are temporal features in a geologic sense; they migrate with time by 

 erosion on their west bank and backfilling on their east bank, or may 

 eventually fill completely. However, new inlets are periodically created 

 when severe storms cause sufficient water overwash to erode breaches in 

 barrier segments. 



The coastline from Southampton east to Montauk Point is a headland 

 region where the Ronkonkoma Moraine and associated outwash sediment are 

 directly eroded by wave action. The small bays and estuaries in the 

 moraine east of Southampton are remnant stream channels which breached 

 the Ronkonkoma Moraine during Pleistocene time and were later sealed on 

 the seaward side by littoral sediments. 



The northern coast of Long Island bordering Long Island Sound (Fig. 2) 

 is characterized in the western half by 10 recessed narrow bays or estu- 

 aries which project southward and terminate at their intersection with the 

 Harbor Hill Moraine. The irregular coastline resulting from these bays is 

 confined to the western half of the north shore of Long Island; the coast 

 along the eastern half is steep and characterized by cliffs where the 

 Harbor Hill Moraine is directly exposed to wave and wind erosion. 



The two Peconic Bays and Gardiners Bay (Fig. 2) in east- central Long 

 Island are flat-bottomed, shallow, brackish bodies of water situated in 

 the intermoraine region. They are bounded on the north by the Harbor Hill 

 Moraine and on the south by the Ronkonkoma Moraine. The eastern side of 

 Gardiners Bay is open to Block Island Sound except for the presence of 

 Gardiners Island. East of Gardiners Bay, the sea floor deepens rapidly 

 and is marked by a series of overdeepened northwest-southeast trending sea 

 floor depressions, some at depths of greater than -300 feet (-91.4 meters) 

 mean sea level (MSL) . 



5. Geologic Setting and Regional Stratigraphy . 



Long Island, a glacial-depositional landform located within the Coastal 

 Plain, marks the most southerly advance by Pleistocene continental glaciers 

 in eastern North America. Geologic data from numerous deepwater well 

 borings show that Precambrian or early Paleozoic metamorphic bedrock, com- 

 posing much of the New England land surface, underlies the entire length of 

 Long Island. These well data indicate the bedrock surface is relatively 

 flat, apparently the result of extensive regional erosion before Cretaceous 

 time, and exhibits a southeast slope of approximately 1 on 55. Information 

 on the physical nature of the bedrock is limited because it is not a usable 

 water aquifer; hence, most water-well bore holes terminate at the bedrock 

 surface. However, some well data show that saprolite (a rock chemically 

 decomposed in situ] overlies fresh, high-grade, metamorphic rock of gra- 

 nitic composition. The altitude of the bedrock surface varies from less 

 than 200 feet (61 meters) below sea level on the north shore of Long 

 Island in Queens County to approximately -1,100 feet (-335 meters) MSL 

 at the eastern end of Rockaway Beach (Fig. 3). In east-central Long 

 Island the bedrock surface lies about 2,000 feet (610 meters) below Fire 

 Island beach; in northern Long Island Sound, bedrock directly underlies 



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