ICE-RETREAT IN GLACIAL LAKE NEPONSET 189 



lack of agreement in composition between the gravels and the adjacent 

 rocks or tills from which they must otherwise have been derived, and 

 the absence of even the most local postglacial deposits of similar 

 character in the region. 



The lake-level was regulated by the altitude of its outlet, which 

 was through the notch southeast of Rattlesnake Hill, as in the case 

 of the earlier lakelet of that name. The outlet stream was marginal 

 as far south as the northeast base of the hill, but there the waters 

 passed onto the ice, on which they continued until the notch was 

 reached, as shown by the absence of erosional or depositional features 

 in the intervening area. 



That there was no outlet over the divide south of Massapoag 

 Pond, which lies some two miles west of Rattlesnake Hill, is shown 

 by the fact that the rock-floor is from ten to twenty feet or more lower 

 than at the Rattlesnake Hill outlet, and as much below the level of 

 the East Sharon and Stoughton Plains, the highest of which it could 

 not, therefore, have controlled. The field evidence, moreover 

 shows that the Massapoag valley was occupied by ice until a late 

 stage in the history of the Stoughton Bay region. 



Stoughton lakelet. — This is by far the largest of the lakelets in 

 the Stoughton Bay region, and receives its name from the town of 

 Stoughton which is located in the middle of its area. Like the East 

 Sharon lakelet, it was compound, being composed of a larger water 

 body at the north and a smaller one at the south, the two being 

 apparently connected by a narrow channel along the eastern margin 

 in the vicinity of Stoughton. Like the East Sharon lake, it was also 

 located, at least so far as the northern or main portion is concerned, 

 at the termination of a rock hill projecting between two converging 

 valleys in which the ice still remained. 



The breadth of the northern portion of the lake from north to 

 south was about one and one-half miles, and from east to west about 

 one and one-quarter miles. The southern portion of the lake was 

 more irregular. From east to west it measured somewhat over a 

 mile in length, but it was less than half a mile in width. 



In the northern half of the lakelet the broad Stoughton plains 

 were deposited. While in a general way these plains present a uni- 

 form upper limit, the plain was in many places never built up to a 



