1893. ] NEW YORK ACADEMY OF SCIENCES 199 
through what are known as Plum Gut and The Race, where a 
depth of over fifty fathoms is found, which would soon become 
sufficiently eroded to nearly empty the trough and convert it 
into a broad river extending east and west, 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 
clearly indicated in the soundings made by the coast survey, 
as pointed out by Prof. J. D. Dana*, and as may be seen by a 
study of the coast survey chart of the region.+ 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 rapidly 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,{ 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 place 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 mainland by a body of 
* “Tong Island Sound in the Quarternary Era., ete.” (Am. Journ. Sci., xl., 
425-437.) 
+ ‘General Chart of the Coast no. viii. Approaches to New York, Gay Head 
to Cape Henlopen.” U-S§. Coast Survey. 
t“ Final Rept. Geol. N. J.” (1868), pp. 343-373. 
