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NEW YORK STATE MUSEUM 



island. The highest points of this ridge arc about 050 to 390 

 feet above sea level. This ridge, which is believed to be a part 

 of the terminal moraine of the great glacier, consists mainly 

 of compact drift and bowlders, running at times into clay and 

 coarse gravel. The considerable number of small ponds along 

 the ridge evidence the compactness of its surface material. The 

 slopes and spurs of the central ridge run into Long Island 

 sound on the north, making an irregular shore line, broken 

 into bays and low headlands. On the south side, the slopes 

 lose themselves in a grassy plain sloping gently toward the 

 coast. In its widest part it is called the Hempstead plains, and 

 stretches for a distance of from 5 to 15 miles between the foot 

 of the central ridge and the Atlantic shore, which is very regu- 

 lar in its outer beach line; but an inner and more irregular 

 beach exists, formed by the shallow waters of Jamaica and 

 Hempstead bays. The Atlantic shore does not anywhere touch 

 the slope of the central ridge, but is separated from it by the 

 wide gravelly plain. 



In 1000 Prof. W. O. Crosby reported in relation to the geology 

 of Long Island and its relations to public water supplies, the 

 main purpose of this study being to determine what light the 

 present knowledge of the geologic structure of Long Island 

 throws upon these problems. The main questions considered 

 were : 



1) Is it possible to obtain a copious supply of water from 

 deep wells on Long Island, 200 feet or more in depth, passing 

 through the blue clay into the gray gravel and the still deeper 

 water-bearing strata of the cretaceous? A supply of quality 

 suitable for domestic purposes and in quantity sufiicient for a 

 substantial addition to Brooklyn's water supply, say 10,000,000 

 gallons, 25,000,000 gallons, 50,000,000 gallons, or more per day, 

 or the equivalent of the yield of a catchment area of 10, 25, 50 

 or more square miles? 



2) What certainty or probability is there that wells 40 to 

 80 feet deep, sunk in the yellow gravel but not penetrating the 

 blue clay, in the region east of Massapoqua, can be made to 

 yield water of suitable quality for domestic supply and in quan- 

 tity equal to the total average catch of rainfall on a catch- 



