variable thicknesses of glacial deposits or thin overburden of Holocene 

 mud (Fig. 3) (Taney, 1961; Williams, in preparation, 1976), 



Reddish-brown sandstones, siltstone and claystones, and extrusive 

 basalts of Triassic-Jurassic age crop out in a broad, north-south orien- 

 ted, half-graben structure from Massachusetts south through Connecticut 

 to Long Island Sound at New Haven. Because the Triassic province in New 

 Jersey is characterized by a complementary half-graben structure filled 

 with similar reddish-brown clastic rocks, Sanders (1960, 1963) has sug- 

 gested that Triassic strata are buried under parts of the western Long 

 Island and New Jersey Inner Continental Shelf. 



Upper Cretaceous-age semiconsolidated strata overlie the granitic 

 bedrock and dip and thicken to the southeast along the entire length 

 of Long Island. These formations (Table 1) consist primarily of silt, 

 clay, sand, and sandy gravels which were deposited in both marine and 

 nonmarine environments. The oldest unit is the Raritan Formation which 

 is composed of the basal Lloyd Sand Member and the Raritan Clay Member. 

 In Nassau County (western Long Island) the Lloyd Sand ranges in thick- 

 ness from 60 to 300 feet (18.3 to 91.4 meters) (Suter, De Laguna, and 

 Perlmutter, 1949) . The Lloyd Sand consists primarily of thin strata of 

 fine to coarse sand and gravel, and also contains thin noncontinuous 

 lamina of clay and silt. The sand and gravel is generally white, gray, 

 and yellow. Because it is both porous and permeable, the Lloyd Sand is 



Table 1. Generalized stratigraphy of Long Island. 



Era 



Period 



Epoch 



Unit 



Character and origin of deposits 



Cenozoic 



Quaternary 



HolocCJ,* 

 (Recent) 





Quartzose sand, beach and dune deposits and 

 fine-grained lagoon sediments. 





Pleistocene 



Harbor HUl Moraine 

 Ronkonkoma Moraine 



20-foot clay 



Gardiners Clay 



Jameco Gravel 

 Mannctto Gravel 



Ground and terminal moraine; stratified deposits of 

 sand and gravel, cobbles, and silt and clay. 



Grayish-green, silty clayey, glauconitic fine sand 

 (marine). 



Grayish-green, silty clay (marine). 



Fine to very coarse sand and gravel; scattered beds 

 of silt and clay (fluvial or glacial outwash). 



Mesozoic 



Cretaceous 



Upper 

 Cretaceous 



Monmouth Group 

 Matawan Group 

 Magothy Formation 



Raritan Formation 

 Raritan Clay 



Lloyd Sand 



Quartzose sand interbedded with silt and clay. 



Silty, sandy, brovmish-gray clay with thin beds of 

 sand and gravel. 



Quartzose fine to coarse sand and gravel; 

 interbedded clay and silty sand is common. 



Precambrian 



or 



Paleozoic 





Crystalline Bedrock 



Undifferentiated, consolidated, metamorphic granite. 



18 



