282 



CAPE COD GEOLOGY 



made in January, 1873, had joined the mainland near Chatham lights. For 

 some time after the gale of November 15, 1871, the bluff near Chatham lights 

 was exposed to the sea. Later the bar was re-formed in the manner shown on 

 the chart of 1887. Since that time the hook on the north side of the inlet has 

 grown southward about a mile. In 1916 the inlet was correspondingly south of 

 its former position, and the Monomoy Beach joined the land at Chatham. 



The swampy tract between Chatham and Morris Island is represented on 

 Champlain's chart as an open passage which, according to Mitchell, became 

 closed between 1752 and 1772. In 1916 the tide was flowing across the swamp 

 and bar on the north side of the island. 



Monomoy bar, on Monomoy Island, undergoes frequent changes. Again 

 resort must be had to the reports of Henry Mitchell 1 for an account of it, from 

 1784 to 1885. 



From this account it appears that the south end of Monomoy has shifted 

 eastward as if it had fallen back with the retreat of the headlands on the north, 

 and the southern tip has advanced southward much more rapidly. During the 

 first period of accurate surveys of the position of the south point, between 

 1840 and 1853, the point gained in southing only about 140 feet. During 

 the next three years, between 1853 and 1856, the point gained 509 feet to the 

 southwest at a rate of 170 feet a year. At the time of the next determination of 

 its position, in 1868, the point was about 2,123 feet farther southwest, an advance 

 made in 12 years at the rate of about 175 feet a year. In June, 1886, the point 

 has grown southward, but at a slower rate, 22J feet a year. Mr. Mitchell con- 

 cluded that the longshore drift from points north of Chatham became lodged 

 somewhere north of Monomoy. It also became evident that the growth of the 

 flying beach was subject to periods of maxima and minima of change. 



Between Monomoy and Great Point, the corresponding flying beach at 

 the entrance to Nantucket Sound, there are numerous shoals of shifting sand. 

 These form a sort of broad belt, which curves eastward. Fear has arisen that 

 the flying beaches of Monomoy and Great Point might be built up by the sea 

 on the crest of these shoals in such manner as to close the entrance to Nantucket 

 Sound. This change, which would be fraught with embarrassment to the coast- 

 wise navigation, seems now, so long as land and sea remain stable, not likely 

 to take place, because the shoals lie well eastward and seaward of the flying 

 beaches, which are not only inclined inward, toward the axis of the sound, but 

 are moving in that direction. This inward movement of the flying beach is 



1 Ann. Rept. [Massachusetts] Harbor and Land Commissioners for the year 1886, pp. 37-46; with 

 map. Boston, 1887. 



