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NEW YORK STATE MUSEUM 



lake beaches which latter there is reason to believe on other evi- 

 dence lie within 300 feet of the upper limit of marine fossil shells. 



When the beaches and bars of Lake Iroquois, a preglacial lake, 

 are compared with the beaches of the marine district in the Cham- 

 plain valley, the evidence is overwhelming that the lake beaches 

 are much more strongly developed than those which may be 

 ascribed to marine action in the latter field, the reason for this 

 being that the lacustrine action continued at a given level for a 

 greater length of time than did the marine waves. There is in 

 short nothing in the local character of a lake beach to distinguish 

 it from a marine beach. The geographic situation and the hori- 

 zontal distribution of the beach phenomena on the other hand may 

 furnish differentiae. Proglacial lake beaches run out against the 

 glacier against whose front the waters are held up; in the opposite 

 direction the beaches converge to one or more spillways whence 

 the overflow discharged to the sea. Marine beaches and correlated 

 shore phenomena develop about the entire periphery of an area 

 of submergence, and phenomena of outflow are necessarily absent. 



This criterion of continuity of beaches has been used in the 

 present survey to distinguish the upper marine limit from earlier 

 higher lacustrine shore lines which, as the evidence indicates, 

 end abruptly as they are traced toward the Covey hill spur of 

 the Adirondacks. In the district where these higher beaches, for 

 which a proglacial lake origin is claimed, disappear, some phe- 

 nomena demand further discussion in relation to the validity of 

 the assumption made in this paper. 



The water planes marked by deltas and beachlike deposits above 

 450 feet on the Mooers quadrangle, come at the international 

 boundary to their northern limit indicating that the ice front im- 

 pinged on the Covey hill spur and separated the waters on the east 

 of the Adirondacks from those on the northwest. If it be supposed, 

 however, that just previous to this stand of the ice the glacier had 

 retreated, as it did later in the final liquefaction, far enough north 

 to open free communication between the Champlain valley and the 

 upper and lower St Lawrence (as Mr Upham has indeed supposed 

 to have been for a time the case), then a beach or beaches would 

 have been continuous about the spur only to be smoothed off and 

 rearranged by the advance of the ice to the position to which the 



