648 CHARLES EMERSON PEET 



water body; (5) evidence of the altitude above sea-level of the Hudson 

 water body. 



1. Absence of distinct wave-wrought features at the outer edge of 

 Brooklyn-Perth Amboy moraine. — There is an absence of wave- 

 wrought features of a decisive character outside of the moraine in a 

 region where the materials are soft and easily washed and which must 

 have been exposed to strong waves from the Atlantic. Although these 

 materials are displayed with a topography which would not offer the 

 best opportunity for effective wave-action, yet it seems incredible 

 that the sea could have been present over the area outside of the 

 moraine, at the levels demanded by the gaps in the moraine and for 

 the time necessary for the tide to scour out these gaps to the required 

 depth, without leaving a decisive record in the easily eroded drift. 

 Three suggestions aiming at an explanation of this are as follows: 

 (a) That these gaps were first made by the wearing of ice-waters 

 before depression took place, and were subsequently deepened by 

 tidal scour when the land had been depressed enough to admit the 

 sea. If this be admitted, the same early conditions as those under 

 the lake hypothesis are assumed, the main diilerence being in the time 

 of depression and in the number of depressions, {h) That ice pro- 

 tected the shore from wave-action. This would seem plausible for 

 the time when, and the places wherej the ice was present, but is diffi- 

 cult of acceptance after the ice-edge had retreated. Shore-ice might, 

 however, have remained for long periods of the year, after the ice-sheet 

 had retreated, (c) The land rose rapidly after the original depression, 

 thus preventing the making of a disiinct record of wave-action. If 

 this was so, equally rapid scouring of the channels must be postulated 

 in order to acccount for the access of the sea to the Hudson Valley. 

 It is doubtful if the rapid rise would be effective unless the movement 

 was very rapid, and then the scouring would be handicapped. 



2. Presence of the overwash plains at the ice-front. — The presence 

 of the overwash plains at the ice-front on Long Island and Staten 

 Island without distinct features to be ascribed to wave-action, or a 

 form that the presence of the sea over them would lead one to expect, 

 argues strongly for an altitude of land above sea-level when the over- 

 wash plain was building. If the submergence hypothesis is tenable, 

 it would seem necessary, as above, to postulate an altitude of land at 



