FRANKLIN COUNTY. 633 



rated from it by as distinct a boundary as they are from the limestones 

 which they cover, but they agree with it in the style of bedding, in the 

 general absence of fossils, and in chemical composition, except that they 

 lack the bituminous matter that colors the Huron shale proper. There 

 are, however, thin seams of true black shale that are scattered through 

 these beds. The same horizon at other' sections contains a much larger 

 proportion of black slate, and this fact helps to justify their reference to 

 the same system. 



In his report on Delaware county. Professor N. H. Winchell proposes 

 for this blue belt the name of Olentangy shale, a convenient and unam- 

 biguous designation, which will be adopted here. 



The Olentangy shale appears to be the stratigraphical equivalent of 

 the beds termed Hamilton shale, by Dr. Newberry, which are found near 

 Front's Station, Erie county, and which are there highly fossiliferous, 

 and contain only Hamilton fossils. All of these fossils, however, are also 

 found in the limestone below, the difierence in the two sections being 

 this: In the lower beds true Corniferous fossils are associated with the 

 rest, while in the upper, no Corniferous forms have been found. The 

 Olentangy shale of Delaware and Franklin counties is very poor in fos- 

 sils of any description ; nothing characteristic is known to occur in them, 

 unless certain fish remains, reported by Rev. H. Herzer, from concretions 

 in these shales at Delaware, prove to be so. 



The correlation of these Devonian limestones and shales of Ohio with 

 the New York divisions of the same age, involves questions entirely 

 similar to those that were met in the geology of our Lower Silurian de- 

 posits in Southwestern Ohio. Eight hundred feet of Lower Silurian 

 limestones and shales are found there, which undoubtedly represent the 

 Trenton limestone, in part, the Utica shale, and the Hudson River group 

 of the New York scale ; but no one can draw the line where one epoch 

 ends and another begins. The growth of these beds was continuous. 

 The interruptions that marked the epochs on the continental border did 

 not make themselves felt in the central sea, but the life of the lower 

 beds held on through the vast cycles of time required for such a growth. 

 It was re-enforced from time to time with the forms belonging to higher 

 horizons, and the result is, that there is here an extricable blending of 

 the forms of life that characterize distinct forjuations at the east. In 

 regard to the designation of these beds, all ambiguity is removed by 

 giving them a name derived from the locality that shows them best. We 

 refer them all to the Cincinnati group, making such divisions of them as 

 the facts here warrant, and as convenience requires. 



In like manner, the Devonian limestones, already described, grew in a 



