CAPE COD GEOLOGY 



133 



of these forces and of the wind have been both constructive and destructive, 

 but destruction has been and still is predominant, and the island is, therefore, 

 gradually being reduced in size. 



CONSTRUCTIVE ACTION 



The constructed forms are mainly barrier beaches, which are of different 

 types. The cliffs supply abundant material for building beaches. The largest 

 barrier beaches on the island are along the south shore. One continuous beach 

 stretches from Nashaquitsa cliffs, at the west end of the island, to Wasque 

 Point, the southernmost extremity of Chappaquiddick. The current along this 

 shore generally runs eastward, so that the openings in the beach migrate east- 

 ward. Much of the material of this beach, at least south of Chilmark and Tis- 

 bury Great Pond, is the waste of Nashaquitsa cliffs, and some is furnished 

 by Squibnocket cliffs. The remainder is waste from the outwash plain. This 

 South Beach, as it is called, probably originated as an off-shore barrier beach 

 and was forced back by the waves until it encountered the land. It now ex- 

 tends in a practically straight line from Chilmark Pond eastward to the south 

 end of Chappaquiddick. The beach in front of the ponds does not bend in, and 

 the openings that are artificially cut through the beach each year are filled 

 within a few weeks. Natural openings have been made in this beach by the 

 waves, especially along the south side of Katama Bay. The records of the 

 United States Coast and Geodetic Survey 1 show openings at the west end of 

 Katama Bay, which work farther eastward from year to year until they reach 

 Wasque Point. 



Another extensive barrier beach forms the east shore of Chappaquiddick 

 Island, connecting it with Cape Poge. Unlike the South Beach, this East Beach 

 is accompanied by dunes, especially along the east shore of Cape Poge Bay. 

 This beach is probably made of material derived from Cape Poge, where the 

 waves are actively cutting away material. No such cutting is in progress along 

 the south shore. The East Beach is also a barrier beach behind which lies 

 an almost continuous lagoon composed of Poucha Pond and Cape Poge Bay. 



On the west side of Cape Poge there is a bar or spit that stretches south- 

 westward in a long curve. This spit, which is made from the waste of Cape 

 Poge, nearly shuts off Cape Poge Bay from the sea, almost converting it into 



1 Whiting, H. L., Report of changes in the shoreline and beaches of Marthas Vineyard as derived from 

 comparisons of recent with former surveys, U. S. Coast and Geodetic Survey Report tor 1886, Appendix 

 No. 9, pp. 263-266, 1887, with map. Also, same author, Topographic iesurveys on Marthas Vineyard, 

 [etc.], U. S. Coast and Geodetic Survey Report for 1889, Appendix No. 14, pp. 459-460, 1890, with map. 



