CAPE COD GEOLOGY 



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Not every body of land that is formed of glacial drift and is tied to a larger 

 land mass has been an island since the glaciers disappeared. When the land 

 stood higher in relation to the sea, the depressions between the elevations that 

 now form most of the islands in the Cape Cod district were simply low places 

 in the land. As the sea rose it would reach the level of one of the depressions 

 and flood it with sea water, making an island out of the detached fragment of 

 land. If, however, the beach action were sufficiently strong a barrier beach might 

 be thrown across the depression as fast as it became lowered below the level 

 of the sea, and thus the beach-tied island may have existed as an island except 

 for some temporary irruption of the sea over the beach barrier. 



The arm of Cape Cod from Town Cove northward consists at present of 

 two islands tied together by a bar at the head of Pamet River. The southern 

 or Eastham member of this insular group is separated from the mainland by the 

 old boat channel from Boat Meadow River through Jeremiah's ditch to Town 

 Cove. A dike that has a gateway just west of the railroad track about a mile 

 north of the Orleans railway station prevents the sea from flowing through this 

 ancient channel, most of which is filled with marsh vegetation. 



The old glacial drift at the head of Pamet River has been cut away and the 

 sea has been brought into contact with a depression, just as it has at Blackfish 

 Creek, in South Wellfleet, where the coast is now about three-fourths of a mile 

 from the head of a depression. Without any change in the level of land and 

 sea, the coast will after a time have receded so far as to admit the ocean to the 

 east end of the creek unless a bar is thrown across the entrance. Blackfish Creek 

 probably represents an early stage of the Pamet River depression before the sea 

 had cut back the coast so far as to tap the valley. 



If we plot the direction of the longshore drift against the chief tangent 

 bars and winged beaches of the Cape and Bay inside it (see fig. 23) it will become 

 obvious that wash from the shores of the Bay become pocketed except where 

 tidal scour carries them out upon the bottom, and that the headland of the 

 Cape is being driven inward by a general southward movement of the coastal 

 waste. 



Work of the Wind on Cape Cod 



The geological action of the wind on Cape Cod consists of the deflation of 

 the glacial gravel of the upland, the erosion of the cliffs, and the formation of 

 dunes along the beaches. 



