Dumps of iron, fluorite, lead, zinc, and other mines may contain fossils for the collector, because nearly all common metals are mined from fissures and cavities in limestones.
Metal-mining areas are usually well known. The state Geological Survey can often supply a list of operating mines; so can a university geologist. Mines, both operating and abandoned, are marked on topographic maps. Currently or recently operating mines are best for fossil hunting, as old dumps weather rapidly. As with all operating quarries, pits, and mines, the collector should ask permission to hunt, and he should ask where it is safe to hunt.
The state Geological Survey can usually suggest a book or paper about a particular mine that describes ore-bearing horizons, gives their formations and age, and sometimes gives detailed lists of the fossils found in each stratum. This was not done specifically for the fossil hunter but for the convenience of geologists or prospectors wishing to identify the ore-bearing formations.
Hunting is limited to the dumps, where the rocks have been cleaned by rains and fossils have been etched loose by acid waters. Many strata are cut through in working a mine, and fossils on the dump may range from Cambrian to Cretaceous. Midwestern metal mines tend to produce ore from one or two distinct formations, making identification easier.
The best fossil hunting will be found in mines in the flatlands of the Midwest and South; the metamorphism that occurred during mountain building in the East and West destroyed or grossly distorted fossils in the rocks, though there are some undisturbed areas. The iron mines in Minnesota are in Cretaceous rocks that contain excellent fossils. The iron is believed to be a fossil itself, concentrated from the sea water by innumerable bacteria. The seabed that is now the iron mine was the home of clams and snails which can be found in the dumps, turned to dark-brown hematite or limonite.
The lead- and zinc-mining area around Joplin, Missouri, is operating in Mississippian-age rocks that contain characteristic invertebrate fossils. Few mines are still operating, but old dumps are everywhere and contain
some fossils as well as mineral specimens. Recently, trilobites, cephalo-pods, and rare new fossils were found in the early Paleozoic rocks exposed at the bottom of barite mines south of St. Louis, Missouri.
The lead and zinc mines, a few of which are still operating in southwest Wisconsin, once covered the area where Illinois, Iowa, and Wisconsin meet. The ore zone here is in Ordovician rock, and dumps have produced fine brachiopods and some trilobites. In southern Illinois and northern Kentucky, the fluorite mines are recovering more lead and zinc than fluorite in Mississippian rocks. Not much waste material is dumped from these mines, but some fossils can be found.
In mines in Pennsylvania producing quartz sand for glassmaking, giant crinoids have been found in the sandstone blocks. They are fragile and difficult to collect but remarkably complete and well preserved for sandstone fossils.
Phosphate strip mines in central Florida, are bonanzas of fossils, because the phosphate is a product of animal life of the ancient Florida seas. The deposits are mostly Miocene, and giant shark teeth, bones of fish and manatee, turtle and alligator plates, and assorted mammal teeth are regularly found in the waste piles. Mammoth teeth and bones of more recent age are occasionally uncovered in the upper levels before the older phosphate-bearing horizon is reached.
Besides mines and quarries, other man-made excavations are probably the best hunting areas for fossils. Fresh material is regularly exposed, and the areas opened for inspection offer much more than is naturally exposed by the slow weathering of shales and limestones. New programs of road building, particularly the interstate highways, are creating road cuts where previously there were none. Roads are widened periodically, and fresh cuts are made. Even old road cuts produce a steady crop of fossils through weathering. Road cuts, except for interstates, are easy places to collect; they are "right beside the road." Interstates are posted with signs warning that no stopping is allowed except for emergency repairs. They may often be reached, however, by driving onto frontage roads and walking down to the road cuts. Some interstates are heavily fenced, with barbed wire on top. Nor are road crews too happy with rockhounds who uproot the grass planted to stop erosion on bare exposures.
Just driving around, particularly on newer roads, is the best way to find road cuts. If an area is known to be fossiliferous, such as around Cincinnati, all road cuts are likely to be fossiliferous wherever shale or
A collector reaches a fossil the previous collector could not reach. Here he uses a twelve-foot pole to dislodge a concretion from a vertical sandstone road cut in Washington. He hopes it will contain a fossil crab.
limestone layers are exposed. Even roadside ditches in fossiliferous areas may be rewarding. Weathering of the limestones releases the fossils and produces topsoil to cover them. Water in the ditches washes the fossils clean and leaves them scattered in the bottom.
Field-trip guides published by state Geological Surveys and by professional geological societies for field-trip meetings often pinpoint prominent roadcuts along the route and describe in detail the formations and fossils exposed. A few states have published roadside geology tour guides for some interesting stretches of highway. One geological society has erected signs along the highway through the Arbuckle Mountains in Oklahoma describing the age and formation of the rocks. State highway departments can usually furnish information about a new interstate highway under construction. Up-to-date road maps often have the interstates under construction designated with dotted lines.
During excavation in 1 9 65 and 1 9 6 6 for Interstate 71 near Cleveland, Ohio, a bed of Devonian shales carpeted with fossil fish was uncovered. Construction stopped on that stretch while museum crews removed 10,000 specimens, including thousands of fish-bearing slabs. Many were species new to science, and this one chance find added more Devonian
fish specimens to scientific collections than had ever been collected previously in the United States.
There is little choice where to collect in a road cut. Alongside the road there may be a pile of rubble from weathering of higher layers. It will give a quick idea of what might be found in the entire cut, although fragile fossils will never appear in the weathered material at the bottom.
Limestones in a weathered road cut stand out as prominent ledges. So do some sandstones. Shales weather away, and a road cut through shale becomes a grassy hillside in a very few years. If the shales are sandwiched between limestone or sandstone layers they will weather back, leaving the more resistent layers of hard rock protruding. It is worthwhile digging back into shales to the unweathered part to see whether soft fossils are locked in them.
A small exposure near Vinita, Oklahoma, along the interstate was a popular collecting place for several years. It is now solidly grassed over. The shales on the hillside weathered rapidly, releasing a multitude of Archimedes screws and brachiopods. Few collected the thin layers of limestone that littered the hillside, although these contained well-preserved brachiopods and rare trilobite parts. One Oklahoma collector painstak-
ingly sampled the hill from top to bottom, digging back into each separate shale layer. He was rewarded by finding a layer near the base which produced crinoid crowns, beautifully preserved. He followed this layer along and found a nest of crinoids that held more than fifty perfect specimens.
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