Historical:Eagle Point Member

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Handbook of Illinois Stratigraphy
Series Bulletin 95
Author H. B. Willman, Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, Jack A. Simon
Date 1975
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Lithostratigraphy: Ottawa Limestone Megagroup >>Galena Group >>Kimmswick Subgroup >>Dunleith Formation >>Eagle Point Member
Chronostratigraphy: Paleozoic Erathem >>Ordovician System >>Champlainian Series >>Trentonian Stage
Allostratigraphy: Tippecanoe Sequence


H. B. Willman and T. C. Buschbach

Name Origin

The Eagle Point Member of the Dunleith Formation (Templeton and Willman, 1963, p. 120) overlies the Beecher Member and is named for Eagle Point, a prominent bluff on the west side of the Mississippi Valley in Dubuque County, Iowa, 2 miles north of the type section.

Type Section

The type section of the Eagle Point 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 Eagle Point Member is 11.8 feet thick.

Extent and Thickness

The Eagle Point Member is commonly 12-18 feet thick in the northern outcrop area and 9-10 feet in the southern area.


The Eagle Point Member is characterized by well defined bands of chert nodules. It consists of slightly argillaceous dolomite-mottled limestone in the type section, but it is dolomite in most of northern Illinois. In the southern outcrop area it is calcarenite containing bands of chert, is finer grained, denser, and more argillaceous than the members above and below.


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