GLACIAL AND POSTGLACIAL HISTORY OP GREAT LAKES BEGION. 325 



GLACIAL LAKES IN THE LAKE ONTARIO BASIN. 



EARLY LAKES. 



When the Lake Ontario ice lobe had retreated far enough to uncover the southern parts of 

 the valleys of the Finger Lakes in central New York, small lakes gathered, at first as separate 

 bodies. With continued recession these lakes were lowered and combined in a complex series 

 of changes that led finally to the later, larger lake that filled the whole basin of Lake Ontario. 

 These changes have been set forth in considerable detail and illustrated by a series of maps by 

 Fairchild. 1 The first local glacial lakes had independent outlets toward the south. The succes- 

 sion of lakes, as given by Fairchild, is as follows: Watkins, Newberry, Hall, Vanuxem, Second 

 Vanuxem, Warren, Dana, Dawson, Iroquois. 



LAKE NEWBERRY. 



The first combination of the dozen or more small lakes in the Finger Lakes valleys into one 

 lake has been called Lake Newberry. Its outlet was southward from Seneca Lake to Susque- 

 hanna River. 



LAKE HALL. 



At a slightly later stage of recession an outlet was opened westward to the glacial waters 

 in the Lake Erie basin. The lake at this stage is known as Lake Hall. 



, LAKE VANUXEM. 



At a slightly later stage a lower outlet was opened eastward to the Mohawk Valley, and 

 this stage is known as Lake Vanuxem. After this there was for a time free drainage east- 

 ward, with only two low, small lakes, one in the Genesee Valley and one in the valley of Cayuga 

 Lake. Later, however, on the readvance of the ice front, Lake Vanuxem was reestablished 

 (Second Lake Vanuxem), after which the waters of the southern part of the Lake Ontario 

 basin again merged with those in the Huron-Erie-Ontario basin. 



LAKE DAWSON. 



When the waters had fallen so as to separate those in Lake Erie from those of the Lake 

 Ontario basin, an outlet was established eastward past Syracuse, N. Y. A number of oscilla- 

 tions of lake level, corresponding to slight retreats and readvances of the ice front, probably 

 occurred. Toward the end of these oscillations the ice front, according to Fairchild, rested 

 against the relatively high ground east of Rochester, forming a barrier across the Lake Ontario 

 basin and dividing the waters into two bodies, Lake Dawson on the west and a smaller lake, 

 draining from Lake Dawson and emptying into the Mohawk, on the east. 



LAKE IROQUOIS. 



When the waters of the Lake Ontario basin fell to the level of the pass at Rome, N. Y., they 

 discharged eastward through the Mohawk Valley. This established Lake Iroquois, which 

 endured for a relatively long time. The land, however, was uplifted around the north and east 

 sides of this basin while the lake was discharging at Rome. This backed the water up on the 

 south and west and caused it to fall away from the northern and eastern shores. 



LAKE FRONTENAC. 



When the retreating ice opened a passage eastward around the north side of the Adirondack 

 Mountains to the basin of Lake Champlain, the lake level fell and the outlet at Rome was aban- 

 doned. At this stage the ice barrier or clam rested about on the Frontenac axis of the pre-Cam- 

 brian rocks and the lake may therefore be called Lake Frontenac. 



i Fairchild, H. L., Glacial waters in central New York: Bull. New York State Mus. No. 127, 1909. 



