In spite of the large amount of data collected by the earlier geologists and engineers, there 

 was still much work to be done. It was apparent that there were many places on Long Island 

 where geologic and hydrologic data were either lacking or were too vague to be of any real value. 

 In 1932, as a result of severe drought conditions and the salting of water-bearing beds in Brook- 

 lyn due to overpumping, the U. S. Geological Survey in cooperation with the State of New York 

 and Nassau and Suffolk Counties, began a systematic and continuous investigation of the ground- 

 water resources of Long Island. A part of this work has consisted of the collection and inter- 

 pretation of geologic data from well logs and well samples, and the publication of records of 

 significant wells drilled since 1906. 



Purpose and scope of present report 



The tables accompanying this report contain geologic correlations and classifications ac- 

 cording to aquifer of most of the important and representative wells drilled on Long Island, and 

 include many of the wells published in the early reports of Veatch, (9) Fuller, (15) and Crosby,^ 

 (11) ; as well as most of the wells published by the Water Power and Control Commission since 

 1937. (30, 34, 35, 36, 53, 55, 59, 62). Correlations for about 2,000 wells are included in these 

 tables. In this report, a geologic correlation of a well is defined as an attempt to group all of 

 the sediments penetrated by a well into specific geologic units. This is shown in the correlation 

 tables by indicating the contacts between the surfaces of the various stratigraphic units in 

 terms of mean sea level. This report, which describes the water-bearing formations of Long 

 Island is followed by a report of the geologic history of Long Island. 



Cross-sections and contour maps have been prepared which show the thickness, geologic 

 structure and distribution of the major geologic units found on Long Island. These have been 

 drawn by the New York Water Power and Control Commission with the assistance and guid- 

 ance of the writer and Wallace de Laguna of the Geological Survey. Many of the geologic corre- 

 lations included in the accompanying tables were made by various members of the U. S. Geo- 

 logical Survey who have worked on Long Island at one time or another since 1932. During the 

 early years, the studies were made by D. G. Thompson, F. G. Wells, Watson Monroe, and H. R. 

 Blank. The geologic work was continued by R. M. Leggette, M. L. Brashears, Jr., and C. M. Rob- 

 erts. In the fall of 1946, the authors began a re-study and re-evaluation of all of the earlier cor- 

 relations and have prepared original correlations for many wells drilled since 1938. 



PHYSICAL GEOLOGY 

 Units of Correlation 



Keeping in mind the limitations imposed by the nature of the data and the necessity for 

 utilizing the results of this report for hydrologic studies, the geologic units shown in Table 1 

 were selected and found to be most practicable. 



Each of the units has a common geologic origin, representing material deposited at approx- 

 imately the same time by a common agency of deposition. A variety of materials may be present 

 in each unit but each consists predominantly of a specific lithologic type such as the Jameco 

 gravel, or the clay member of the Raritan formation. The units may comprise part of a single 

 geologic formation as in the case of the Lloyd sand member of the Raritan formation. Or the 

 unit may consist of several formations of a similar lithologic nature as in the case of the upper 

 Pleistocene deposits, which include all material laid down after the close of Jacob time. 



The selection of the geologic units here used is based to some extent on the fact that almost 

 all of the available information is in the form of logs, compiled by well drillers and supplemented 

 by a smaller number of logs compiled by geologists from microscopic examinations of well samples. 

 Subdivisions of the geologic column therefore depend largely upon lithologic differentiation, 

 general stratigraphic relationships, and mineralogical composition. In most instances standard 

 correlation criteria such as fossil and mineral content, grain size, color and sorting were not 

 available since this type of information is not included in ordinary well logs. A great deal of 



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