W. A. Yerwiebe — Coi'velation of the Devonian Shales^ etc. 33 



Aet. II. — Correlation of the Devonian Shales of Ohio and 

 Pennsylvania; by W. A. Yerwiebe, Ohio State University. 



Correlation of the Devonian Shales of Ohio and Pennsylvania, 



The outcrop of the Devonian shales of Ohio occupies a nar- 

 row belt extending roughly north from the Ohio river through 

 the center of the state to Lake Erie. It also follows the lake 

 shore to the east and extends into Pennsylvania and ]^ew 

 York, widening as the lake becomes narrower. The dip of the 

 rocks in central Ohio is toward the southeast, but very gentle, 

 averaging about 30 feet to the mile. In northern Ohio the dip 

 becomes more and more directed toward the south and finally 

 becomes southwest in Warren and McKean counties of north- 

 western Pennsylvania. 



As is well known, the subdivisions of the Devonian were first 

 studied and named in I^ew York state. They were independ- 

 ently studied in Ohio and also in Pennsylvania. When the 

 time came for more refined correlation of the rocks in these 

 states great difficulty was encountered. The earlier formations 

 including those below the Onondaga limestone were found to 

 be missing in Ohio. The Onondaga because of its lithologic 

 character was traced without much difficulty from its outcrop 

 in New York, through Pennsylvania by means of well sections, 

 to its outcrop in Ohio. However, a real problem developed 

 when the attempt was made to trace the shales and shaly 

 sandstones reaching a thickness of thousands of feet in New 

 York in the same way. These are so similar among themselves 

 in lithologic character and yet each appears so different, due to 

 lateral gradation, that no satisfactory correlation has been 

 offered up to the present. 



Statement of Problems Involved. 



A clear statement of the problems involved will assist 

 materially in understanding the present status of the question 

 and will also serve as a summary of work done in the past. 



First: Where shall the limit of the Devonian be placed? 

 The lower limit as a rule presents no difficulty but the upper 

 limit has been much discussed and shifted, at least in Ohio. It 

 has been variously placed at the top of the Chagrin shale, 

 Cleveland shale and Bedford shale. 



Second: Shall the 2000 feet of shale in eastern Ohio be 

 considered synchronous with the 800 feet of shale on the 

 western outcrop or shall the thinning be ascribed to overlap ? 



Third: Does the Huron shale extend from the river of that 

 name in central Ohio east into Pennsylvania, or does it repre- 



Am. Jour. Sci.— Fouuth Series, Vol. XLIV, No. 259.— July, 1917. 

 3 



