Middle Ground (Boothroyd, personal conununication, 1971). Therefore, 

 Middle Ground had its beginnings as a clam flat on a surface of glacio- 

 marine clay, which is anchored on a slight bedrock rise (see Problems 

 of Interpretation, Section III, 4), and changed to a rapidly accreting 

 mid-channel bar as the estuary continued to fill. 



Drill hole PIF shows a thick sequence of estuarine sands from -65 feet 

 up to a buried peat layer at -28 feet and then general coarsening from 

 there upward. The stratigraphy determined by McCormick (1968) agrees 

 with this sequence. McCormick found that the western fine-grained facies 

 Ca fine, mud-flat sediment) has been replaced and overlain by the coarser 

 eastern coarse-grained facies (a coarse channel sediment) as the estuary 

 migrated landward in response to barrier transgression and sea-level rise. 

 Between about -38 feet to -48 feet there are alternating sandy and muddy 

 layers in drill hole PIF. The coarser, more angular, more feldspathic 

 sediment above the peat layer perhaps represents a higher energy environ- 

 ment, that is, the encroachment of the major channel of the estuary. The 

 drill hole is located on the eastern margin of the estuarine channel where 

 the marsh peat is eroding in response to the meandering of the Parker 

 River channel, which apparently moved westward over this spot centuries 

 ago. Cottages on the channel are rapidly losing their foundations. His- 

 torical accounts by previous inhabitants affirm the modem eastward move- 

 ment of the estuarine channel . 



Drill hole PIF went to a depth of 65 feet. No clay was found, but 

 nearby drill holes indicate that clay should not be far below the 65 

 feet horizon. Deeper bedrock topography probably accounts for the lower 

 clay horizon. Insufficient drilling depth left a small, but perhaps sig- 

 nificant, question unanswered. 



Drill logs for holes PIA and PIB are nearly identical. In both holes, 

 grain size varies upward from the clay horizon. PIB shows a coarse gra- 

 vel or weathered layer above the indurated clay; the weathered material 

 probably became the floor of the developing estuary. The alternating 

 silt and sand layers noted in PIF are also present in PIB, confirming 

 that the main channel of the estuary migrated back and forth significant- 

 ly through time. The peat layer at -11.5 feet in PIB is probably salt- 

 marsh peat that has been compressed by advancing barrier dune sand. 



Figure 31 is a sketch drawn from seismic data and drill-hole logs of 

 holes PIC, PIE and PIG. These drill holes were selected for correlation 

 due to their proximity and interrelated depositional sequence. It is 

 suggested that during the low stand of the sea, after deposition of the 

 glacioraarine clays, the estuary maintained a major channel east of its 

 modem change. The original barrier then was farther seaward (Anan, 

 1971) , and the estuary surrounded the drumlins at th.e southern end of 

 Plum Island. McCormick 's map of sediment distribution agrees with a more 

 eastward location of the younger estuary. Clams flourished in the low- 

 energy fringing mudflats along the irregular drumlin shoreline. While 



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