Devonian Shales of Ohio and Pennsylvania. 37 



On the other hand, since the Chagrin formation has received 

 its name purely on lithologic grounds it is self-evident that it 

 should be unrecognizable between the Yerraillion River and 

 the Huron River since the lithologic character of the shales 

 changes so markedly here. The true state of affairs then seems 

 to be that the 200 feet of black shale exposed along the Huron 

 River and named Huron are the stratigraphic equivalent of the 

 Cleveland as well as the upper part of the Chagrin shales. 



As regards the low^er portion of the Chagrin some difficulty 

 is encountered at the outset since its lower limit w^as never 

 clearly defined. This is largely due to the fact that it does not 

 outcrop and can be known therefore onlj^ from well records. 

 A scrutiny of these in the reports of the Ohio Geological 

 Survey reveals the fact that the lithologic character of the 

 Chagrin extends down to the limestone (Delaware). Some 

 typical and reliable sections which illustrate this point very 

 beautifully may be found in vol. vi of the Geol. Survey Ohio 

 Publications. On page 429 a Cleveland w^ell is cited in detail 

 which shows but 95 feet of black shale in the lowest 500 feet. 

 Another deep well drilled at Akron (idem, p. 358) shows but 20 

 feet of black shale in the lowermost 620. feet and but 200 feet of 

 black shale in a total of 1862 feet, the remainder being prin- 

 cipally blue, and light and dark grey. Hence to be consistent 

 the top of the Delaware should also mark the base of the Chagrin. 

 \i we accept this premise then a new element is introduced into 

 the discussion. Toward the western outcrop of the Devonian 

 shales (between the Vermilion and Huron Rivers) a shale 

 formation called the Olentangy, carrying a well-defined lime- 

 stone near the top (Prout limestone), has been described. This 

 rests directly upon the Delaware and is overlain wherever the 

 contact is visible, by a black shale. The question now arises 

 whether this formation shall be considered the w^estern equiva- 

 lent of the lower part of the Chagrin or not. On lithologic 

 grounds it might well be, on paleontologic ground it should 

 not be. These tw^o, however, are not totally irreconcilable. 

 As was indicated above, the Chagrin is known on the outcrop 

 only toward its upper part and the fossils collected in this por- 

 tion are generally thought to indicate affinity with the Chemung 

 of INew^ York.* This portion is represented by a part of the 

 black shale in the west (where the lower part of the Chagrin 

 outcrops). The lower portion (Olentangy) carries a fauna 

 which is quite generally accepted to be Hamilton in age.f We 

 must assume then that the term Chagrin applies to a series of 

 rocks in Ohio which are the time equivalent of the upper 



* Prosser, Chas. S., Geol: Surv. Ohio, Bull. 15, p. 510. 



•fStauffer, Clinton R., Geol. Snrv. Ohio, Bull. 10, 1909, p. 156, + 177. 



