minerals. Widely scattered samples from the same horizon are then examined for similar 

 minerals or suites of minerals. Whether this procedure could be used to define certain beds 

 occurring throughout Long Island, is a matter upon which one can only speculate at present 

 since neither the facilities nor time have been available to make a large scale study of this 

 type. If the heavy mineral composition varies as much from place to place horizontally as does 

 the lithology, particularly in the case of the Magothy ( ?) formation where the need for differ- 

 entiation is greatest, then this technique will be of little value in future correlation studies. 



Electrical logging: Electrical logs have recently been procured for a few deep wells. 

 These have not yet been studied in sufficient detail to determine their usefulness in geologic 

 classification of the Long Island sediments. Thus far a preliminary examination of these logs 

 has not yielded much additional information beyond a differentiation of the log into major 

 geologic units which can also be readily determined from well samples. Electric logs can only 

 be obtained from uncased rotary wells. 



Usually the first 100 or 150 feet of record are missing due to the installation of casing in 

 rotary-type wells to prevent caving at the surface. In some instances this prevents logging 

 of the critical Pleistocene-Cretaceous contact. Electrical logs also record the relative salinity 

 of the water-bearing formations since the conductivity of the strata will vary directly as the 

 chloride content of the formation water. Electrical logging might be of assistance in corre- 

 lating certain beds within the Magothy (?) formation but here again the rapid lithologic 

 variations horizontally characteristic of this formation cast considerable doubt upon the 

 feasibility of this method. Logs are now available for wells at Long Beach, Westbury, Baldwin, 

 and Bay Park in Nassau County and for two wells at the Brookhaven National Laboratory 

 in central Suffolk County. 



The logs of some of the deep abandoned cased wells in Kings County and elsewhere 

 might be checked by radioactivity logging but would be handicapped by lack of basic control 

 data to interpret a log of this type on Long Island. 



STRATIGRAPHY 



Long Island is composed of consolidated rocks overlain by loose unconsolidated sediments. 

 The consolidated rocks are dense metamorphic and igneous basement rocks of pre-Cambrian 

 age. The unconsolidated sediments overlie a southeasterly sloping bedrock platform, and consist 

 of upper Cretaceous and Pleistocene sands, gravels, and clays. (See table 1, Stratigraphic 

 Sequence for Long Island). 



The Cretaceous sediments rest directly upon bedrock and are divided into the Raritan 

 formation and the overlying Magothy ( ?) formation. The Raritan formation which has long 

 been recognized as the equivalent of the Raritan formation of New Jersey, is composed of a 

 sand member (Lloyd sand member) and a clay member both of which are widely distrib- 

 uted on Long Island. The Magothy (?) formation, which consists of a great thickness of 

 alternating fine sands, clays, silts, and some coarse beds of sand and gravel, is thought by 

 some geologists to represent a northeasterly thickening of the Magothy formation of New 

 Jersey. This correlation has never been satisfactorily established and it is probable that the 

 so-called Magothy formation of Long Island includes not only the equivalent of the Magothy 

 formation of New Jersey but also some of the younger Cretaceous beds in New Jersey. The 

 primary reasons for the failure to solve this problem are the marked change in lithology 

 between the Cretaceous beds of Long Island and those of New Jersey and the lack of paleon- 

 tological data in the Long Island sediments. 



No definite occurrences of Tertiary strata are indicated by present evidence, but their 



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