lithology and history of filling for the Orient Point Channel are pro- 

 vided by a 240- foot (73.2 meters) foundation boring (Figs. 2 and 6) at 

 the tip of Orient Point which penetrated the western part of channel K. 

 The descriptive log (Table 3) shows that the channel fill lithology con- 

 sists of three major groupings down to -220 feet (-68 meters) MSL. The 

 top 41 feet (12.5 meters) is fairly dense, poorly sorted sandy gravel, 

 which is either outwash detritus from the Harbor Hill Moraine (late 

 Wisconsin age) or actual parent moraine material. From 41 feet (12.5 

 meters) down to 146 feet (44.5 meters) the sediment is compact, mica- 

 ceous, silty, fine sand which becomes finer with depth. Below 146 feet 

 to the bottom of the boring, the material has the appearance of glacial 

 lake varves consisting of alternating layers of light and dark clayey 

 silt and fine sand (Fig. 11). The compact nature of these materials 

 suggests that they were under greater consolidation pressures in the past 

 than in the present, which may be the result of ice loading or subjection 

 to subaerial exposure. The remaining 300 feet (91.4 meters) of sediments 

 in the channel from the end of the boring to the channel bottom may be a 

 continuation of the varve deposits, or possibly glacial sediment or rem- 

 nants of Cretaceous or Tertiary strata. Presence of lake sediments in 

 the Orient Point Cliannel is consistent with occurrences of lake deposits 

 from Long Island Sound, and the Fishers Island region of Block Island 

 Sound as discussed before. These widespread occurrences support sugges- 

 tions that large freshwater lakes periodically occupied this region. The 

 age and regional extent of the lake deposits are difficult to determine 

 because of gross lithological similarities between Holocene estuarine 

 deposits and the Gardiners Clay (also widespread but Sangamon in age and 

 of marine origin). A detailed study of the lithologies and paleontologic 

 contents of the various units is needed before accurate stratigraphic 

 correlations can be made. Three Mile Channel (Fig. 6) is west of the 

 Orient Point Channel and separated from it by a pinnacle of Cretaceous 

 rock which projects within 90 feet (27.4 meters) of the sea floor. The 

 depth of channel J exceeds -500 feet (1-152.4 meters) MSL and the sediment 

 filling the channel is inclined westward and probably similar in sediment 

 character to the description in Table 3 for the Orient Point Channel. 

 Channels J and K bifurcate to the south into seven smaller distributary 

 channels which breached the southern leg of Long Island and continued onto 

 the shelf where they probably intersected the Block Channel. The south- 

 ward continuation of Three Mile Channel is -225 feet (-68.6 meters) deep 

 (MSL) immediately north of Three Mile Harbor; it is cut to -195 feet (-59.4 

 meters) MSL and over 3 miles (4.8 kilometers) wide on the south shore shelf 

 (Fig. 10). This anomalous northward channel thalweg gradient is apparently 

 due to over-deepening on the north by glacial scour. Three Mile Harbor is 

 an estuary resulting from submergence of the incompletely filled remnant 

 channel depression by the sea. Expression of many of these channels as 

 present-day lakes and estuaries is common for the eastern part of Long 

 Island, and is the same for the northwest coast of Long Island where the 

 large embayed estuaries superpose nearly buried channels. 



Three channels on the shelf south of the Montauk area of eastern Long 

 Island are shown in Figure 10. The two westernmost channels are fairly 

 steep-sided, compared to other channels also cut into Cretaceous material. 



49 



