This unit includes:
The fossil comes from the Mazon Creek deposit in Illinois, one of the world's major Lagerstätten (fossil mother lodes). The area is famous for its ironstone concretions that have preserved in fine detail impressions of a wide variety of plants and soft-bodied animals of the Pennsylvanian period (300,000,000 years ago, somewhat older than indicated on the card and in the notes). The back (outside) of the nodule is nondescript, as is typical of Mazon Creek fossils, but the front (interior) shows one large and one small leaf of a fern in sharp detail.
Other Things of Science units containing fossils appeared in 1941 (Fossils, unit 8), 1952 (Ancient Marine Life, unit 141), 1963 (Fossils, unit 274), 1970 (Fossils, unnumbered), and 1977 (Fossils, unnumbered).