PENNSYLVANIA CONODONT ASSEMBLAGES 



from 

 LA SALLE COUNTY, NORTHERN ILLINOIS 



INTRODUCTION 



Although more than a dozen reports describing natural assemblages 

 of conodonts have been published, almost none have given sufficient strati- 

 graphic information to enable subsequent workers to visit the collecting 

 sites and be reasonably certain of securing assemblages without considerable 

 investment of time. Because of the coincidence of the Pander Society meeting 

 in De Kalb with the revival of interest in natural assemblages of conodonts 

 and because of the general inaccessibility of all previously collected 

 natural assemblages, we have prepared this guide. The guidebook, however, 

 is mainly a guide to the vicinity of Bailey Falls (figs. 1 and 2), which is 

 the topotype locality for Scottognathus and Duboisella and the most pro- 

 lific assemblage collecting locality known outside of Scott's Heath locality 

 in Montana. Glen Merrill (Lane, Merrill, Straka, and Webster, 1971) has 

 recognized examples of his Midcontinent and Appalachian biofacies faunas 

 in the Bailey Falls section also and has identified more than a dozen 

 genera and nearly 50 partial species in the limestones near the falls. 



In order to further our primary purpose of making natural 

 assemblages generally available for classroom and research use, we have 

 included a number of sections as optional stops near the end of the guide- 

 book. Two are local variations of the Bailey Falls section, three are 

 sections from older parts of the Pennsylvanian (fig. 3) in northern Illi- 

 nois, and two are additional localities of Rhodes (localities 7 and 2 

 [Rhodes, 1952] from Adams and Macoupin Counties in western Illinois re- 

 spectively) . All have yielded abundant faunas and the last have also 

 yielded assemblages. The Adams County locality is also the topotype 

 locality of Illinella Rhodes, 1952. The last pages in the guidebook 

 show an optional-locality map (fig. 11) and small inset maps (fig. 12) 

 taken from quadrangle topographic sheets which will guide you to any 

 of the optional localities you wish to visit. 



ACKNOWLEDGMENTS 



We are greatly indebted to the Marquette Cement Manufacturing 

 Company for permission to enter their property and to Mr. Henry Janz, 

 Township Road Commissioner, for access to Bailey Falls along the extension 

 of Bailey Falls Road. Dr. and Mrs. Hugh Black of Bailey Falls Road were 

 both gracious and helpful, especially during early stages of planning. We 

 have drawn heavily on H. B. Willman's intimate knowledge of the La Salle 

 area and on Illinois Geological Survey Field Guidebook Series 8, which 

 covers much of the same area. Persons who have directly contributed their 

 labors to the success of the field trip are Margaret Whaley, Mildred New- 

 house, Susan Avcin, Dr. Lois Kent, Patricia Perkins, and James Rogers. We 

 are grateful to all. 



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