S02 H. L. FAiRCHiLi) POST-GLACtAL SUBMERGENCE OF LOi^G ISLAND 



The only conspicuous shoreline is the clifflike front of the moraine on 

 Staten Island and on Long Island as far northeast as the meridian of 

 Manhasset. There now seems little doiiht that this is an erosional fea- 

 ture. The conditions favoring erosioTi appear to have been: (1) Less 

 amount of outwash ; (2) steeper original front of the moraine; (3) 

 deeper offshore waters, and (4) perhaps exposure to stronger winds. 

 Over most of the island the offshore waters were shallow and weak and 

 could do no more than distribute the detritus. Near Brooklyn the ap- 

 parent cliff probably represents the advanced position of the ice-front. 

 While the waves in the Southampton -Bridgehampton district were level- 

 ing the deserted moraine the Avaters in the Brooklyn- Jamaica district 

 were prol)baly eroding the bold front of the heavy moraine. From Queens 

 to Lake Surprise the base of the cliff has been buried by the heavy out- 

 wash of gravel. 



ABSENCE OP MARINE FOSSILS 



This has never been seriously urged as an objection to marine origin 

 of the Long Island plaiiis, as it is recognized that great sand terranes 

 are sometimes entirely devoid of organic remains; but it has been used 

 as objection to marine genesis of the Hudson Valley deposits. 



The writings of Lewis contain references to marine shells being found 

 on the island ; but these occurrences are not described and some of them 

 are much above the marine plain. As shells occur in the pushed-up drift 

 of the moraines, and even masses of beach deposit composed largely of 

 marine mollusks occur associated with Pre-AYisconsin clays in the heart 

 of the moraines, it is probable that all of Lewis' fossils are older than the 

 frontal plain. Watson also speaks of shells, some being found in the 

 "channels.^' No value is placed on these accounts, and the chances are 

 small of ever finding any fossils in the sand-plain. It is possible that 

 they may be found in some quiet-water deposits in the moraine valleys. 



Explanation for the lack of marine fossils in the Hudson Valley has 

 been already published (28, page 242; 30, page 4). All the earlier and 

 higher waters of the Hudson-Champlain inlet and strait were confluent 

 with the sea, but not saline. The Hudson today is sealevel, but brackish 

 only to about the highlands. As long as the glacier front excluded the 

 marine waters of the Saint Lawrence Gulf, all the flood now represented 

 by the Saint Lawrence River, as well as the large volume from the melt- 

 ing ice, was forced soutli through the narrow passes at Whitehall and at 

 West Point. With this flow of fresh water it would appear quite impos- 

 sible for saline water and marine fauna to enter the Hudson Valley, and 

 before this flow ceased the lower Hudson Valley was partly, if not fully. 



