190 /■'. .)/. Kindle— Stratiyraphic Relations of the 



entirely fail. In the succeeding discussion we shall see to 



what extent the application of the overlap theory to the shales 

 of the Ohio group, and their consequent separation into forma- 

 tions originating in distinct seas and belonging to different 



Fig. 1. 



Fig. 1. Map of the Ohio shale group after Professor Orton. 

 indicates approximate position of sections shown in fig. 3. 



Line A-B 



systems, affords an adequate explanation of all the facts which 

 are known about them. 



The overlap hypothesis. — The grounds on which the overlap 

 theory rests as applied to the Cleveland and Huron shales will 

 now be considered. Inspection of the accompanying map by 

 Prof. Orton* of the Ohio shale group, figure 1, will aid the 

 reader in following the discussion. The theory proposed by 

 Ulrich assumes that the portion of the Ohio shale group called 

 * Geol. Surv. of Ohio, vol. vi. 



