Amazingly Talented RocksSoutheastern Pennsylvania is dotted with sites where rocks ring when struck by a hammer. These include the Stony Garden (Haycock, Bucks County), the Devil's Race Course (Franklin County), and others in the South Mountain region and at Pottstown. By far the most famous site, and the most studied, is in Upper Black Eddy in Bucks County. It is located a mile west of the Delaware River near the New Jersey state line.
Set in a forested area, the Ringing Rocks appear in a field which has no vegetation except lichens. Ten feet thick and seven acres around, the rocks are composed of diabase, in other words part of the earth's basic crustal structure. There is nothing unusual about them except that when struck hard, they ring. In June 1890 Dr. J. J. Ott, backed by a brass band, played a few selections on the rocks for an appreciative Buckwarnpurn Historical Society gathering. Ott, in short, had learned what other investigators have since confirmed: that the rocks don't have to be in their natural location to ring. They do not even have to be intact.
Curiously, though made up of the same materials, not all of the Ringing Rocks ring --only about 30 percent of them, according to those who have experimented with them.
Though this is undoubtedly a natural phenomenon, it is an odd one for which no fully satisfactory explanation has ever been proposed. In 1965 geologist Richard Faas of Lafayette College, Easton, Pennsylvania, conducted laboratory experiments using sensitive equipment. He learned that when he struck a ringing rock, a series of subaudible frequencies were produced, and these added up to a tone that could be heard by the human ear. He could not, however, determine a specific physical cause.
Some writers have made remarkable almost occult ---claims for the ringing rocks, asserting that something about the rock field spooks animals, even insects, which make a point of keeping their distance. There is nothing especially mysterious about this, according to investigator Michael A. Frizzell, since the area is barren, open, and hotter than the surrounding forest during the summer, thus generally inhospitable to living creatures.
More interesting is a claim made by the late Ivan T. Sanderson, though since then there has been no published replication: - There are some larger rocks which, when hit appropriately, give rise to a whole scale; ... two different ringers when knocked together while suspended on wires produce (invariably, it seems) but one tone, however many different combinations are used."
Ringing rocks have been noted all over the world. Curiously, the kinds of rock possessing such talents vary. The absence of clear patterns in the creation of such odd geological phenomena continues to frustrate theorists.