ANCIENT WATER LEVELS OP dl A MTLAIN-HUDSON VALLEYS 203 



beaches may now be traced. Such an oscillation of the ice margin 

 as is here merely suggested, undoubtedly took place, and the possi- 

 bility of it constitutes the weak point in the argument presented in 

 this report in the attempt to fix the upper marine limit. 



Such diffused shore lines might be expected to exhibit a trace 

 in the waterworn character of the glacial drift along the belt in 

 which the overridden shore lines were formed, in the case of a tem- 

 porary and slight advance of the ice, one which, in this field need 

 only have amounted to an oscillation of from 10 to 15 miles. 



In this connection, it should be stated that certain peculiarities 

 of the drift before referred to along the western border of the 

 Mooers quadrangle from Deer Pond northward to the English 

 l iver at Cannon Corners are not inconsistent with an advance of 

 the ice such as is here considered possible. Waterworn drift vary- 

 ing from gravel to very coarse cobblestones with on the whole an 

 unstratified structure and ice-swept contour covers the slope be- 

 tween the TOO and 800 foot lines quite above, however, the latest 

 lake levels of this latitude. 



These deposits lie, it should be noted, on the east of Blackman's 

 rock, one of the large spillways of bare Potsdam sandstone, only 

 the northern extremity of which appears on the map. It has seemed 

 to me that the waterworn materials are to be ascribed to stream 

 action contemporaneous with the position of the ice front along 

 this line rather than to the involution in the drift of an earlier 

 beach deposit formed at a higher stand of the sea than is advo- 

 cated in this report. The fact that there are no clear traces of 

 such smudged beaches around the Covey Hill slope has confirmed 

 me in the belief that this objection to the accepted marine limit 

 has in this case no clearly observed facts upon which to rest. 



A second objection to the view that the higher beaches in the 

 Champlain district are of lacustrine origin may be raised from 

 the fact that along the slope of the Adirondacks the lowest shell- 

 bearing layers of the marine series, as at Mooers on the Big 

 Chazy, and Freydenburg's Mills on the Saranac, are found rest- 

 ing directly on the boulder clay without intervening nonfos- 

 siliferous beds or those bearing nonmarine fossils attributable 

 to the deposits of a lake. The absence of lacustrine deposits 

 in. these two localities in the northern part of the area can 



