Old rocks of Delaware County


Who cares about a bunch of old rocks? For the untrained eye, they may seem boring from a distance. I thought rocks were boring too until I saw the Grand Canyon. But if you look at the creek beds and rock walls in our county with the same enthusiasm that you look at larger, showier rocks, you might see them differently.

Tuesday, Jan. 7, is Old Rock Day. Rocks are an important resource that we rely on for many material items that we use every day. You may have heard the saying, “If it can’t be grown, it must be mined.” Every single physical object that we use either comes from plants or rocks and minerals, and plants are grown in soil that is made up of nearly 50 percent rocks and minerals. So you could say that we rely on rocks for everything in our lives.

Many of the soils in our county are so rich because of the glacial deposits from which they formed. Agriculture continues to thrive here partially due to the minerals that glaciers carried. Not only were the glaciers from 11,000 years ago significant to the geology and soils of our county, but so were the warm, shallow seas from about 400 million years ago. The ancient sea that covered the region was filled with snails, clams, and other shelled animals. Their shell fragments and fossils are what make up the limestone that covers the western half of Delaware County. The Olentangy River is not only the dividing line of our county, it is also the line between the limestone and shale on either side.

The Olentangy Caverns is a unique attraction that is made up of the karst limestone on the western side; the brittle shale layers and sandstone are on the eastern side. The shale can be seen in the river banks of Highbanks Metro Park, as well as many other creek beds on the eastern side of the Olentangy River.

Karst topography is fascinating to look at, but it also poses threats for landowners. Karst is an area underlain by limestone, which is easily dissolved by water, and therefore forms sinkholes. While our limestone is much more durable than in other parts of the country, landowners in Concord, Scioto and Radnor townships should be cautious of this.

Homeowners in the eastern part of the county need not worry about sinkholes, but should be conscious of the high radon levels present in the shale under their houses. My house lies just east of the Olentangy River, and we have 30 times the amount of radon that is accepted by the Environmental Protection Agency in our basement. The shale deposits affecting us today were carried from the Appalachian Mountains by the forces of wind and water, at least 350 million years before humans even existed.

On a much smaller time scale, it takes about 500 years for one inch of topsoil to form. Rock has to be broken into tiny pieces, which happens through freezing and thawing, rain, stream and wind action, as well as root action. Eventually rock gets broken down into sand, silt and clay, and mixes with leaves, and other organic matter. You can imagine that this is a long process. While it is a much shorter time period than it takes rocks to form, it is still hard for us to fathom.

This is why it is imperative to protect our soils with cover crops, crop rotations, no-till, and other conservation practices. Mother Nature does not have the time restrictions that we do as humans. Farming without conservation practices can remove the topsoil that took 500 years to 400 million years to form, if you count the time it took the original rocks to form.


By Erin Wolfe

Delaware Soil & Water Conservation District

Erin Wolfe is the outreach coordinator of the Delaware Soil & Water Conservation District. For information, go to www.soilandwater.co.delaware.oh.us.

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