typical back barrier-beach sedimentary sequences where modern marine sands 

 overlie compact, organic- rich muds. Figure 12 shows the typical areal and 

 vertical variation of the major Holocene sediment types for the shoreline 

 from Fire Island east to Montauk Point. These same sediment sequences in 

 the cores offshore indicate that barrier-spit complexes existed offshore 

 in the past, the same as they do today for that area, and that as sea 

 level rose the barriers moved toward the mainland. Thickness of the 

 Holocene sediments along this segment of the south shore is difficult to 

 determine; several cores show an excess of 10 feet (3 meters) with a 

 general decrease in thickness offshore. 



Eastern Long Island between Orient Point and Montauk Point is the 

 second area where Holocene sediments (confirmed by C-'-'* dates) were 

 retrieved in cores. In many places, possible estuarine or lake sediments 

 are exposed on the sea floor or covered by several feet of medium to 

 coarse, reddish-brown sand. 



3. Major Surface and Buried Paleodrainage Channels . 



Locating, identifying, and tracing ancestral stream and river channels 

 and flood plain erosion surfaces have been of considerable interest to 

 geomorphologists, geologists, and foundation and mining engineers for many 

 years. Such channels are elongated geomorphic depressions resulting from 

 normal fluvial and glacial erosional and depositional processes. The 

 channels may be exposed at the land surface or be buried under thick over- 

 burden composed of more recent sediments. If the channels are buried, 

 present land surface morphology may provide only subtle clues to their 

 existence. Until the last few decades, study of fluvial channels on land 

 was limited to areas with natural exposures and the use of bore holes. 

 The possibility of submerged channels existing on the continental shelves 

 was surmised but remained unproven until Lindenkohl (1885) discovered the 

 morphologically expressed Hudson (submarine) Channel seaward of New York 

 Bay during a 1842-44 hydrographic survey. The significance of this dis- 

 covery was first described in 1863 in professional literature by Dana, 

 1890. Dana was apparently one of the first scientists to hypothesize 

 that the Hudson submarine channel represented a conduit through which the 

 Hudson River flowed in earlier geologic times when sea level was signifi- 

 cantly lower and the shelves were dry land. This astute observation pro- 

 vided the stimulus for other researchers to initiate detailed surveys of 

 the Atlantic shelf to examine the Hudson and other channel- canyon systems. 

 found to cut the shelf. Later development of sophisticated echo sounders 

 and navigation equipment was instrumental in providing data for compiling 

 accurate physiographic maps of the shelf surface. Detailed information 

 on various features of the Atlantic shelf was presented by Veatch and 

 Smith (1939) and Smith (1939); a very interesting history of exploration 

 was summarized by Stearns (1969) . The technological development of high- 

 power continuous seismic reflection equipment was important in allowing 

 researchers to examine and map the shelves and accompanying submarine 

 channels in the third (vertical) dimension. This equipment showed com- 

 pletely buried fluvial channels were present where no hint was suggested 

 by sea floor topography, and for the first time submarine channels on the 



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