H. B. Willman and T. C. Buschbach
The Everton Dolomite (Ulrich, 1907, p. 251-252) is named for Everton, Arkansas.
Extent and Thickness
The Everton Dolomite occurs in subsurface in southwestern Illinois. It is exposed only a few miles west of Illinois near Rockview and Dutchtown, south and west, respectively, of Cape Girardeau, Missouri. Although over 500 feet thick in southeastern Missouri and probably also in extreme southern Illinois, the Everton strata thin rapidly northeastward. They are 100-125 feet thick in Monroe County, Illinois, and are probably not present in Illinois north of St. Clair County, although a small exposure in Calhoun County, assigned to the Shakopee, may be Everton.
A major unconformity separates the Everton from Canadian rocks below, and a strong unconformity separates it from the St. Peter Sandstone above.
The Everton Dolomite has been penetrated in only a few wells in Illinois, but at least locally it consists of a sandstone overlain by a dolomite. As these units were formerly considered unnamed formations, the Everton was classified as a group (Templeton and Willman, 1963), but more recently differentiation of the Everton in Illinois has seemed less feasible and the Everton is here classified as a formation.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
ULRICH, E. O., 1907, in A. H. Purdue, Cave-sandstone deposits of the southern Ozarks: Geological Society of America Bulletin, v. 18, p. 251-256.
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