- Trails are open 24/7 at no charge. Enjoy a Winnie-the-Pooh themed TRAIL TALES Storybook Walk.
What’s Happening: Weather Whiplash
At Crossroads, we’ve been experiencing a bit of weather whiplash this winter — thaw one day, sleet rattling the windows the next. In Door County, that’s hardly surprising. In fact, more than 25 years ago…several years before Crossroads at Big Creek became a non-profit organization, but rather, when the land was still the 60-acre school forest of the School District of Sturgeon Bay, rapidly fluctuating weather helped inspire the creation of a nature center. The Sturgeon Bay Education Foundation recognized that if conditions could shift from mild to bitter in a matter of hours — as they often do— students needed a place where they could step out of the elements and continue learning.
A central feature of the plan was a stunning fireplace built of Door County stone. Around that same time, a local farmer was subdividing his property, which meant dismantling an old stone wall. He invited the school to collect the rocks.
So, a group of school employees and members of the Sturgeon Bay Education Foundation Board borrowed a couple of trucks and headed out. I was easily the least efficient member of the team because, for me, the outing was a fossil hunt. I knew there would be many weather swings in the years ahead. So, during construction, I asked the mason to place fossil-rich stones at about kids’-eye level. If we were going to build ancient geologic history, we might as well make it accessible.
On Saturday, February 21 at 2:00 p.m., our Saturday Science program will feature an Indoor Fossil Hunt. If we get a thaw, we may venture outside to search for fossils strategically placed in the entry garden. But regardless of the weather, learners of all ages will discover and identify examples of Silurian fossils indoors. Each participating family will receive a free fossil identification pamphlet.
So why do we have fossils here?
The Door Peninsula is made of rock formed roughly 430 million years ago, during the Silurian Period. At that time, the land that would become Wisconsin was located near — and at times slightly south of — the equator. Our region lay beneath a warm, shallow tropical sea.
That sea teemed with life: solitary and colonial corals, brachiopods (often nicknamed “lamp shells”), and early relatives of modern squid. When these creatures died, their hard shells and skeletons settled into lime-rich sediment on the sea floor. Over immense spans of time, as many seas advanced and retreated, these sediments were buried, compacted, and hardened into many layers of limestone.
But the rock we see today is not limestone — it is dolostone (also called dolomite rock). I sometimes say dolostone is like limestone on steroids — a little stronger, a little more resistant. The difference, however, isn’t steroids; it’s magnesium.
After the limestone formed, magnesium-rich fluids moved through the buried rock, replacing some of the calcium in the mineral calcite (calcium carbonate) with magnesium to form the mineral dolomite (calcium magnesium carbonate). Geologists aptly call this transformation dolomitization. Scientists agree on the chemistry but continue to study exactly when and under what conditions those magnesium-rich fluids altered vast stretches of the original limestone.
The resulting dolostone is generally more resistant to erosion than pure limestone. That durability helped the Door Peninsula endure — and be sculpted by — the repeated advances of Ice Age glaciers that ultimately shaped the Great Lakes basin.
Stone tells the deep-time story. Fish tell the modern one.
More than 400 million years after tropical seas covered this region, the newly formed Great Lakes became a freshwater paradise for fish. But that story took a dramatic turn in the 20th century, when invasive species such as sea lamprey and alewife nearly devastated the lake ecosystem.
– by Coggin Heeringa, Interpretive Naturalist
For more information, please check out our Crossroads calendar or stop by the Collins Learning Center and pick up a printed calendar. Our trails are open all day every day, free of charge, thanks to donors like you!
Crossroads at Big Creek Learning Center and Nature Preserve is located at 2041 Michigan Street, Sturgeon Bay. Crossroads is a 501(c)(3) organization committed to inspiring stewardship of the environment through education, research, and outdoor experiences. We welcome your support.
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