Figs. 3, 9. Buckhorn member of Dunleith formation. Dolomite, argillaceous, with green shale partings; contains bentonite zone. About 6 feet thick. Shown on columnar section (fig. 3) as underlying St. James member (new) and overlying Glenhaven member (new) of Guttenberg formation. Age is Middle Ordovician.
[Notable exposures in Dixon-Oregon area, northern IL.]
[GNC remark (ca. 1966, US geologic names lexicon, USGS Bull. 1200, p. 514): In the copy of the guidebook used by the compiler [G.C. Keroher], in figure 3 the name Buckhorn had been crossed out and the name Red Oak written in. Likewise, the name Glenhaven had been crossed out and the name Garnet written in. Thus, the sequence would read (descending) St. James, Red Oak, Garnet. However, in figure 9, the name Glenhaven had not been changed. Since the compiler had no way to determine what changes, if any, had been made in other copies of the guidebook, it was impossible to be certain which names were to be retained.]

Source: US geologic names lexicon (USGS Bull. 1200, p. 514).