DESCRIPTION OF FORMATIONS AS MAPPED 



ROCK SURFACE 



Except on the western end of the island there is little data with regard to the depth to rock 

 and about all that it is possible to do is to hang the whole eastward extension of the contours on 

 the wells at Coney island, Long Beach, Brookhaven Laboratory, Greenport and Orient point 

 and to draw them approximately parallel to the Connecticut shoreline. 



The result is a concave surface sloping to the south and east from the rocky shore of 

 Connecticut. On the island the only outcrops are along East river in Long Island City. This sur- 

 face has a dip of about 70 feet to the mile and the deepest point at Sayville is at about Elevation 

 —2100. 



This is an extension of the rock surfaces in Manhattan, Westchester county and Connecti- 

 cut. It may be that it is as rough as it is in those localities. This is true of the western edge of the 

 island where the only real attempts at drawing accurate contours have been made (GW-2 and 

 13). 



It is known that the depression of East river was caused by solution of dolomitic limestone 

 involved in two folds and faults, one on either side of Welfare island (12). Tunnels under the 

 river have shown this solution of the limestone at very considerable depths and it has caused a 

 good deal of trouble even during the excavation of the deep city water tunnels. 



A study of these contours seems to indicate that East river is paralleled by a somewhat 

 similar depression further to the southeast end at a lower elevation. 



Determination of these contours is complicated by the fact that frequently there is doubt 

 as to whether the reported rock was the top of the solid rock or of the decayed rock, which last 

 in many cases is of considerable depth. Doubtless, the ordinary driller would report only solid 

 rock, but this doubt is always present. 



It is thought that in Long Island City the Lloyd and Raritan may never have been deposited. 

 Down towards Coney Island along the tip of the Hudson gorge deposits of these formations 

 have not been identified, but they may have been deposited there and subsequently eroded away. 



Running south from Brooklyn Navy Yard there seems to be a rock ridge which is covered 

 by a hill composed of Magothy, Jameco and Gardiners formations with a possibility of Raritan 

 and Lloyd underneath. The persistence of this hill through a number of strata suggests that the 

 ridge may be wider and longer than shown here, thus making it a better base for a hill. 



In general this rock is gneiss with interbedded Inwood limestone and in the northwesterly 

 corner there is a heavy intrusion of diorite. 



This underlying rock does not appear to be capable of carrying water except in small 

 amounts seeping through cracks along East river, nor does it appear that faults cut by the city 

 tunnel under Long Island were pai'ticularly wet (Berkey and Blank — City Tunnel No. 2). 



LLOYD GRAVELS 



This formation appears to underly the entire island except at the extreme west end. The 

 limit at present is roughly a line from Flushing bay to Coney Island. It is thought that these 

 gravels were never deposited in the northwesterly end of the island, but perhaps they may have 

 been deposited and then eroded off farther to the south. The upper surface of this formation 



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