PAPERS ON GEOLOGY AND GEOGRAPHY 221 



STRATIGRAPHY OF THE SOUTHERN HALF 



OF THE LA SALLE ANTICLINE^ 



L. A. Mylius, State Geological Survey, Urbana, III. 



GENERAL RELATIONS 



The La Salle anticline is an anticlinal fold which runs a 

 little west of north and a little east of south through east- 

 ern Illinois. It appears in outcrop in La Salle County and 

 extends without outcrop evidence to Lawrence County, 

 Illinois ; from that place it is not as well understood. The 

 Galena-Trenton limestone outcrops at La Salle, and from 

 that place to Lawrence County, Illinois, underlies a zone 

 of anticlinal folding over 200 miles long. There is no rock 

 section outcropping from which to make any direct studies 

 on the conditions which underline the southern part of the 

 La Salle anticline, as practically all the area is covered by 

 from 50 to 200 feet of glacial drift. The western limb of 

 the anticline has a very steep dip, while the eastern is usu- 

 ally not so steep, and in places a double fold exists. 

 Practically all the oil production in Illinois has been from 

 structures associated with this La Salle anticline in Law- 

 rence, Crawford, Clark, and Cumberland counties. 



PURPOSE 



The purpose of this paper is to establish, if possible, 

 from data obtained by the study of well logs and samples, 

 facts bearing on the ages of the folding along the La Salle 

 anticlinal zone ; also to apply the age of folding to a prac- 

 tical consideration of oil accumulation, and to the inter- 

 pretation of folds in the lower formations from shallow 

 test holes. It is realized that well log interpretation can 

 not give unquestionable results, but it is hoped that in this 

 area where direct study of the rock section is impossible 

 some facts obtained from well logs may be logically linked 

 with paleontological interpretations made elsewhere for the 

 seas in which the different formations were deposited. 

 The area discussed is approximately 90 miles in length by 

 20 miles in width and consists of parts of Douglas, Edgar, 

 Coles, Clark, Cumberland, Jasper, Crawford, Richland, and 

 Lawrence counties. 



1. This paper is preliminary to a more detailed discussion of the subject in a forth- 

 coming bulletin of the Illinois State Geological Survey. Points that have been con- 

 sidered as proof of these conclusions will be detailed at that time. 



