During interglacials, the sea repeatedly invaded the region 

 leaving a series of marine, and marginal marine deposits. Many of 

 these deposits are preserved on the southeastern Virginia coastal 

 plain (Oaks, 1964), but with the possible exception of Unit E no Pleis- 

 tocene deposit in the area southwest of Channel A (Figure 6) appears 

 to have survived late Wisconsin erosion. On the broad high between 

 Channels A and B, a section of Pleistocene sediments apparently re- 

 mains between the Miocene surface and the erosion surface mapped in 

 Figure 6. 



During much of Holocene time this upland would have formed a south- 

 ward extension of Delmarva Peninsula restricting the Bay mouth to the 

 area occupied by Channels A and D (Figure 6) . If the Holocene uplift 

 postulated by Harrison et al (1965) is taken into account, the relative 

 rate of sea level rise in Chesapeake Entrance must have been very slow; 

 consequently conditions changed only slightly from the onset until 

 about 5,000 years BP when drowning of the upland between channels A and 

 B opened the Bay mouth. 



If the foregoing is a true representation of the Holocene advance, 

 then fill in the Pleistocene Channels probably could not have origi- 

 nated with the advance of a sediment mass from the northeast as a land 

 barrier would have existed in this direction until after the time of 

 deposition indicated by radiocarbon dates on material within the fill 

 (Harrison et al 1965, Maynard Nichols personal communication). 



The fine gray sand comprising much of the surficial sediment 

 blanket in Chesapeake Bay Entrance probably did not begin to form until 

 after drowning of the upland between Channels A and B since it overlies 

 and extends well bayward of this high. Recent work by Ludwick (1970) 

 indicates that the surface layers of this sand mass are being actively 

 formed by currents and waves, and it seems possible that active sedi- 

 mentation may still be taking place. 



Gross bottom morphology in the Bay Entrance is judged to be largely 

 due to the accretion of the fine gray sand and little related to events 

 predating its deposition. Little if any topographic expression of the 

 old Pleistocene erosion surface now remains in the Bay Entrance. The 

 major positive topographic features are areas of accretion of the fine 

 gray sand on the sand flat surrounding Cape Charles and over the Horse- 

 shoe area. Chesapeake channel and the main entrance channel are the 

 principal negative features. Both appear to be due as much to accre- 

 tion of sediment masses to the flanks as to scour, the north wall con- 

 sisting of the southern edge of the sand flat surrounding Cape Charles 

 and the southern wall consisting of sand accreted around Cape Henry and 

 on Tail of the Horseshoe. 



Evidence of this can be seen on geophysical records which cross 

 the north wall of Chesapeake Channel and the main entrance channel 

 (Appendix A). On Chesapeake Channel records (lines E and DE) , a 



36 



