CAPE COD GEOLOGY 



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or "inner" moraine, the Harbor Hill moraine of Fuller, a belt of frontal deposits 

 traceable from New York Narrows along the north coast of Long Island to Fishers 

 Island and along the south coast of Rhode Island, where, at Point Judith, the 

 moraine, interrupted by the sea, is recognizable by soundings made southwest 

 of Cuttyhunk, thence northeastward through the Elizabeth Islands to Woods 

 Hole, and thence along the main arm of Cape Cod peninsula to Orleans. In the 

 area covered by this report the second moraine is called the Falmouth moraine. 



The terms "outer" and "inner" moraine, formerly and still sometimes ap- 

 plied to the Nantucket and the Falmouth moraines respectively, are not appro- 

 priate, for although they occupy these positions from the middle of Long Island 

 eastward to the east coast, their positions west of Roslyn, on Long Island, are 

 reversed. This change of alignment of the front may mean that in its second 

 stage the ice sheet was thinner on the east and thicker on the west than the first 

 Wisconsin ice sheet, a difference that may have arisen from a shift of the snow 

 fields inward in the gathering ground. A tilt of the continent toward the south- 

 west over New England might have had the same effect, but no evidence of such 

 a movement has been found. 



The nature of the retreat of the ice front between the first and the second 

 substages of the Wisconsin stage is indicated in the Cape Cod region by numer- 

 ous ice block holes between the Falmouth and the Nantucket moraines. The 

 formation of these holes was accompanied by stagnation of the ice far within 

 its front at Nantucket. Blocks of ice several yards thick appear to have re- 

 mained at some places until after the glacier had readvanced into that field at 

 the second substage. The interval between the two chief advances of the Wis- 

 consin glacier in this region was, therefore, not long enough to permit these out- 

 lying blocks of ice to melt. 



Nantucket Moraine 



The marginal deposits of the Wisconsin ice sheet on Nantucket consist of 

 an outwash plain built up in front of the ice, a depression back of the head of the 

 terrace formed by the plain, and, north of this, a belt of low hills and hollows 

 strewn with boulders and drift. This series of deposits is here called the Nan- 

 tucket moraine. The knobs and basins of this moraine, which is regarded as sub- 

 marginal, differ from those of the frontal moraines in other areas/for they are 

 composed largely of flexed and contorted beds of an older glacial series, whose 

 eroded surface was crumpled and wrinkled by the forward-moving Wisconsin ice. 



The island of Tuckernuck extends the characteristic morainal topography of 

 Nantucket westward along the line of the ice front. The plain on the south side 



