ANCIENT WATER LEVELS OF CIIAMPLAIN-HUDSON VALLEYS 221 



geological textbook by Alonzo Gray and C. B. Adams. 1 The sub- 

 mergence indicated by the fossiliferous clays in the valley of Lake 

 Champlain was placed at 400 feet above the present sea level. 

 New England and New Brunswick are regarded as having then 

 formed a large island, separated from the mainland of New York 

 by a strait, " which extended from the valley of the St Lawrence 

 through the valley of Lake Champlain, of the Champlain canal 

 and of the Hudson river. The summit level of the canal indicates 

 the most shallow part of this strait which had a depth of about 

 125 feet." 



Ebenezer Emmons 2 speaks of the " clays of Champlain and Al- 

 bany " as marine and of the " connection by water of the Gulf of 

 St Lawrence and the bay of New York." " New England and a 

 part of New York were an island separated from the central part 

 of New York by a narrow strait." 



Mr Upham 3 in 1892 advanced the idea that at the close of the 

 last glacial epoch the Hudson valley formed a glacial lake bounded 

 on the north by the barrier of the ice sheet during the retreat from 

 the basin of Lake Champlain and the St Lawrence valley. The 

 barrier of this lake on the south was thought to have been due to 

 an elevation of the present mouth of the Hudson which afterward 

 sank beneath sea level. The subsidence of this coast is still going 

 on, and the submerged channel of the Hudson has been mapped 

 by the United States Coast and Geodetic Survey. The absence of 

 marine fossils from the postglacial beds of the Hudson valley is 

 taken as evidence that this valley has not been occupied by the sea 

 either as an estuary or a strait at higher levels than the present 

 since the ice age. 



DeGeer 4 believed that the Catskill delta was formed at a s time 

 when New England and the contiguous portions of Canada were 

 made an island by a strait on the west and the enlarged gulf on 

 the north. 



From a rapid review of several localities he constructed a chart 

 of isobases of equal change of level. In the Hudson and Cham- 



'Gray, Alonzo & Adams, C. B. Elements of Geology. N. Y. 1853. 

 p.160-61. 



2 Mannal of Geology. Phila. I860, p.247-48. 



s Bost. Soc. Nat. Hist. Proc. 1892. 25:335. 



4 Bost. Soc. Nat. Hist. Proc. 1892. 25:335. 



