the land) of about 70 feet followed by resubmergence to present depths. 

 According to Kaye and Barghoom (1964) , relative sea level in the Boston 

 area stood at +60 feet or higher at about 14,000 years B.P. During 

 crustal rebound following glacial retreat, relative sea level dropped to 

 -70 feet mean low water (MLW) , reaching this level about 10,000 years B.P. 

 At this time sea level gradually rose to -2 feet MLW by 3,000 years B.P. 

 As a consequence of these events, parts of the study area now lying at to 

 -70 feet MLW were subject to a marine regression and transgression while 

 deeper areas were brought within range of high-energy shallow marine 

 processes. Because crustal rebound occurred concurrently with an eustatic 

 rise in sea level, the study area remained under shallow-water marine 

 conditions for some time longer than experienced by stable areas. Thus, 

 the prolonged time of shallow submergence permitted a greater reworking 

 and redistribution of Pleistocene sediments in the Boston area than in 

 more stable shelf areas with a similar wave climate. As a result of 

 shallow marine reworking, glacial till projecting above the glaciomarine 

 clay was eroded and coarse lag deposits were formed on the surface. 



The effects of reworking and redistribution of glacial drift in the 

 littoral and nearshore environment can be observed along the existing 

 coast in the study area where glacial drift features, chiefly drumlins, 

 are being eroded and the material transported downdrift to form modern 

 spits and beaches. Where the drumlins have been reduced to near sea 

 level the remaining coarse material has formed a lag pavement. Finer 

 sediment eroded from glacial drift deposits is, according to size, either 

 carried in suspension out of the area or carried downdrift to be deposited 

 on beaches and spits or in adjacent shoreface' and offshore bar deposits. 



Because of the extensive occurrences of a thin surficial veneer of sand, 

 pebbles, cobbles, and boulders, Willett, et al. (1972) concluded that this 

 surficial skin was the result of widespread redistribution of drift 

 during the Holocene regression-transgression episode occurring around 

 10,000 years B.P. Another possibility is that the material in the thin 

 widespread deposit is reworked ground moraine essentially in situ, related 

 to the late Wisconsin glacial stage. However, there is evidence that the 

 late Wisconsin glacier did not overrun the Boston Basin; Judson (1949), 

 Kaye (1961) , and Upson and Spencer (1964) implied that such a ground 

 moraine was never present in the study area. 



Outside of the shallow nearshore, littoral and shore zone of the 



present-day coast, it is unlikely that the gravel can be moved under 



existing offshore hydrodynamic conditions. Thus, nearly all the gravelly 

 sediments are probably relict. 



b. Greenish -Gray Mud . The history and origin of the ubiquitous 

 greenish-gray mud associated with the transparent unit appears to be com- 

 plex. There are probably two or more superimposed mud units of grossly 

 similar character deposited at various times under different environmental 

 conditions. 



Oldale, Uchupi, and Prada (1973) reported that the upper part of the 

 acoustically transparent unit which has been widely sampled, consists of 



39 



