Named for Mouse Creek five miles west-northwest of the "type exposure" (also called type section in NW1/4, NE1/4, NE1/4 sec 8, T73N, R22W), Lucas Co, IA on the Iowa shelf. Is the basal formation of the Marmaton Group of Des Moines Supergroup. Overlies Mulky Coal Member of Swede Hollow Formation (new) of Cherokee Group of Des Moines Supergroup. Divided into Excello Shale Member at base and Blackjack Creek Limestone Member at top. Excello is a dark gray shale with phosphate nodules that grades up into green-brown fossiliferous mudstone that total 4.9 ft thick. The Blackjack Creek is a massive, argillaceous, skeletal calcilutite 2 to 4 ft thick. Underlies the newly named Morgan School Shale of the Marmaton. Nomenclature chart. Graphic section. Of Pennsylvanian, Desmoinesian age.

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