St. James Member

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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>St. James Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence

Primary source

Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.

Contributing author(s)

H. B. Willman and T. C. Buschbach


Original description

The St. James Member of the Dunleith Formation (Templeton and Willman, 1963, p. 119).


Named for St. James Cemetery in Stephenson County, 3 miles northwest of the type section.

Other names

The St. James Member is called the "Gray" in the lead-zinc district.


Type section

Type location

The type section of the St. James Member is located in the same exposure as the Buckhorn type section (a quarry at Buena Vista (NW SW NE 15, 28N-7E)), where the St. James is 13.3 feet thick.

Type author(s)

Type status

Reference section

Reference location

Reference author(s)

Reference status

Stratigraphic relationships

The St. James Member of the Dunleith Formation overlies the Buckhorn Member.

Extent and thickness

The St. James Member commonly is about 14 feet thick in the dolomite facies in northern Illinois and 8-12 feet thick in the southern limestone facies.


In northern Illinois the St. James Member is light tan, pure, medium-bedded, vuggy dolomite, but thin green shale partings are common in the upper 2-4 feet. It has black speckles but not as many as the Buckhorn. In the southern area the St. James is a coarse-grained, gray to brown, faintly gray-speckled calcarenite that locally has a few inches of conglomerate at the base.




Well log characteristics


Prasopora simulatrix (fig. O-5) is common in the upper few inches of the St. James Member in the extreme northwestern part of the state but has been found eastward only as far as Rockford, where it is rare.

Age and correlation

Environments of deposition

Economic importance



TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation