Category: StreetSmartNaturalist

Overlooked but not Forgotten

Many people, including me, have written extensively about the famous white limestone from Indiana. In my book Stories in Stone, I call the Salem Limestone, “America’s Building Stone,” and as far as I have been able to discover, it is the only building stone used in all 50 states. Recently, however, I have learned of another white limestone often mistakenly described as Salem. Much to my pleasure, being a native of Kentucky, that other stone hails from quarries in Warren County, Kentucky, in the southwest corner of the state.

The story of the Bowling Green Oolite comes from research by Western Kentucky University geologists Mike May and Ken Kuehn. They found that the oolitic limestone was popular from the 1870s to the 1920s with the quarries shutting down around 1937. During that time it became famous for its pure white color and received a gold medal at the World’s Columbian Exposition in Chicago in 1893 and the highest award at the Louisiana Purchase Exposition (St. Louis World’s Fair) in 1904. A 1923 Kentucky Geological Survey Publication, written I am sure without any bias, described the Bowling Green rock as “The Aristocrat of all the limestones.”

The publication further noted one unusual aspect of the stone—petroleum “impregnated” the rock. Oil gave the rock a dingy and unpleasant color when first quarried and carved, but soon the evaporation of the occluded petroleum left behind a stone of “great whiteness and remarkable beauty.” And it goes without saying that Bowling Green Oolite had superior strength and durability.

Episcopal Church of Saint Thomas (from St. Thomas web site)

Like the Salem, the Bowling Green Oolite, formally known as the Girkin Limestone, is Mississippian in age. The Girkin is most famous as the stone where the Mammoth Caves of Kentucky formed. The stone crossed state boundaries, with structures such as the U.S. Custom’s House in Nashville, TN and the Hall of Records in Brooklyn, NY; and religious boundaries, going into Methodist, Presbyterian, Catholic, and Episcopal churches, as well as a synagogue. One of the most famous buildings is the Episcopal Church of Saint Thomas in Manhattan, finished in 1913, during the prime years for usage of white limestone from the Midwest.

I suspect that most buildings that I think of as Salem Limestone are Salem, particularly in areas in the west, but I now know that some may have been mislabeled. I look forward to finding more buildings from my home state.

Footprints in the Ash

Over the past couple of years, a controversy has arisen over possible human footprints in central Mexico. The disagreement centers on age and maker. Is the ash where the prints are preserved 40,000 or 1.3 million years old and did people out for walk produce the foot-shaped impressions or did more recent people inadvertently alter the rock and subsequent weathering and erosion form the marks? The simmering debate raises many questions but to me the focal point is the fact that the tracks occur in an abandoned building stone quarry.

Footprints in ash layers, from from web site of Sarah Metcalfe, University of Nottingham

The debate began in July 2005 when Dr. Silvia Gonzalez and her colleagues at Liverpool John Moores University reported that they had found 40,000-year-old human and animal footprints preserved in volcanic ash. The ash had fallen along a shoreline of a shallow lake in the Valsequillo Basin, about 80 miles southeast of Mexico City. If the dates are correct, it would make them the earliest evidence for people in the Americas. Gonzalez’s team based their analysis on accelerator mass spectrometry dating, electron spin resonance, Argon-Argon dating, and optically simulated luminescence dating. Knowing that the dates would be controversial, Gonzalez said at the time “It’s going to be an archaeological bomb and we’re up for a fight.”

By the end of 2005, a team at Berkeley Geochronology Center at the University of California Berkeley had responded. They reported that the ash dated to 1.3 million years old. Either the tracks belonged to our ancestor Homo erectus or, more likely, the impressions were not footprints but marks that resulted from quarrying. The California team also relied on Argon-Argon dating, as well as a paleomagnetic data. Their most recent and detailed analysis of the quarry site ash appeared in the March 2009 issue of Geology.

Numerous small quarries dot the Valsequillo Basin. The ashy layers split into thin sheets that can be used in roads and walkways. The track-rich quarry was abandoned relatively recently, according to Joshua Feinberg, formerly a graduate student at UC-Berkeley and now a professor at the University of Minnesota, but not before workers had removed several feet of lake sediments to get to the underlying hard beds of ash. As happened with the quarries examined by Gerta Keller for evidence that gases released by voluminous basalt flows led to the extinction of the dinosaurs, the Mexican quarry workers made the story possible by exposing the ash.

Quarried stone from web site of Sarah Metcalfe, University of Nottingham

“[T]he past quarrying activity really is an essential part of this story,” wrote Feinberg in an email to me. Not only did it reveal the tracks but he suggests that quarry workers left the marks in the ashy layer and that over time they eroded into shapes that Gonzalez’s team misinterpreted as human footprints. I will let the scientists duke out the when and who of the story but I do take pleasure in knowing that yet another building stone quarry makes the world a bit more interesting.