A very old cover in Central Park?

This cover found in Central Park has some characteristics of a very early manhold cover. The structural design (the underside) of this cover is not clear. However almost all of the manhole covers in New York City (if not the world) are designed with one overriding concept, the cover should be level with the surrounding terrain. To do this the physical holes are topped with a rim, which is placed at the level of the surroundings. The cover is then seated within that rim, the seat being exactly the depth of the cover thickness. The cover, the rim and the terrain are all even; no horse or person will ever trip over that manhole. This cover instead is constructed to sit on the edge of the seat, like either a pint of ice cream or a stopper in a bottle. There will almost certainly be an edge to trip over. This plus the very minimal design suggest that this could be a very early example of a cast iron man-hole cover in New York City.