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CAPE COD GEOLOGY 



to end abruptly in a platform that stands from 200 to 300 feet above sea level, 

 confronting from 30 to 50 miles eastward the floor of the Bay of Maine, which 

 lies about 600 feet below sea level, a difference of level of nearly 900 feet in the 

 latitude of Cape Ann, brought about by diastrophic movement. To what 

 extent this drop from the edge of the lowland affects the depth of the bed rock 

 floor under Cape Cod there is no positive evidence. 



Pre-Pleistocene Formations 



No pre-Pleistocene formations have been recognized in outcrops on Cape 

 Cod. Beds of upper Cretaceous clay are exposed on the south shore of Nonamesset 

 Island, near Woods Hole, at the southwest corner of the Cape, and Cretaceous 

 beds probably lie not far beneath the surface in the neighboring region, in the 

 town of Falmouth. No deep borings have been made on the Cape to show 

 whether or not Cretaceous rocks lie upon the bed rock floor. 



Fragments of Eocene friable shelly marl have been found by W. O. Crosby 

 in the gravel near the top of the bluff south of Highland Light. These drifted 

 fragments appear to have been brought from the north and east by glacial 

 action at the time the Jameco gravel was laid down and are the only known 

 Eocene marine sediments found in the region. They were probably brought 

 from the bottom of the Bay of Maine. 



All the beds of gravel and boulders carry fragments derived from the 

 Paleozoic and older rocks of the coastal region of eastern New England. Among 

 these fragments are pebbles of Upper Cambrian quartzite carrying casts of 

 shells of brachiopods. One fragment of semi-quartzite found in 1915 in the 

 gravel bed beneath the "clay-pounds" or supposed Gardiners clay at Highland 

 Light carried Devonian fossils. Fossiliferous Devonian rock has since been 

 found in place in the town of Rowley, Mass. 



Drift derived from conglomerate like that of the Carboniferous areas 

 around Boston and in the Narragansett Basin, found in the glacial deposits of 

 the arm of Cape Cod, show that such rocks may form a part of the floor of the 

 Bay of Maine and the outer part of Massachusetts Bay, if not also the floor 

 of Cape Cod Bay. 



Pleistocene Formations 



The Pleistocene formations of the Cape Cod district include series com- 

 parable to those that form the middle and upper part of the series exposed on 

 Marthas Vineyard and Nantucket. Beds of fossiliferous sand at the lower part 



