32 



CAPE COD GEOLOGY 



Of these shells Dall remarked that Corbula densata had been found in the 

 Upper Miocene of Virginia, that it occurs in the Pliocene of South Carolina, and 

 that the Venericardia is one of a recent type rather than the Miocene V. granulata. 

 The shells in these beds of sand at Gay Head had not been dissolved out, as are 

 those in the underlying beds, a fact which implies a more recent origin than the 

 apparently conformable contact of the beds of Pliocene sand in these deeper 

 water deposits would indicate. The shells are broken as if by pressure exerted 

 during the dislocation and folding of the beds. 



If the beds of Miocene greensand and their shallow-water molluscan remains 

 indicate the maximum depth and encroachment of the sea upon the Massachu- 

 setts lowland during the Miocene epoch, the beds of Pliocene sand at South- 

 ampton may be interpreted as marking a much shallower sea, which presumably 

 covered the site of the New England Islands. 



The deposit at Gay Head was found under the lighthouse at an elevation of 

 80 feet above the beach, but this elevation has no certain relation to the elevation 

 of the formation prior to its deformation. The remnant of the formation on 

 Marthas Vineyard was little more than a foot thick. The deposit on Long Island 

 is apparently not more than a few feet thick. 



The Sankaty sand on Nantucket Island, certain beds of which are by Dall 

 referred to the newer Pliocene, is described below as a Pleistocene interglacial 

 marine deposit. 



Quaternary System 



PLEISTOCENE SERIES 



EARLY INVESTIGATIONS 



New England is mantled with deposits of till, gravel, sand, and clay, the 

 superficial parts of which, at least, were laid down by an ice sheet that came 

 down southward to a front that extended along the New England Islands from 

 Nantucket westward across Lond Island. On Cape Cod. and the islands south 

 of it these glacial deposits have been subject to great disturbance, as well as to 

 erosion during epochs at least as long as those in which they were laid down 

 (see PL 6). 



In the earliest surveys of the New England Islands and Cape Cod the older 

 granitic gravel and sand were usually assigned to the Tertiary system, the de- 

 posits of which in this region are inextricably intermixed with the Pleistocene 

 beds by folding, faulting, and commingling. Thus, in the reports of Hitchcock, 

 Lyell, and Shaler, the older Pleistocene as now determined was not distinguished 



