Ohio State Parks harbor a surprising array of awe-inspiring geologic features, from yawning recess caves to rock shelters hanging perilously from hillsides in the Hocking Hills. These geologic wonders stand in such stark contrast to the surrounding land that it might appear as though they were placed there by some momentous event. Jolting shifts in the Earth’s crust have indeed played a part in molding the Ohio landscape in the ancient past.
But a more subtle force than the sudden violence of earthquakes has transformed solid blocks of rock into monumental landforms. The steady flow of water has shaped delicately arching roofs, carved out passageways, hollowed out alcoves and precisely balanced boulders.
The Hocking Hills region boasts the state’s greatest legacy of geologic marvels including Old Man’s Cave, Ash Cave, Rock House, Cedar Falls and Cantwell Cliffs.
The natural wonders so abundant in the Hocking Hills region are etched into the Black Hand sandstone. This remarkable rock layer extends in a crooked band from the Ohio River into east-central Ohio.
The Black Hand sandstone gets its intriguing name from a huge image of a human hand sketched in soot on the face of a cliff in the gorge of the Licking River near Newark. The large black hand was destroyed by construction work on the Ohio and Erie Canal in the late 1820’s and was believed to be drawn by prehistoric Indians to show the way to the great flint deposits at Flint Ridge.
The Black Hand sandstone was formed in the middle of the Mississippian period, about 330 million years ago, when the climate was balmy and much of Ohio was covered by a shallow sea.
At that time, distant mountaintops to the east and southeast were whipped by wind and water, eroding coarse sand and pebbles from their lofty peaks. These particles tumbled through large mountain streams flowing northward into Ohio’s sea, and collected in a long narrow delta with finger-like branches.
At first the delta deposits were smooth and uniform, but as the sediments accumulated over time, changes in the stream flow and sea currents dumped piles of coarse sand and concentrated larger pebbles in some places.
Eventually, finer sand and mud washed down from the mountains, accumulated over the top of the delta, and buried the coarse sand.
This process continued for nearly 85 million years, and the weight of this heavy burden pressed down the delta sediments. Specks of silica along with iron oxide carried in the ground water helped cement the sand grains and pebbles into a solid rock formation 80 to 250 feet thick.
As shifts in the Earth’s crust uplifted the area and the sea drained away, rainfall began collecting in rivers and streams, gradually cutting channels over the landscape. The same slow process that formed the sandstone bedrock millions of years before began to slowly dismantle it.
During the Pleistocene Epoch, two million years ago, temperature plummeted and great ice sheets from Canadian highlands crept south into Ohio. Glaciers advanced and retreated at least four times, plowing through 56 of Ohio’s 88 counties, until the final retreat of the Wisconsinan glacier 13,0000 years ago.
Near the edges of the glaciers, huge volumes of meltwater gushed through the stream channels, speeding up the erosion process. Over thousands of years, the constant drip of percolating groundwater through tiny pores in the bedrock began to wash away the cement, while the steady stream and occasional torrent raging over the top loosened the grains and carried them away.
Where the streams crossed narrow but deep cracks in the rock known as joints, water easily penetrated and erosion gained a foothold, slicing through entire layers of rock millions of years in the making.
Because the middle of the Black Hand sandstone formation is cross-bedded and less firmly cemented than the top and bottom layers, the middle zone proves more vulnerable to erosion.
Thus, the hollowed recesses and rock shelters are formed in the “softer” middle zone while the very resistant upper and lower zones remained intact as the roof and floor.
The ancient rock monuments we marvel at today seem both timeless and eternal. As we lift our eyes to admire them and step inside to explore, we share an experience with Ohio’s very first human inhabitants.
We have preserved them in our parks and natural areas to pass them along as a legacy to future generations.
But these natural wonders are not permanent. Even the resistant rock layers atop our beloved recess caves and rock shelters must eventually yield to the unstoppable force of erosion.
Meanwhile, as long as we have them to inspire us and feed our imaginations, they have the power to transport us back thousands of years in time to the days of Ohio’s untamed wilderness.
-Credit given to “Ohio State Parks Magazine”
Written by Jean Backs – Editor