228 ILLINOIS STATE ACADEMY OF SCIENCE 



ville time. This folding may have brought the Chester age 

 to a close, destroying the Chester sea. 



The significance of these points is that any structure 

 which exists in the Mississippian will be reflected through 

 to the Ordovician horizons in spite of any unconformities 

 which exist, and that the major features of the structure in 

 the Pennsylvanian rocks will be closely associated with 

 more accentuated structure in all horizons below the Penn- 

 sylvanian. If shallow key horizons in the Pennsylvanian 

 or Mississippian can be relied upon, for interpreting the 

 structure of deeper horizons, then prospecting by* such 

 a method is practicable. 



CONCLUSIONS 



1. The southern part of the La Salle anticline in any- 

 thing like its present magnitude did not exist before the 

 close of Chester time. 



2. The big movement which caused the main, struc- 

 tural features of the La Salle anticline took place immed- 

 iately prior to and during Pottsville time. 



3. The folding shown by Mississippian beds will be re- 

 flected in similar degree in the underlying strata. 



4. The folding exhibited by Pennsylvanian strata will 

 be reflected in more accentuated form in all the underlying 

 strata. 



