16 



CAPE COD GEOLOGY 



sea level in southeastern Massachusetts and Rhode Island. Fragments of an 

 Eocene fossilif erous limestone have been recognized by W. 0. Crosby in the glacial 

 drift near the top of the bluff at Highland Light, on Cape Cod, and fragments of 

 a reddish friable sandstone containing Eocene fossils have been found in glacial 

 deposits on Chappaquiddick Island. These fragments may have been dragged by 

 glaciers from the bottom of the Bay of Maine, where, possibly, Eocene beds still 

 exist, but they afford scant evidence that the Eocene sea encroached upon the 

 lowland of southeastern Massachusetts inside the present shore line. 



The Eocene rock found by Crosby J in the glacial gravel at Highland Light 

 was described by him as occurring about half a mile south of the lighthouse up 

 to a height of 125 feet and for 20 to 30 rods along the face of the cliff. It is a firm, 

 massive white, calcareous sandstone, which effervesces freely with acid, and yet 

 to the eye is composed principally of rounded grains of transparent quartz. 

 It contains also minute grains of glauconite, vestiges of lignite, and grains of 

 iron oxide. The fossils, which are in the form of molds or internal casts, are only 

 fragments. Crosby's list and notes are given below: 



Eocene Fossils Found in Fragments of Limestone in Drift at Highland Light, Cape Cod 



Venericardia planicosta, Lamarck. Found also 



in lower Eocene of Virginia 

 V . puna Lea? 

 V. alticosta Conrad? 

 Casts of fragments of two other species of 



Venericardia 

 Ostrca divaricata Lea. Possibly 0. sellaeformis 



Conrad. Found also in the lower Eocene of 



Alabama 

 0. virginianae? 



Ostrea sp. A large thick shell 

 Plicatula fdamentosa Conrad, or a form very 



near this species 



Camptonectes clavatus Conrad. Found also in 

 middle Eocene in South Carolina 



Axinaea staminea Conrad? Fragmentary 

 shells, difficult to determine 



Cardium sp. 



Yoldia or Nuculana sp. 



Corbula sp. 



Turritella sp. 



Natica sp. 



Cidaris sp. 



Galaxea sp. 



Crosby inferred that these fossil-bearing boulders were derived from an 

 Eocene bed somewhere north of Cape Cod, in the region of the floor of Massa- 

 chusetts Bay, but more recent investigations indicate that the boulders brought 

 to that part of the Cape by the ice were moved west of south. These Eocene 

 boulders were evidently found in drift that had been shifted and worn by the 

 action of water after they had been released from the ice. If the clay of the so- 

 called "clay pound" at Highland Light is of the same age as the Gardiners clay, 



1 Proc. Boston Soo. Nat. Hist., 20, pp. 136-140, 1879. 



