LCC students trudging up the Allegheny Plateau (copyright Dale Antolik)
I accompanied Dr David Pierce’s Physical Geology class to Lake Metroparks’ Chapin Forest Reservation the other day and learned a lot about the area I’ve lived in for the past 45 years. In fact, I not only learned about the geomorphology of the county, I learned what the word means, too: it’s the study of the Earth’s topography.
Lake County has two distinct geomorphic areas separated by the Portage Escarpment, which I-90 roughly follows. North of I-90 is the relatively flat Lake Plain. The plain extends south and includes North Ridge, Middle Ridge and South Ridge Roads, all of which were, at one time, the lake (or sea) shore.
South of I-90 are the foothills of the Allegheny Mountains, the hilly Allegheny Plateau–which for decades, many of us have casually referred to as The Snow Belt. Little Mountain is the most prominent feature of the area.
Outcrop of Sharon Conglomerate Sandstone
Dr. Pierce then directed the class’s attention to a large outcrop of the youngest rock layer in Lake County, 300-320 million-year-old Sharon Conglomerate Sandstone. The conglomerate in the sandstone is quartz, aka Lucky Stones.
The Conglomerate was deposited as a delta formation when our area was closer to the equator. A large river system carried the quartz and sand in its bedload and then dropped the load when it flowed into a large, ocean-like body of water. The sand and quartz pebbles settled out and consolidated into Sharon Conglomerate Sandstone.
When the Wisconsin Glacier passed through our area 10 to 12 thousand years ago, it scrubbed and scoured the surface of the land right down to the bare Conglomerate bedrock, leaving behind an expanse as bleak and barren as a moonscape.
So how was the flora abounding in the Chapin Forest Reservation resurrected?
Through the process of weathering.
All rocks at or near the Earth’s surface, as well as rocklike substances used in building and paving, decay and crumble with age. They’re experiencing weathering, the physical breakdown and chemical alteration of materials exposed to water, air and living things.
Weathering differs from erosion in that erosion depends on the movement of an agent such as wind, water or a glacier to alter a substance, whereas weathering occurs on site without movement.
Chemical weathering is altering the composition of this particular outcropping, and the agents of change are the tiny mosses and lichens clinging to it.
In the process of deriving nutrients from the rock, these non-vascular plants gradually reduce the rock to a pile of sand and quartz stones surrounding the rock—one grain of sand at a time.
Eventually, organic matter from the area combines with the sand to form a layer of soil from which ferns, weeds, and even trees eventually sprout and grow, as seen in the photo of the larger outcrop above. You’ll also see tree roots that have migrated to the surface and trail across the rock, seeking to gain purchase in the thin layer of soil forming on the Conglomerate.
A young beech sapling appears to stand on tiptoe as it clings to its base.
The tree roots themselves exert a chemical weathering effect on the outcropping through the release of organic acids.
Great oaks from little acorns grow. Big deal. But where would those little acorns be without the unrelenting chemical action of Moss Might and Lichen Power?
Gotcha, great oak!
For more information about the above, talk to any one of Dr Pierce’s students. I’m impressed by how sharp, how interested and how interesting the group is.
My thanks to Dr Pierce for fact-checking my text.