H. B. Willman and T. C. Buschbach
The Beecher Member of the Dunleith Formation (Templeton and Willman, 1963, p. 120) overlies the St. James Member and is named for Beecher Street in East Dubuque, Jo Daviess County.
The type section of the Beecher Member is part of the Dunleith Formation type section (in an exposure in the Mississippi River bluffs on the north side of East Dubuque (SE 19, 29N-2W)), where the Beecher Member is 6.3 feet thick.
Extent and Thickness
The Beecher Member is commonly is about 8 feet thick in the northern outcrop area and 12 feet in the southern area.
In the type section the Beecher is lithographic to fine-grained, dolomite-mottled limestone, typical of the northern limestone facies, but in most of northern Illinois it is relatively pure, noncherty, mainly massive, vuggy dolomite. High purity and massiveness differentiate it from the cherty Eagle Point Member above and the more argillaceous St. James below. In the southern limestone facies it is coarse-grained, gray to pink, almost wholly massive, pure calcarenite.
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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