to the Ohio Shale Problem. 161 



(or the Olentangy shale when present) and the Bedford shale. 

 Under the accepted belief that the Chagrin overlies the Huron, 

 Orton's proposal was fully warranted on the grounds of logic 

 and convenience in classification. But if it can be shown that 

 the Chagrin, in which I see nothing else than the westwardly 

 overlapping continuation of the Chemung of Pennsylvania and 

 New York, is really older than the Huron, then the most con- 

 vincing of the reasons on which he based his contention that 

 the Cleveland should be placed in the same system to which 

 the Chemung and Chagrin are referred, are materially weak- 

 ened if not entirely set aside. In that case too, the striking 

 similarities exhibited by the faunas of the Cleveland and 

 Huron no longer call for explanation, while the no less notable 

 faunal discordance between the Chagrin and the Huron also is 

 readily understood. 



The most widely recognizable and on all counts the most 

 important of the breaks that have been determined in the 

 Devonian and Waverlyan deposits of southeastern North 

 America, is the one marking the overlapping base of the 

 so-called Devonian black shale. This boundary is everywhere 

 sharply defined. It is always unconformable ; and the time 

 value of the stratigraphic hiatus which it marks varies greatly 

 from place to place. At one point the black shale is in con- 

 tact with an Ordovician formation, at another with Silurian, 

 at still other places with early, middle, or late Devonian 

 formations. And very decided crustal movements preceded 

 and progressively induced the advance of the waters in which 

 these black shales were laid down. Thus, during the late 

 Devonian (Chemung) the middle Appalachian region was sub- 

 merged and invaded by Atlantic waters which finally extended 

 over the eastern third or half of Ohio. During the Chattanoo- 

 gan, on the contrary, the surface of the continent tilted so that 

 these Chemung areas were emerged and the southern areas, 

 which for a long time prior to this had formed part of a great 

 median land mass, sank beneath waters invading from the 

 Gulf of Mexico. This submergence left a great thickness of 

 siliceous shale (Woodford) in Oklahoma. In Ohio it left the 

 three divisions of the Ohio shale, the Huron, Olmsted, and 

 Cleveland, all of which — the second and third certainly and 

 the first probably — thin by overlap eastwardly across northern 

 Ohio until the last is finally lost before reaching the Pennsyl- 

 vania border. All of these facts and criteria positively indi- 

 cate that extraordinary geographic changes set in following 

 the close of Chemung sedimentation in Ohio. Decided faunal 

 changes too were introduced. What more evidence need be 

 offered in testing the propriety of drawing the Devono-Waver- 

 lyan boundary at the top of the Chagrin in Ohio and not at 

 the top of the Cleveland ! 



