ACKNOWLEDGMENTS 



We thank Donald Lowry (ISGS), who prepared the 

 SEM photographs, and Curtis Klug (University of 

 Iowa) and Donald Mikulic and Beverly Herzog (ISGS), 

 who reviewed the manuscript and provided useful 

 suggestions. 



Editoral Board 



Jonathan H. Goodwin, Chair 



Michael L. Barnhardt 

 Heinz H. Damberger 

 Anne L. Erdmann 

 Beverly L. Herzog 



David R. Larson 

 Donald G. Mikulic 

 William R. Roy 

 C. Pius Weibel 



ILLINOIS 



resources Printed by Authority of the State of Illinois/1997 7800 



printed with soybean ink on recycled paper 



