1893.] NEW YORK ACADEMY OF SCIENCES 199 



tlirougli what are known as Plum Gut and The Race, where a 

 de])th of over fifty fathoms is fouucl, which would soon become 

 sufficiently eroded to nearly empty the trough and convert it 

 into a broad river extending east and Avest, until, with subse- 

 quent subsidence the sea could enter and gradually transform 

 it into the Sound as we now know it. Such a river channel is 

 clearl}' indicated in the soundings made by the coast survey, 

 as pointed out by Prof. J. D. Dana^'S and as ma}- be seen by a 

 study of the coast survey chart of the region. f If the depths 

 were relatively the same then as now the first outlets would 

 have been to the eastward, but as tidal erosion has proceeded 

 much more rapidl}' there than at the western outlet, due to the 

 more easily eroded strata, it is not safe to assume this, and I 

 am inclined to think that the outlet was wholly at the western 

 end for a considerable period, until the subsidence was suffi- 

 cient to cause a break to be made through the eastern end of 

 the moraine, and permit the sea to enter. Tidal scouring would 

 then soon effect the depths which we see at Plum Gut and The 

 Race. 



The present rate of coastal subsidence, as calculated by Prof. 

 Geo. H. Cook, I and other authorities, is about two feet per 

 century. At this rate, six thousand years ago practically the 

 whole of the area included within the present twenty fathom 

 contour would have been above sea level — only the deepest parts 

 of the trough of the Sound being below it— one })lace near 

 Eaton's Neck showing thirty-two fathoms and another near 

 Horton's Point reaching a depth of twenty-seven fathoms. This 

 area, as may readily be seen, includes the whole of Staten Island, 

 Long Island, Block Island, Martha's Vineyard and Nantucket, 

 besides a respectable portion of the submerged coast eastward 

 and southward. It is also probable that at least a part of this 

 area to the eastward, which at the present time is lower than 

 the twenty fathom contour, has become disproportionately so 

 in modern times by tidal scouring, and that it was actually and 

 relatively higher formerly than now. 



Under these circumstances we should, therefore, have had, 

 during a considerable period of time, a continuous strip of 

 land, except for the river outlets, all the way from New Jersey 

 to Massachusetts, separated from the uuiinland by a body of 



* " Long Island Sound in the Quarternary Era., etc.'' (Am. Journ. Sci., xl.. 



425-437.) 



t " General Chart of the Coast no. viii. Approaches to New York. Gay Head 

 to Cape Houlopen." U- S. Coast Survey. 



t " Final Kept. Geol. N. J." (1808), pp. 343-373. 



