[Annals N. Y. Acad. Sciences, Vol. XXII. pp. 295-319. 13 November, 1912] 



GEOLOGIC AGE OF THE BEDPOED SHALE OP OHIO 1 

 By Geokge H. Girty 



(Presented in abstract before the Academy, 7 October, 1912) 



The Bedford shale takes its name from Bedford, in Cuyahoga County, 

 Ohio. The typical locality is the gorge of Tinkers Creek below the falls, 

 where the formation comprises about 75 feet of bluish clay shale lying 

 between the Berea sandstone above and the black slaty Cleveland shale 

 below. To the west, the lower portion of the Bedford develops a sand- 

 stone member which is quarried as the "Cleveland bluestone," while the 

 upper portion undergoes a change of color to a strong red. In fact, the 

 Bedford is better known as a red than a blue formation. 



The fossils of the Bedford shale are largely confined to the basal por- 

 tion, though a few species are represented by rare individuals at higher 

 horizons. At Bedford, fossils are abundant in immediate contact with 

 the Cleveland shale, where they are more or less crushed, and also a few 

 feet higher in large calcareous concretions, where the surface characters 

 are apt to be obscured. Some of them are broken and rounded as if by 

 wave or current action, but this is not the general character of their 

 occurrence. 



The Bedford shale lies close to what has been considered the boundary 

 between the Devonian and Carboniferous systems, and it is the purpose 

 of the present paper to present such evidence as I have bearing on the 

 geologic age of the formation. The question then is whether the Bedford 

 shale shall be included in the Devonian or the Carboniferous system. I 

 shall treat this largely as a paleontologic question, and my fossil evi- 

 dence is derived from typical sections at Bedford and other points in 

 Cuyahoga County. 



It will not be out of place to consider some of the principles controll- 

 ing such an attempt as I have taken in hand. 



Theoretically, the great geologic systems were defined by movements cre- 

 ating extraordinary changes in the conditions of land and water, always 

 undergoing changes more or less gradual, and these conditions entailed 

 corresponding changes in the character of the plants and animals which 

 had in them their habitat. As expressed lithologically, the rocks of the 

 several systems, perhaps generally in the typical region and not infre- 



1 Published by permission of the Director of the U. S. Geological Survey. 



(295) 



