and exhibit thalweg depths of -155 and -185 feet (-47.2 and -56.4 meters) 

 MSL. The broad channel to the east has a thalweg depth of -120 feet (-36.6 

 meters) MSL and seems to either intersect or underlie the Ronkonkoma 

 Moraine at Montauk Point. Cores 16, 18, 19, and 21 in Figure 10 show that 

 upper parts of the channels are filled with fine to coarse sand and pebbles. 

 This sediment composition contrasts with onshore borings 1 and 2 in the 

 Montauk Harbor area (a submerged remnant channel depression) which exhibit 

 25 to 30 feet (7.6 to 9.2 meters) of cohesive silt and clay (Fig. 12; 

 App. A). These fine-grain sediments presently filling Montauk Harbor 

 are probably Holocene estuarine deposits. 



Projecting these Long Island buried channels north across Long Island 

 Sound and connecting them with present-day surface drainage systems in New 

 England is speculative without further information. The Hudson is the only 

 river in western Long Island which is presently large enough to be capable 

 of eroding the six channels which have been shown to cross western Long 

 Island. Lovegreen (1974) documented the existence of three ancestral 

 Hudson channels in New Jersey west of the present channel which are less 

 than 300 feet (91.4 meters) deep and situated within 5 miles (8 kilometers) 

 of the present river channel. Based on stratigraphy, Lovegreen suggested 

 that one of the channels is Cretaceous age, whereas the other two are of 

 Pleistocene age; these bracket the probable ages of all the western Long 

 Island channels reported here. Ascribing all nine channels to erosion by 

 the Hudson River would suggest the river has shifted channel position over 

 a considerable area (~30 miles; 48.3 kilometers) during the past 100 

 million years. Such lateral channel migration may result from crustal 

 warping due to tectonism or from glacial loading and unloading. An alter- 

 native explanation to ascribing all the channels to the Hudson River is 

 that during earlier geologic periods surface water runoff was greater (i.e.. 

 Pleistocene interglacial stages) and a number of major rivers occupied the 

 region which have since disappeared. If this were true, evidence of major 

 channels should exist in the bedrock for the eastern New York and south- 

 western Connecticut mainland on the Long Island Sound north shore. 



The pre-Tertiary surface contour map by Grim, Drake, and Heirtzler 

 (19 70) gives some indications that the channels crossing central Long 

 Island may be related to the ancestral Housatonic and Quinnipiac Rivers 

 in central Connecticut. Three Mile and Orient Point Channels appear to 

 connect with the deep east-west channel in southern Long Island Sound 

 extending from 73°20'W. to 72°40'W., and with the present course of the 

 Connecticut River, respectively. Study of the intricate subbottom drain- 

 age history and further attempts to trace these channels across Long 

 Island Sound and onto the Connecticut and New York mainland are being 

 made by Williams (in preparation, 1976). 



III. SURFACE AND SUBSURFACE SEDIMENT CHARACTER AND DISTRIBUTION 



Information on the character and areal distribution for Long Island 

 shelf sediment (Fig. 17) was derived from sediment analyses of the cores 

 in Figure 2. Granulometric and textural data were derived solely from 

 the CERC cores, but visual descriptions were obtained from the other data 



50 



