58 



CAPE COD GEOLOGY 



The geological and biological evidence available in the New England Islands 

 indicates that the land there was higher than now during the stage of the first 

 Wisconsin or Nantucket moraine, and that it afterward sank to its present level. 

 The rise before the end of the Wisconsin stage and the subsequent sinking of the 

 land are in accordance with glacial theory and the doctrine of isostasy. The tract 

 submerged during glaciation should be occupied by glacial cover during the re- 

 treat, when the marine clays of the retreatal stage would be laid down. The 

 laminated blue clay of the Gardiners stage appear to have been laid down on 

 such a tract. The marine Sankaty sand, laid down after an early ice invasion, if 

 correctly understood, bears a similar relation to the margin of the ice sheet, whose 

 terminal moraine probably lay south of Marthas Vineyard and Nantucket. 



The late Pliocene and Pleistocene terraces in Maryland show a progressive 

 uplift of the continent during the period of their formation. The history of the 

 terraces on the islands from the late Vineyard stage onward shows that, despite 

 occasional depression below sea level, uplift has here also prevailed, but the 

 terraces in Maryland * that stand above the present strand may be of pre- Wis- 

 consin age. 



WISCONSIN STAGE OF GLACIATION 

 General Relations 



The general position and leading features of the terminal moraines in south- 

 ern New England have long been known, but recent surveys have considerably 

 modified the earlier views regarding the western extension of the moraine on 

 Nantucket and of that on Cape Cod, and have reduced the estimates of the 

 thickness of the drift laid down by the Wisconsin ice. The estimated thickness 

 of the Wisconsin drift is here still farther reduced, and certain knob-and-basin 

 areas that were formerly regarded as Wisconsin moraines of indefinite thick- 

 ness are here attributed to the deformation of older beds. 



The Wisconsin glacial deposits here considered lie in two distinct areas. 

 The earliest deposit is an "outer" terminal moraine, here named the Nantucket 

 moraine, seen on Nantucket, Chappaquiddick, Marthas Vineyard, No Mans 

 Land, and Block Island, and extending westward from Montauk Point, on Long 

 Island, as the Ronkonkoma moraine of Fuller, nearly to Roslyn, N. Y. There the 

 low mounds of this moraine are covered and apparently crossed by the second 



iShattuck, G. B., Pliocene and Pleistocene, Maryland Geol. Survey, pp. 66-76, 1906. The author 

 recognized five terraces, namely, the so-called Lafayette terrace (now regarded as older than the Pleisto- 

 cene), traceable at elevations above the existing wave-cut terrace of the shore between 260 and 500 feet; 

 the Sunderland, between 100 and 220 feet; the Wicomico, 45 to 90 feet; the Talbot, 10 to 30 feet. 



