<)3*> NKW YOKK STATE MUSEUM 



Long Island sound. Tlio inference is that at a time immediately 

 before the last advance of the ice the area was exposed to ordinary 

 stream action Oj^ening out valleys on the gravels and sands, the 

 mouths of these streams reaching the sea below the present sealevel. 



There are other evidences, liowever, which show that ice action 

 lias considerably modified and enlarged certain of these valleys. 

 Such enlarged valleys constitute the bays and harbors of the north 

 shore. These harbors have thei-r bottoms 27 feet below sealevel in 

 IIem]>stead bay, (Jl feet in Oyster bay and 33 feet in Manhasset 

 bay. This depth in each case is probably less than the original depth 

 of the depressions, for there has been some infilling by glacial 

 deposition — prol)ably small as judged by the tilling in of valleys 

 extending above sealevel — and some infilling through post-glacial 

 deposition by tides and currents. Arguments for the excavation of 

 these embayments subsequent to the formation of the Columbia 

 gravels and sands have already been given on p. G28. Homologous 

 depressions occur eastward on this island in Coldspring and North- 

 port harl)ors. They are also found on Marthas Vineyard in Lagoon 

 pond and Menemsha pond, and on Block island in Groat pond. 



As to the period of this valley-making, excepting the modification 

 and enlargement by ice action, it is clearly older than the main 

 or inner moraine at Roslyn, a deposit believed to be equivalent to 

 the Cape Cod moraine. Whether the stream erosion preceded or 

 followed thr)se fraguients of an older moraine which on this sheet 

 mark the western extension of the outer or Nantucket moraine, 

 appears to be locally undeterminable, because the two sets of phe- 

 nomena are not found in association. If a comparison with Marthas 

 Vineyard and Block island holds good, the erosion of the valleys 

 should l>e here as there anterior to both moraines. In all of these 

 New Flngland islands, the valleys do not occur as such on the south 

 of the moraines, because that area has been buried beneath the out- 

 wjuih plains of the first or outer moraine on the eastern islan<ls and 

 of l)oth the first and second, or inner and outer moraine on Long 

 Island. 



The time involved in the excavation of these valleys is indetermi- 

 nate. They are largely excavated in gravels and sands of a porous 

 structure. Much of the existing rainfall passes through the 



