IV 



from 30 to 200 feet and almost continuous from Astoria to Orient Point. 

 These two sets of hills are the results of glacial action, and the more 

 southern chain marks the southern limit of the drift." Merrell shows 

 that this drift is quite thin in many places, and thus lacks in part one 

 of the characteristic features of a true terminal moraine. 



'' South of the backbone, as the central range of hills is called, the 

 surface is nearly level, gently sloping southward in an unbroken grav- 

 elly plain ; while between this ridge and the north shore is a second 

 plain, with an elevation of 50 to 100 feet. From many of the deep 

 bays on the north shore valleys extend through the hills in a southerly 

 direction. These depressions, thirty in number, between East New 

 York and River Head, average about twenty-five feet -i^ in depth and are 

 usually occupied by small streams flowing southward. These valleys 

 Merrell thinks are the beds of rivers formed by the melting of the ice 

 sheet in the Champlain Period. ' ' 



'* There are no important lakes or rivers on Long Island, but there 

 are numerous ponds of clear cold water, without visible inlet or out- 

 let. The existence of these ponds depends on the fact that in the 

 stratified sands of the island, which are underlain by clays, a uniform 

 water level or plane exists, f which rises northward from low tide level 

 on the south shore at the rate of 2j4 feet per mile. The largest of 

 these ponds is lake Ronkonkoma, which is three miles in circumfer- 

 ence and has a rafaximum depth of 83 feet. Thus we find a long, 

 low island with a prominent ridge nearer the north than the south with 

 long, low, sloping hills to the sea on the south. ' ' 



' * Stretching to the east of Long Island are a number of smaller is- 

 lands. Shelter, Robbins, Plum, Gull and Gardiner ; these are to be 

 considered as possessing the same physical or geological characteristics. 

 A still more interesting fact is that Block Island and Martha's Vine- 

 yard and Nantucket are thought to be of much the same character and 

 that we here see the remnants now overlain with moraine drift of 

 what was once a continuous tract of land. ' ' 



' ' The inroads of the sea combined with the gradual depression of 

 the coast has resulted in a submergence of portions of the fringe leav- 

 ing the higher parts in the form of islands." J 



^E. Lewis, Jr., Am. Jour, Science, Series III., Vol. 13. 



f Dana, Manual of Geology, p. 664. 



"j: A. H. Hollick, Observations on the Geology and Botany of Martha's Vineyard, 

 Trans. N. K Acad. Scz., 13, 1893, p. 8. 



N. S. Shaler, Report on the Geology of Martha's Vineyard, Seventh Annual 

 Report U. S. Geol. Surv., 1885-86. 



F. J. H. Merrell, Notes on Geology of Block Island, Trans. N, K AcacH. Sci.^ 

 15, P- 16. 



