44 



CAPE COD GEOLOGY 



Sanderson Smith recognized the northern aspect of these forms from Gardi- 

 ners Island, of which Dall recently remarked: 



The material appears to be practically identical from both localities and to represent the 

 fauna now existing in the Gulf of Maine or on the coast north of Cape Cod, a little colder water 

 being indicated than is now found south of the Cape. 



The fauna agrees with that of the upper beds in the Sankaty sand on Nan- 

 tucket in denoting colder water, and Fuller, 1 in his report on Long Island, refers 

 the Sankaty sand to the horizon of the Jacob sand. 



Of the species identified by Sanderson Smith and named in the above list 

 as coming from the Jacob sand, the following have been identified from the San- 

 katy sand: 



Crepidula fornicata Peden magellanicus 



Neverita (Natica) duplicata Venericardia (Cardita) borealis 



Lunatia (Natica) heros or triseriata Venus mercenaria 



Area transversa Mya arenaria 



Aside from Peden magellanicus and associates of Venericardia (Cardita) 

 borealis, the peculiar northern fauna of Pacific types in the upper part of the 

 Sankaty sand is not found in the Jacob sand. As the Jacob sand lies near the 

 middle of a great series of Pleistocene deposits of glacial origin (either as originally 

 deposited or through the rehandling of the material during submergence) it should 

 not be correlated with the Sankaty sand because of a similarity in the marine 

 fauna brought about by cooler water, for such changes of temperature must have 

 occurred as many times as ice sheets advanced. Furthermore, the physical evi- 

 dence on Cape Cod and Nantucket as to the stratigraphic position of the equiva- 

 lents of the Gardiners clay and Jacob sand indicates that the Sankaty sand under- 

 lies both these Long Island formations as well as the Jameco gravel. The prob- 

 able representatives of the Gardiners clay and overlying Jacob sand of Long 

 Island are, as Fuller first noted, found in the "clay pounds" of Highland Light 

 and in the overlying yellow sand beneath the lighthouse. The shell-bearing 

 Pleistocene beds encountered some 200 feet below sea-level in borings at Province- 

 town probably belong to a formation lower than the entire section in the outer 

 cliffs of Cape Cod and are nearly in the position of the Sankaty sand. The San- 

 katy sand is, therefore, here regarded as a fossiliferous facies of a marine shallow- 

 water deposit laid down along the east coast of Massachusetts during the first 

 interglacial stage, in a stratigraphic position equivalent to that of the glacial sand 

 and gravel of the Weyquosque formation, which contains no contemporaneous 

 fossils on Marthas Vineyard and Block Island. 



1 Fuller, M. L., Geology of Long Island, IT. S. Geol. Survey Prof. Paper 82, p. 114. 



