After some clearing of the mind:

In the boundary of the Constitution Marsh and the Foundry Cove, is a
long stonework "dam" that has been breached in the middle, or just
appears to be, once a road to the island. The feature was associated
with rice cultivation in the Constitution Marsh part of Constitution
Island, and its fortification, across the Hudson River from (in Cold
Spring, NY, named by founding father George Washington due the spring
there) West Point, NY, the US Military Academy. The lack of road
(though one could walk down the modern R.R. tracks to it) has
preserved the island where once America strung a giant chain to stop
the advance of the British Royal Navy in its efforts to "divide and
conquer" the Colonies. The lack of road(s) has preserved the ecology
of the Constitution Marsh, held now by the State of New York and
Scenic Hudson, previously held by the Audubon Society. Similarly, the
lack of roads will preserve American forests!

(See "Bernard Romans: Cartographer for the U.S. Continental Army" by
Remo Salta, "Revolutionary War overlooks Dutch-born patriot"  in
"Mercator's World: The Magazine of Maps, Globes, and Charts" Vol. 1
Number 3 1996)

George Myers