Historical:Winslow Till Member

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Pleistocene stratigraphy of Illinois
Series Bulletin 94
Author H. B. Willman and John C. Frye
Date 1970
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Lithostratigraphy: Glasford Formation >>Winslow Till Member
Chronostratigraphy: Cenozoic Erathem >>Quaternary System >>Pleistocene Series


H. B. Willman and John C. Frye

Name origin

The Winslow Till Member of the Glasford Formation was informally named the Winslow till (Frye et al., 1969, p. 25) for Winslow, Stephenson County. It is herein formally named a member.

Type section

The type section is in roadcuts west of Winslow, SW SE SW Sec. 21, T. 29 N., R. 6 E., where 12 feet of dark gray clayey till, the upper 3 feet of which is leached, is exposed.

Stratigraphic relationships

Its stratigraphic relations are not adequately known, but its placement within the Glasford Formation is made on the basis of the Sangamon Soil that occurs above it. It may be still another lithologic variant of the Ogle, or it may be a stratigraphic equivalent of the Sterling Member, but, in either case, it has a distinctly different composition and should be treated as a distinct member. The Winslow Till is commonly bounded at the base by bedrock or by a residual soil developed in bedrock.

Extent and thickness

The geographic extent of the Winslow Till Member is shown in figure 6. It is generally less than 20 feet thick.


The till of the Winslow Member is distinguished from the till of the Ogle Member that partly surrounds it by its much higher clay content and gray color. Its typical composition is given in table 2.

Age and correlation

Its age is not firmly established, but it is judged to be in either the Monican or Jubileean Substages of the Illinoian Stage.


FRYE, J. C., H. D. GLASS, J. P. KEMPTON, and H. B. WILLMAN, 1969, Glacial tills of northwestern Illinois: Illinois State Geological Survey Circular 437, 47 p.

ISGS Codes

Stratigraphic Code Geo Unit Designation