Pentremital limestone. Exposed in Washington County, Arkansas, in the Arkoma basin. Exposures are usually in bluffs. Follows quite closely the distribution of the Archimedes limestone. In most localities, is divided into an upper and a lower limestone member by sandstone and shale. With the included sandstone, is about 80 feet thick in East Mountain. Is 90 feet thick at mouth of Mill Creek. In general, attains maximum thickness in outliers of the Boston Mountains, south of Fayetteville, and becomes thinner to the north, disappearing in T. 17 N., R. 29 W. Consists of a hard, gray, calcareous limestone, somewhat darker in color than the Archimedes limestone, and very fossiliferous. Contains crinoid stems, brachiopods, corals. Overlies Washington shale and sandstone (new); underlies unnamed coal-bearing shale. Age is Early Carboniferous. Report includes geologic map of Washington County, stratigraphic table, columnar sections.
Type locality not designated. Named from the fossil PENTREMITES which is present in this formation.

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