CAPE COD GEOLOGY 



215 



EOCENE MATERIAL IN RECENT WRECKAGE 



Fossiliferous phosphatic pebbles from a formation having no counterpart 

 in New England were left on the beach near Southwest Point on July 17, 1877, 

 by the wreck of the schooner William S. Skull, bound from Port Royal to Vine- 

 yard Haven. These pebbles, which are light yellow, rather porous, and contain 

 numerous cavities from which shells had been weathered out, were at first 

 thought to be peculiar to some Miocene formation not exposed on the island, 

 but inquiry proved that they came from the Eocene Cooper marl of South 

 Carolina. 1 



Coal often washes ashore from wrecks on or near the coast of Block Island, 

 and some pieces of crystalline rock foreign to southern New England may 

 have been carried to the beaches of the island from wrecks such as that of the 

 barkentine Alexander Campbell, laden with paving blocks from Maine, which 

 sank 7 miles southwest of Block Island on November 27, 1888. 



Pleistocene Formations 

 CLASSIFICATION 



Everywhere except along the strand and in the marshes Pleistocene or glacial 

 formations make up the great mass of Block Island, forming its surface material, 

 entering into its soil, and constituting its subsoil. These formations are exposed 

 in the Mohegan Bluffs, on the south coast, and at Clay Head, on the northeast 

 coast. They were early recognized as mainly of glacial origin and, together with 

 the surface boulders, were indicated on geological maps as part of the terminal 

 moraine that is traceable from Nantucket westward across Marthas Vineyard 

 to Long Island and thence far into the interior of the Continent. Later geologic 

 work showed that the glacial deposits of the island are divisible into several 

 beds of boulders, gravel, sand, and clay, and that the surfaces of these beds 

 show traces of old land forms that were in their time as distinct as the present 

 surface of the island. 



All the boulders, cobbles, pebbles, and granitic sands of the island except 

 the Cretaceous fragments already described appear to have been carried from 

 the mainland on the north, several varieties of rock having been identified 

 with those of ledges that lie as far north as Cumberland, R. I., and George's 

 Hill, in Leominster, Mass., The succession of glacial events has been set forth 

 in the introductory chapters of this report. What is here stated concerning them 



1 Dall, W. H. On the "land phosphate" of the Ashley River district, South Carolina, Am. Jour. Sci, 

 48, pp. 300-301, 1884. 



