Pleistocene-age till and outwash deposits from at least two glacial epi- 

 sodes overlie the Cretaceous strata and are responsible for much of the 

 present-day relief on Long Island. Early Pleistocene glacial advances are 

 thought to be represented by the Mannetto and Jameco gravels which are buried 

 in places by the Gardiners clay which is believed to result from estuarine 

 sedimentation during Sangamon time. Wisconsin Glaciation is well represented 

 by the Ronkonkoma and Harbor Hill (terminal) Moraines and associated outwash 

 sand plains that extend south of the moraines across the Long Island Inner 

 Continental Shelf. The two moraines extend the length of Long Island and form 

 the two forks at the eastern end. 



The same bedrock surface that underlies Long Island forms nearly the 

 entire mainland of Connecticut (Table 2). The only exception is in the New 

 Haven area where a thick Triassic basin about 11 kilometers wide is present. 

 To the east the basin is in fault contact with granitic bedrock; to the west 

 the sandstones overlap the bedrock. Sanders (1963) first suggested that the 

 basin continues south under the Sound and western Long Island, and this 

 idea has been supported by results of magnetic surveys by Grim, Drake, and 

 Heirtzler (1970). The bedrock surface of Connecticut has been deeply scoured 

 by numerous glacial episodes and many of the river valleys were greatly deep- 

 ened and widened; the bedrock is veneered with glacial deposits generally less 

 than 10 meters thick except for the buried river valleys where thicknesses 

 vary from 35 meters at the Housatonic River mouth to 244 meters at the 

 Quinnipiac River (Upson and Spencer, 1964; Haeni and Sanders, 1974). 



Table 2. General stratigraphy of Connecticut. 



Era 



Period 



Epoch 



Character and origin 



Cenozoic 



Quaternary 



Holocene 

 Pleistocene 



Estuarine and marine soft organic muds 

 from fluvial and shelf sources; modern 

 marsh peat along coast 



Localized and discontinuous ground 

 till, moraine segments, and stratified 

 sand and gravel outwash deposits 



Mesozoic 



Triassic 





A basin of sandstone, siltstone, con- 

 glomerates and basaltic dikes intersect 

 the shore at New Haven, Conn.; may con- 

 tinue under Long Island Sound toward 

 the Long Island mainland 



Paleozoic and 

 Precambrian 







Metamorphic and igneous crystalline 

 basement rock. 



Along the north shore of Long Island, Holocene and modern sediments con- 

 sist primarily of sands eroded from glacial bluffs exposed to wave attack. 

 Fine-grained organic silts and clays in association with tidal marsh peat 

 deposits are common from sea level to mean high water (MHW) along both the 

 Long Island and especially the Connecticut shores, and thick accumulations of 

 gaseous soft muds are present in the deeper parts of the Sound. 



6. Bathymetry. 



Detailed morphology of Long Island Sound is provided by NOS hydrographic 

 charts and bathymetric maps at scales of 1:80,000 and 1:125,000, respectively. 



16 



