Historical:St. James Member
H. B. Willman and T. C. Buschbach
The St. James Member of the Dunleith Formation (Templeton and Willman, 1963, p. 119), which overlies the Buckhorn Member, is named for St. James Cemetery in Stephenson County, 3 miles northwest of the type section.
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.
The St. James Member is called the "Gray" in the lead-zinc district.
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.
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.
TEMPLETON, J. S., and H. B. WILLMAN, 1963, Champlainian Series (Middle Ordovician) in Illinois: Illinois State Geological Survey Bulletin 89, 260 p.
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