besides the world's largest glacial pothole, pennsylvania has a little-publicized but mystifying natural wonder known as the ringing rocks. a couple of miles west of upper black eddy on the delaware river are four and a half acres of broken pock-marked red rocks which ring mysteriously when struck with a hammer or thrown onto the huge pile. in 1890 a dr. ott of pleasant valley assembled a musical scale of these stones and gave a concert accompanied by the pleasant valley brass band. these jagged stones differ from others in the area and no one knows where they came from or how they became to be pock-marked and broken into these jagged pieces. for size, note leaf in cavity of rock in close-up. some rocks are as big as footballs, others weigh many tons, but all are exceptionally heavy for their size.
from america's natural wonders: strange forests, mysterious caverns and amazing formations
by c. b. colby