In northern Kings and northwestern Queens Counties, where bedrock lies close to the 

 surface and is overlain chiefly by coarse glacial deposits, drillers occasionally confuse large 

 buried glacial boulders with the bedrock surface. 



The strike of the buried surface of the bedrock floor is approximately northeast-southwest. 

 It has a dip of about 80 feet per mile, and a relief of as much as 100 feet in the northwestern 

 part of the Island (64). The strike assumes a more easterly direction toward the eastern part 

 of the Island and the relief is probably considerably less where the Cretaceous covering has 

 protected the surface from glacial scouring. In general, the bedrock surface is a gently inclined 

 southeasterly sloping peneplain. 



In Kings County, well records indicate bedrock ranges in depth from about 50 feet to 

 700 feet below sea level. It crops out at the surface in Queens County near Long Island City 

 and Astoria, and dips to about 1,100 feet below sea level in the southeastern part of the County. 

 In Nassau County its depth ranges from about 160 feet to an estimated depth of about 1,800 

 feet below sea level, increasing toward the southeast. Beneath Suffolk County, bedrock ranges 

 in depth from about 400 feet below sea level at Lloyd Neck to an estimated depth of about 2,200 

 feet in the south-central part of the County. 



Most wells which tap bedrock usually produce water of poor quality and insufficient 

 quantity. The occurrence of a good supply depends upon the penetration of water-bearing 

 joints and fractures, whose locations are impossible to predict in advance. Bedrock wells on 

 Long Island are few in number and are confined almost entirely to the industrial sections of 

 Long Island City and Astoria in northwestern Queens, where bedrock lies close to the surface 

 and only a thin veneer of impermeable till overlies it. The salinity of the water in most of the 

 rock wells near the East River is high but some wells yield fresh water. Drilling several hundred 

 feet into bedrock has usually proven to be a fruitless task since bedrock is the lowest limit 

 of profitable drilling for water on Long Island. 



Upper Cretaceous deposits 



The Upper Cretaceous deposits on Long Island are represented by the Raritan formation 

 and Magothy ( ?) formation. It is usually possible to distinguish between these two formations 

 in well logs. This is not always the case, however, since the distinction is primarily lithologic 

 and is subject to some variation depending upon local depositional environment. The contact 

 is commonly marked by a change from the basal coarse sands and gravels of the Magothy ( ?) 

 formation to the solid clays of the Raritan formation. This problem is further discussed in 

 the detailed descriptions given below. 



The contact between the Pleistocene and the Cretaceous deposits is an erosional uncon- 

 formity with considerable relief and in most places is marked by an abrupt lithologic and 

 mineralogic change. In some places, the mineralogic differences provide the best evidence, in 

 others the lithologic differences are more easily recognized. Since the determination of the 

 depth of this contact and the lithologic and mineralogic differences on either side of it is of 

 considerable importance, some of the major criteria used in establishing the contact will be 

 emphasized. 



A common feature helpful in establishing the contact surface, is an abrupt change from 

 the coarse clean sands and gravels of the Pleistocene to the silty clays, fine sands, and solid 

 clays of the Cretaceous. The Cretaceous sands are composed of minerals which have been sub- 

 ject to long weathering and consequently consist only of chemically stable minerals or the 

 highly altered equivalents of the less stable minerals. The chief mineral constituents are angular 

 quartz grains with much smaller quantities of tourmaline, rutile, zircon, kaolin, partially or 



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