RELATIONS OF GRAVEL DEPOSITS 201 



valley loo feet or more below the present surface. This valley — 

 the ancjent outlet for the Sudbury valley drainage, is supposed to 

 continue beneath Wellesley to the valley of Rosemary Brook, and 

 thence northward to the present Charles River at Riverside. The 

 broad marshy area east of Needham, in which the bed-rock surface 

 is known to lie at a considerable depth below sea-level, was probably 

 occupied by a tributary of the Charles which entered the main river 

 just north of Highland ville. The valley between South Natick and 

 Dedham contained no single preglacial stream. The largest unbroken 

 upland region is the broad band extending westward from the Nepon- 

 set River across Dedham, Westwood, Dover, and Sherborn, which 

 in preglacial times separated the lowlands on the north and south 

 into two distinct drainage systems, since united along the course of 

 the Charles River. 



DESCRIPTION OF THE DEPOSITS. 



In a provisional classification we may recognize the following 

 types of deposits as occurring in this portion of Lake Charles : 



1. Flat-topped delta-fans — typical gravel plains — the level of 

 which varies but a few feet in a single plain. These deltas almost 

 invariably have a beautiful ice- contact slope, but the common lobate 

 front may or may not be developed. For this class of deposits the 

 common name of "sandplain" is used, although the plains considered 

 consist largely of gravel. 



2. Kettle plains, or deposits with a definite maximum elevation, 

 but so broken up by kettle-holes as to have httle semblance to plains. 

 In origin, they differ from true sandplains only in having been formed 

 among crowded ice-masses. 



3. Eskers, or deposits of glacial streams. These are often con- 

 spicuously tributary to deltas. 



4. Irregular deposits of gravel along the sides of valleys, usually 

 consisting of great numbers of small hills or kames densely crowded 

 together, for which the name "moraine-terrace" is sometimes used. 



5. Kames — the name comprising all small, irregular hills of sand 

 and gravel not included under (3) or (4). 



6. Thin coatings or undulating deposits of gravel, apparently 

 having no definite relations. 



