generally follows the rock surface but with a slightly flatter slope (60 feet in a mile) . The thick- 

 ness increases towards the south and the thicker portions are, in places, divided by clay beds 

 into one or more separate aquifers. Not much is known about the Lloyd in eastern Suffolk, but 

 at Brookhaven Laboratory it is reported that the formation is present but is not a good aquifer. 

 The Lloyd has long been used as a source of water supply chiefly on the north shore from Flush- 

 ing to beyond Huntington and on the south shore on the beaches, particularly Rockaway and 

 Long Beach. In general these Lloyd wells have some artesian flow when first drilled. The south- 

 ern wells are apt to yield water with a high iron content which requires treatment. The Lloyd 

 well at Orient point is reported to be saline. As the Lloyd formation does not cross Long, Island 

 sound, it must, of necessity, terminate somewhere in that body of water. How freely it com- 

 municates with the waters of the sound has not been determined, but it is known that salt water 

 intrusion does take place in certain spots. There is no information as to how far out to sea this 

 stratum runs. It is possible that it extends all the way to the escarpment terminating the Con- 

 tinental Shelf. If this is the case, the outcrop probably would be at great depth and, if it follows 

 the known trend under the island, should be of great thickness. 



RARITAN 



The second member of the Raritan formation, officially known as the Raritan clay member, 

 lies on top of the Lloyd gravel and usually extends beyond it so that these clays constitute a 

 fairly effective seal except where erosion has removed it leaving the Lloyd exposed. The Rari- 

 tan probably once covered most of the island with a surface slope of about 60 feet to the mile. 

 Information with regard to it is scanty in Nassau county and almost absent in- Suffolk. As this 

 is not an aquifer, it is seldom drilled except for a well passing through it to the Lloyd gravel. 



This formation was exposed to erosion after it was laid down, was then deeply buried by 

 the overlying Magothy beds which in turn were heavily eroded. This second erosion exposed the 

 Raritan to the west of a line running from Oyster Bay to Coney Island except for certain isolated 

 patches of Magothy and other places where the rock surface was uncovered. Nowhere has it 

 been clearly demonstrated that the Raritan was eroded in such fashion as to expose the Lloyd, 

 but this almost certainly happened in the sound, in some of the north shore bays and perhaps 

 in the Gravesend region. 



After the main Magothy erosion, the exposed Raritan surface was further cut by outflow 

 streams from the subsequent glaciers. All these erosions have given the Raritan surface in 

 Queens and Kings a most complicated pattern which is particularly difficult to decipher at the 

 limit of the overlying Magothy. Little definite information is available as to the erosion of this 

 stratum where it is covered by the Magothy. Where it is not so covered it is described below. 



PRE-GLACIAL AND 

 MAGOTHY SURFACES 



According to the geologists, the Magothy strata were deposited all over the present island 

 in great depth. They extended northward into Connecticut. The subsequent Magothy erosion 

 removed vast quantities of this fresh deposit including all of it in Connecticut. The excavation 

 of Long Island sound, of the North Shore bays, numerous stream valleys along the south shore 

 and in the west end of the island exposed large areas of Raritan, rock and possibly Lloyd. This 

 resulted in a land mass somewhat similar to that now existing, except that it was lower by the 

 thickness of the glacial deposits. It probably had considerably more relief and variation of topo- 

 graphic features than the present island, and lacked the North fluke. The water parting was 

 probably about on the line of the older Wisconsin moraine, and there was a group of hills, still 

 visible, on or near the Nassau-Suffolk county line. 



To draw contours intelligently, it is necessary to attempt to restore the drainage plan. This 



174 



