Named as the second from base of 11 formations assigned to the Marmaton Group of the Des Moines Supergroup. Type section is at the center of the east line, NW1/4 sec 18, T72N, R22W, Lucas Co, IA on the Iowa shelf. The name is derived from the former school site approximately 1 mile to the southeast. Summit Coal Member (a name extended into IA from MO). The only named member, occurs in top 0.1 ft. Upper part of the Morgan School was included in the basal Little Osage Shale in earlier reports. Base not exposed. Is 5.7+ ft thick at type where it consists of green, silty, calcareous shale that grades into green, silty, noncalcareous mudstone. Ranges from less than 1 ft thick in Clarke Co to 19 ft thick to southeast in Wayne Co, IA on the Iowa shelf. Generally coarsens upward from shale to siltstone. Contains carbonate nodules in upper part. Overlies Little Osage Shale Member of the newly named Mouse Creek Formation, basal formation of Marmaton. Underlies Stephens Forest Formation of Marmaton. Of Desmoinesian, Pennsylvanian age. Nomenclature chart. Graphic section.

Source: GNU records (USGS DDS-6; Denver GNULEX).