66 



CAPE COD GEOLOGY 



The earlier explanations of the commingling of contorted drift with older 

 soft beds, including the conception of icebergs grounding on a shallow sea floor, 

 of violent disruption of the earth's crust, and of mountain building, have given 

 way to the conception that an overriding ice sheet ploughed and pushed the soft 

 beds over a coastal plain. In 1886 Merrill * expressed the opinion that the dis- 

 locations on Long Island were due to the advance of the Pleistocene ice sheet over 

 the soft deposits of the coastal plain. Upham 2 somewhat later took the same view 

 regarding the distortion of the beds at Sankaty Head, on Nantucket, and at Gay 

 Head, on Marthas Vineyard. In 1894 Hollick 3 in considering the structure of 

 beds studied by him on Staten Island, Long Island, and Gardiner's Island in 

 connection with the facts reported by Shaler and others on Marthas Vineyard, 

 compared the theory of mountain building as applied to this structure with that 

 of glacial thrust and concluded, from the coincidence of the terminal moraine 

 with the zone of dislocation, that glacial action alone was the cause of the folding 

 and faulting in the beds. He also noted at Cold Springs, on the north shore of 

 Long Island, that the lower Cretaceous beds there exposed were undisturbed, 

 and he predicted that if excavations were made elsewhere below the limit of dis- 

 turbance of the upper beds by the ice sheet similar undisturbed strata would be 

 found. 



In 1906 Veatch * showed by the records of well borings made along the north 

 shore of Long Island that beneath the crumpled and dislocated Cretaceous beds 

 that lie immediately under the glacial drift there are undisturbed basal Cretaceous 

 beds that dip seaward. 



Two facts appeared to lend support to the idea that these disturbances were 

 due to mountain building forces, which were suggested by Shaler as the cause of 

 the dislocations on Marthas Vineyard. One of these facts was the great extent 

 of the area of the disturbed beds in the New England Islands. The disturbed 

 area between New York Narrows and Sankaty Head amounts to at least 2,200 

 square miles, and as that area may be 20 miles wide it may have once included 

 more than 4,000 square miles of the sea floor and the islands, exclusive of the 

 vast shoals east of Nantucket and Cape Cod. If the disturbances were practically 

 simultaneous throughout this great area, glacial thrust appeared to be an inade- 



1 Merrill, F. J. H., On the geology of Long Island, Ann. New York Aead. Sci., 3, pp. 258-259, 1886. 

 Also On some dynamic effects of the ice sheet, Proc. Am. Assoc. Adv. Sci., 35, pp. 228-229, 1886. 



2 Upham, Warren, Marine shells and fragments of shells in till near Boston, Am. Jour. Sci., 37, 

 ser., p. 270, 1889. 



3 Hollick, Arthur, Dislocations of certain portions of the Atlantic coastal plain strata and their 

 probable cause, Trans. N. Y. Acad. Sci., 14, pp. 8-20, 1894. 



4 Veatch, A. C, Underground water resources of Long Island, U. S. Geol. Survey Prof. Paper 44, 

 pp. 16-19, 1906. 



