Stone Row in Delaware Water Gap

Norman Muller writes:
...images of a stone row I was shown in the Pennsylvania side of the Delaware Water Gap two years ago.
The walls are made of local siltstone, but on top, every 15 or 20 feet, were rounded cobbles of quartzite. These were not found on the ground in the vicinity of the wall, but must have come from the Delaware River some 100 to 200 feet below. Also note the rounded and relatively thin stone leaning against the row. This is a common accent often overlooked by researchers. Just this spring I found one leaning against a probable Indian wall in Milford, PA