Mound with hollow, Shirley

Took one interesting walk last weekend but my path brought me right up in the face of some private property. As you can see from the map, this site is between a lawn and a marsh called "Spruce Swamp".

I was headed for the eastern and southern portions of the swamp's verge, thinking that is the most likely place to find things, where you can look outward towards an open space. Sure enough, parting the bushes and stepping through:

The ferns help you see there is a hole in the middle.

This looked like it might have been another:

I wanted to walk all the way around the pond, looking for other examples, but you can see why I could not go any further in this direction.
For reference, the edges of the marsh also had what looked like old stone wall - between these "mounds" and the water:

The presence of short linear stretches of wall -  adjacent to mounds with hollows - is very typical. The intuition to go where the view outward is to the west is just that - an intuition. But I believe when an intuition is firmly established, that it should be possible to confirm statistically.