CAPE COD GEOLOGY 



211 



on the island, the number of Indians had dwindled to 51 in 1774, and a century- 

 later only a single survivor of the race was alive. An occasional stone arrow 

 or celt found in the soil of the island is now the only witness of their one-time 

 lordship. 



In addition to the map that accompanies this report (Plate 29) there is 

 available for reference a large-scale map published by the U. S. Coast and 

 Geodetic Survey, which shows the topographic features of the island in great 

 detail. 1 Were it not for the cordons of beaches and strips of marsh land that 

 connect the several parts of Block Island, it would appear on the map as two 

 larger and several much smaller islands. The northern part of the island, known 

 as "Corn Neck" or "The Neck," rises gently from the western coast to the 

 steep bluffs of Clay Head and Balls Point, on the east coast. This part of the 

 island is extended into the waters of the Sound by a sandspit of recent formation, 

 known as Sandy Point. A dangerous shoal lies farther north, on the site of an 

 isle that disappeared within historic time. 



The main southern part of the island, including the highest elevation, 

 Beacon Hill, which reaches an altitude of 210 feet above mean sea level, ends 

 abruptly on the south coast in steep cliffs, 110 to 150 feet high, known as Mohegan 

 Bluffs, a wall of boulder clay, other clay and sand, which, from the ravages 

 of sea waves below and rainfall above, displays fallen masses or the gullied slopes 

 of mountains in miniature. The boulder-strewn beach at the base of these 

 bluffs is one of the most desolate tracts on the eastern coast of the United States, 

 an ever-changing ragged coast, the terror of shipwrecked mariners and the 

 despair of the owners of the land along the brink, who from time to time witness 

 the fall of their land into the sea. 



GEOLOGY 



The formations exposed above sea level in the cliffs of Block Island consist 

 of beds of gravel, boulder-clay, other clay and sand, ranging in age from Upper 

 Cretaceous to and through Pleistocene. The glacial deposits include boulders 

 of granite and gneiss derived from the ancient crystalline rocks of the adjoining 

 mainland. The formations that lie below sea level near the island and the main- 

 land probably include several hundred feet of beds of Cretaceous clay and sand, 

 which lie upon the seaward sloping surface of a basement of ancient crystalline 

 rocks. 



iU. S. Coast and Geodetic Survey, Chart 356, scale 1/10,000. 



