“The plaque draws attention to this boulder that was unearthed near Nankin in Ashland County in the summer of 2017 by the Kinder Morgan Co. during construction of the Utopia East Pipeline,” said Dr. Nigel Brush, professor of Geology at AU. “It was found on the property of the John Keener family by a neighbor, Robert Brownson, who recognized its significance and reported it to the State Historic Preservation Office in Columbus.”
Brush said that Brent Eberhard of the State Historic Preservation Office then contacted Dave Dyer, who is the Curator of Natural History at the Ohio History Connection in Columbus: Dale Gnidovee, who is curator of the Orton Geological Museum at Ohio State University; and Brush to see if those respective institutions might be interested in recovering the boulder for display.
“Since Ashland University was closest to Nankin, they gave us first option on the boulder and we were very pleased to display it and tell its story,” Brush said.
Dr. William Reinthal, an adjunct faculty member in Geology at Ashland University, explained that this large igneous boulder originated on the Precambrian Shield in Canada and was formed deep underground over a billion years ago, probably at the base of an ancient volcanic mountain range.
“So, this rock has been through the wringer. Chemically eroded, this rock then began its new transformation into soil, until it was, unexpectedly, unearthed during pipeline excavation, only to be preserved for our benefit and study, at Ashland University,” Reinthal said. “This rock, quite literally, speaks of the Earth, and deep time.”
Reinthal noted, “The oldest, black portion of this boulder is a mafic-rich, hornblende-biotite, quartz monzonitc. This rock was later subjected to compressional stresses that yielded a characteristic 60/120 degree set of joint fractures that were often terminated, perpendicular to the angular intersections, by horizontal fractures. This produced a repeating trapezoidal pattern.”
Reinthal said that at a later date, a pink granitic magma came into contact with this black quartz monzonite and flowed into the joint fractures, spreading them apart and eventually isolating trapezoidal chunks of the monzonite in a matrix of granite. “This event also occurred deep within the earth as evidenced by the pegamatitic or coarse texture of late elements of the granitic inclusion, which formed veins containing large potassium feldspar crystals,” he added.
After hundreds-of-millions of years of erosion, overlying layers of rock were removed and the roots of this ancient volcanic mountain range were exposed. This rock was subsequently fragmented by weathering into boulders, cobbles and smaller sediments, Brush said.
“Some of these rock fragments, including this boulder, became embedded in a Canadian glacier during the Ice Age and were carried south into Ohio where they were deposited as glacial till when the ice sheet melted,” he said. “The boulder may have been deposited in this manner during the most recent glacial stage – the Wisconsin, some 70,000 to 10,000 years ago. Notice the large, shallow, polished glacial groove running from left to right across the front of this boulder.”
Finally, buried in a glacial till deposit near Nankin, the mafic minerals in the older quartz monzonite in this boulder, weathered away faster than the felsic minerals in the younger granite, he said. “This differential weathering produced the marked relief on the surface of this boulder with the more resistant granite standing out above the more deeply incised monzonite,” Brush said.
“Ashland University would like to thank the family of John Keener for donating this boulder, Kinder Morgan for loading the boulder and Simonson Construction Services for providing a truck to transport the boulder to campus and a large forklift for unloading the boulder,” he said.