before drilling deeper. It is believed that the correlations for a number of the earlier deep 

 wells were based upon examinations of much contaminated rotary well samples. This has led 

 to considerable confusion in interpreting well logs, particularly in Kings and Queens Counties. 



Jetting methods: Much of the data available for the northern parts of Kings and Queens 

 Counties are based upon information from test borings for City Tunnels 1 and 2. The primary 

 purpose of these borings was to determine the depth and character of the bedrock. The casings 

 in many instances were washed in rapidly with relatively little attention being given to the 

 details of the overburden. These logs, therefore, lack the details found in logs of water wells 

 where the record of the overburden is of major importance. 



Drive-point method: Where the water table is close to the surface and a small supply of 

 water is desired for domestic purposes, small diameter wells are frequently constructed by 

 driving a well-point and attached pipe to relatively shallow depths. Many wells of this type 

 have been driven along the south shore of Nassau and Suffolk Counties. Little information of 

 geologic importance can be obtained from the records of such wells. 



Other aids to correlation 



Hydrology: Much hydrologic information in the form of pumping test data, interference 

 studies, and hydrographs from automatic water-stage recorders has been obtained by the 

 Geological Survey. In most instances the hydrologic data substantiates geologic correlations. 

 Hydrologic interference between wells screened in the Jameco gravels in Kings and Queens 

 Counties has been recorded on many occasions by the Geological Survey (68). Mutual inter- 

 ference has also been observed between several wells screened in the Lloyd sand member of 

 the Raritan formation in Queens and Nassau Counties by Leggette (32) . Jacob has also noted 

 a similar effect between Lloyd wells situated in the southern part of Queens and Kings Counties 

 (46) (49). In much of the remainder of Long Island, much hydrologic data has been obtained 

 in water-table wells. 



Paleontology: Fossils visible to the naked eye are rarely found in Long Island sediments. 

 Only in the case of the Gardiners clay, a marine inter-glacial deposit which contains shells, 

 shell fragments, foraminifera, and diatoms (33), has such evidence been of value for corre- 

 lation purposes. Fossil plant leaves, spores, and small pieces of lignite have been found in 

 many of the Cretaceous beds but these have not been studied in much detail. 



Marine Cretaceous fossils are rarely found in Long Island sediments since the formations 

 are predominantly terrestrial in character. A few specimens were noted in the early reports 

 of Veatch (9) and Fuller (15). In several instances it has been shown that some of the 

 "Cretaceous" fossils mentioned in these earlier reports are of Pleistocene rather than Creta- 

 ceous age. In addition, many of the Cretaceous fossils noted in other early papers on Long 

 Island geology have been found in Pleistocene drift deposits, and consequently are of no value 

 in identifying the strata in which they are found. In most cases, it has been found that the 

 presence of shells in a sediment is a fairly safe indication that the deposit is probably not older 

 than Pleistocene in age. It should not be assumed that all shell-bearing layers are from the 

 Gardiners clay, a subdivision of the Pleistocene, since shells are frequently found in later 

 Pleistocene sediments and also in recent clays. Shell-bearing layers from formations older 

 than Pleistocene in age may be found in unexplored parts of the Island but the data are 

 very meager. 



Heavy minerals: In some coastal plain areas where paleontologic data are scarce, heavy 

 mineral studies have been used to trace beds over somewhat limited distances. This technique 

 involves the separation of minerals from sand residues according to specific gravity of the 



II 



