CAPE COD GEOLOGY 



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The geologic mapping of the Cape Cod peninsula in detail was not under- 

 taken until 1889, when Mr. C. W. Coman prepared maps showing the distri- 

 bution of the unstratified drift or till on the surface, the distribution of the 

 superficial stratified gravel and sand, and the changes in the swamps and marshes, 

 as well as the narrow areas of beach and dune sand along the coast. This work 

 was done under the direction of Shaler for the United States Geological Survey. 



In 1897 Grabau 1 described the plains of Truro, Wellfleet, and Eastham 

 on Cape Cod. The northern of these three plains, the Truro plain, which has 

 an average elevation of 80 feet, he ascribed to deposition in front of the ice in 

 the form of a delta, but was doubtful whether it had ice-contact slopes on the 

 east, north, and west. The Wellfleet plain, which has an average elevation of 

 140 feet, he regarded as presenting a doubtful ice-contact slope in the depression 

 between the Truro and the Wellfleet plain. The Eastham plain he noted as slop- 

 ing westward from the present eastern coast, where the surface has an elevation 

 of 75 feet, and as showing construction by streams flowing from the east, off 

 the present coast of Cape Cod. He regarded the Truro plain as a product of 

 streams flowing from the northeast and northwest at a time later than the 

 formation of the highest Wellfleet plain. He favored the hypothesis that glacial 

 barriers held up the water in an embayment of the ice front rather than the 

 hypothesis of marine submergence. Grabau was the first geologist to show 

 that the arm of the Cape, which occupies the position of an interlobate moraine, 

 presented evidence that a glacial lobe once lay outside of Cape Cod and that 

 the deposits were mainly waterlaid instead of normal lateral accumulations of till. 



In 1898 Shaler 2 published a report on the geology of Cape Cod in which 

 he recognized a series of deposits of gravel, sand, and clay beneath the surface 

 moraine, and hence older than it. Among these deposits he placed the dark 

 clay (here tentatively correlated with the Gardiners clay) which he included 

 in his "Barnstable series." He described other divisions (the "Truro series" 

 and the "Nashaquitsa series"), but as later work has shown that these divisions 

 include the clay of the "Barnstable series" as well as other beds, the nomen- 

 clature of Shaler's report has been replaced by tentative correlations with the 

 deposits of Long Island and Marthas Vineyard. There is doubt as to the true 

 position of the beds of clay at Barnstable, and although the name ' 'Barnstable 

 clay" might be useful for local designation, and although Shaler's use of "Barn- 

 stable series" has priority over the name Gardiners clay, used by M. L. Fuller 



1 Amadeus W. Grabau, Science, new series, 5, 1897, pp. 334-335. 



2 N. S. Shaler, Geology of the Cape Cod district, Eighteenth Annual Rept., U. S. Geol. Survey for 

 1896-97. Part II. Washington, 1898, pp. 497-593. 



