Holocene silt and clay. They also reported that borehole samples in 

 the transparent unit under Boston Harbor showed the upper part to be com- 

 posed of Holocene silt and clay and the lower part of glaciomarine silt 

 and clay of late Pleistocene age. 



On the basis of core and seismic reflection data, Willett, et al. 

 (1972) also identified two units of silt and clay filling many depressions 

 in bedrock and till deposits. Since the interface between the two units 

 is commonly marked by a veneer of sand and gravel or glacial till, they 

 inferred a glacial advance following deposition of the lower unit and 

 preceding deposition of the upper unit. Willett, et al . believed this 

 advance could be associated with Kaye's (1961) Drift III, and the upper 

 clay unit might correlate with his Clay III (Table 1). 



Setlow (1973) distinguished two marine clay units in the project 

 NOMES site. The lower unit averaged 50 feet in thickness and was sep- 

 arated from the upper unit by an erosional unconformity. The upper unit 

 averaged about 25 feet in thickness but thinned rapidly and pinched out 

 against till outcrops. Setlow believed that the lower unit probably 

 correlated with Kaye's (1961) Clay II, and the upper unit with his Clay 

 III (Table 1). T 



Foraminifera in greenish-gray mud are extremely rare and are absent 

 in most samples. Since remains of other marine animals are comparably 

 rare, little can be gleaned of the origins of this deposit from faunal 

 evidence. However, the almost complete dominance by El'phidiym spp. of 

 the few foraminifera recovered suggests a marginal marine environment 

 (Phelger, 1960). The barren sections possibly represent time periods 

 with either very rapid deposition or a dominance of environmental condi- 

 tions precluding or sharply restricting productivity. Alternatively, this 

 scarcity may be due to leaching of tests originally present in the deposit. 



Foraminifera in a section of clay and overlying greenish silt corres- 

 ponding to Judson's (1949) Boston clay and marine silt (Table 1) were 

 studied by Stetson and Parker (1942) and Phleger (1949) from samples 

 obtained in the Boston area. Phleger (1949) found that foraminifera were 

 extremely sparse in the clay section, but that the marine silt contained 

 more foraminiferal fauna dominated by species of Elphidium. Few of the 

 other species found in the clay by Phleger (1949) and by Stetson and 

 Parker (1942) occurred in the ICONS samples processed for microfauna. 



The general confinement of the greenish-gray mud to valleylike de- 

 pressions in the acoustic basement suggests that it was deposited at a 

 lower stand of relative sea level in estuaries bounded by interfluves of 

 the acoustic basement material. The paucity, or complete absence of 

 remains of marine organisms in most places also favors such an origin as 

 opposed to "blanket- sedimentation" in deeper water with subsequent 

 erosion of material over the acoustic basement outcrops. 



The sediment distribution pattern, fauna or lack of fauna, and lithology 

 of the greenish-gray mud, all indicate it is relict; there is no evidence 



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