10,500 B.P. Both authors admit room for improvement in fixing the curves 

 to dates so far removed from the present. Mclntire says (personal commun- 

 ication, 1971) that he might revise his time-level relations, particularly 

 the more distant ones. Kaye and Barghoom suggest a higher sea stand during 

 deposition of the glaciomarine clay. 



Clay deposits were lifted above sea level during unloading of the earth's 

 surface with deglaciation. These clays were mantled with a thin layer of 

 coarse-grained weathered material. The maximum relative low stand of the 

 sea at -60 feet does not explain clay induration at this level or below. 

 Therefore, induration may have been due in part to the diagenetic altera- 

 tions suggested by Coleman and Ho (1967) . 



Both sea- level curves agree on the low stand of the sea. Since most 

 of the sediment recorded in the drill logs was deposited after the low 

 stand of the sea, it is therefore significant to make the agreement between 

 these two sea-level curves for the period from 10,000 B.P. to the present. 

 Figures 30 and 31 are dated as about 10,000 B.P. or at the low stand of 

 the sea. The lower part of Figure 31, which shows how the southern Plum 

 Island basin was closed off, could have a date of about 4,000 B. P., 

 due to the relative levels of the marsh sequence and of the sea at this 

 time. In general, the drill-hole data show a rather uniform rise in sea 

 level after a low stand at about -60 feet. This rise allowed the develop- 

 ment of shellfish flats in low-energy fringing environments as well as the 

 more rapid accretion on the dynamic sand flats. 



54 



