The upper Cretaceous beds that underlie the glacial depoaita on most of 

 Loiig Island and crop out in some places are also of iiEportanc® because of their 

 influence on the coiofigtiration of the main water table ^ The uppermost beds of 

 that series^ -which are s-epposedly of Magothy age^ coijoprise interbedded sands and 

 silts totalling several hundred feet in thickness^ Underlying these sands and 

 silts are clays assigned to the Raritan formation^ which in turn are underlain by 

 Hoyd sand^ also considered to belong to the Raritan fonaation* The Lloyd sand^ 

 an excellent water-bearing bed, rests unconformably an the ancient crystalline 

 rocks, and dips toward the southeast about 100 feet to the mile. The sands of 

 the Magothy f orsnation, as well as the Lloyd sand, all have the main water table 

 on Long Island as the source of their head# These sands unquestionably affect 

 the shape of the main water table* 



In many areas over the island it is difficult to establish the bottom of the 

 main water-table aquifer* 



EikELY GROUMWirATER RECORDS 



In 1851 water-level measurements were made in about 50 shallow wells in the 

 southern parts of Kings and Queens Counties* These were reported by McAlpine 

 (1) in 1852* However, neither the exact locations of the wells nor the dates of 

 neasuresients are Eiven* 



The earliest known contour map of the water table of ai^ part of Long Island 

 appeared in 1867 in a import by Kirkwood (2)* It covered the area lying between 

 Jainaica and HeB5)stead and extending about 8 miles inland from the south shore* 

 The aieasurements upon which this map was based presumably were made in the late 

 fall of 1859 or the early spring of 1860 (3)* In 1854 Stodda37d (4) reported 

 elevations of the water table at several wells in Brooklyn in connection with a 

 study of possibilities of water supply from undergrotmd sotirces in that area* 



