Hog pens and animal burrows

Hillsides may have untold quantities of loose fossils in their soil, weathered from fossiliferous shales and limestones near the surface, but covered by grass and weeds. There is no more helpful animal than the hog for rooting out loose fossils in such places. A hog pen, though not the pleasantest place in which to collect, can contain lots of fossils. One Chicago area club has frequent field trips to a hog pen in Indiana that is paved with large crinoid stems and crinoid slabs showing sporadic plates and even crowns. Such burrowing animals as the badger may go below the plant covering and bring up a few fossils. Tar pits

The major collecting site of this sort is the well-known La Brea tar pit in Los Angeles. But some day an amateur may stumble onto another tar pit. As in the peat bog, animals became mired in the tar as they came to drink. Predators attacked the helpless Pleistocene animals and themselves became stuck. All sank slowly into the dense oil, which has kept their bones perfectly preserved. Thousands of bones and complete skeletons, even leaves and flowers, have been taken from this tar pit. Sorry, no private collecting. Caves

Dry areas of the Southwest have a climate that preserves anything that crawls into a cave and dies. A few ice-age animals did just that, such as the extinct ground sloths found lying on or near the surface. The preservation is really mummification, with hair still covering the bones. These extremely fragile fossils are rare enough and ugly enough so that any collector finding one is likely to turn it over to a museum. Caves were also the haunt of ice-age man. No cave should be indiscriminately dug up, lest its scientific evidence be lost. Fissures

In cave areas where limestone is being quarried, occasional fissures may be encountered. Here joints in the rock have allowed water to sink rapidly from the surface. Such fissures may also have trapped animals that fell into them. A wealth of bones, mostly of tiny Pleistocene rodents, can come from such cracks. Florida has been particularly rich in these fossil-bearing crevices.

Deposits much older than Pleistocene are occasionally found as crevice fillings. The only evidence that northern Illinois was covered by seas more recent than Silurian comes from Devonian fossils, primarily fish teeth, found in a gray shale that filled a deep crevice in the lighter-colored Silurian dolomite. This was exposed briefly during quarrying, long enough for a sharp-eyed collector to sample the unusual shale and discover fossils of an unknown sea. Permian bones, a rich concentration of small amphibians and reptiles, were found near Fort Sill, Oklahoma, in fissures in much older Ordovician limestone.

Any cracks running into what is otherwise solid stone may be filled with fossil-bearing material of a recent age, particularly if the fill is quite different in appearance from any other material in the quarry.

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