Pennsylvanian-age Mecca Quarry Shale from Illinois and Indiana contains enriched values of Mo and other heavy metals. Average values range up to 1,160 ppm Mo, 8,970 ppm Zn, 160 ppm U, 320 ppm Pb, 250 ppm Se, 420 ppm Cu, 450 ppm Ni, and 5,970 ppm V for full thicknesses. Pennsylvanian Logan quarry shale of Indiana carries similar enrichments of heavy metals. For both shales trace element contents correlate markedly with specific lithologies. Most samples were analyzed by quantitative X-ray fluorescence. Near-shore deposition in brackish waters for the Indiana locations; deeper, more characteristically marine environment for Illinois. Despite high trace element values in both shales (e.g., near ore grades for Mo), their thinness (generally less than 1 m) and the fine-grained dispersed nature of their host phases relegate these shales to the status of long-term resources, unless improved beneficiation techniques can be devised or appreciably higher grades can be found. The association of these shales with subjacent minable coals, however, improves their economic outlook.--Modified journal abstract.