Where to Look for Plant Fossils
Pennsylvanian plants are most commonly found in shales directly overlying coal beds. The shales are believed to be of nonmarine origin like the coals and may contain fossils either in ironstone concretions or on the bedding planes. The shale layers as well as the concretions should be examined. Where the bed directly overlying the coal consists of black slaty shale or limestone containing marine fossils, plant remains are rarely abundant or well preserved.
Beneath the coals there generally is an underclay that is interpreted as the material in which the coal forest grew. The underclay is in turn underlain by a sandstone, and both are believed to be mostly nonmarine. Stigmarian axes and “roots” are common in many of the underclays. Plant fossils are common in the sandstone but generally are poorly preserved, except in the local shaly lenses.
The best place to look for plant fossils in northern Illinois, except for the strip mines of the Mazon Creek area, is probably in the spoil heaps from shaft mines. The Colchester (No. 2) Coal has been extensively mined by the longwall method. This technique causes the mine roof to settle when the coal is removed, and the haulage ways are kept open by removing the roof shale. Inasmuch as the roof shale is the Francis Creek Formation of the Mazon Creek area, it may contain abundant plant-bearing concretions. The shale is not everywhere fossiliferous, however, and in many spoil heaps fossils are rare.
Tools for Collecting
Collecting Equipment
The collector of plant fossils should have the following tools and equipment:
① Hammer—a bricklayer’s hammer will work well.
② One or two chisels, preferably one large and one small.