H. B. Willman and John C. Frye
The Eocene, which means "dawn of the recent," was so named because its flora and fauna contained only a small proportion of recent species.
Extent and Thickness
The Eocene Series (Lyell, 1833) in Illinois occurs in a small area in Pulaski and Alexander Counties. It is exposed only in Pulaski County in the hills from Mounds west to Cache Valley. The Eocene sediments are all assigned to the Wilcox Formation.
LYELL, CHARLES, 1833, Principles of geology: v. 3, London, p. 52-55, 57-58.
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