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NEW YORK STATE MUSEUM 



the lines as shown on a map. The method of interpretation 

 would consist in distributing the lines of flow between the nearest 

 observed striae as converging or diverging lines projected into 

 parallelism with the nearest observed striae farther downstream. 

 The attempt might be made to bend the lines so as to show how 

 the local irregularities of the topography would ordinarily deflect 

 the ice. In fact, only one station in this area was found in which 

 it was clear that the striation had been thus influenced by local 

 slopes. 



It is important to note that, just as the ice moved southwest- 

 ward across this district, so in the retreat of the ice sheet, its 

 front would be expected to recede from the district as a wall of 

 ice approximately at right angles to the lines of striation. From 

 this may be deduced the probability that the northeastern slopes 

 of the Adirondacks were freed from the Labradorian ice sheet 

 while it still lay against the northern end of the Green moun- 

 tains. As another probability in consequence of this mode of re- 

 treat, a connection w r ould be established between the Lake Ontario 

 basin, the upper St Lawrence and Lake Champlain along the low- 

 lands at the base of the Adirondacks before the lower St Law- 

 rence was open for connection with the Atlantic ocean. Other 

 effects of this mode of retreat of the ice front would be found in 

 the existence of shores of temporary, ice-dammed lakes on the 

 Adirondack side of Lake Champlain, which had no counterpart on 

 the Green mountain side so far north and at so early a time as 

 when the ice was but partly withdrawn from the upper, open 

 mouth of the Champlain valley. It might well thus be found that 

 beaches exist on the west side of the valley at high levels without 

 their counterpart on the east side of the valley. These possible 

 deductions from the striation of the region in relation to local 

 relief are mentioned because, as will later be shown, certain ob- 

 servations lead to the same conclusions. 



Glacial erosion 



It is difficult to estimate the amount of erosion by the direct 

 action of the ice sheet in this area. The principal streams are 

 obviously not flowing in their preglacial or interglacial channels, 

 for, except where they are intrenched in modern postglacial 



