Welcome. I teach introductory geology and historical geology at a community college, and every semester somebody stays after class to ask the same question: "Where can I actually go and find a fossil?" The answer, if you live anywhere between Ohio and eastern Iowa, is practically anywhere the bedrock is showing. I got tired of drawing the same map on the back of syllabi, so here it is on the World Wide Web instead.

Everything on this page is about common marine invertebrates: shells, stems and corals from the shallow seas that covered the middle of North America hundreds of millions of years ago. You will not find dinosaurs here. Dinosaurs are out West and they are somebody else's department. What you will find, in an afternoon, with a bucket and a willingness to get your knees dirty, is more than most people see in a lifetime.

Two stretches of geologic time did most of the work.

The Ordovician (very roughly 450 million years ago, give or take a good deal). The rocks of the Cincinnati area — southwestern Ohio, southeastern Indiana and northern Kentucky — are thin beds of limestone alternating with soft gray shale, and they are so stuffed with fossils that the beds themselves are largely made of shells. Geologists the world over use the word "Cincinnatian" for the upper part of the Ordovician because of these outcrops. Brachiopods, bryozoans, crinoid stems, horn corals, snails, straight-shelled nautiloids and, if you are patient, trilobites.

The Mississippian (about 350 million years ago, again roughly). Southern Indiana, western Kentucky, Illinois, Missouri and Iowa have thick, pale Mississippian limestones. The famous building stone quarried around Bedford and Bloomington, Indiana, is Mississippian, and if you look closely at a courthouse wall you will see it is full of crinoid fragments. The beds around Crawfordsville, Indiana are known to museums everywhere for complete crinoids, and the Mississippian of Illinois and Kentucky gives up blastoids by the handful.

In between and around those you have Silurian dolomite (northern Illinois, eastern Wisconsin, Indiana) and Devonian limestone (the great coral reef at the Falls of the Ohio across from Louisville, and the Devonian of eastern Iowa). All of it was sea floor. Iowa, Illinois and Indiana were sitting near the equator at the time, under warm, shallow, clear water — think of the Bahamas — and everything that had a hard shell left it behind for us.

Later on, the glaciers scraped the top off much of this and buried it under till, which is why you need a roadcut, a quarry, a creek or a river bluff to see any of it. Nature and the highway department have done the digging for you.

Roadcuts. Anywhere a road has been blasted through a hill, the bedrock is exposed and weathering has been loosening fossils out of it ever since. The best ones are on state and county roads with a wide shoulder or a pull-off. Never stop on an Interstate; it is illegal and it is how people get killed. Even on a quiet road: park entirely off the pavement, work facing traffic, wear something bright, and never dig under an overhang. Shale weathers into a slope of loose chips at the base of the cut, and that slope is where the fossils are — you rarely have to hammer at all. Whether you may collect on a particular highway right-of-way is a question for the county or state highway department, and the answer varies, so ask. I use county roads and I have permission for the cuts I take students to.

Creek beds. My favorite. A creek that cuts through limestone does two things: it exposes the bedrock in its banks and bottom, and it sorts the loose material into gravel bars. After a good rain, walk the gravel bars and look at what has been freshly turned over. Crinoid stems, horn corals and brachiopods sit right on top, tumbled smooth. The water does the work of freeing fossils from the rock. Wear old sneakers you don't mind soaking, and go in late summer or fall when the water is low.

Quarries. The richest sites of all, and the most dangerous, and always private. Some quarry operators welcome organized groups (a college class, a rock and mineral club) on a weekend with a signed waiver and hard hats. Never, ever climb a quarry fence on your own. There is a long list of reasons and most of them end with a broken neck.

Excavations and construction sites. A new basement or a sewer trench in limestone country turns up fresh rock. Ask the foreman. Sometimes they say yes.

Your own driveway. Honestly. Crushed limestone gravel from a local quarry is full of crinoid columnals and brachiopod fragments. It is a fine place to learn what to look for before you go anywhere.

When to go. Spring after the freeze-and-thaw has loosened things, and fall when the weeds die back and you can see the ground. Right now (late September) is perfect. A day or two after rain is better than a dry spell. Low sun in the morning or evening throws shadows that make the shapes stand out.

You need far less than the catalogs would like to sell you.

• Safety glasses. Non-negotiable. A chip of limestone in the eye ruins the day and possibly the eye. If you bring children, they wear them too.
• A rock hammer (a geologist's pick with a square face and a pointed or chisel end). A carpenter's hammer is not a substitute: the face is hardened for nails and can chip on stone, sending steel splinters flying. Most days the hammer stays in the bucket.
• A cold chisel or two for splitting shale along the bedding.
• Gloves, because limestone edges are sharp.
• Newspaper and zip-top bags to wrap specimens. Shale fossils are fragile; wrap each one and put a slip of paper in the bag with the date and the location.
• A field notebook and pencil. A fossil without a location is a paperweight. Write down the road, the county, the rock layer if you can tell, and what else was found with it.
• A five-gallon bucket to carry it all. Not a backpack; you will fill it with rock and regret it.
• A hand lens (10x) for bryozoans and small trilobite bits.
• Water, a hat, sunscreen, and a road map. The county highway map from the courthouse is better than the gas station kind.

At home: an old toothbrush, a bowl of water, and patience. Most Ordovician material cleans up with a brush. Do not put shale in water and leave it; it will fall apart. A dental pick from the drugstore does fine work. Leave the acid to the experts.

I am not a lawyer, but this much is simple.

• Private land: ask the landowner. Every time. A creek running through a farm is that farmer's creek. Most people say yes if you knock on the door, explain yourself, and offer to show them what you find. Close every gate you open. Do not leave holes. Do not bring a crowd unless you asked about a crowd.
• National parks and monuments: no collecting, period. Not a pebble.
• State parks and nature preserves: no collecting in every Midwestern state I know of. Look, photograph, enjoy. The Falls of the Ohio State Park in Indiana has one of the finest fossil beds on Earth and it is strictly look-but-don't-take; go anyway, it is wonderful, and the interpretive center will teach you more in an hour than I can here.
• National forests have generally allowed hobby collecting of common invertebrate fossils in small amounts, but the rules can differ by forest, so call the ranger district and ask before you go.
• Highway right-of-way: ask the highway department, as I said above.
• Quarries and construction sites: permission in writing, hard hat, and go with a group.

Beyond the law: take what you will use and leave the rest for the next person. A common brachiopod does not need to come home by the hundred. If you find something that looks unusual — a whole trilobite, a complete crinoid crown, a bone of any kind — note exactly where it came from and get in touch with a university geology department or a natural history museum before you clean it up. They will not take it from you; they may ask to look, and a find with good location data is worth ten times one without.

Nine times out of ten it is one of these. (No scanner in my office, so you get words. My students say I explain better with my hands anyway.)

Not a fossil: concretions (round lumps of harder rock), geodes (hollow, lined with crystals, common in the Mississippian of Iowa and Illinois and a fine thing in their own right), and "dendrites" — fern-like black stains on rock surfaces that are mineral, not plant. If it looks like a leaf but has no veins and no thickness, it's a dendrite.

Locations kept to the county on purpose. Several of these are on private land and the owners were kind enough to let me in; they did not sign up for company.

• March 20, northern Kentucky. First trip of the year, cold and muddy. A shale slope at the base of a county-road cut gave up a rolled-up trilobite about three-quarters of an inch across, complete, sitting on the surface like it had been set out for me. I have been looking for twenty years and this is my fourth.
• April 17, southeastern Indiana, with my historical geology class. Eighteen students, one creek, four hours. The take: brachiopods by the dozen, bryozoans, two very nice horn corals, a small nautiloid section, and one student who found a trilobite tail shield and has now changed her major. I count that as the find of the day.
• May 30, Montgomery County, Indiana. A spoil pile from a drainage ditch, permission from the farmer. A crinoid crown (the calyx with the arms attached, about an inch and a half) in the Mississippian shale. Fragile; it came home wrapped in my sweatshirt.
• July 10, western Kentucky. Blastoids weathering out of a gray shale bank, nine of them in an hour, plus a hand-sized slab with a spiny brachiopod.
• August 28, Adams County, Ohio. Big ribbed brachiopods, the size of a half dollar, and a slab of bryozoans I am keeping for the classroom.
• September 18, eastern Iowa. Devonian this time: a slab of colonial coral with the little tubes showing, a big horn coral, and a brachiopod with the wide "wings" the Devonian ones are known for. Also a geode I did not crack open yet. Last trip before midterms.

Photos: the department's scanner is broken and the film from Iowa is still at the drugstore. I will add descriptions of the good ones when it comes back.

The fall field trip is Saturday, October 16. Meet in the parking lot behind the science building at 7:30 a.m.; we are back by 4. Bring everything in the "What to bring" list, a lunch, and the waiver form from the lab, signed. Safety glasses will be provided but bring your own if you have them. If it is raining hard we go the following Saturday; check the note on my office door.

Your specimen collection (ten labeled specimens, with locality, formation and age) is due the Monday after Thanksgiving. Labeled means where and when, not just what. Anyone who hands in an unlabeled bucket of crinoid stems knows what grade that is.

Recommended reading: the state geological surveys of Ohio, Indiana, Illinois, Kentucky and Iowa all publish inexpensive pamphlets on common fossils of their state; the library has them at the reference desk. There are also several good general fossil field guides in the library's 560s. And for the bigger picture, anything about the history of life.

• Weather Watching with Walter — useful for planning a creek walk.
• Science at Home: Kitchen Experiments
• Mr. Delgado's 7th Grade Science
• Rockhounding in the Mojave — the mineral side of the hobby, out West.
• Jake's Bug Collection — a young collector who labels his specimens. Good man.
• The ResearchTriangle neighborhood