I was looking for more Mound Swamp 2006 photos, and while I was doing that, I came across this one from the same year, taken a mile or more away, standing in my driveway:
House of Undocumented Age (Circa 1700?), detail of the stone retaining wall and NE entry to yard.
Sometimes the light hits the stone just right, so that you can see the marks made by whatever tools were used as field stones were dressed to fit this wall together.
Sometimes the imaginative investigator can observe Something Serpentine about those marks: