The rock formations with greatest exposure in the Piedmont region are the late 

 Precambrian and lower Paleozoic igneous and metamorphic rocks of felsic composition 

 which make up the bulk of northern New Jersey, and most of Connecticut and the New 

 England states. This rock is closely related in age and composition to the basement bedrock 

 beneath Long Island. From outcrops in northwestern Long Island and from water-well bore 

 holes and foundation excavations it is known that the Long Island area is underlain by 

 Precambrian and early Paleozoic metamorphic granitic gneisses and schists. Data from wells 

 reveal that the bedrock surface is deeply weathered and has a fairly regular slope of about 

 80 feet per mile to the southeast. Depth to bedrock varies from surface outcrop in 

 northwestern Long Island to a reported 1,100 feet under Rockaway Beach. (Suter, 

 deLaguna, and Perlumtter, 1949.) Because of the presence of the deeply weathered surface 

 and fairly even topography it is thought that the bedrock represents a peneplain erosion 

 surface on which Cretaceous sedimentary rock were later deposited subsequent to large-scale 

 regional subsidence. Very little is known about the character of the crystalline bedrock 

 because it is a poor water aquifer, and few drill holes have penetrated below the upper 

 surface. Lower Paleozoic clastic sedimentary rocks of northeastern Pennsylvania, northern 

 New Jersey, and eastern New York are also present. 



Rocks of Triassic age are presently exposed in elongate fault structures presently 

 confined to the Connecticut (Connecticut and Massachusetts) and Newark Basins 

 (Pennsylvania, New Jersey, and New York). The rocks consist of argillaceous, red and gray, 

 arkosic, sandstones and siltstones with an abundance of Late Triassic or Early Jurassic 

 basaltic volcanics, intrusive diabase, such as the Palisades Sill which forms the prominent 

 western topographic escarpment on the Hudson River. Metamorphic hornfels are found 

 adjacent to the diabase sills and dikes as a consequence of the thermal alteration. Some 

 authors have suggested (based on similarity of rock types and overall rock stratigraphy and 

 structural framework of the basins) that the Connecticut Basin is actually a half-graben 

 structure and serves as the eastern structural component of a once prominent full-graben 

 structure which would have included the Newark Basin as the western half-graben 

 component. Subsequent erosion has partially removed the strata filling the central position 

 of the graben in New York and Connecticut where older underlying Paleozoic rocks are now 

 exposed. Deposition of thick Coastal Plain strata has buried any possible evidence of Triassic 

 rock under Long Island or New Jersey. If this connected graben hypothesis were true, then 

 most of the central part of the graben would be deeply buried under western Long Island 

 and northern New Jersey. Triassic rock has never been encountered in deep wells drilled 

 through the Coastal Plain strata into Precambrian basement rock on Long Island or New 

 Jersey, but proponents of this hypothesis suggest that the Triassic rock has been removed by 

 extensive subaerial erosion which preceded submergence of the region and deposition of 

 Cretaceous-Tertiary strata. Because of the low density of bore-hole coverage through Coastal 

 Plain rock it is likely that deeply buried remnant pockets of Triassic strata are present in 

 Long Island Sound or under the New York Bight Continental Shelf. 



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