Cibioides lobatulus (Walker and Jacob) is dominant in a few samples and 

 is generally present in quantity. Other genera well represented in sandy 

 sediments are Quinquelocutina , Eosalina, Ammonia, Buooetla, and 

 Poroeponides. Mollusk shells, where found, are usually fragmented; the 

 majority are derived from the blue mussel, Mytitus edutis Linne', and the 

 quahog Meraenaria mevoenaria LinneT 



d. Gravel . Gravel is a common sediment in the study area and often 

 appears in thin layers at or near the bottom surface. Willett, et al . 

 (1972) referred to the surface gravel as a thin widespread "skin" cover- 

 ing large areas of the bottom, and ascribe its distribution to Holocene 

 reworking of glacial till deposits exposed on the sea floor. Thicker 

 deposits of gravel occur in places but are most prominent in the project 

 NOMES site off Nantasket Beach (Setlow, 1973) . 



Subbottom gravel occurs frequently as thin discontinuous lenses in 

 sand or silt-clay deposits and as a component of glacial till encountered 

 in a few places below the transparent unit. Nearly all surficial gravel 

 occurs in a matrix of either sand or a sand-silt-clay combination. In 

 most places the gravel is poorly sorted and particle sizes range from 

 granules to large boulders. The gravel particles are composed of many 

 rock and mineral types, and are generally well rounded but tend to be 

 irregular in shape (Fig. 12). 



Gravel occurs frequently in the study area as inclusions in other 

 sediment types, either in randomly scattered erratic particles in fine 

 sand, silt, or clay, or in quantity sufficient to class the sediment as 

 gravelly. The latter often occurs in medium or coarse sands. Biogenic 

 particles in gravelly sediments are sparse and consist mostly of the 

 same organisms found in the sand bodies. 



e. Silt . Gray to brown silt, sandy silt, and clayey silt, distinct 

 from silty phases of the greenish-gray mud previously described, occurs 

 in local patches throughout the study area. Most of the silt is brown 

 in color and contains various amounts of sand and clay; plant and wood 

 fragments and mica are present in greater abundance than in other sediment 

 types. 



These sediments occur primarily as thin surficial deposits, although 

 similar material is present in the subsurface at a few locations. In a 

 few samples from the surficial deposits, the silt contains abundant coal 

 fragments suggesting a source area in Boston Harbor (Mencher, Copeland 

 and Payson, 1968) . Some of these deposits may have originated from 

 deposition of current or wave-borne detritus carried out of the harbor 

 area; other deposits are probably the result of dredge spoil disposal. 

 The stratigraphic relationships of the subsurface deposits are unknown. 



2. Sediment Distribution . 



Surface sediments in the study area are of heterogeneous character and 

 distribution is often complex and seemingly without discernible pattern. 



34 



