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NEW YORK STATE MUSEUM 



already well above sea level, the outflowing stream in the gorge 

 on the south had more deeply excavated its channel so as to per- 

 mit the draining of the waters of Lake Albany and the region on 

 the north to a lower level. A general southward tilting of the 

 whole region would have accomplished the same result during the 

 early lake stage. 



In choosing between the above views, it has to be noted that 

 after the barrier was instituted in the upper Hudson valley 

 between the lake waters of the Champlain and Albany dis- 

 tricts the water levels established in the former area according 

 to my interpretation of them as shown in plate 28 are tilted now 

 much more steeply than those of the Albany clay region in the 

 middle and southern Hudson valley. On account of the apparent 

 close approximation of the water levels in the lower and middle 

 Hudson valley to the line of comparison above mentioned it 

 seems probable, though not to my mind thoroughly demonstrated 

 by the analysis I have been able to make of the mass of details 

 presented by the district, that the land remained fairly stable 

 during the retreat of the ice sheet from New York narrows north- 

 ward, such changes of level as are indicated by the altitude of 

 the proglacial deltas and terraces being due to fluctuations in the 

 water levels and the excavation of the drift in the Hudson gorge 

 during the time that Lake Iroquois discharged through the Mo- 

 hawk valley into Lake Albany. The land was then relatively to 

 its present attitude tilted down on the north so that the line of 

 comparison in plate 28 was essentially parallel to sea level. Fol- 

 lowing this essentially stable phase an actual down tilting to the 

 north ensued with an axis of no change of level somewhere not 

 far north from Albany, bringing the Champlain district into 

 parallelism with the later shore lines including the marine limit 

 as indicated in plate 28, and producing a corresponding uplift in 

 the lower Hudson valley. This change of itself would have pro- 

 duced a rise of the waters in the glacial lake on the north of 

 Albany in an increasing ratio with the northing and an apparent 

 lowering of the shore lines in the valley south of Albany. This 

 probably was the time of maximum water hight over the divide 

 south of Fort Edward. The excavation or reexcavation of the 

 Hudson gorge in the far south, favored by the increased current 



