Correiipondence. 211 
took place all at once, allowing the water of the ocean to flood the 
whole Island, for in this case we would have to provide for another 
elevation followed Ijy a second subsidence, of which there is no proof 
whatever, unless it be in the stratified deposits of the north side of 
the Island which reach the altitude of 260 feet at Harbor Hill, but 
we know that such deposits can be formed by subglacial streams 
without an oscillation of land. It seems to me that the sea is nearer 
to our door than it ever has been since it overflowed its ancient bound- 
ary already referred t(». 
The Island remains very much the same as it came from the hand 
of the glacier, the only change being made by the inroads of the sea 
along the coast. There is not so much sinking as a wearing away of 
the superficial deposits of which the Island is chieflj' composed. 
As the sea invades the land, bays become part of the ocean, 
marshes become bays and swamps marshes ; and this accounts for 
stumps of trees being found under water; for some of the swamps 
and other depressions go down below the present level of the ocean, 
and where the land barrier, which protects them, has been swept away, 
the trees, which grew in them, of course become submerged. 
That these marsh lands existed at one time south of the present 
sea beach is evident from the quantities of turf that are washed upon 
shore during heavy storms. It seems certain that the streams that 
laid down the stratified deposits on the south side of Long Island and 
^lartha's \'ineyard came from the mainland ; I think I was the first 
to notice this fact, and it seems to be confirmed by professor Shaler 
as he says in his report: "That the material transported by sub- 
glacial streams, and accumulated in the kame and terrace deposits, 
was transported for a greater distance than the detritus that was 
carried in the body of the ice.'' 
This fact has not been sufficiently noticed in treating of the geologj" 
of Long Island, as it explains much that otherwise remains obscure. 
I claim that the indentations and bay depressions on the north side 
of Long Island owe their origin to subglacial streams, and not to spurs 
of ice as maintained by Dr. F. J. H. Merrill, late of Columbia College.* 
I have traced the connections of these streams from the sound to the 
sea, and while it is diflicult to follow them in all of their ramifications, 
yet their relationship can be proven, I think, beyond all question. 
The connection, of course, is now lost between the Island and the 
mainland, but the corresponding depressions on both sides of the 
sound suggest, if they do not imply, that they were at one time 
united. They must have been, of course, if it be true that the sub- 
glacial streams came from the mainland. Martha's Vineyard has 
the same bay indentations on the north ending in |)onds or marshy 
depressions as on Long Island. Professor Shaler sees some relation- 
ship i)etween them and the kame and terrace formations of the plain 
country on the south. and he notices the same fact.whicli I have often 
*See Ills impcr on tlie Geology of Loiii; Isslaiid. AiiiiaU of New York .Vcud. of SilPiice, 
Vol. iti, 1H*1. 
