FOR SEVERAL MONTHS I HAVE been collecting fossils in Ohio, working over both shale and limestone. Ohio has a wide variety of fossils in an excellent state of preservation. Here I shall concentrate on marine fossils, in particular trilobites and crinoids, but I shall also discuss some plant fossils I found in eastern central Ohio. My emphasis will be on the fundamentals of fossil collecting: how to find a good site, how to remove the fossils and how to clean and display what you have found.

Many amateur collectors particularly prize trilobite and crinoid fossils. The trilobite was an arthropod distinguished by the division of its body into three lobes, one lobe on each side and one in the middle. The body was further divided into cephalon (head), thorax (central section of the body) and pygidium (tail). Trilobites probably were scavengers that crawled over the ocean bottom, feeding on biological debris. They had jointed legs, but the legs and other appendages are rarely preserved in the fossils. The harder exoskeleton is well preserved in the shales of Ohio.

The crinoids were an ancient group of echinoderms. Some were free-floating but most were attached to the bottom by a stem and some rootlike branches. These crinoids must have appeared to be more plant than animal; they resembled lilies and grew in stands as though in a garden. The body was cup-shaped and had a mouth on top surrounded by five branched and flexible arms. The cup, arms and stem are preserved in fossils, but a whole crinoid is difficult first to find and then to get out of the rock without damage. Usually a collector uncovers only parts of a crinoid, but even they can reveal much about the nature of these animals.

An easy way to find a fossil site is to have an experienced collector lead you there. When that opportunity is not open, you must seek out the sites through detective work. Since most sites will be on private property, you should always get permission before you enter the area. Failure to do so may lead to prosecution, particularly if you enter private mines and quarries. The owners of some quarries in Ohio automatically have anyone caught on their property jailed.

Some of the most likely places to find fossils are cuts through hills for roads or railroads. Scout through such a cut

watching for fossils weathered out of the rocks; dig into any likely looking outcroppings of sedimentary rocks. If you see pieces of fossils, explore the site with further digging. Fresh road construction is also promising (although here again permission may be needed). For example, when an interstate highway was being built in Cleveland a few years ago, the crews clearing the ground broke into a magnificent deposit of fossilized fishes that was only a few minutes from my office near the downtown area. The Cleveland Museum of Natural History carefully unearthed the fossils and now has a fine collection of fossil fishes. The deposit was small, and although I and others have searched through the nearby shale (the site of the deposit is now covered by the highway), we have not found any more fossil fish.

Another likely place to investigate is along a stream bed that cuts through the soil and down into the bedrock. As you walk along the stream watch for fossils embedded in the rock. You might also occasionally crack open a piece of rock. If you do find a fossil in such a rock, investigate the shores of the stream to find the outcropping of shale or limestone from which the rock came.

My friend Edgar Roeser took me to a stream near Cincinnati where parts of trilobites could be found in the walls of the stream bed and various other fossils were visible in the hard limestone slabs along the stream. Still, most of the rock exposed at low water proved to be nearly barren, yielding only common specimens or poor ones. We were looking for a particular type of trilobite known as a flexicalymene. After we had discovered some fossils in a particular layer, Roeser showed me how the layer continued upstream and disappeared into the water.

After mentally extrapolating the level of the layer we waded into the stream at an appropriate place and began to pry up slabs of shale from the bottom, groping in the water we had muddied. Within a few hours we each had pulled up about five "flexis," some in very good condition. (To find this place Roeser marched me through several miles of poison ivy and poison oak. The resulting rash nearly drove me crazy for two weeks, but the flexis were worth it.)

Another good prospect for fossils is a mine dump or a quarry. (Never enter an abandoned mine tunnel!) The rock there is often broken up by the mining operations and weathered by exposure. Many people prefer this type of location because it requires little digging. In a quarry near Toledo I met a collector who is particularly adept at this kind of hunting. He was marvelous at spotting "rollers"-rolled-up trilobites-lying partially weathered in the dump piles around the quarry. I suspect he took keen pleasure in showing us his huge rollers (each two inches or so in diameter) after my friends and I had spent half the day rummaging in the quarry in the hot summer sun, usually finding only a few odds and ends of small trilobites.

The best trilobite I found all summer was one I picked up from the dumps within the first hour of my first trip to hunt for fossils. It was a small roller about an inch in diameter and in almost perfect condition. The individual facets of its compound eyes could be seen clearly. All the other trilobites I found in the area had to be pried out of the walls of the quarry with exhausting effort.

Once a fossil location is found you should make a map of the area or identify the site on a large-scale map. This procedure not only will help you to remember the site but also will enable others to follow your map to the location. With many sites on a map you may also be able to correlate the type and abundance of fossils at several sites. If the map is topographical or geological, you might be able to predict the location of other fossil-bearing sites in the area.

For the purpose of correlation you should label each fossil when you collect it. Write the name of the site and the date on the container in which you put the fossil. You probably should also indicate the depth or level from which the fossil came. When you return to that site, you can then continue to work at the same level rather than wasting time on unrewarding levels.

Fossils are found in sedimentary rocks, some of which are easier to deal with than others. The limestones in Ohio

sometimes yield good specimens, but in general I find their hardness an obstacle to fossil collecting. The Ohio shales are softer and much easier to open up to expose fossils, and so one can work through a lot more shale than limestone in a day. It is also far easier to remove a specimen from soft shale than it is from harder rock.

If the fossil-bearing rock lies in the side of a cut such as one made for a road, you should be able to see the continuation of the stratum on the opposite side of the cut. If the stratum is straight and contains fossils, you may be able to find fossils all through it. If it is strongly folded or fractured, it is not promising, because even if it once contained fossils, they would probably have been destroyed by the folding or fracturing.

I have collected most of my fossils on the slopes above stream beds or in quarries. Either kind of site can be dangerous if there is much loose rock above the collection level. Mining operations in a quarry often leave heavy boulders overhanging shale that looks promising. Jeff Aubry, who is widely known for his collection of fossils from Ohio and the surrounding states, was once hit by a rock in the quarry I frequented this summer. He was unconscious for several hours. If more rock had come down the slope, he might have been killed. Even if you have had experience with collecting, do not dig below a large overhang of rock no matter how tempting the place may seem.

The general strategy for digging on a slope is to level a section so that slabs of rock can be lifted and examined. When I worked on a slope, I began digging well above the stratum in which I was interested. My initial cut was high enough so that a straight line downward would cross through the stratum at least a meter in from the slope. Digging out the overburden took hours and considerable effort with a pick and shovel. Sometimes the overburden itself yielded interesting fossils, but usually this stage of the digging was simply tiring.

When I finally had the overburden cleared away, the shale at the level I was interested in was exposed for several square meters. Along the sides and the back of the exposed area I pounded long chisels to a depth of four or five centimeters with a sledgehammer, rocked them slightly and then removed them. Next I carefully drove a long chisel horizontally into the side of the shale layer several centimeters below the top surface in order to pry up a slab. The chisel holes at the rear and the sides facilitated the proper fracturing of the slab.

After lifting the slab I examined the bottom of it and the top of the layer of shale under it. If I saw no fossils, I stood the slab on one edge and split it further by tapping a small chisel or screwdriver into the other edge with my hammer. Although the shale is easily split, the splitting should be done with restraint. I have destroyed some beautiful trilobites by heavy-handed hammering.

Digging out the overhang and the slabs this way is hard work and can take hours or even days. Some people prefer to dig directly into the wall. The advantage of the longer and more careful work becomes apparent if you open up a slab that holds several good fossils. Single fossils can be recovered by digging straight into the wall, but the chances are slim that you can avoid damaging the delicate types such as the flat trilobites or the complex crinoids. On the other hand, if you can lift out a slab with several good fossils in it, you have a valuable discovery because the slab will be far more impressive than a single fossil cleaned and removed from its matrix.

Scott Vergiels of Temperance, Mich., recently showed me a slab he had wrestled out of the quarry near Toledo. It

contained a complete crinoid and seven trilobites. I was impressed. Vergiels told me of a remarkable slab Aubry had dug out of the quarry: it had 26 complete trilobites in it.

Unless the fossil you uncover is notably solid (some of the brachiopods may be solid enough) the specimen should be left in its matrix until you have carried it home. I recommend that you avoid cleaning the specimen while you are in the field. If part of the specimen is chipped when the fossil is exposed, gather up the chips. I prefer gluing them to the matrix so that I can reconstruct the fossil at home. A dilute white glue (which is water soluble and so can be loosened easily) will do. If the fossil seems to be in danger of falling apart, I apply a small amount of glue near the loose edges. Capillary action pulls some of the glue under the loose pieces and secures them after a few minutes.

Many fossil collectors prefer to carry out all but the largest slabs in small baskets. If you use a basket or a box, avoid packing one specimen on top of another; the specimens can easily damage each other. If you wrap your specimens in newspaper, paper towels or plastic foam, you can carry them in a backpack.

Many fossil specimens can be cleaned roughly with an old dental tool or even a safety pin. With a trilobite fossil I pick at the shale, being careful not to flick away any of the fossil itself. Fine metal points are needed to remove the shale in the narrow crevices of the trilobite and to expose the arms of a crinoid.

Excellent cleaning can be done with an air gun (a miniature "sand blaster") that many avid fossil collectors have bought, although the cost is now more than $1,000. The gun blows a fine powder from a small nozzle that one directs at a glancing angle to the specimen, removing the matrix without damaging the fossil. Different powders are available for different types of fossil. For example, a harder powder (aluminum oxide) may work best for a hard brachiopod and a softer powder (sodium bicarbonate) for the delicate work needed to expose a crinoid. If the fossil is harder than the surrounding matrix, the stream of powder is directed at the fossil surface at a glancing angle; the matrix is flicked away by the impact. If the fossil is softer than the matrix, the stream must be directed at the matrix or the fossil will be damaged. The air gun is useful only if there is a difference in hardness between the matrix and the fossil so that the impact of the powder can fracture the shale at the interface.

Dental tools are handy for the reconstruction of broken fossils. A loose piece of fossil can be lightly coated with dilute glue and then positioned on the fossil with a dental pick. I lick the tip of the tool in order to provide a little adhesion between the tool and a dry surface on the loose piece.

Some chemicals will remove shale or limestone through a reaction that leaves the fossilized material unaltered. For example, some acids will eat away limestone without damaging a fossil that is composed of silicon dioxide. With specimens in shale I prefer to avoid chemicals, since I get better results with a dental pick and an air gun. If the specimen is in limestone, however, one often must resort to chemicals.

The matrix in which a fossil is found can be cut down to a convenient size and then flattened on the back with an abrasive masonry disk (sold in hardware stores). The disk is mounted on an electric drill the same way a drill bit is. Flattening the back of a rock (the matrix, not the fossil) enables you to glue it to a mounting board. Roeser has assembled displays of some of his fossils by gluing the flattened back of the rocks to canvas stretched on a frame as for a painting Fossils can also be put in a display case.

My most rewarding digging was done in the stone quarry near Toledo. The quarry contains part of the rock unit known to fossil collectors as the Silica Formation, which was formed 350 million years ago in the Middle Devonian period. It was part of the sea in what is termed the Michigan Basin. The basin held a saltwater sea that extended into Ontario and for a while into New York. After the sea had receded and disappeared uplifting, warping and erosion of the ground exposed and removed much of the Silica Formation. What remains is rich in fossils.

Six zones of sediment deposition have been identified in the Michigan Basin. Only two of them are important in the Toledo quarry. One zone is called the coral-brachiopod zone; it consists of limestone. and calcareous shale holding fossils of corals and large brachiopods and a few bryozoans, crinoids and blastoids. The other zone is called the diverse-fauna zone. It was originally mud flats and now consists of clay stone or shale with little calcareous content. It holds fossils of bryozoans, brachiopods, ostracods, trilobites, corals and other marine animals.

Some people believe the ancient sea at the site of the quarry must have been no deeper than about 150 feet. If it had been deeper, the corals would not have received enough sunlight for growth. If it had been considerably shallower, evidence of turbulence from the surface waves would appear among the fossils. Very shallow water would probably have been too rough for crinoids and other rather frail animals. Much information about the fossils of the quarry has been collected in a book, Strata and Megafossils of the Middle Devonian Silica Formation, by Robert V. Kesling and Ruth B. Chilman, published at $10.50 by the University of Michigan Museum of Paleontology, Ann Arbor, Mich. 48104.

The quarry is divided into a northern and a southern section by a county road. The southern section is closed to collectors because it is still being mined. The northern section has not been mined in years and is open to amateur collectors, although I have heard a rumor that new owners will soon close it. The northern section is partly filled with water that has run off from the surrounding land. At the sides of the quarry are steep cliffs where the fossil-containing strata of limestone and shale are exposed.

Fossils can also be found in the piles of shale and limestone mined and then dumped on the surrounding land. Corals and

shells turn up in quantity on flat land at the northern end of the quarry, where layers of fossils formerly underground have been exposed by uplifting and weathering. Although I explored the dump piles and the ancient reefs, I spent most of my time working with friends (Roeser, Vergiels, Dave Watson and Mike Walsh) on a ledge about halfway up one of the cliffs.

The rock layers along the cliffs have been labeled and connected geologically with layers in the southern section of the quarry and with layers elsewhere in the Michigan Basin. The labels are numbered units that begin in the limestone under the shale. Unit 11, an easily workable layer of shale, was approximately at eye level when I stood on the ledge. Under it was a narrow stratum of hard limestone, Unit 10, about six inches thick. (The thickness of the units are not constant throughout the quarry.) Near belt level was a thicker layer of shale, Unit 9B, which extended downward some six feet, ending on more limestone under the floor of the ledge. Although various types of fossils were below and above me, I concentrated on Unit 9B. Toward the top of the unit several good specimens of trilobites had been collected. Toward the bottom of the unit the trilobites were rarer but usually larger.

Two types of trilobite are predominant in the Silica Formation. Phacops rana crassituberculata is normally found in units 8 (shale) and 10 (limestone). P. rana milleri is usually in units 7 and 9. Since the "crassies" are farther down, they must have existed at an earlier time than the milleri, although some slabs dug out of the Silica Formation contain both types of trilobite, indicating that for a time they coexisted.

My procedure for digging on the cliff was first to remove the overburden above the preferred level and then to split out large slabs of shale. Early in the morning I dug into the wall at about face level, chopping and shoveling my way back for about two feet. The cut was about four feet wide. Then I extended the cut downward, chopping out the hard limestone as fast as I could but being more careful with the shale. Most of the shale was weathered because it was near the surface. Water seepage had made some of it so fragile that it crumbled in my hands. The only fossils I recovered from this shale were the harder brachiopods.

By midafternoon I had reached a level between my belt and my knees. Now the cut was much deeper into the wall because of the slope. The shale was less weathered and could be split off in large slabs. Here I worked slower for fear of damaging the fossils. Some of my stronger friends managed to pry out slabs weighing 100 pounds or more. Although these large slabs are difficult to handle, they eventually save the collector much time. An old dictum of fossil collecting is that the more you can dig out in a promising spot, the better your chance is of finding rare and prized specimens. Some of my friends work like human power shovels, clearing out large cuts into the slope in a day.

If I reached a promising specimen, I naturally slowed down considerably. Ordinarily a rolled trilobite was firm enough so that it and its surrounding matrix could be chipped out of a larger slab without much concern that it would be damaged. Flat trilobites and all crinoids required more attention. Usually a bit of dilute white glue had to be applied to a flat trilobite before its surrounding matrix could be safely chipped out of a slab. Crinoids are difficult to recover without damage unless one is extraordinarily lucky in splitting open a slab just the right way. Without such luck one must work patiently with small chisels and delicate taps of a hammer to follow the full length of a crinoid and then free the slab in which it lies. One of the saddest sights in the world is a fracture line running directly across a good crinoid or trilobite specimen.

Trilobites molted periodically during their lives, shedding their exoskeleton in order to form a new and larger one. These molts are relatively abundant in the shale, sometimes frustratingly abundant when they appear to be a whole trilobite. I found one trilobite that had died after it had molted and before a larger exoskeleton had hardened. These specimens, called soft-shells by collectors, are difficult to spot because they blend into the color of the shale more than the normal trilobite fossils do. The soft-shells are also difficult to recover intact because the fossil is quite fragile. Fossils of the appendages and soft underside of trilobites are rare, and they are not found at all in the Silica Formation. The preserved exoskeleton consists of calcium carbonate and calcium phosphate that had hardened the original chitinous covering.

In addition to trilobites Unit 9 contains phyllocarids, clams, large brachiopods and many other fossils. One of my friends, Zarko Ljuboja, dug a slab containing nine fossil starfish out of the rock unit. I have witnessed several large trilobites, both rolled and flat, being split out of the shale. Alas, I was always working next to the person who found the large specimen, never at the right place to get one for myself.

Of all the fossils I have found or seen the trilobites remain the most fascinating, particularly because of the evolution that apparently shaped them. Many different types of trilobite have been identified around the world. The animals had a variety of shapes and sizes the length of adults ranging from six millimeters to 75 centimeters. They first appear in the fossil record from earliest Cambrian times (some 600 million years ago); by middle Paleozoic times they had become specialized, and by the end of Permian times (225 million years ago) they had waned and disappeared. During their peak period they were apparently abundant in fairly shallow waters, feeding on small organisms and organic waste on the muddy bottoms. Judging from the many rollers found at fossil sites, many trilobites died at a time when they were rolled up.

The adaptations of trilobites led into a variety of evolutionary paths. For example, the eyes of different species of trilobites were noticeably different. Some of the trilobites had small crescent-shaped eyes, some had large eyes that dominated their cheeks, some had small eyes mounted on stalks that extended from their cheeks and some had no eyes at all. One can guess at why the eyes evolved in these different ways. The large eyes may have been for trilobites that lived in deep water where the light was dim. The blind trilobites may not have needed eyes because they spent their lives burrowed in the mud.

The trilobites I saw at the Toledo quarry had compound eyes with the facets arranged differently in the two subspecies. The P. rana milleri specimens had eyes with eight facets in each vertical row and an average of 104 facets per eye. The P. rana crassituberculata specimens had eyes with six or seven facets in a vertical row and only 77 per eye.

In some of the trilobites each facet of the compound eye consisted of two layers of material, arranged so that the outside and inside surfaces were simple convex shapes and the surface between the layers was a more complex shape. According to research done by the paleontologist Euan N. K. Clarkson of the University of Edinburgh and the physicist Riccardo Levi-Setti of the University of Chicago, the form of the composite lens is approximately the ideal one for the elimination of spherical aberration.

The outer layer of the trilobite's eye consisted of calcite, a birefringent mineral of the kind I discussed in this department for December, 1977. In general when light travels through a birefringent crystal, it is split into two rays according to the polarization of the rays with respect to the crystal axes. Such a splitting of light rays would have made an interpretation of the environment by a trilobite virtually impossible, but evolution gave rise to a lens with the calcite crystal oriented advantageously. When light entered the lens, it traveled along the optical axis of the crystal and was not affected by birefringence. Hence the trilobite saw only a single image.

I also collected a number of plant fossils from a strip-mining operation in the hills of eastern central Ohio. Large amounts of shale had been put in dumps on the surface, but all of it was barren of fossils. At one end of the mined area, on the side of a gentle hill, a small stream had cut its way into a lower layer of shale. Along the slopes of the stream the shale was full of plant fossils.

Roeser and I dug into the slopes, cleared the overburden and finally got a flat working area on the shale layer. Although the plant fossils were abundant, recovering a whole specimen was difficult because of the orientation of the fossils and the nature of the surrounding rock. Where the marine fossils from the Silica Formation were usually nicely exposed when I split open a slab of shale, the plant fossils were almost randomly oriented in the slab. When I split such a slab open, the fracture was likely to cut through several specimens. Nevertheless, the fossils were so abundant that by the end of the day Roeser and I each had plenty.

Most of the plant fossils from the site appear to be seed ferns, which are fernlike plants that bear seeds rather than spores as true ferns do. We found examples of Sphenophyllum, which had a circular array of fan-shaped leaves on the end of a slender stem. There was also Alethopteris, which had long leaflets extending to the sides from a central rib with a prominent central vein. Various other fernlike plants (Pecopteris and Neuropteris) were dug out of the walls. Roeser discovered a layer of Sphenophyllum that extended along the slope at a slight slant for at least 10 feet.

All these plants were deposited in a stagnant muddy lagoon some 230 to 320 million years ago. Since the plants were not hardened by mineral matter, their preservation depended critically on the absence of oxygen and aerobic bacteria. Apparently the plants Roeser and I uncovered had dropped into the stagnant waters and had been covered with mud before decay could set in.

Ohio is rich in fossils, yielding specimens from several of the ancient ages. Many other areas of North America, however, are equally rich in these specimens and others as well. Why not take a walk along a stream bed or a road cut and see what kind of animals and plants lived in your area long ago? You are likely to wind up with a pleasant addiction: fossil collecting.

Bibliography

INVERTEBRATE FOSSILS. Raymond C. Moore, Cecil G.-Lalicker and Alfred G. Fischer. McGraw-Hill Book Company, 1952. 9

THE ELEMENTS OF PALEONTOLOGY. Rhona M. Black. Cambridge at the University Press, 1970.

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