38 W. A. Yerwiehe — Correlation of the 



Hamilton, the whole of the Portage, and^Drobablj the whole 

 of the Chemung (provided we assume the Cleveland to be 

 but a local facies of the Chagrin). 



Huron shale: This name was unfortunate from the begin- 

 ning. It was suggested in a loose way and has been used 

 loosely and in an indefinite manner ever since. Prosser* has 

 suggested that the name should be replaced, but does not wish 

 to take the responsibility until more field work is done on 

 the problem. It seems to the writer that the term Ohio shale 

 given by Andrews in 1870 and intended to be applied to the 

 black shales extending through central Ohio from the Ohio 

 Kiver to Lake Erie might well supplant the term Huron, thus 

 avoiding needless duplication and the possible addition of another 

 term. As nearly as can be determined from the literature, the 

 term Huron is used to designate a section of black shales inter- 

 mingled with a trifling amount of blue shales occurring typically 

 along the Huron River and reaching a thickness of perhaps 

 200 feet.f It has been assumed that this shale represented the 

 basal portion of the Ohio shale and that since the latter was 

 thought to be equivalent to three formations in northeastern 

 Ohio it must underlie the Chagrin. No conclusive evidence 

 exists that this is the case and it would be more logical to con- 

 sider it as being the much thickened Cleveland shale. In this 

 connection the reader is referred to the well records cited in 

 the paragraph on the Chagrin formation. Dr. Kindle, in at- 

 tempting to find some method of distinguishing the Cleveland 

 and Huron, has suggested that the former never contains any 

 spherical concretions, but does contain many layers of ' cone in 

 cone ' while the opposite holds true of the Huron. This is per- 

 haps a satisfactory method of differentiation locally, but it is 

 too insecure and unscientific to be used in correlating separated 

 areas. 



The true relationship of the Huron to the Ohio Devonian 

 shales may be simply stated as follows : Two wedges of shales 

 present themselves, one thinning toward the east, the other 

 thinning toward the west. The former is characterized by a 

 black color and slaty texture, the latter by blue and grey colors 

 and a softer texture. Both are entirely isochronous, the thin- 

 ner portions of the one corresponding to the thicker portions of 

 the other. In other words, the blue and grey shales of the 

 Chagrin or Erie formation are gradually replaced on going 

 west from the boundary of Ohio by black shale. This is called 

 Cleveland shale as far as the Yermillion Piver and mostly 

 Huron shale beyond that. One exception must be made here 

 and that is the very bottommost part retains its typical charac- 



*GeoL Surv. Ohio, Bull. 7, 1905, p. 23. 



f Prosser, Chas. S., Jour. Geology, vol. xxi, No. 4, p. 362, 1913. 



