THE ROCK ROLLING BENEATH WISCONSIN

Carol King was talking like a geologist when she sang,

“I feel the earth move under my feet.”

On our land, you don’t have to look very far to hit what I thought until recently was solid rock.  When we dug the foundation for our barn, we hit pure white sandstone.  When we trenched to try to stop the spread of oak wilt, we dug into that same stone.  A little higher up the hill, the rock pokes right out of the ground in places.  Throughout the Driftless Area, the rocky outcroppings are one of the things that earns it high ratings on the scenic-o-meter.

...Blue Mound, some of the newest rock in the state, as viewed from the top of our land.

But what is that rock?

According to Roadside Geology of Wisconsin by Robert H. Dott, Jr., and John W. Attig, mountains, inland seas, volcanoes, glaciers and major earthquakes formed our rock in the dim past going back to granite created when molten magma cooled 2,800 million years ago.  That ancient rock is still visible in the Baraboo Hills.

When geologists read Wisconsin’s history, they find a few pages missing.  About 400 million years of rock record evidently just dried up and blew away, so we’ll skip to the end when the ice ages slowly swept glaciers back and forth over this part of the world during the past 2.5 million years.  (practically yesterday) The last one began about 100,000 years ago and it’s only been about 10,000 years since the most recent glacier edged north.

Geologists believe because the ice was thinning as it reached Southwestern Wisconsin Highlands that the modest raise in elevation was just enough to finesse each glacier to the east and west around it.  All that ice just eased on by the southwest corner of Wisconsin and neighboring parts of Illinois, Iowa and Minnesota.  What glaciers leave behind is called drift.  That’s why this area is called the Driftless Area.

..the rocky outcropping at the top of our ravine.

Our rock was shaped not by frozen water, but instead by running water.  Our soil is mostly made of loess, fine-grained clay and silt particles that were blown here by the wind and piled up at one point to a depth of 2 feet, which helps make good soil.

I have a lot to learn before I can read rock, but I did learn a little stone vocabulary at the presentation on Groundwater and Geology of Southwest Wisconsin by Bill Batten and Madeline Gotkowitz at a workshop sponsored by the Military Ridge Prairie Heritage Area last Saturday held at Folklore Village Folk Arts and Culture Center.

Wisconsin’s newer layers of rock have melodious names like Saint Peter Sandstone, Maquoketa Shale and Silurian Dolomite.  They were laid down in thick deposits at the bottom of ancient seas.

When you find fossil shells of trilobites, brachiopods and snails captured in Wisconsin stone, you are looking back in time to a very placid place.  Fossils don’t form in turbulent water, says Batten.  Those beautiful shapes are an echo of peace –the kind of long, deep stillness we can only imagine.

But in an earlier epoch, that self-same spot may have made Pompey look like a picnic.  Volcanoes erupted, seas advanced and receded.  Plates shifted Again and again.

The next time you settle down on a sun-warmed slab of sandstone, hold on tight.  Though we are too short-lived to see it, that rock is bobbing about like an ice chip in the tumbler of time.

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