PLEISTOCENE GEOLOGY OF NASSAU CO. AND BOROUGH OF QUEENS 657 



other similar passes at higher levels. Their coincidence of level is 

 apparently accidental ; but their repetition not only determined the 

 level to which delta construction should reach in the temporary 

 lake behind the moraine at this stage, but the fact also explains the 

 failure to depart from that approximate level while the ice main- 

 tained its position. With the possibility of the water spilling over 

 through several or all of these channels, the drainage, if the time 

 were short, would hardly concentrate on any one of them. That 

 the time was short, is shown by the small delta built at this level. 

 Where the outpouring stream from the ice was strongest, the delta 

 pushed out about a mile. 



The deep drainage furrow dissecting the delta on a north and 

 south line indicates a sudden falling off in the water lev^el. This 

 undoubtedly points to a change in the position or in the solidity of 

 the ice barrier on the west, such as to permit the confined waters to 

 escape into New York bay at a lower level than the passes in the 

 moraine. The fact of such a change of level is indicated in a small 

 delta at about 40 feet in the vicinity of College Point. 



College Point delta 



A poorly developed delta fringes the southern slope of the bar of 

 glacial drift which connects College Point with the village of White- 

 stone. The northern slope and much of the crest of this ridge are 

 morainal, though sands are exposed here and there beneath this ice- 

 laid coating. At a point about due south of the bottom of Powell 

 cove, a section open in June 1900 showed the fore set and top set 

 beds of a typical delta structure extending southward. The struc- 

 ture as in fig. 9 indicates a period of building at about 35 feet above 

 the present sealevel, followed by a rise of the water level of about 5 

 feet, the whole indicating clearly a water body north of the main 

 moraine at about 40 feet above the present sealevel. 



The ice front had now evidently retreated along a part of the 

 line somewhat north of its position at the Port Washington stage. 

 That this retreat was not without slight advances, is probably indi- 

 cated by the evidence of rising water level in the College Point 

 delta ; but the opening of crevasses in the ice margin and their sub- 



