VOLUME XXXI NUMBER 7 



THE 



JOURNAL OF GEOLOGY 



October-November ig2J 



THE PALEOZOIC ROCKS FOUND IN DEEP WELLS 

 IN WISCONSIN AND NORTHERN ILLINOIS^ 



F. T. THWAITES 

 Geological and Natural History Survey, Madison, Wisconsin 



INTRODUCTION 



The study of the Paleozoic formations penetrated by deep 

 wells in Wisconsin and northern Illinois was begun by the writer 

 in 191 2, when the entire collection of samples of drill cuttings that 

 had been collected from that area by the United States Geological 

 Survey^ was donated to the University of Wisconsin. Since that 

 date the co-operation of many well drillers and engineers has 

 enlarged the collection until it now includes over 8,000 specimens. 

 Its study has been carried on in connection with work on the out- 

 crops for the Wisconsin Geological and Natural History Survey, 

 mainly under the direction of Dr. E. O. Ulrich, of the United 

 States Geological Survey. In the last few years the State Survey 

 has paid well drillers five cents for each sample with a minimum of 

 $2.50 for each record; sample bags with attached labels are fur- 

 nished. After study of the samples blue prints showing the geo- 

 logical section, casing log, water levels, yield, and other data are 



' Published by permission of the state geologists of Illinois and "Wisconsin. 



2 M. L. Fuller, E. F. Lines, and A. C. Veatch, "Record of Deep Well Drilling for 

 1904," U.S. Geol. Survey Bull. 264 (1905), pp. 76-77. M. L. Fuller and Samuel San- 

 ford, "Record of Deep Well Drillings for 1905," U.S. Geol. Survey Bull. 2g8 (1906), 

 pp. 176-79, 295-96. 



529 



