40 



CAPE COD GEOLOGY 



Weyquosque Formation (Glacial) 



This formation is named from exposures found for the last thirty years at 

 the east end of Nashaquitsa cliffs, on the south side of Marthas Vineyard, at the 

 locality known to the inhabitants as Weyquosque. In its more sandy phases 

 the deposit has a peculiar brownish or greenish shade, its color appearing to 

 depend upon the presence of glauconite derived from the Miocene greensand bed 

 at the Gay Head district. The gravelly phases of the deposit contain pebbles of 

 granite and other undecomposed feldspathic rocks. At Weyquosque (Nasha- 

 quitsa) the formation rests on a bed of fossiliferous gravel composed of debris 

 derived from Miocene deposits, or possibly from the Aquinnah conglomerate, and 

 from lignitic Cretaceous beds, commingled with a few pebbles of granitic and 

 similar rocks, such as characterize the glacial series. This local basal layer is evi- 

 dently of later origin than the Aquinnah conglomerate, which is of early Pleisto- 

 cene age. The upper part of the bed at Nashaquitsa is cross-bedded on a large 

 scale and is succeeded unconformably by a bed of boulder clay. Similar deposits, 

 also tinged with green or brown, occur on Nonamesset Island and at the base of 

 the Pleistocene on Block Island. In the Gay Head cliffs, beds of gravel and sand 

 occupying the same basal position give way in places to the basal deposit of coarse 

 cobbles and boulders called the Dukes boulder bed. 



In 1889 about 70 waterworn fish teeth, chiefly those of sharks, were col- 

 lected at Nashaquitsa. They were evidently redeposited from broken-up beds 

 of Aquinnah conglomerate or from Miocene fossiliferous deposits. 



The beds of Weyquosque glacial sand and gravel lie essentially at the same 

 horizon as the marine Sankaty sand of Nantucket and Cape Cod. 





Sankaty Sand (Marine) 



In 1896 the gravel and sand lying above the Dukes boulder bed at Gay Head 

 were referred to the horizon of the fossiliferous sand on Nantucket and named 

 the Sankaty beds, because of the identical structural relations beneath the un- 

 conformably overlying Wisconsin drift and of the belief then held that the beds 

 of fossiliferous sand at Sankaty Head are of Pleistocene age. It now appears 

 probable that the Sankaty beds are a constituent part of the older Pleistocene de- 

 posits as here defined, and that the beds constitute a marine fossiliferous forma- 

 tion lying along the east coast of Massachusetts in a position equivalent to the 

 beds of glacial sand and gravel on Marthas Vineyard and Block Island that are 

 here named the Weyquosque formation. 



In reports on investigations made long ago at Sankaty Head by Verrill and 



