42 



CAPE COD GEOLOGY 



time. He also found a single specimen of the extinct species Chrysodomus stonei 

 Pilsbry. 



The occurrence of a species that is elsewhere unknown above the Miocene 

 on the Atlantic coast and of a species of older Pleistocene age, so regarded, has 

 to be taken with much circumspection in determining the age of the deposit. I 

 found in the beds at Squam Head a shark's tooth of the type of Charcarodon, 

 together with triturated shells, showing that the Miocene deposits there had been 

 worked over into the overlying Sankaty beds. Again at Nashaquitsa cliffs, in 

 1899, I collected more than seventy fossil Tertiary shark's teeth from beds of 

 older Pleistocene gravel, unaccompanied by other traces of organic remains. 

 The redeposition of organic remains is common in the shore phases of several 

 fossiliferous beds on this coast. The isolated occurrence in these beds of organic 

 forms that are elsewhere peculiar to older strata should have little weight in 

 determining their age. 



Dr. Wilson confirms earlier observers in recognizing a lower and an upper 

 series of layers in the Sankaty sand, characterized by faunal differences. The 

 lower beds he described as containing prevailingly species of Ostrea, Venus, and 

 Mya, along with mud crabs, an assemblage indicating shallow water protected 

 from the open sea. The upper beds carry an Arctic fauna — Macoma incongrua, 

 Serripes laperoussi, and Pandora crassidens. The association of the local newly 

 identified species Aslarle sankatyensis with these species in the upper shell beds 

 led Dr. Wilson to regard it also as a cold-water form having a northern range or 

 as one that had become extinct. 



In regard to the horizon carrying Macoma incongrua, Dall stated * that he 

 regarded this species as probably upper Pliocene; but he was under the impres- 

 sion that the lower beds carry this Arctic fauna, whereas Wilson states that the 

 Arctic fauna was found in the upper beds. Although the beds at Sankaty Head 

 are tilted, and although the same beds between that plain and Squam Head, 

 as observed in 1915, are folded over into a vertical position, nothing has been 

 found at Sankaty Head to warrant the belief that the beds there are overturned 

 in such a way as to lead to the supposition that the lower one is of Pleistocene age 

 and the upper one of upper Pliocene age. Dall wrote as follows: 2 



There is no particular reason why Macoma incongrua should not be Pleistocene as well 

 as Pliocene, since it is now living on the Pacific side. I take it that the glacial epoch cut off the 

 intercommunication between the two sides of the continent; but there is no reason why some 

 of the Pliocene species should not have lingered on into the Pleistocene on the Atlantic side. 



1 Letter to J. B. Woodworth dated November 14, 1916. 



2 Letter dated November 9, 1916. 



