H. B. Willman and John C. Frye
The Gulfian Series (Hill, 1887, p. 298, 300) is named for its occurrence along the Coastal Plain of the Gulf of Mexico, and is presumed to include all Cretaceous rocks in Illinois.
In southern Illinois most of the Cretaceous rocks were deposited during the youngest part of the Gulfian, although the basal Tuscaloosa Formation may represent early deposits of the series. Cretaceous rocks in western Illinois were probably deposited during early Gulfian time.
HILL, R. T., 1887, Topography and geology of the Cross Timbers and surrounding regions in northern Texas: American Journal of Science, v. 33, p. 291-303.
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