OLENTANGY SHALE OF CENTRAL OHIO 343 



Let us return once more to the typical Olentangy shale of central 

 Ohio, which we have seen is of Upper Devonian age. It rests 

 disconformably upon the Delaware limestone, which represents 

 some of the lower Traverse beds of the Michigan region. There 

 is thus a great hiatus between the Delaware limestone and the 

 Olentangy shale in central Ohio, cutting out the greater part of the 

 Traverse group. This hiatus increases southward, so that in 

 Pickaway County the Olentangy shale lies in places upon the lower 

 Columbus and elsewhere upon the Monroan, and in all cases it is 

 succeeded by the black Huron shale. At Bainbridge, in Ross 

 County, it even rests upon the Niagaran. The Olentangy is still 

 represented at Vanceburg, Kentucky, on the Ohio River and near 

 Fox Springs, Fleming County, Kentucky, according to W. C. 

 Morse. A generalized north-south section through the region 

 named brings out the magnitude of the post-Traverse erosion, and 

 also shows that the Olentangy shale is of the nature of a lentil, 

 disappearing to the north and to the south. The source of the 

 Olentangy was probably local and circumscribed, representing 

 perhaps an accumulation in Upper Devonian time of a residual 

 soil produced from the weathering of the underlying rocks. It may 

 possibly be an extension of some of the eastern gray shales of the 

 Upper Devonian, such as the Cashaqua. The Black Huron shale 

 I hold to be a deposit of carbonaceous mud washed into the shallow 

 Upper Devonian sea by the rivers coming from the Devonian 

 peneplanes to the south and representing probably our best case 

 of an estuarine deposit in the American Paleozoic. The details 

 of this and the relation of the Huron to the Chattanooga shale, 

 which latter I consider mostly a terrestrial residual soil, reworked 

 in Mississippian time by the encroaching sea, are set forth at 

 length in the monograph on The Devonic Formations of Michigan 

 to which reference has several times been made. 



