The Cat Island Channel deposit is expressed topographically as a ter- 

 racelike feature with the foreslope facing northwestward. Reflection 

 profiles show that this feature was deposited in the lee of a small 

 acoustically opaque ridge which may be a bedrock or till feature (Fig. 16). 

 Internal reflections within the sand deposit indicate presence of rela- 

 tively high-angle internal bedding planes dipping northwestward and par- 

 allel to the topographic foreslope (Fig. 15). This suggests that the 

 deposit grew by progradation from the suspected till or bedrock ridge 

 toward the northwest and may have been formed by overwash deposition of 

 a relict Holocene transgressive shoreline. Alternatively, the deposit 

 may be a modern tidal channel deposit which is probably still actively 

 accreting by northwestward progradation. ICONS cores 154 and 155 were 

 obtained from the sand deposit. Size-analysis data for representative 

 samples from these cores are in Appendix B. Sand from the two cores in 

 the Cat Island deposit is mostly in the medium to coarse-size range. The 

 estimated composite mean diameter of the cored material is 1.61 phi (0.312 

 millimeter), and the phi sorting is 0.74. The sand is clean and composed 

 largely of quartz grains. The total volume available is estimated to be 

 1.12 X 10^ cubic yards assuming a maximum indicated thickness of 21 feet 

 (6.4 millimeters). 



(2) Nahant . This deposit is centered at 42°24.7'N., 70''50.2'W. 

 about 2.9 nautical miles (5.37 kilometers) east of Nahant. The site lies 

 in 98 feet (2.98 meters) of water and has only a slight rise in the bottom 

 (Fig. 17). Only one seismic reflection profile (on east-west line) 

 crosses the site (Fig. 18). The profile shows the deposit is a thin 

 'Wedge-shaped body abutting a small topographic high in the sea floor and 

 extending to a feather edge 4,100~feet (1,250 meters) to the east. Core 



157 from the site contained 5 feet (1.52 meters) of coarse sand and 

 gravel under a 1-foot silt layer (App. B) . The silt contained abundant 

 coal fragments characteristic of sediments in Boston Harbor (Mencher, 

 Copeland, and Payson, 1968) and probably originated in that locale. 



The seismic reflection profile indicates that the Nahant deposit may 

 be 30 feet (9.1 meters) thick where it abuts the small rise in the sea 

 floor. If the entire deposit is usable sand, and assuming it is half as 

 extensive in the north-south direction as in its east-west extent, a total 

 volume of 4.66 X 10^ cubic yards of material is available. Assuming the 

 sand layer is no thicker than 5 feet (1.5 meters) as in core 157, the 

 approximate volume is 0.78 X 10^ cubic yards. 



(3) Nantasket East . This site is centered at 42°18.8'N., 

 70°47.6'W. about 3.9 nautical miles (7.2 kilometers) off Nantasket beach in 

 60 to 70 feet (18.2 to 12.3 meters) of water in a swale between two out- 

 crops of the basement reflector (Figs. 19 and 20). 



The north-south seismic reflection line crossing the site (Fig. 18) 

 shows the external form of a low terrace underlain by the transparent unit. 

 There are strong internal reflectors in the upper subbottom, some of which 

 show high-angle internal bedding. 



48 



