Rocking Stone & Perched Boulder, Milford/ Hopkinton MA.
The first 2 pics are the rocking stone, which is different from a drum stone. Drum stones are shell shaped and were worked out (usually) from the boulder platform they balance on. Drum stones also have a distinct sound they project as well as a high frequency vibration. The rocking stones on the other hand, such as this one appear to be more crude. They still balance on a ledge and weigh a few tons, and can be manipulated with the push of a hand, which is still awesome. Here is the Rocking Stone:
Nearby to some cairns and stone mounds was this other perched boulder. It did not rock (but perhaps it did at one time):