314 H. 1^ LITTLE PLEISTOCENE GEOLOC^Y OF WATERVILLE, MAINfi 



restored by melting during the retreat of the ice^ as is advocated by many,^ 

 would be likely to have allowed subaerial erosion of glacial gravels, with 

 a fairly rapid encroachment by the sea as melting progressed. 



The above considerations make it seem probalile that such illustrations 

 as plate 13, figure 2, and plate 11, figures 1 and 2, represent subaerial 

 erosion in this area. That the point is not absolutely proven is well 

 realized. 



The presence of ice-floated boulders in the clay shows that local glaciers, 

 at least, still persisted a.s far south as the headwaters of the Kennebec. 



There seems to be evidence that the period of subaerial erosion was 

 short and submergence comparatively rapid. This conclusion is based on 

 two observations. The first is seen in the character of the erosional un- 

 conformities, as shown in tlie photographs referred to above. Several 

 small undulating erosional surfaces would not be likely to persist in 

 loose, coarse gravel for any length of time. Second evidence, which seems 

 to point in the same direction, is seen in plate 15, figure 1. Here a 

 fragment of sand is inclosed in the upper gravel of the esker. The gravel, 

 which is elsewhere almost horizontally stratified when seen from this 

 angle, here dips in rapidly toward the sand inclusion from all sides and 

 lies in confusion over it. The sand is similar to that immediately over- 

 lying the gravel elsewhere and grading into marine clay above. In all 

 probability it is a fragment of marine sand. The only explanation occur- 

 ring to me is that an ice, fragment became embedded in the esker, and 

 that its melting allowed gravel from the side and compact sand from 

 above to fall into the cavity. Since the area affected is less than 10 feet 

 across, the time in which the ice fragment persisted and also the time 

 before the deposition of the sand must have been short. 



The chief difficulty in connection with the marine clay and sand is the 

 question as to their upper boundary. As near as the writer can deter- 

 mine, their upper level in this vicinity is just below 160 feet. In several 

 places, especially between Winslow and Benton, across the river from 

 Waterville, it was found that ledge usually rose through the clay very 

 near the 160-foot contour line. Nothing of the character of a cross- 

 section could be found there, however, to show the relationship. During 

 the final work on this paper a n^w exposure was found along the Maine 

 Central Eailroad tracks about one-half mile above Benton. Here the 

 tracks had crossed a slate ridge at a high grade. To lower this it was 

 necessary not only to cut down the ledge, but also a long approach to it, 



6 For a recent statement of this theory in regard to the "Leda" clay see W. A. John- 

 ston : "Late Pleistocene oscillations of sealevel 'n the Ottawa Valley." Canada Depart- 

 ment of Mines, Ottawa Mnsenm Bulletin 24, lOPi, p. 13. 



