The working face of the strip mine is a good place to start looking, as the various strata can be examined there. If any prove fossiliferous, like rock can be searched for later in the dump, where it is easier to break. It is also fruitful to ask permission to collect from newly exposed coal seams. Fossils may be locked in the coal or right on its surface.
Petrified, often pyritized, logs and coal balls are found in the coal seams. The Coal Age trees did not have a well-defined woody structure like modern trees and show no growth rings. Invariably the logs are crushed and flattened, suggesting not only soft wood but great pressures. While the wood will cut and polish, there is little pattern. Huge wood sections found around Knoxville, Iowa, are cut and polished to show secondary mineralization of calcite that created white, fan-shaped patterns in the black calcified wood.
Logs or coal balls replaced by pyrite will soon disintegrate and are best left behind. Mines in Indiana and Illinois are the best places to look for coal balls, as are a few mines in Kansas and Kentucky. The wood is more common, especially in central Illinois, southern Iowa, and Pennsylvania.
A few coal seams may contain pyritized gastropods, cephalopods, and brachiopods. Near Farmington, Illinois, the miners were amazed by the week-end armies of collectors who came to brush off every square inch of the newly exposed coal seam with brooms. Embedded half in the coal and half in a black shale resting on the coal were fat gastropods (Shansiella), and occasional small brachiopods, straight cephalopods, and, rarely, large coiled cephalopods. The fossils were found in small depressions in the surface, suggesting that the organisms were washed in when sea water flooded the coal swamp. Iron and sulfur, prevalent in areas of decaying vegetation, provided the chemicals for replacement of the fossils by pyrite or marcasite.
Black organic shale occurs in some mines in a thin layer right above the coal. It will usually contain fossils of animals able to survive in shallow, brackish water, such as some fish, scallops like Dunbarella, brachiopods (Lingula, Orbiculoides), and cephalopods. Plant fossils are uncommon in black shale. The black shale is usually finely layered and easily split. Fossils found in it are often pyritized, and unless the shale
Shansiella carbonaria, the golden snail, its substance replaced by pyrite. From a Pennsylvanian coal seam at Farmington, Illinois.
breaks cleanly around the fossil they are difficult to prepare. Such pyri-tized fossils tend to disintegrate even after cleaning and spraying.
Fish fossils are perhaps the most sought-after fossils in the black shale. They are almost never found in any other rock layer in coal mines. Since the black shale is quickly weathered in the dumps, fossils must be collected from the freshly exposed shale and coal seams. Besides the thousands of fish, including some portions of giant sharks, collected from the black shales near Mecca, Indiana, others have been found near Braidwood, Illinois, and Des Moines, Iowa. Undoubtedly coal mines elsewhere would provide fish fossils if a thorough search was made in the black shales. These shales may appear for a few weeks during mining and disappear, only to reappear a mile away during later stripping.
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