Ringing Rock Park is located near the town of Pottstown
I first tried to hit the rocks using the rental mini-van metal jack, but no tones were produced. Some of the larger boulders produced some bell-like tones when stuck with a 10 pound rock.
The boulders themselves are basaltic rocks that intruded into the surrounding red shale (or so says the Philadelphia Mineralogical Society). After doing some web research, it appears that the best implement to produce sound is a hammer of some kind. One web page states that different hammers will produce different sounds when hit against the same rock. Perhaps a light claw hammer and a 2-pound sledge hammer would make for an interesting set of drum sticks.