feet (3 to 8.2 meters). These cores display a stratigraphic sequence 

 across the shoreface (Fig. 9) similar to that shown by the cores along 

 the west transect (Fig. 9). The east transect passes slightly seaward 

 of the shoal (Fig. 30) and a silt-clay horizon is present at -80 feet 

 (-24.4 meters) MSL (cores V-22, V-23, and V-24) which is correlative with 

 the Gardiners Clay described above for the west transect. Based on the 

 sediment descriptions from cores along the three transect lines, a poten- 

 tial sand thickness for area M is judged to be 6 yards (5.5 meters). 



n. Area N. Area N at the western end of the study adjoins the shelf 

 region studied by Williams and Duane (1974) (Fig. 29). It lies within the 

 60- foot (18.3 meters) depth contour and contains 11 cores which show con- 

 siderable variation in continuous sand content (App. A). Part of the 

 stratigraphic variation may be explained by the presence of three major 

 buried river channels which trend north-south (Fig. 13) and reach dimen- 

 sions of several thousand yards in width and over 350 feet (106.7 meters) 

 in depth. The textural and mineralogic nature of the channel-fill detri- 

 tus is uncertain but information on channels from other areas indicates 

 the fill may be quite variable depending on composition of the original 

 source rock and hydraulic competence of the rivers. The minimum sand 

 thickness is judged to be 2 yards (1.8 meters), while the potential 

 recovery is 3.5 yards (3.2 meters). 



Since the borrow sites discussed above are based on a regional study 

 of sediment distribution, additional exploration by seismic profiling and 

 coring in the offshore sites is necessary to accurately delimit the borrow 

 material size parameters and volumes. For example, a detai.led followup 

 study was conducted by the U.S. Army Engineer District, New York, before 

 initiation of the Rockaway Beach nourishment project where an offshore 

 sand source at East Bank Shoal seaward of Coney Island and west of 

 Rockaway Inlet was used. A similar data collection program is under- 

 way off Westhampton Beach and will be completed in late 1975. 



V. SUMMARY 



The study area covers about 800 square miles (2,072 square kilometers) 

 of the Long Island Atlantic Inner Continental Shelf from Atlantic Beach 

 east 110 miles (177 kilometers) to Montauk Point and includes the Gardiners 

 Bay-Block Island Sound region in eastern Long Island. Basic ICONS survey 

 data consist of 735 miles (1,183 kilometers) of seismic reflection records 

 and 70 vibratory cores (average length: 9.7 feet; 3 meters). Supplemental 

 data consist of 82 cores and borings and 225 miles (362 kilometers) of 

 seismic records. All these data were obtained on the inner shelf between 

 the beach and water depths of 105 feet (32 meters), about 10 miles (16.1 

 kilometers) offshore. 



The shelf south of Long Island is a submerged continuation of the 

 surface underlying the Long Island mainland. Long Island is underlain 

 at depths of about 1,100 feet (335 meters) at the south coast by a 

 southeast-sloping metamorphic bedrock surface which is overlain by 

 unconsolidated and semi consolidated Cretaceous-Tertiary, and Quaternary 



77 



