clay itself. The Raritan clay has a low permeability but water may pass slowly through it, 

 and, because of the large area underlain by the Lloyd, the total amount of such seepage would 

 be considerable. A second possibility depends on the presence of areas in which the clay mem- 

 ber of the Raritan contains sufficient sand to appreciably increase its permeability, and so make 

 possible an easy movement of water into the Lloyd at these places. A third possibility, as 

 explained above, depends on the suggestion that there may be valleys cut through the clay 

 and now filled with sandy material of Magothy age. The answer to- this important problem 

 will have to agree with what is known of the geologic history of the Island and also with the 

 hydrology of the Lloyd sand. Up to now not enough data are available to determine the relative 

 importance of these three possibilities. The true picture, when it is determined, will have an 

 important bearing on the proper development of the ground water contained in the Lloyd. 



Following the presumed erosion of the upper surface of the Raritan clay the deposition 

 of sediments was resumed. In New Jersey, the deposit which overlies the Raritan is called the 

 Magothy formation, and the same name has been applied to the sands and clays which overlie 

 the Raritan formation in Long Island. This correlation has not been verified and indeed is 

 open to considerable question. In New Jersey, the Magothy formation has a thickness of 25 to 

 30 feet near the Delaware River which increases to about 175 feet near Raritan Bay 50 miles 

 to the northeast. On Long Island, 50 miles farther to the northeast, the so-called Magothy 

 formation has a measured thickness of nearly 1,000 feet even though the top of the formation 

 has been subjected to erosion. It cannot now be said whether the great increase in thickness 

 from a maximum of 175 feet in New Jersey to over 1,000 feet in Long Island represents an 

 actual increase in the thickness of the Magothy formation or whether the tentative correlations 

 on Long Island have through error included in the Magothy formation several younger beds. 



The problem actually is more complex than this. The great majority of the Upper Creta- 

 ceous formations which overlie the Raritan in New Jersey are unquestionably marine. The 

 beds contain marine fossils and glauconite, a mineral which is formed in the sea, character- 

 istically at depths of several hundred feet, and in areas where other sediments are not being 

 deposited. The individual formations in New Jersey can be traced over wide areas for the 

 composition and other characteristics are fairly constant. In these respects the New Jersey 

 material is so different from the so-called Magothy of Long Island, that it is doubtful if any 

 attempt should be made to apply the same formational names in both areas. Certainly the 

 conditions of deposition must have been very different. The Long Island material, lacking 

 glauconite and the marine fossils, and showing marked variation in detail over short horizontal 

 distances, may well be terrestrial rather than marine. Whatever its environment at the time 

 of its deposition, its rate of formation was probably more rapid than that of the New Jersey 

 material. 



Little can be deduced concerning the details of the deposition of the so-called Magothy. 

 In many places the lower part of the formation contains beds of very coarse sand or gravel, 

 not unlike those of the Lloyd sand member of the Raritan. However, existing evidence suggests 

 that these are not a continuous deposit for these beds are not encountered in all wells, and 

 even in those in which sand and gravel are found the thickness and relative depth are not 

 the same. In some areas there is a suggestion that the gravel lenses form a step-like series 

 down the dip, each lens overlapping the lens to the south of it, in much the same manner that 

 shingles overlap on a roof. Geologically this picture is logical for it duplicates in detail some- 

 thing of the pattern of overlap shown by the formations themselves. About the best that can 

 be said is that there are extensive beds of coarse sand and gravel near the bottom of the Magothy 

 and that this is therefore an important water producing horizon. As to the origin of the 

 gravels little can be said except that the coarse material suggests a comparatively steep 

 gradient and, at least from time to time, a rapid flow of water. The absence of all except the 



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