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Nothing’s set in stone, but new map is good start

Source: Joe Blundo. The Columbus Dispatch, Tuesday, October 17, 2006.

Underground Ohio is no longer quite so hidden.

The state has a new bedrock map, a colorful pastiche of shales, limestones and dolomites that I look forward to understanding some day.

In the meantime, I can at least appreciate the effort required to chart in intricate detail the subterranean strata above which we work and play. It is as if someone scraped away several hundred feet of surface to reveal what’s beneath.

This is the state’s first bedrock map since 1920. Even the geologists who made it concede that’s a darn long time — and these are people who talk about the Paleozoic Era the way I talk about last Tuesday.

"We have been working on it for my entire career," said geologist Mac Swinford of the Ohio Geological Survey. "That’s 24 years of collecting data."

Because I’m going through a geological phase (you may remember my June 11 story on the rocks exposed by the Rt. 33 bypass), I had Swinford and Thomas Berg, survey division chief, point out some fascinating bedrock facts.

Here are a few:

  • It has always seemed odd to me that the highest point in the state (about 1,550 feet) is not in hilly southeastern Ohio but near Bellefontaine.

    The high spot is represented on the map by an area of orange that designates the so-called Bellefontaine Outlier. Without getting too technical (because I can’t) let’s just say the Outlier is a knob of really hard rock laid down hundreds of millions of years ago.

    When the glaciers came along between 2 million and 10,000 years ago, they couldn’t erode it. But they piled sediment (glacial till) on it that reaches 160 feet thick atop Campbell Hill, the highest point in the state.

  • At the other extreme, a valley hundreds of feet deep angles through western Ohio, not a particularly canyonesque area to the naked eye.

    The ancient Teays River that once flowed northwest through Ohio cut this chasm. The valley is 450 feet deep at its deepest spot in Concord Township in Champaign County.

    We can’t see it because the glaciers that destroyed the Teays River drainage system buried it under 720 feet of till.

  • The hardest part of Ohio may be South Amherst in northern Ohio, where Berea sandstone reaches 200 feet thick. It was formed 350 million years ago.

    The sharpest rocks in the state may be the flint deposits in southeastern Licking County. The roundest rocks are concretions — cannonball-like masses that form in shale and are common in Franklin County.

  • Amid the map’s streaks of color lies a circle of chaos that even my untrained eye recognized as weird.

    It’s the so-called Serpent Mound Impact Structure in Adams County, where geologists surmise that a meteorite struck 250 million to 300 million years ago. The name comes from the Serpent Mound, built there by American Indians, perhaps 1,000 years ago (or five minutes ago in geological time).

    The impact area, where Adams, Highland and Pike counties meet, is about 4 miles in diameter. Instead of lying in tidy layers, the bedrock there is shattered and upended, as if hit by a giant hammer, Swinford said.

    Talk about cosmic location: First it was indented by a celestial body, then sculpted into a serpent whose head is aligned to the summer solstice.

I think I see a new tourism slogan developing: Ohio — where heaven meets Earth.

Joe Blundo is a Dispatch columnist.
jblundo@dispatch.com

Ohio Governor’s Residence and Heritage Garden
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