SOME GLACIAL AVASH-PLAINS. 99 



well defined line of wash-plains can l)e traced from the 

 south side of the Blackstone River at Woonsocket north- 

 eastward to the southwest corner of the Bhie Hills. The 

 Woonsocket (70) outwash plain stands at an elevation of 

 about three hundred feet above the sea. At Sharon (64) 

 there is an extensively developed plain also at an elevation 

 of three hundred feet. A few miles northeast (82) of this 

 plain begins the deposit built along the edge of the ice when 

 the Neponset valley was occupied by the retreating front. 

 This deposit has an elevation varying from 140 to 150 

 feet above sea-level. At the base of Little Blue Hill, the 

 plains of this stage have been suffused by a fan supplied 

 by the drainage coming through the pass between Little 

 and Great Blue Hill, evidently after the retreat of the ice 

 from the Canton stage, but while the sheet still clung about 

 the northern base of the Blue Hill range. 



Immediately north of Canton Junction station, the head 

 of the plain of this stage shows grouped terraces and the 

 intraglacial ground is heavily strewn with boulders dropped 

 from the melting ice. The Neponset valley with its 

 marshes thus represents an unfilled area whose existence 

 as such depends upon the position of the ice front. 

 About Islington (81) on the west side of this depression, 

 there are local plains and eskers, but the development of 

 plains along this western line was so feeble that the Ne- 

 ponset valley was scarcely invaded by them. 



North of the Woonsocket-Sharon line of plains lies the 

 Mechanicsville esker-fan in the town of Bellingham. As 

 shown in the accompanying figure, the esker and the notch 

 in this deposit are abnormal, the esker in its breadth and 

 the notch in its depth. The notch gives passage to a 

 stream and a pond lies in the axis of the esker at the head 

 of the plain, showing that the ice-wall was intact the en- 

 tire length of the plain. It seems likely as noted on p. 87 



ESSEX INST. BULLETIN, VOL. XXIX 7* 



