completely kaolinized muscovite, and weathered white chert grains. Carbonaceous material as- 

 sociated with pyrite or marcasite is commonly observed in Cretaceous samples. 



Although the Pleistocene deposits are chiefly characterized by coarse texture, they may 

 also consist in part of sandy clays, solid clays, and fine sands. When these materials overlie sim- 

 ilar Cretaceous deposits, it is very difficult to determine the Pleistocene-Cretaceous contact 

 from a well log without the aid of samples. Glacial sands may contain all the minerals found 

 in the Cretaceous sediments, and in addition usually contain a significant amount of rock frag- 

 ments such as gneiss, schist, granite, pegmatite, diabase, sandstone, limestone, shale ; and min- 

 erals such as amphibole, pyroxene, fresh muscovite and biotite, chlorite, and unweathered 

 feldspar. Some of the glacial clays contain shell fragments, partially carbonized wood or other 

 fairly fresh organic material. 



Careful interpretation is called for where only a small amount of typically Pleistocene ma- 

 terial is present since the glacial deposits in some localities may be composed of a large per- 

 centage of re-worked Cretaceous material. Contamination of samples is another factor which 

 also must be kept in mind in correlating well samples. This is more fully discussed under meth- 

 ods of well drilling. 



Color alone is not a sufficient criterion for differentiating between Cretaceous and Pleisto- 

 cene deposits. In general, the Cretaceous sediments are light or brightly colored except where 

 a high percentage of lignitic material imparts a dark gray or black color. Most of the glacial 

 sands are rusty brown in color due to iron staining but they may also be gray, white or tan in 

 color. Brown iron-stained zones are also frequently observed in the Magothy ( ?) formation, 

 and therefore it should not be taken for granted that a brown colored sand is Pleistocene in age. 

 Red has often been considered a characteristic Cretaceous color but some of the late Pleistocene 

 till deposits in Kings and Queens Counties, and other Pleistocene clays are also reddish colored. 

 Green-colored clays may result from the presence of large amounts of glauconite or chlorite and 

 may be of Pleistocene or Cretaceous age. Some of the residual clays resulting from the weather- 

 ing of the bedrock are also greenish in color due to the presence of chlorite, hornblende and 

 other green-colored mineral constituents of the original rock. 



^ Rari+an formation — Lloyd sand member *-''''-*' " 



The lower water-bearing sandy portion of the Raritan formation is referred to as the Lloyd 

 sand member of the Raritan. It was first defined by A. C. Veatch (9) , who named it after Lloyd 

 Neck, a locality in northwestern Suffolk County where several old wells derive water from this 

 aquifer. The Lloyd sand member does not crop out at the surface anywhere on Long Island. It 

 extends an unknown distance northward beneath Long Island Sound where it is probably over- 

 lain by younger Cretaceous, Pleistocene, or Recent sediments depending upon how much erosion 

 occurred during or after Cretaceous time. The upper surface of the Lloyd slopes in a southeast- 

 ^ly direction. It varies in thickness from about 20 feet in northwestern Queens to about 300 feet 

 or more in southeastern Suffolk County. 



The water-bearing zones in the Lloyd sand member consist of medium to coarse sands and 

 fine to medium gravels. They consist almost entirely of clear quartz. The coarser particles com- 

 monly exhibit a sub-angular to rounded water-worn appearance. Lithologically the Lloyd 

 varies from beds of fairly clean coarse sand and gravel to fine sandy clay, clayey sand, and very 

 thin layers of clay. The amount and nature of the clay present varies considerably from local- 

 ity to locality. The coarse zones in some places do not yield as much water as might be expected 

 due to the presence of much clay in the pore spaces between the coarse material which reduces 

 its permeability considerably. This is exemplified by test wells recently drilled at the Brook- 



