GLACIAL AND POST-GLACIAL HISTORY 641 



of phenomena that must be accounted for in any explanation of the 

 Hudson water body. They are: (i) the rise in. level of the deltas 

 and gravel plateaus northward; (2) the submerged channels, both in 

 the lower Hudson and in the upper Hudson as far north as Troy; 

 (3) the gap in the moraine at the Brooklyn Narrows, and the gap in 

 the moraine at Perth Amboy, occupied by Arthur Kill (see Fig. 8, 

 p. 426); (4) the scarcity of wave- wrought features. 



I. The rise of the gravel plateaus northward. — Under either of 

 the above hypotheses the land was relatively lower at the north during 

 the presence of the water body than it is now, and there has been 

 subsequent greater northern uplift. This greater northern uplift is 

 necessary to account for the disappearance of the Hudson water 

 body, if it was a lake, because the depth of the floor below the delta 

 levels exceeds the known amount of the cutting of the outlet. 



If the Hudson water body was a lake, the amount of northern 

 uplift necessary to produce the present altitude of the deltas is greater 

 than the amount necessary if they were formed in the sea, for the 

 following reason: As the ice was retreating, the outlet was being 

 lowered, so that the more northerly deltas must have been made at 

 successively lower levels, unless there was some action to maintain 

 the water-level. If the amount of cutting of the outlet be distributed 

 among the sixteen or more different stands of the ice south of Street 

 Road, it would cause but a small amount of fall between the successive 

 stands. Even if the effect of the accession of the waters from Lake 

 Iroquois by way of the Rome outlet- be taken into consideration, and 

 reasonable allowance be made for the increase in rate of cutting after 

 that, it makes the fall in water-level between successive positions 

 of the ice a comparatively small amount, much less than could be 

 read from the topographic maps. Inequality in level of deltas due 

 to this cause is much less than that due to unequal building up at 

 the successive positions of the ice. In the aggregate, however, the 

 amount of fall of water-level is considerable. If the cutting of the 

 outlet during the history of the Hudson water body was 122 feet, it 

 requires that the last delta made in this water body undergo an uplift 

 of 122 feet more than would be required if they were all built in the 

 sea at one stand of the land. 



2. Origin 0} the submerged channels. — Under the first hypothesis 



