34:2 Geology of Long Island. 



Astoria to Orient Point. These two ranges of hills are the re- 

 sult of glacial action, and the more southern chain marks the 

 southern limit of the drift. 



Upham and others, in speaking of these ranges, have called 

 them moraines. If the word moraine is to be thus used, and 

 present custom in the United States appears to sanction the use, 

 it must be taken in a different sense from that accorded to it in 

 most regions of glacial action. In Switzerland and other moun- 

 tainous countries, the term is applied to great accumulations of 

 boulders and rock detritus, piled up along the sides or front of 

 a glacier. Throughout most of Long Island and at many points 

 on the New England coast, however, the thickness of the drift 

 on the ridges marking the southern limit of glacial extension is 

 very slight and in some cases it is wanting. In these cases, the 

 term moraine would be synonymous with the southern limit of 

 the continental glacier. 



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

 the surface is nearly level, gently sloping southward in an unbro- 

 ken gravelly plain ; while between this ridge and the north shore 

 is a second plain with an elevation of 50 to 100 feet, and espe- 

 cially noticeable between Port Jefferson and Eiverhead. 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 Riverhead, have been ex- 

 plored by Mr. Elias Lewis, Jr., of the Long Island Historical 

 Society.* He finds them to average about 25 feet in depth and 

 to be occupied usually by small streams most of which flow south- 

 ward. These valleys are evidently the beds of rivers formed by 

 the melting of the ice sheet in the Champlain Period. 



There are no important lakes or rivers now on Long Island, 

 but there are numerous ponds of clear cool water, without visi- 

 ble inlet or outlet. The existence of these ponds depends on the 

 fact that in the stratified sands of the island, which are under- 

 lain by clays, a uniform water-level, or plain, exists, f which 

 rises northward from low-tide-level on the south shore at the 

 rate of 12| feet per mile. Wherever a basin has been excavated 



* Am. Jour. Sci., Series III, Vol. XIII. 

 f Dana, Manual of Geology, p. 664. 



