A drive across Greene County reveals a generally flat terrain that is punctuated by small hills and ridges, and in a few places, deep gorges and wide river valleys. All of this terrain, as well as the County’s productive farmland and deposits of valuable sand and gravel are remnants of giant sheets of ice called continental glaciers. At least four times over the last two million years glaciers have completely covered the County, the most recent one retreating from our area about 16,000 years ago.
Heavy, constant snowfall to the north became ice under its own weight, and the force of gravity pushed it southward. Sometimes over a mile high in Ohio, these glaciers were unimaginable bulldozers that completely obliterated forests and plugged up the old river systems.
Sometimes the climate would moderate and the glaciers would melt as fast as they advanced, and the pieces of rock that they had crushed and carried along were deposited in long ridges of sand and gravel along the front of the glacier that we call moraines. When a glacier was melting, rivers of ice would form inside of it, and sand and gravel was deposited in long lines which were left behind for geologists to call eskers.
A third type was gravel and sand that collected in a hole in the glacier, and when it departed, they were deposited as low lumpy hills called kames. Over all of this the finer crushed material in the ice was left behind like a big blanket called glacial till, the source of the county’s rich soils. As the climate warmed and the glaciers retreated the melting ice became torrents of water that roared southward carrying the glacier’s debris.
In places these flood waters cut deep gorges such as those near Clifton and Cedarville. They also filled up the river valleys that existed prior to their arrival, with deposits of sand and gravel.
Each glacier left behind a barren landscape that over time was re-colonized by plants and animals. The glacial period, or Pleistocene Epoch, was a time of marvelous animals that roamed what is now Greene County. Herds of wooly mammoths, mastodons, and long-horned bison roamed, and ground sloths, short-faced bears, saber-toothed cats, and many other wondrous creatures once called the county home when it was not covered with ice.
Not long after the last glacier left Ohio all of these creatures became extinct, for reasons scientists still argue about. Some say a changing climate changed the vegetation to a type that could not support the big animals. Others say humans, which first entered Ohio as the last glacier retreated, hunted the big animals to extinction. Some say it was a combination of these things. In any case, most of the small and medium-sized animals and birds survived and are still with us today.