

 few of the characteristics of normally developed drainage systems. 



