Ringing rocks, also known as sonorous rocks or lithophonic rocks, are rocks that resonate like a bell when struck. Examples include the Musical Stones of Skiddaw in the English Lake District; the stones in Ringing Rocks Park, in Upper Black Eddy, Bucks County, Pennsylvania; the Ringing Rocks of Kiandra, New South Wales; and the Bell Rock Range of Western Australia. Ringing rocks are used in idiophonic musical instruments called lithophones.
Early investigations Several early scientists became interested in the ringing rocks; however, none were able to formulate a credible theory on the ringing ability of the rocks or the formation of the boulder fields.
Edgar T. Wherry (1885–1982), mineralogist and botanist, became interested in the ringing rocks while teaching at Lehigh University. Wherry theorized that the ringing was due to the texture of the diabase rocks and that they were supported by other rocks. He identified the boulder fields as a type of felsenmeer.
At the 13th Annual meeting of the Bucks Historical Society in June 1900, Charles Laubach, a noted local geologist and naturalist, described the geology of the diabase "trap" sills with reference to sites such as Bridgeton, Stony Garden, and others.
Benjamin Franklin Fackenthal (1851–1941), local industrialist and trustee of Franklin & Marshall College, became interested with the ringing rocks. Although not a professional geologist, Fackenthal made extensive observations on all of the boulder fields.
In 1965, geologist Richard Faas of Lafayette College took a few of the rocks back to his lab for testing. He found that when the rocks were struck, they created a series of tones at frequencies lower than the human ear can hear. An audible sound is only produced because these tones interact with each other. Although Faas's experiments explained the nature of the tones, they did not identify the specific physical mechanism in the rock which made them.
Sites in Pennsylvania
Although there have been over a dozen diabase ringing rock boulder fields identified in the Pennsylvania and New Jersey area,For an extensive inventory of sites, see Pontolillo, J., and Pontolillo, J. (1993) "Ringing Rocks Sites in Pennsylvania and New Jersey" INFO Journal #68. the majority are either on private property or have been obliterated by urban development. There are three sites north of Philadelphia which are readily accessible to the public: Ringing Rocks County Park, Stony Garden, and Ringing Hill Park.
Ringing Rocks County Park
Ringing Rocks County Park, also known as Ringing Rocks Park, is a Bucks County park near Upper Black Eddy in Bridgeton Township. Originally, the land was acquired by the Penn family from the Lenape (Delaware Nation) through the infamous 1737 Walking Purchase. It is not clear who made the original land warrant for the area now covered by the Ringing Rocks County Park. On the 1850 property map of Bucks County, the owner appears to be Tunis Lippincott; however, there is no warrantee listing under that name. The earliest published description of the Bridgetown boulder field is found in Davis 1876. The seven-acre boulder field was purchased in 1895 by Abel B. Haring, president of the Union National Bank in Frenchtown, New Jersey. Apparently, Haring wished to protect the ringing rocks from development, and even refused an offer from a manufacturer of Belgian blocks for the right to quarry the stones. On August 22, 1918, the land which contains the Bridgeton Boulder Field was donated by Haring to the Bucks County Historical Society. The grant included 7 acres 8.08 perches of land. A right-of-way was granted by John O. McEntee for access to the park. Later, the land was transferred to Bucks County and operated as a county park. Additional land acquisitions have increased the size of the park to 129 acres.
Ringing Hill Park
Ringing Hill Park is located three miles northeast of Pottstown, Pennsylvania in Montgomery County. The boulder field was first identified in 1742 when a road was cut between Pottstown and New Gosenhoppen (Pennsburg). In 1894, the Ringing Rocks Electric Railway Company was incorporated to purchase the remote Ringing Hill for an amusement park and provide trolley service (1894 to 1932). At the time it was created, the park was approximately out of town. The park was purchased in 1932 by Walter J. Wolf and operated as an amusement park and skating rink. On September 1, 1957, the park was sold to the Ringing Hill Fire Company.
Stony Garden The Stony Garden, largest of the three public ringing rock boulder fields, is located on the northwest slope of Haycock Mountain in Bucks County, Pennsylvania, near Bucksville. The garden is actually a series of disconnected boulder fields which extend for nearly half a mile, and were formed where the olivine diabase unit crops out along the base of the mountain. The site is undeveloped, and is accessible by a hiking trail which leads from a PA Game Lands parking area on Stony Garden Road. It was purchased by the Commonwealth of Pennsylvania around 1920 as part of PA Game Lands Tract #157, which covers Haycock Mountain.
Buckwampun Historical Society meetings The ringing rock boulder fields were popular places for meetings of the local Buckwampun Historical Society. Two annual meetings were held at the Bridgeton site (in 1893 and 1898), and one at Stony Garden (in 1890). The Bucks County Historical Society also had a meeting at the Bridgeton site in 1919, the year after they acquired the property.
At the third annual BHS meeting in June 1890 a local physician, John J. Ott of Pleasant Valley, gave a musical performance using boulders taken from the Stony Garden boulder field. The suggestion for the construction of the lithophone was made by the historian William J. Buck. The rocks weighed approximately apiece, and apparently Ott was able to change their sound by slightly chipping the boulders. He played several selections using a steel hammer and accompanied by a brass band. "The clear, bell-like tones of the rocks could be heard above the notes of the horns." The tunes included "Home Sweet Home" and a composition of his own entitled "Sounds from the Ringing Rocks" – possibly a takeoff from the 1873 piano music score of the same name.
Formation These boulder fields in southeastern Pennsylvania and central New Jersey formed from a group of diabase sills in Newark Basin. The sills were formed when stretching of the Earth's crust allowed mafic magma to travel up from the upper mantle inject into the sedimentary basin 200 million years ago (early Jurassic Period). Phenocrysts of two minerals that had crystallized in the upper mantle, olivine and pyroxene, quickly settled out of the magma and collected along the base of the sills. When fully solidified, this crystal-rich layer formed a separate rock unit thick. By the Pleistocene Epoch, the sills had been exposed to the surface by crustal uplift and erosion. During the Pleistocene, outcrops of the olivine diabase were not buried by the glacial sheets; however, they were subjected to severe freezing, or periglacial, conditions. The periglacial environment caused the outcrops to be broken into extensive boulder fields.
Geology
The basal olivine unit is similar to the one found in the Palisades Sill in New Jersey and New York. The olivine diabase unit is significantly harder, denser, and more resistant to weathering than the upper portions of the diabase sill.
Most observers did not make the distinction between the upper "normal" diabase which is found over wide areas, and the thin olivine diabase unit found at the base of the sills which actually produces the ringing rock boulder fields. A main factor in the confusion is the outward appearance of the rocks. Both the normal and olivine diabase rocks are dark grey to black in color. Microscopic examination is often required to identify the differences.
Although the Newark series diabase sills crop out in a belt throughout the length of the Appalachian Mountains, only a narrow band of outcrops in southeastern Pennsylvania and New Jersey develop ringing rock boulder fields. The probable reason is that these areas were at the southern edge of the Pleistocene glaciers, and would have been subject to extreme periglacial conditions. Periglacial boulder fields are a common feature in Pennsylvania and New Jersey.
All of the observed ringing rock boulder fields in southeastern Pennsylvania and New Jersey are a form of felsenmeer (felsenmeer is a German term meaning "sea of rock"). These barren block fields occur in periglacial environments where outcrops of resistant rock are exposed with a slope of less than 25°. Frost wedging breaks up the upper portion of the rock formation, and the slight dip of the field allows the fine weathering materials to be flushed away before soil can develop. Often, the boulders are lifted and rotated by the accumulation of snow and ice, leaving a considerable amount of vacant space between them. The felsenmeer boulder fields form in-situ due to the low-slope angles. In situations where the slope angles are steeper than 25°, gravity tends to move the boulders downhill to form scree or talus slopes. In fields where the angle is too flat, the spaces between the boulders fills with soil and the boulders break down due to weathering.
Because the olivine diabase unit is relatively thin there was an additional requirement for the formation of the ringing rock boulder fields: the olivine diabase unit had to be dipping in the same direction as the slope of the ground surface. This specific dip-slope situation allowed broad expanses of olivine diabase to be exposed and provided enough material to create the fields. In all of the observed boulder fields the structural dip of the unit was approximately 8-10°, and the ground surface slope was <15° in the same direction. Typically this occurred where the olivine diabase unit dipped at right angles into a shallow drainage. Where the olivine diabase does not dip in the same direction as the ground surface there are generally numerous boulders embedded in the soil (boulder colluvium), but no boulder fields.
Ringing ability
There has been a great deal of controversy concerning the ringing ability of the boulders; conversely, there has been an almost complete lack of testing to support the conjectures. Conditions such as size and shape of the boulders and the way that the boulders are supported or stacked certainly influence the sounds that the boulders make but do not in themselves impart the ringing ability.
Although the sound is often described as metallic, it is most likely due to a combination of the density of the rock and a high degree of internal stress. The sound can be duplicated on a small scale by tapping the handle of a ceramic coffee cup.
The iron content of the diabase is often identified as the source of the ringing ability. Actual chemical analysis of the Coffman Hill diabase shows that iron content (as ferric oxide) of the rock ranges from 9% and 12%. Although comparatively high for an average igneous rock (3% is typical for granite), it is within the normal range for a basalt. This point suggests that the iron content is not a primary factor in the ringing ability.