224 



NEW YORK STATE MUSEUM 



area since the hight and during the retreat of the Wisconsin 

 ice sheet. 



I have elsewhere commented on the difference in the inclina- 

 tion of the water levels in the lower Hudson and the Cham- 

 plain valleys. The diagram, plate 28, has been prepared to 

 spread before the eye some of the details bearing on this gen- 

 eralization. A particular explanation of the diagram will be 

 found at page 254. In this graphic interpretation of the ancient 

 water levels it will be seen that those of the lower Hudson are 

 made to incline at about one half the angle of those over the 

 Champlain valley. It would be a very hasty conclusion to infer 

 without particular facts to support the view that this differ- 

 ence of rate of inclination is simply due to a more rapid rise 

 of the land on the north. These evidences of water level cover 

 a period as long as the entire retreat of the ice sheet, a time 

 as yet of unknown duration but presumably measured by tens 

 of thousands of years so that there has thus been time for many 

 changes of level. 



The terraces of the Hudson are too discontinuous and unre- 

 lated within short distances to draw very certain conclusions 

 from their levels particularly in the district from the High- 

 land canyon northward to the beginning of the Albany clay 

 cover on the rock terraces. In the diagram, plate 28, I have 

 compared the proglacial delta levels with the line A-B. This 

 line accords well with the rise in level of these deposits 

 toward the north till the vicinity of Newburg when great irre- 

 gularity appears in terrace levels most of which bear the signs 

 of deposition in the presence of the retreating ice tongue in 

 the Hudson valley. Not only these latter but also those on the 

 south which appear to decrease southward in elevation at a 

 regular rate as indicated by the line A-B might plausibly be 

 interpreted as made in a succession of water levels essentially 

 parallel with the steeper inclined water planes over the Cham- 

 plain district. In this view it is necessary to regard the entire 

 eastern part of the State tilted to the north to such a degree 

 that the line L-M on r>late 28 is at s^a level or parallel to 

 sea level, and to regard the waters from the ice front at all 

 stages of retreat as discharging through the Narrows in a some- 



