The remaining four cores are from the terrace fringing Cape Charles. 

 These cores (CIO, 15, 39 and 21) contain a surficial layer 1 to 3 feet 

 thick composed of medium to very coarse, iron-stained, quartzose sand 

 (Figures 12 and 13) . The sand is distinctly different in texture and 

 appearance from the underlying and surrounding fine gray sand which is 

 characteristic of the terrace. Unlike other sediments in the study area 

 these brown sands contain a significant content of shells and shell 

 fragments, mostly surf clams ( Spisula) and razor clams ( Ensis) . 



Two of the cores on Cape Charles terrace containing coarse brown 

 sand (CIO and 15) lie close together on the rim of a large semi-closed 

 depression off Fisherman Island. Geophysical records across the core 

 sites show that these cores were taken in an area of sand waves 3 to 8 

 feet high. Ludwick (1970) recently reported on these sand waves and 

 noted that coarse brown sand occurred in the area. He suggests that 

 the sand may be relict. Core 39 is from the flank of a peaked sym- 

 metrical feature about 10 feet high which may be a solitary sand wave. 

 Core 21 was retrieved from a relatively featureless area of the 

 terrace. 



The fact that the coarse brovm sand in the cores from Cape Charles 

 terrace all appear to be identical and the cores are in line northeast- 

 southwest suggests that the sand may be continuous between core sites. 

 If so the sand occurs in a narrow band as cores to either side of the 

 line contain fine gray sand. 



The thickness of the fine gray sand covering most of the study 

 area is generally greater than the penetration of cores made for this 

 study. Deeper borings made along the Chesapeake Bay Bridge-Tunnel 

 show this deposit reaches a maximum thickness of 120 feet near 

 Fisherman Island and has an average thickness of more than 10 feet. 



This sand is remarkably uniform in texture and appearance. The 

 mean diameter of 95 samples obtained from cores in the deposit at 

 various depths from the water-sediment interface to 12 feet downhole 

 range from .098 to .216 mm (3.35 to 2.08 phi) with a standard devia- 

 tion of .25 phi (Figure 14). 



Most of the gray sand samples are well sorted. There is no pro- 

 nounced size differences between samples from shoals and depressions 

 on Cape Charles terrace, probably a result of the uniformity in avail- 

 able sand rather than uniformity in the distribution of wave and 

 current energy over the terrace area. 



A sharp lithologic break occurs in cores from the south slope of 

 Tail of the Horseshoe where the medium to very coarse sand and gravelly 

 sand exposed in Thimble Shoals Channel is thinly buried by fine gray 

 sand near the outcrop line. Except for cores penetrating to this 

 coarse stratum few cores in the study area show sharp lithologic con- 

 trast in vertical section. 



26 



