Beneath Prairie Seas
Ouch!!! Pain shoots up your leg and into your spine as you fall backwards, splashing in the surf. In terror, you see a creature as long as you that looks something like a giant scorpion. One of its pincers is grasping your foot, and you’re not too sure you’re going to survive. “Will it drag me into the deep and drown me? Or will it kill me with a poisonous bite?”
Having already shaken the horrid creature off, you crawl onto the beach in agony as the sea scorpion crawls away. Looking at your foot, you see blood, but the bite really isn’t that serious. Basically, you just pinched, and the pain was mostly in your head.
In your panic, you didn’t even drop your booty — a handful of exquisite crinoids and a trilobite. The crinoids, or “sea lilies,” are dead; they were torn from the seafloor by a violent storm the other day. But the trilobite is quite alive. You forget all about the bite you just received as you hold the bizarre, ancient creature. The sun beats down fiercely, and you’re glad you brought some suntan lotion along.
Such is life during the Silurian and Devonian periods, some 345-435 million years ago. Prehistoric Indiana is located south of the Equator! It’s mostly underwater, too. About the only land you’ve seen are some sandy beaches resting on coral reefs. There are no palm trees, flowers or grasses. You haven’t seen or heard a single insect or bird. It’s almost as if you landed on an alien planet — with beautiful sandy beaches!
Geology & Fossils
For many millions of years, Indiana has generally been a flattish area of low elevation that has frequently been submerged under shallow seas. It’s possible that there were dry land areas inhabited by dinosaurs during the Mesozoic Era. But most Mesozoic rocks and fossils have long since been eroded, perhaps even before Ice Age glaciers began scouring the land.
Thus, Indiana’s fossils consist primarily of marine invertebrates from the older Paleozoic Era. Fossil fans have talked about adopting a type of crinoid found near Crawfordsville as state fossil. Crinoids found in Ordovician to Mississippian formations are among Indiana’s most abundant fossils. Indiana has supplied beautifully preserved crinoids to museums and universities throughout the world.
But Indiana’s most famous and important souvenir of ancient seas is Indiana limestone. Adopted as the state rock in 1971, it might be thought of as Indiana’s official fossil.
A souvenir of ancient seas, limestone is made of the remains of countless marine animals, but mostly from the shells of tiny animals. It is made of a mineral called calcium that is used to make bones and shells. Fossils of larger animals that sank to the seafloor after they died are also found in limestone. Limestone covers vast areas of the Midwest and is of great commercial importance.
Indiana is home to some of the most famous limestone in the world. Formed during the Mississippian Period, more than 300 million years ago, it is called Salem Limestone, or “The Salem.” (It is named for the city of Salem.) It is known for its strength, attractive color, durability, and abundance.
During the Silurian and Devonian periods (345-435 million years ago), what is now Indiana lie south of the equator. Coral reefs dotted warm, shallow seas covering northern and central Indiana. Over millions of years, sediments buried the reefs, which became part of limestone. Quarries operate in these ancient reefs (which are now on dry land). The chief deposits are in south central Indiana, though extensive layers underlie much of the southern part of state. Indiana is the world’s leading producer of limestone.
Many of the most important buildings in the United States, such as the Empire State Building in New York City, are made of this building stone. People also use Salem Limestone for carving artwork. Limestone quarries supply crushed stone used in road construction and lime, a product used in agriculture.
While ancient seas left limestone, exotic forests left coal. More bituminous coal occurs in Indiana than anywhere else in the nation, most of it in the Illinois Basin in southwestern Indiana. Obtained primarily in southwestern and central Indiana, petroleum is another important fossil fuel.
Ancient Fossil Hunting
One of North America’s most famous fossil-collecting areas is in the Ordovician (435-500 million years ago) rocks of southeastern Indiana and adjacent parts of Ohio and Kentucky. These rocks are located around an enormous uplift called the Cincinnati Dome. The best places to search for fossils of marine invertebrates called bryozoans, which resembled corals, are in this region.
Indiana in the Ice Age
During the Ice Age, glaciers covered about 80% of Indiana, reaching south to the Ohio River and even beyond into Kentucky. Southcentral Indiana was untouched.
In northern Indiana, evidence of these glaciers include moraines (low ridges of mounds composed of earth materials deposited by glaciers) and marshes and swamps. Drained wetlands, especially in the northwest, have become rich farming areas. Most of Indiana’s hundreds of natural lakes are found in the northern third of the state.
Fossils in Our Lives
Indiana place names reveal its prehistoric heritage. Indiana communities named for coal include Carbon, Carbondale, Coal Bluff, Coal City, Coal Creek, and Coalmont. Oil probably led to the naming of Petroleum. Gas City and Gaston are named for natural gas.
Bedford, Indiana, calls itself “Stone City” and the “Limestone Capital of the World” because of its limestone quarries. The village of Limedale is named for its limestone quarries and a lime kiln.
Brachiopods are also especially common here. In some places, beds as much as two feet thick contain so many brachiopods that their shells touch each other. Such a rock is called a brachiopod coquina.
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