CAPE COD GEOLOGY 



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ceded 200 feet. At the same time the bar had moved inward about 200 feet. 

 On the ocean side of the harbor Whiting found the bar still more reduced in 

 width and height than it was in Mitchell's survey, and he recommended that the 

 East Harbor be closed. 



In 1890 Marindin found that the outer beach back of East Harbor had come 

 in still farther since the survey of 1867, so that the width of the barrier there 

 had been reduced; also that although the harbor opposite the town showed 

 scouring and deepening, the mud flats between Stevens Point and Long Point 

 had advanced somewhat into the harbor. 



The surveys of Monomoy and Provincetown harbor showed that much 

 more material is being transported southward along the Cape to the sand bars 

 of Chatham and Monomoy than northward to Provincetown because of the 

 greater force of the northeast storms. Moreover, Cape Cod is fended on the 

 southeast by great shoals from the full force of the waves. During a northeaster 

 the Provincetown spit is driven in from the ocean side, hence the bar that ends 

 in Long Point. Only a small part of the sand and gravel taken from the high 

 cliffs of Truro and Wellfleet appear to lodge above sea level on the Provincetown 

 bar, and Nauset Beach and Monomoy probably draw supplies from the shore 

 north of the middle of the coastline, between the ends of these bars. The low 

 plain of Eastham becomes thinner toward the west, as does to some extent the 

 high plain of Wellfleet, which also decreases in thickness westward owing to the 

 widening and deepening of the hollows in that direction, and the consequence 

 is a reduction in the quantity of gravel and sand that is fed to the longshore 

 current on the ocean side. Marindin shows that the rate of retreat of the coast 

 is most rapid along the Truro plain — about 8 feet a year as compared with 

 5 feet a year along the Eastham plain — so that a large part of the material 

 handled by the waves and currents comes from the erosion of the high cliffs 

 of Wellfleet and Truro. This more rapid retreat on the north turns the curving 

 coast farther to the west of north and diminishes the southward component of 

 longshore shift of material during northeast gales. The drift of sand toward 

 the Provincetown bar being thus increased, if it should counterbalance the loss 

 from the decrease in thickness of the deposits above sea level as the coast recedes, 

 would tend to establish stability and to preserve Provincetown harbor, at least 

 in outline. 



On the inside of the arm of the Cape there are a number of islands and 

 offshore bars that end on the south in Billingsgate Island. On Des Barres' 

 chart (1780) no barrier beach is shown between the land at South Truro and 



