Harmony Hill Shale Member
Willman, H. B., Elwood Atherton, T. C. Buschbach, Charles Collinson, John C. Frye, M. E. Hopkins, Jerry A. Lineback, and Jack A. Simon, 1975, Handbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p.
H. B. Willman and T. C. Buschbach
The Harmony Hill Shale Member of the Glenwood Formation (Templeton and Willman, 1963, p. 52).
Named for Harmony Hill School.
In some areas in the Upper Mississippi Valley the Harmony Hill Shale Member is the only unit included in the Glenwood and is called the Glenwood Shale.
The type section of the Harmon Hill Shale Member is located 1 mile southeast of Harmony Hill School in a ravine 5 miles north of Grand Detour, Ogle County (W1/2 SE SE NE 24, 23N-9E), where the member is 5.9 feet thick.
The Harmony Hill Shale Member is the uppermost member of the Glenwood Formation. The Harmony Hill is conformable, usually gradational, with the underlying members, but it locally rests unconformably on the St. Peter Sandstone. It is unconformably overlain by the Pecatonica Formation.
Extent and thickness
The Harmony Hill Shale Member is the most widely distributed member of the Glenwood Formation but is locally absent in the outcrop area and is generally absent in subsurface in northeastern Illinois. It is commonly 1-5 feet thick but has a maximum thickness of 27 feet in southwestern Ogle County.
The Harmony Hill Member is a green, pyritic, finely laminated shale containing thin laminae of silt and very fine sand, but in places it becomes very sandy, and locally it is black. Phosphatic pellets are common near the top.
Well log characteristics
The Harmony Hill Shale Member contains a few fragments of scolecodonts, Lingula, and minute, dark red algae or spores.
Age and correlation
Environments of deposition
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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