Limestone results from an accumulation of the bodies of ancient sea creatures, giant mollusks and shellfish, on the sea floor. The source of this marine water may have been from ancient oceans. As sea creatures decomposed, and were layered down under more debris of plant and sea life, they became“ lithified,” or compressed into rock.
We find horn corals, brachiopods and shelled creatures in this limestone. It is much harder and resistant to erosion, but its layering is not so apparent. Being harder it is a better building material than sandstone. We see Bedford limestone used in the construction of many buildings on IU’ s campus, Washington, D. C., and even the Kremlin in Moscow. Limestone will be here for many many years, with its characteristic caves and sinkholes.
A good friend who worked at the Indiana Geologic Survey years ago helped me understand the types of sandstone and its derivatives.
He was first curious about early maps of the county that listed a“ Limekiln Ridge” in Brown County State Park. He told me kilns, a type of oven, were early methods of heating limestone rock that turned into powder that farmers used on their fields. Unsure how these early farmers knew to apply it, local acid soils were neutralized with the powdered lime, producing a better crop of hay or potatoes. This method proved successful over time.
If there was a limestone ridge, my friend thought
it might have eroded over time. No kilns were found on our forays in the park.
He showed me a method of testing sandstone particle size. He touched a piece of sandstone to his tongue. You may have had sand in your mouth— maybe as a youth playing in a sandbox— and know it is gritty. Sandstone has larger particles than siltstone, and siltsone has larger ones than clays, the tiniest particles of all. Based on particle size he could determine how the rock was layered.
To demonstrate, he placed water into a jar with sand and let it settle. The heaviest particles settle first, then sandstone and silts, followed by shale and siltstone particles. The lightest clay particles were at the top. This might explain why the early Brown County potters would find clay on the tops of ridges.
Though regional shifts occur, and strata will not always settle appropriately, this can help us understand the layering of bedrock and its consistency.
Our Brown County hills present many challenges to those of us who live here, but we adjust and deal with them, even during the snowy and icy part of winter.
You may have wondered how these hills got here, what glaciers had to do with their construction, and when that period occurred. I’ ll cover our glacial period next time.
Drive, hike, and ride carefully to enjoy this magnificent place and these hills of ours. •
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