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|category6=Chert |tree2=Grassy Knob Chert

|category6=Chert |tree2=Clear Creek Chert

...ndbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p. The Bailey is overlain conformably by the Grassy Knob Chert and in many localities is not readily differentiated from it (Weller et al.

rect 118 101 221 134 [[Grassy_Creek_Shale|Grassy Creek Shale]] rect 398 49 493 132 [[Grassy_Creek_Shale|Grassy Creek Shale]]

...ndbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p. ...where only the upper 38 feet of the formation, overlain by the Clear Creek Chert, is exposed.

...ndbook of Illinois Stratigraphy: Illinois State Geological Survey Bulletin 95, 261 p. ...Illinois are largely siliceous-- cherty, silty limestone and dolomite, and chert formations. They may have originally extended over all of Illinois, unless