Clay member — Queens County: The clay member appears to underlie the entire County 

 with the exception of parts of the northwestern section of the County, and in the vicinity of 

 the mouth of Flushing Bay. Test borings in this area, at La Guardia Airfield, revealed glacial 

 sands and clays resting directly upon bedrock. 



The elevation of the upper surface of the clay member varies from about 25 feet above 

 sea level in northern Queens County to about 600 feet below sea level at Far Rockaway. Its 

 thickness ranges from about 30 to 300 feet, increasing toward the southeast. 



Clay member — Nassau County: Except for scattered erosional irregularities in and around 

 the north shore necks, the clay member extends throughout the remainder of Nassau County. 

 It appears to be completely eroded beneath parts of Great Neck and the northern part of Man- 

 hasset Neck. These old erosional channels, now filled with younger permeable deposits, readily 

 permit downward percolation of water into the underlying Lloyd sand. In at least one area. 

 Port Washington, heavy pumping from Lloyd wells has caused an inflow of sea water through 

 these old channels. Extensive buried valleys in the Raritan clay member may exist in other 

 areas but available data is too meager to determine their existence, if they do exist. The top 

 of the clay member ranges from about 16 feet above sea level at Great Neck to about 1,100 

 feet below sea level on the barrier beach in southeastern Nassau County, and its thickness 

 ranges from about 60 feet to 300 feet. 



Clay member — Suffolk County: Only a very limited amount of data concerning the clay 

 member is available for Suffolk. Deep wells, which penetrate the clay, are confined to the 

 northwestern corner of the County, two wells at Brookhaven National Laboratory in central 

 Suffolk County, and two wells on the north fluke at the northeastern end of the Island. The 

 top of the clay here ranges from about 100 to 1,400 feet below sea level. The thickness of the 

 clay ranges from about 100 to 300 feet. The accompanying contour map of the top of the clay 

 is of necessity highly generalized. It is quite conceivable that buried valleys which cut though 

 the clay may exist in the County but well data is too meager to permit the identification of 

 such features. 



Magothy (?) formation 



The beds included within this unit represent the uppermost Cretaceous deposits on Long 

 Island. The application of the name Magothy to these beds originated largely through the work 

 of some of the early investigators who believed that they represented a northeasterly thick- 

 ening of the Magothy formation which crops out in New Jersey. The question mark following 

 the term Magothy indicates the present uncertainty regarding the exact geologic age of the 

 great thickness of sediments on Long Island included within the term. Inability to differentiate 

 the unit at this time has greatly influenced the decision to continue the use of the questionable 

 term Magothy ( ?) formation in this report. 



The Magothy ( ?) deposits consist chiefly of fine clayey sands, fine sands, silts, layers of 

 solid clays, and several coarse water-bearing zones composed of sand and gravel. The most 

 commonly observed colors of the beds are light and dark gray, brown, buff, yellow, and occa- 

 sionally some red and pink layers. The thickest and most extensive of the water-bearing zones 

 occurs in the lower part of the Magothy (?) formation, just above the Raritan clay. 



The Magothy (?) consists almost entirely of angular clear quartz and contains small 

 amounts of chert, kaolin, partially kaolinized muscovite, and dark heavy minerals. The coarser 

 beds commonly consist of subangular to rounded milky quartz pebbles. Lignitic material is a 

 fairly common constituent of the deposits along the south shore. The lignite may be brown or 

 black, may consist of tiny particles or large chunks in which the original fibrous structure of 

 the wood is still very apparent. Pyrite or marcasite, a brassy, metallic-looking sulphide of iron 

 is frequently associated with the lignitic material as scattered nodules or in thin solid layers. 



18 



