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CENTRAL OHIO AREA
These two locations are excellent examples of the Ohio Shale, which is a black shale. The black color of the Ohio Shale comes from the high amount of organic material present in the rock. These rocks were deposited on the floor of a moderately shallow ocean during the Devonian period, approximately 360 million years ago. This rocks yields some small marine fossils but has an abundance of oil and gas, which can be smelled on a fresh rock surface.
At this location, once can see excellent examples of the Ohio Shale (described above). Within the Ohio Shale at this location, there are large seemingly perfectly round, iron concretions. These concretions are usually formed around small pieces of organic material. These concretions are extremely heavy and make nice lawn decorations.
These caverns show a good example of groundwater at work. The rocks are formed from the dissolution of Devonian-aged limestone by the groundwater over a long period of time. Once in the caves, you will notice the presence of stalagmites and stalactites, which are composed of calcite, which was once part of the limestone before it was dissolved.
As one drives south on Rte. 23 south towards Circleville, one can see some very unassuming geologic structures. The gravel pit at the intersection of 23 and 270 is a remnant of the outwash plain of the Pleistocene glaciation. Further south on Rte. 23, you can see a moraine and the Circleville esker, both of which are associated with the Pleistocene glaciation.
Old Ma’s Cave in Hocking Hills State Park is not really a cave. Old Man’s Cave is a large overhanging outcropping of the Black Hand Sandstone. The Black Hand Sandstone was deposited in a deltaic setting during the Late Mississippian, roughly 300 million years ago.
The entire area in the southwestern part of the state is covered with very fossiliferous limestones. These limestones were formed in an ancient ocean during the Ordovician Period, approximately 450 million years ago. When looking at these limestones, one can find brachiopods, bryozoans, corals, and trilobites.
When visiting the eastern part of Ohio, one can see large amounts of coal. Coal is one of this country’s most useful natural resources. The coal of eastern Ohio was formed in ancient swamps roughly 305 million years ago from the remnants of ancient trees.
When visiting Put-in-Bay, one can also have a chance to see possibly the world’s best example of glacial grooves. The grooves on South Bass Island were formed when large rocks became lodged between the bedrock and the Pleistocene glacier. The rocks were dragged through the bedrock, leaving these awesome ice-aged remnants.