appear to be present in southern Nassau County. The upper surface of the formation ranges 

 from about 220 feet above sea level in east-central Nassau to about 150 feet below sea level 

 at Long Beach. Its thickness ranges from about 60 to 800 feet. In many parts of Nassau County, 

 where the Gardiners clay is missing, the upper beds of the Magothy are in contact with and 

 closely connected hydrologically with the overlying beds of Upper Pleistocene age. As a result 

 the ground water in the Magothy frequently exists under water-table conditions and does not 

 exhibit artesian conditions common to the lower beds of the Magothy. 



More wells have been drilled into the Magothy ( ?) formation in Nassau County than in 

 any other part of Long Island. The coarse beds just above the Raritan clay are tapped by 

 many public supply wells, particularly those for the principal south shore communities; as 

 at Freeport, Rockville Center, Lynbrook, and Valley Stream. The increase in withdrawals by 

 these rapidly growing communities may cause an inflow of sea water in the future as the salt 

 water has already been drawn into the Magothy beneath the Long Beach area to the south. 



Magothy (?) fortnation — Suffolk County: Except for the western part of the County, 

 limited areas along the southern barrier beaches, and a small area in the vicinity of the Brook- 

 haven National Laboratory in the central part of the County, little is known of the topography 

 and depth of the upper surface of the Magothy (?) formation. Outside of these areas infor- 

 mation as to the depth of the Magothy consists of widely scattered well logs which make it 

 impossible to contour the surface beyond Lake Ronkonkoma, with any degree of certainty. 



The high Cretaceous terrace which exists in eastern Nassau County continues eastward 

 into Suffolk where at places such as in the West Hills area it rises more than 300 feet above 

 sea level. East of the West Hills area, the surface of the Magothy descends gradually and lies 

 below sea level in the eastern half of the County, except for the region near Port Jefferson. 

 There, evidence from a few wells indicates that the Magothy surface rises somewhat above 

 sea level in a small area. It seems probable that most of the high ground in the eastern part of 

 Suffolk County consists of Upper Pleistocene rather than Cretaceous deposits. 



Buried valleys of pre-Pleistocene age may exist in several places in the County but the 

 details of these important buried features can only be brought out by a widespread pro- 

 gram of test drilling. A suggestion of such a valley is indicated by the unusual thickness 

 of the upper Pleistocene deposits in the Nissequogue River Valley near Smithtown. Along 

 the south shore of Suffolk County, considerable doubt exists regarding the depth of the 

 top of the Magothy. This situation is due primarily to lack of well samples. Because of the nature 

 of the sediments the age of these deposits cannot be easily established from a study of well 

 logs, but must be based on detailed microscopic studies of the mineral and fossil assemblages 

 in the sediments in that area. Only well logs are now available. 



In the western part of Suffolk County, many domestic wells draw water from thin coarse 

 zones in the upper part of the Magothy (?) formation. Private companies seeking larger 

 quantities of water for public supply purposes, generally have to drill wells several hundred 

 feet or more in depth before a satisfactory zone is penetrated. A test well at Brookhaven 

 National Laboratory showed that large supplies of fresh water are available from the lower 

 part of the Magothy ( ?) formation in central Suffolk County. 



The top of the buried Magothy surface ranges from about 300 feet above sea level in the 

 West Hills to an unusual depth of 250 feet below sea level at one locality on the south fluke. 

 The thickness of the Magothy increases from about 230 feet in northwestern Suffolk to about 

 1,000 feet in the southeastern part of the County. 



Jameco gravel 



The Jameco gravel is considered to be one of the earliest of the Pleistocene outwash 

 deposits on Long Island. Some indications of an older deposit, the Mannetto gravel, have been 



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