30 



CAPE COD GEOLOGY 



nants. Fossils found in glacial drift on Nantucket must have been derived from 

 Miocene beds. In 1890 I found a Tertiary fossil near Shimmo Point and Miocene 

 fossils near Polpis Harbor, both on Nantucket. I also found a nodule of green- 

 sand in the drift 1| miles west of the town of Nantucket, and in 1915 I found a 

 waterworn tooth of a shark (Megalodon) in a bed of Sankaty sand at Squam Head, 

 near the east end of Nantucket. The Miocene deposits of Nantucket, like most 

 of those of Marthas Vineyard, Block Island, and Long Island, were probably 

 wholly removed by the action of the sea and of the ice at the beginning of Pleisto- 

 cene time. 



The Miocene marine deposit of southeastern Massachusetts affords the 

 northernmost trace of the Atlantic Ocean on the east coast of North America 

 in mid-Tertiary time. (Fig. 2, p. 28). 



PLIOCENE SERIES 



A thin bed of marine sand containing a Pliocene marine fauna was found 

 by Gratacap near Southampton, Long Island, and fossiliferous sands of Pliocene 

 age have been recognized by Dall at Gay Head, on Marthas Vineyard. 



Dall, 1 who examined and identified the marine fossils in a large collection 

 made at Gay Head, states that, ' 'On the whole, these specimens indicate a more 

 recent fauna than the Miocene on Marthas Vineyard and may perhaps be re- 

 garded as representing the Pliocene." These deposits of marine fossiliferous sand 

 have apparently nothing in common with the so-called "Lafayette formation" 

 of the southern coastal plain, though they occupy about the same stratigraphic 

 position. The results of Dall's investigations at Gay Head would seem to favor 

 their reference to an early rather than to a late Pliocene age, and they are, there- 

 fore, probably somewhat older than the ' 'Lafayette formation." 2 No apparently 

 equivalent beds of marine sand of Pliocene age have been recognized on the 

 coastal plain north of Virginia. 



Shell-bearing beds of sand have been found on Long Island, Gardiner's 

 Island, Fisher's Island, at Gay Head, on Marthas Vineyard, and particularly at 

 Sankaty Head, on Nantucket. Most of the fossil shells are those of species now 

 living either in adjacent marine waters or along the coast south of New York. 

 In the upper part of the section at Sankaty Head forms have been found which, 

 though not now known on the Atlantic coast, are living in the seas of Alaska. 

 Prior to the discrimination of the several divisions of the Pleistocene deposits in 



1 Dall, W. H., Notes on the Miocene and Pliocene of Gay Head, Marthas Vineyard, Mass., Am. 

 Jour. Sci., 48, p. 300, October, 1894. 



2 On the general nature and interpretation of the so-called Lafayette formation, see Shaw, E. W., 

 U. S. Geol. Survey Professional Paper 108-H, pp. 128-132, 1918. 



