GEOLOGY OF THE POUGHKEEPSIE QUADRANGLE lOI 



show that the clays, and overlying sands and gravels are best 

 explained as depositions under such conditions.^ Woodv^^orth's 

 liA'pothesis does not call for so great a subsidence of the land as the 

 other, and logically explains the present bisected character of the 

 clays as their original condition. The proximity of the ice during 

 the deposition of the so-called Champlain deposits is shown in 

 several ways. It seems quite reasonable, however, to explain the 

 upward more or less perfect passage from coarse to finer detritus in 

 the Hudson gorge as due to gradual deepening, and a passage from 

 fluviatile to estuarine conditions which would furnish the conditions 

 for the accumulation of the finer material. 



Terraces. The finer material in question takes the form of 

 stratified deposits of clay, capped with sand and gravel, which occur 

 in the form of terraces at various places along the Hudson gorge. 

 A number of these are in this quadrangle. 



Such a terrace begins somewhat over a mile north of Fishkill 

 Landing and extends for a mile north of that point, varying in 

 width from about one-fifth to three-fourths of a mile. It is about 

 100 feet high at the outer edge and a few feet higher at the inner 

 edge. It is followed on the north by a lower terrace varying from 

 30 to 40 feet in height, with varying depths of clay and covered 

 with coarse gravel. On the west bank of the Hudson at Roseton 

 and at Danskammer gravel-covered terraces also occur. These are 

 somewhat higher than the north terrace on the east bank. Terrace 

 deposits also occur at ]Marlboro. 



At New Hamburg the deposits are a good deal coarser and 

 have a terrace delta form. The coarse sands and gravels of this 

 terrace and their general relations, as well as the Roseton and 

 Danskammer terraces, are thought by Woodworth to " compel the 

 belief " that they were deposited against the ice. In the case of the 

 Roseton terrace, he states that there are signs of inthrusting of drift 

 from ice movement (loc. cit. p. 119) and 'further that the terrace 

 can not be attributed to a river pouring into an estuary after the 

 disappearance of the ice. 



The diminishing altitude of the terraces northward has been inter- 

 preted as favoring the idea of their formation against the ice in 

 glacial lakes. The coarser material overlying the clays has been 

 attributed to the retreat of the ice front beyond the mouths of tribu- 

 tary stream valleys, allowing an influx of coarser sediments. 



1 Ancient Water Levels of the Champlain and Hudson Valleys. N. Y. 

 State Mus. Bui. 84, 1905, p. 66-265. 



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