ILLINOIS STATE GEOLOGICAL SURVEY 



In the laboratory the limestone samples 

 were crushed to less than 5/^-inch size and 

 dissolved in 10 percent acetic acid. Shales 

 were dissociated by boiling and by the use 

 of the Campbell microfossil washing ma- 

 chine. Residues were screened and the por- 

 tion retained between the 20- and 100-mesh 

 screens was concentrated by gravity sep- 

 aration in tetrabromoethane. Specimens 

 picked from the heavy residues were 

 grouped, first by sample and location num- 

 ber, then regrouped by genus and species. 



Acknowledgments 



The project was directed by C. W. Collin- 

 son. D. H. Swann selected sections to be 

 sampled in Illinois and gave helpful advice 

 on the stratigraphic aspects of the study. 

 Discussions of taxonomy with A. J. Scott 

 proved most helpful. Valuable criticism of 

 the manuscript was given by C. W. Collin- 

 son, D. H. Swann, and H. B. Willman. 

 Marie Litterer prepared the text figures. 



Edmund Nosow of the Kentucky Geolog- 

 ical Survey collected samples from two sec- 

 tions in Kentucky (localities 7 and 8) and 

 provided information about them. Ned 

 Smith of the Indiana Geological Survey 

 aided in the selection of suitable outcrops 

 in Indiana. A manuscript by T. G. Perry 



Fig. 1. — Localities from which conodonts were col- 

 lected. See outcrop diagrams (figs. 2-13) for 

 detailed descriptions. 



LOG. I-REILY LAKE NORTH 



NORTH QUARRY 



Limestone, gray, medium 

 to coarse, shaly, very 

 shaly and fossiliferous 

 toward base 20' 



Shale, gray, soft, 

 fossiliferous 5'6" 



Limestone, coarse, 

 fossiliferous. 2' 



Limestone, gray,weathers\ 

 buff, nodular, stialy. 2'6" 



Limestone, ligtit gray, 

 coarse, fragmental, 

 with) I'to 4' gray 

 fossiliferous stiale 

 bed. 12' to 17' 



Stiale, gray, fossil., 6" 

 dork limestone lentil 

 near top 3'6" 



Limestone, gray, fossiliferous 4 





Fig. 2. — Reily Lake North, locality 1. Small quarry 

 in Mississippi Valley bluff about 1.1 miles 

 northwest of Reily Lake, SEi/4 SE14 sec. 24 (ex- 

 tended), T. 6 S., R. 8 W., Chester quadrangle, 

 Randolph County, Illinois. 



and Ned Smith gave additional information 

 about the Glen Dean Formation in Indi- 

 ana. A. K. Miller loaned Pella Beds mate- 

 rial from the State University of Iowa re- 

 pository, P. E. Cloud and W. H. Hass 

 loaned Barnett Formation type specimens 

 from the U. S. National Museum, and M. 

 G. Mehl of the University of Missouri made 

 available figured specimens from the Caney 

 Shale. 



STRATIGRAPHIC SUMMARY 



The Glen Dean Formation, although 

 highly variable in lithology, is a well de- 

 fined unit in its extensive outcrop area 

 around the southwestern, southern, and 

 southeastern margin of the Illinois basin 

 and in the subsurface within the basin. It 

 overlies the Hardinsburg Formation with 

 apparent conformity and is overlain by the 

 Tar Springs Sandstone, unconformably in 



