228 



CAPE COD GEOLOGY 



reach of the waves, which undermine and remove the materials delivered by- 

 landslides to the beach. No exact estimate of the rate of recession of Mohegan 

 Bluffs is available, but the Coast Survey chart of the island issued in 1914, 

 which shows the coast line as it existed in 1913, furnishes a basis for concise 

 comparisons in future years. 



Sandy Point, at the north end of the island, is continued under water as a 

 long, narrow spit or bar to the site of an island that was tied to Block Island 

 by a bar that was passable on foot at low tide. According to Livermore, the land 

 at the end of the point, which was called "the Hummock," was a small elevation 

 covered with bushes and small trees, including wild plum trees. It appears to 

 have been washed away about a hundred years ago. Sandy Point now stands 

 at the north ends of two beaches, one crescentic in form, making southeastward 

 past Cow Cove toward Grove Point, and the other forming the straight shore 

 of the west side of Corn Neck. Between these two beaches lies Sachem (Chagum) 

 Pond. The beach on the west side is backed by a line of dunes. 



The beach on the west side, at Great Salt Pond, is tied to two small drift 

 "islets, which partly inclose that body of water. 



Crescent Beach, on the east coast, is the longest stretch of beach on the 

 island that is unbroken by headlands, and is near the center of population during 

 the summer. In the southern part of Corn Neck it is cut back into low bluffs, 

 and farther south it is thrown across what would otherwise be open passageways 

 into Great Salt Pond. The beach is swept by gales that veer from northeast 

 round to southeast and is constantly undergoing minor changes that involve 

 a slow gain of the sea upon the land. It is notable for its fine black sand, most 

 of which accumulated in the form of dunes south of its mid-point. The beach 

 has derived a large share of its material from Clay Head, but some pebbly 

 drift is fed into it from the bluffs south of Clay Head. 



Were it not for the southern stretch of this beach the sea would pass freely 

 between the two main parts of the island. At least two or three small islets of 

 glacial drift that lie in or near these cordons of sand are tied by them to the 

 island. (See Plate 31, fig. 2.) 



DUNES AND WIND ACTION 



Narrow tracts of low dunes that are well tufted with beach grass lie back 

 of the east beach and along the west side of Corn Neck. The sand is com- 

 posed mainly of quartz, garnet, and black iron ore or magnetite, which are 

 washed by the waves out of the glacial drift. The magnetite sand deserves 

 special mention because of its local abundance. 



