PLEISTOCENE GEOLOGY OF NASSAU CO. AND BOROUGH OF QUEENS 637 



deposits where clays do not occur, finding its way out near sealevel 

 in springs, as in the village of Oyster Bay. At best, surface streams 

 would have cut but slowly on these deposits, as they do now, the 

 excavation in post-glacial time being practically nothing in the form 

 of mechanical abrasion. 



The share which the ice and the subglacial streams may have had 

 in the excavation of the harbors, is discussed in connection with the 

 moraine on p. 643. 



Wisconsin epoch. Moraines and attendant sand plains. 

 The existence of two lines of moraines in this area has already been 

 set forth in the account of the topography. Both of these deposits 

 are largely composed of materials which have been water-worn, 

 in this feature rellecting the nature of the terrane from which the 

 materials were eroded and on which they were deposited. The ice 

 sheet on leaving the bed rocks of the mainland and the north shore 

 of what is now Long Island sound passed over tlie Columbia gravels 

 and sands, gathering debris from these older water-worn deposits ; 

 hence the water-worn pebbles which abound in the moraine even 

 when the materials are truly ice-laid without stratification. True 

 boulder clay occurs in small patches, but much of the till is sandy, 

 and even in its coarser phases often exhibits traces of water action 

 closely followed by a shoving of the deposits into contorted drift. 



The outer deposits consist of a few low knobs rising like kames 

 from the surrounding gravels. They bear a few boulders on their 

 surface and frequently in road cuts reveal a tliin patch of till. 

 West of Searington rolling surfaces of till composed of a gravelly 

 boulder clay give the deposit, along with its steep southerly front, 

 something of the aspect of the main moraine as it exists southwest 

 of Lake Surprise. These knobs and their rare attendant basins have 

 a much less strong development than those heavier accumulations 

 which lie in the form of a strong ridge immediately north of them. 

 The deposits do not afi;ord in themselves precise indexes of the posi- 

 tion of the ice front at the time they were made. They appear to 

 be submarginal deposits laid down when the ice front lay somewhat 

 to the south of them, and are best compared with the kame moraine 

 in the eastern part of Nantucket. 



The inner or main moraine exhibits likewise the two phases of 



