Neighborhood Nature

Our Family's Nature Blog

Finding Fossils We Can’t Collect March 12, 2009

Filed under: Fossils,Geology,Rocks,Soil,Upcoming Events — saltthesandbox @ 2:54 pm
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While living a life consumed with raising boys and exploring living things for this blog, part of me is always thinking of the past. Sure, I think about my childhood and how it compares with the ones my boys are living. I also think about folks who built and visited Columbus Park a century ago.  Heavy rains bring ancient lakes and beach ridges to mind. But some things take me even further back, like a certain gray stone found in many buildings in the Park:

These blocks of limestone make the brick building stronger and more attractive.

The blocks of limestone make the brick building stronger and more attractive.

Looking closely at the blocks of limestone, there are fossils — evidence of ancient life and clues to the origin of this stone:

The yellow arrow points to a fossil stick coral. The red arrow points to a cross-section view of a brachiopod shell.

The yellow arrow points to a fossil stick coral. The red arrow points to a cross-section view of a brachiopod shell.

The rock is limestone, made of tiny bits of broken fossil hashed together and then cemented with a mineral called calcite. Because the fossils, like corals and brachiopods, are only found in sea water, this rock must have formed on the bottom of an ancient sea. Because these particular fossils match extinct species that lived about 350 million years ago, we know that’s when this limestone formed.

This limestone has other uses in the Park. On the covered terrace of the Refectory, limestone has been carved into urns and made into steps and building decorations:

Limestone urns and steps on the Refectory's covered terrace.

Limestone urns and steps on the Refectory's covered terrace.

A closer look at this limestone reveals another common fossil from the ancient sea:

The blue arrows point to fossil crinoid stems. can you find more examples in this rock?

The blue arrows point to fossil crinoid stems. Can you find more examples in this rock?

This type of limestone was quarried in Indiana and has an appropriate name: The Indiana Limestone. The fossils that we see today have been etched out in bas-relief as decades of acid rain dissolved the once-polished surface of the rock.  Go here for more information about fossils found in Indiana Limestone (photos half way down the Web page).

For the collectors in our family, finding fossils can be frustrating when we can’t take them home. So Dad’s found other ways to let kids collect fossils from the Indiana Limestone. Over years of collecting in southern Indiana, he’s scraped up several gallons of rusty-red soil from hilltops formed on Indiana Limestone. The dirt is filled with tiny fossils dissolved out of the rock over thousands of years (by rain less acid than what humans make today). Go here to see close-up views of the fossils we find.

Our family takes this “red dirt” to special events where kids collect its fossils. The next event will be the ESCONI Gem, Mineral, & Fossil Show on March 14-15, 2009:

ESCONI activity: Collecting fossil sealife from weathered Indiana Limestone.

ESCONI activity: Collecting fossil sea life from weathered Indiana Limestone.

Perhaps we’ll see you there?