80 



CAPE COD GEOLOGY 



islands and of the coast. Conspicuous among the recent deposits that form a 

 fringe along the shore, standing but little above ordinary high tide, are the 

 southward extension of Nauset Bar, the bars and beaches at Chatham, and the 

 forelands at Siasconset and Surfside, on Nantucket. 



On the low south coasts of Nantucket and Marthas Vineyard bars formed 

 by the sea cut off the drowned extensions of the valleys of glacial streams, form- 

 ing ponds of salt or fresh water. 



As a consequence of such changes along the coast, lighthouses have been set 

 back from time to time or new ones have been built to replace earlier structures 

 that have fallen into the sea, as at Chatham and Nauset, on Cape Cod. Surveys 

 showing the retreat of the coast have been made from time to time by the United 

 States Coast and Geodetic Survey, the reports of which give the most complete 

 account of these changes. 1 



The early charts do not afford sufficiently precise positions to warrant their 

 free use in estimating the changes in the coast line during the three centuries in 

 which this region has been occupied by European settlers. The earliest map of 

 Cape Cod and the New England Islands that pretends to give much detail was 

 apparently drawn in the second decade of the eighteenth century, probably by a 

 Boston pilot named Southaek. 3 The part of this chart that represents the coast 

 from Block Island eastward is reproduced in Plate 7. The most that can be 

 inferred from this chart concerns the occurrence and position of small islands and 

 shoals. The coast line proper is sketched with very little regard to what must 

 have been its actual alignment and position. The upright part of the arm of 

 Cape Cod north of Nauset is represented as an island separated from the hori- 

 zontal part of the arm by a crooked passage between Nauset Harbor and Cape 

 Cod Bay. The chart bears an inscription on which is based the statement that a 

 whale boat was taken through this passage in 1717. Captain Townshend's 



1 For localities surveyed or reported, see General index of scientific papers contained in the annual 

 reports of the United States Coast and Geodetic Survey from 1845 to 1881, inclusive; Appendix No. 6, 

 Report for 1881, Washington, 1882. Other data will be found in the annual reports of the Massachusetts 

 Board of Harbor Commissioners, continued as the Harbor and Land Commissioners. See Seventh Ann. 

 Rept., January, 1873, House No. 65, for report of Henry Mitchell concerning Nauset Beach and the 

 peninsula of Monomoy (pp. 94-108), and for report on Haulover Break, Nantucket (pp. 109-117). 

 More elaborate recent surveys are those by H. L. Marindin, On the changes in the shore lines and anchor- 

 age areas of Cape Cod (or Provincetown Harbor) as shown by a comparison of surveys made between 

 1839 and 1867, and 1867 and 1890. United States Coast and Geodetic Survey, Appendix No. 8, pp. 283- 

 286, pis. 11-12, 1891. Also cross-sections of the Shore of Cape Cod . . . between the Cape Cod and Long 

 Point lighthouses, Appendix No. 9, pp. 289-341; both in part 2, Report for 1891. Also, by the same 

 author, On the changes in the ocean shore lines of Nantucket Island, Massachusetts, from a comparison 

 of surveys made in the years 1846 to 1887 and in 1891. Appendix No. 6, pp. 243-252, pis. 24-27, Rept. 

 U. S. Coast and Geol. Survey for 1892. 



2 Townshend, C. H., Notes on an early chart of Long Island Sound and its approaches, U. S. Coast 

 and Geodetic Survey for 1890, pp. 775-777, pi. 71. 



