In Bridgeton Township, upper
Bucks County, Pennsylvania, there's a big field of
rocks. It's a pretty striking thing - right out in the middle of the otherwise green and
verdant woods is around 8
acres of rocks,
boulders really, sticking up into the sun. Originally a layer of
igneous rock, the soil and softer rock above it were
eroded away (possibly by the
Delaware River), and then split into individual rocks by water which would seep in and then freeze. But that's not the interesting part.
The interesting part about Ringing Rocks is that the rocks, (obviously), ring. Hit the rocks with a metal object and you get a nice, clear, mellifluous tone. All the rocks ring, though only in about one out of every three rocks are tones produced in the human-audible range of the frequency spectrum. The exact reason for this is not absolutely clear, though it is believed to be related to the metallic content of the rocks (high in iron and aluminum), and perhaps to tension inside the rocks attributable to the aforementioned pattern of water freezing and thawing. Rocks with similar properties have been found in other places, including India, England, and China, but not in such abundance nor with identical physical makeup, and it is not clear whether this is the same phenomenon in action. Every now and then (first in 1890), someone will take samples of the rocks and use them in some sort of musical arrangement, the uniqueness and actual artistic value of which is usually overshadowed by a host of godawful "rock music" puns.
The rock field itself is the central attraction of Ringing Rocks State Park, which also includes parking, a picnic area, bathrooms, some walking trails, and a few waterfalls which can get pretty impressive in the spring thaw. It's a nice place to bring kids, and the uniqueness and natural beauty means it retains its appeal even to the older crowd - we came here on (I believe) the last day of high school, hit the rocks, ran races across the boulder field, walked along the (mostly dry) waterfalls. Fun will be had by all. Remember to bring a few hammers or the like to make music with.