Geologic History of Folmont and Surroundings

If you stand on one of the great sandstone boulders on top of Bald Knob Summit you are 2,900 feet above present sea level and your feet are touching rock made mostly of sand and pebbles of quartz and feldspar that were deposited there over 300 million years ago in a slowly flowing river or on the shore of a storm-tossed sea.

If you are very lucky you may find fossils of the flora and fauna that died in the sand.  On the left is an early amphibian called Amphiniamus yelli.  On the right is Lebachia, an early relative of conifers.  Look closely and you may find a 300 million year-old fossil.

How can we touch something that old and how did it turn from a loose water deposit into solid rock 2,900 feet above sea level?  For millions of years after those grains were deposited countless layers of new materials were deposited on top and gradually built up pressure and heat, which, along with chemical reactions, fused the grains together, trapping the decayed remains of countless living things.  As time passed colossal tectonic forces then squeezed the continent to push these rocks up into a great mountain chain, once higher than the Rockies.  Thus, the area gradually changed from seas, rivers and swamps to dry land exposed to the elements of wind, water and ice that gradually wore down the mountain to what it is today.

That boulder you stand on is part of a sedimentary rock stratum called the Pottsville Formation.  It is the bottommost section of the Pennsylvanian Series of rocks famous for producing the great coal beds of the state.  The once overlying rocks of the Allegheny Formation contained several rich seams of coal that still exist west of Folmont and have been mined extensively in Somerset County.  The rock strata in our area of Allegheny Mountain dip to the west at a steeper angle than the land surface.  That is why there are coal beds west of Folmont, but none beneath us.  This westward dip has not only saved our land from the ravages of strip mining, but it continues to protect our water supply from any pollution originating in those mines.

Step off that boulder and head East, past Shawnee View or Hawk's Nest Road, then down the hill to the valley of Breastworks Run.  With each step you travel further back in time, through the so-called Mauch Chunk Shale, the uppermost section of the Mississippian Formation.  This rock, composed of interbedded sandstones and shales, holds the water that the "upper Folmontese" draw from their wells.  It lies in the cracks and interstices of the sandstones, held in pools at various levels by impervious shales and mudstones.  Near the bottom, at about 2,600 feet elevation, you find cool springs emerging from the Loyalhanna Limestone.  You have now traveled back another 10 million years, or about 3,000 years per vertical inch of rock.

Beneath the Loyalhanna, which is about 40 feet thick, is the Pocono Formation, from 500 to 1,000 feet thick.  These rocks outcrop on the eastern face of the Allegheny Front.  The Pocono is interbedded sandstone and shale and provides the well water supply for Folmont homes in the valley and a few of the deeper wells on top.  On and on below the Pocono are the Devonian, Silurian, Ordovician and Cambrian series of rocks.  The chart at left illustrates the various rock strata, their ages and a life record.

Allegheny Mountain eroded down over the millennia as surface rocks disintegrated into soils and were washed away into streams and rivers that carried them to sea.  Various flora and fauna evolved on the changing landscape, constantly adapting to changes in the chemical nature of the soils and wild fluctuations in the weather.  All traces of this history are forever gone, but the changing landscape provided homes to all sorts of new species of plants and animals.

After millions of years of warm climate that produced great swamps and forests and the many species of animals that thrived in them, a worldwide climatic cooling began the Great Ice Age. At times the climate was cooler and wetter and at times warmer and drier than today.  The Great Ice Age began a million or more years ago, in what is called the Pleistocene Epoch, about the time that modern man's ancestors began to appear.  The last major ice sheet to spread across the North Central United States reached its maximum extent about 20,000 years ago, but it never reached our area.  It never came closer than northwest Butler County, at Moraine State Park.  As the climate warmed, Allegheny Mountain stood aloof above the raging rivers that developed in the lowlands as the great Laurentide glacier, beginning about 20,000 years ago,  melted and receded back to the Arctic. 

During the times of glaciation, the parts of Pennsylvania that were not covered with glaciers had a climate much colder than now.  The ground was frozen to some depth throughout the year in a condition called permafrost. This climate caused frost heaving that pushed up large block of rock, including the ones on Bald Knob Summit and those you can find on the eastern face of the mountain.  You can even find some of these grey sandstone and conglomerate rocks in the valley of Breastworks Run.

Because of the cold climate, animal and plant life was quite different during the Ice Age.  At the height of the late Wisconsinan glaciation, about 20,000 years ago, Pennsylvania was covered with tundra, principally grasses, some spruce trees, and some other low shrubs. As the ice melted and the climate warmed, other forms of vegetation started to repopulate the area.  Both deciduous and evergreen forests developed. This succession started with spruce, pine and hemlock and eventually oak, chestnut, maple and hickory.

Of the many animals that were here during the ice age, many have become extinct, such as the saber-toothed cat, the mastodon, the camel and the sloth.  Evidence from archeological sites near Pittsburgh indicate that man was in Pennsylvania either during the last glaciation or shortly thereafter.  But that is the beginning of the next chapter in the history of Folmont.