Probably named for Cape La Croix Creek and assigned as basal formation of Ordovician (Cincinnatian) Maquoketa Group (revised). Formerly called Randol (for Randol School) shale (Gealy, J.R., 1955, Ph.D. Dissert.), but Randol turned out to be preempted in IL by Rodgers (1972). Rodgers' usage then grew popular with oil geologists and Silurian stratigraphers (J.W. Baxter, IL G.S., personal commun., 1984). Deemed best to herein change Randol to new, formal Cape La Croix. Type section (adapted from Gealy) is stream bank exposure in east fork of Cape La Croix Creek, N1/2SW1/4SW1/4SW1/4 sec. 13, T31N, R13E, Cape Girardeau 7.5 min quad, Cape Girardeau Co, southeastern MO. Reference section at type section of Ordovician (Cincinnatian) Cape Limestone in city of Cape Girardeau near intersection of Broadway and North Main streets. Consists of light-bluish-gray, light-olive-gray, and medium-light-gray calcareous and non-calcareous, platy shale. Weathers light-brown, yellowish-brown, and brownish-gray. Occasional limestone beds and nodules; fossil fragments. Contains two very thin, siliceous, pyritic beds oxidized to red and yellow. Thickness at type about 17 ft.; ranges 10 to 55 ft. Disconformably overlies Cape Limestone. Underlies (with possible slight disconformity) Ordovician (Cincinnatian) Thebes Sandstone of Maquoketa Group. Age is Ordovician (Cincinnatian, Richmondian). Report includes stratigraphic columns, correlation and nomenclature charts, and type section maps.

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

Cape La Croix Shale of Maquoketa Group is mapped undivided with Thebes Sandstone and Orchard Creek Shale, both of Maquoketa Group, in MO and IL. Consists of dark-gray to greenish-gray to brown, locally silty, moderately calcareous, graptolitic shale. Also contains very minor brown-gray, finely crystalline, argillaceous limestone occurring as nodules and thin interbeds. Overlies major

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