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NEW YORK STATE MUSEUM 



plain valleys he placed the isobase at New York and that of 600 

 feet elevation near Plattsburg. 



Mr S. P. Baldwin in ism 1 regarded the heavier sand deltas of 

 the rivers tributary to Lake Ghamplain as the shore equivalent 

 of the deep water clays with marine fossils and hence as marking 

 the limit of salt-water invasion. In his opinion the sea did not 

 reach higher than 150 feet at Whitehall and was 500 feet at St 

 Albans in Vermont, giving a postglacial tilting of the land at the 

 rate of 3 feet to the mile. 



The higher beaches, '558 feet at St Albans as noted by De Geer. 

 are described as slight and regarded as due to a glacial lake held 

 in by the concave front of the retreating ice sheet. This lake it 

 was believed penetrated into the Hudson valley through the White- 

 hall-Fort Ann valley. 



1 Pleistocene History of the Champlain Valley. Am. Geol, 1894. 

 13:170-84; map pi. 5, at p.170. 



