Rock Hounds Drawn to Indiana Road Cuts

ByABC News
March 11, 2004, 2:20 PM

B E D F O R D, Ind., March 15 -- The hills of southern Indiana presented a uniquechallenge for roadbuilders during the construction of Indiana 37 inthe late 1960s and early '70s. When they couldn't go over the hillsor around them, they went through them.

The resulting "road cuts," shear walls of exposed rock, are asdistinctive a feature in the southern half of the state ascornfields are in the northern half.

It wasn't long after their appearance that the road cutsstarting drawing geologists and amateur rock hounds, who were eagerto get a closer look at these exposed slices of earth.

Indiana University geology professor Robert Wintsch said thecuts along Indiana 37 offer a unique learning experience. Wintsch,who teaches freshmen geology courses, will take his classes onfield trips to local streams, quarries and to the rock walls alongthe highway.

"It's a beautiful place to explain how things that lived in theocean that covered Indiana 350 million years ago have beenpreserved," he said.

According to Wintsch, the makeup of cuts varies from place toplace along the highway. The northernmost ones, just north andsouth of the Beanblossom Creek valley north of Bloomington, arecomposed of a siltstone layer, called the Edwardsville Formation,topped with a layer of limestone, called the Harrodsburg Formation.

Finding Collectible Pieces

"The siltstone is cemented together poorly," Wintsch said."It will wash away like a sand dune. The limestone is moreresistant. That's why you get overhangs the siltstone underneaththe limestone washes away."

For fossil and geode seekers and rock hounds, the place tosearch is the point of contact, where the siltstone meets thelimestone, Wintsch said.

"That's definitely where you find most of the fun, collectiblepieces," he said.

As you travel farther south you move into an area of thickerlimestone, called the Salem Formation. This is where the quarriesare found.

"It's homogenous so it doesn't break apart easily. This allowsit to be cut up into large pieces," Wintsch said. "But fossilsand geodes are very rare in this type of limestone."