80 BULLETIN OF THE ESSEX INSTITUTE. 



c. Esker-fans, small plains of gravel and sand built 

 at the mouth of subglacial tunnels and channels in the 

 ice ; associated with an esker or esker-like chain of de- 

 posits made in the ice-sheet at the same time — e. y., 

 Newtonville, Mass. ; Saylesville, R. I. 



d. Wash-cones, steeply sloping deposits, with ice- 

 contact slope on the iceward side culminating in a high 

 point, with gentler slope outward, in the manner of allu- 

 vial cones — e. g., Sprague Hill, Bridgewater ; the de- 

 posit south of Waban Station, Mass. ; deposits near Davis- 

 ville, R. I. 



With these general types are associated minor topo- 

 graphic features due to the mode of origin of the deposits 

 or inherent in their relations to preexisting formations. 

 Some of these features are here described : 



Drainage creases. — The largest plains of the outermost 

 moraine in this area bear strongly defined drainage fur- 

 I'ows, thought by all to mark the paths of streams flowing 

 out from the ice-front at the time it lay along the head of 

 the plains. By analogy with the channels on existing 

 plains of like origin we should infer that these streams 

 flowed in the open air. 



These creases may traverse the entire breadth of the 

 plain from the ice-contact to the distal margin. Many 

 furrows are traceable only on the lower, outer margin of 

 the plain for the reason that the later deposition of gravel 

 in the form of fans along the ice-front clogged up and 

 effaced the upper portions of such furrows. 



During the construction of a delta in a water basin with 

 constant level, the delta margin grows forward with the 

 discharging streams running on the lobate axis. If the 

 water level suddenly fall oft", we should expect a stream 

 to become diverted to the fuirow between two lobes. To 

 what extent the lobate aspect of some of the large creased 



