to the Ohio Shale Problem. Ill 



total thicknesses ranging from 55 feet to 100 feet. The three 

 formations, then, namely, the Bedford, the Cleveland, and the 

 Olmsted, which are almost certainly represented in the shale 

 complex under Lodi, would more than make up the balance 

 left of the shale complex at Huron "River after deducting its 

 estimated westerly thinning of 1000 feet. In other words, the 

 loss of 1000 feet between Lodi and Huron River, which leaves 

 but 116 feet of the shale at the former place to be accounted 

 for, would be. much more than made up by the upper forma- 

 tions of the complex which we have every reason to regard as 

 continuously developed between the two points. 



It being plausibly established that the northwesterly and 

 westerly thinning of the shale complex affects only its pre- 

 Olmsted portions, we may now proceed to the consideration of 

 the Chagrin and Huron divisions. I shall start with the asser- 

 tion that west of the Carter axis a larger proportion of the 

 shale complex belongs above the top of the Chagrin than is the 

 case to the east of the mentioned axis ; and this will presently 

 end in the probable inference that practically the whole of the 

 shale series usually referred to under the term Huron belongs 

 above, and not beneath, the Chagrin. 



That the assertion just made is founded on indubitable evi- 

 dence becomes wholly clear when we recall the fact already 

 mentioned that the Olmsted shale begins at West Cleveland to 

 wedge in between the underlying Chagrin and the base of the 

 typical Cleveland shale. As described, this wedge of distin- 

 guishable shale — the Olmsted of dishing — thickens steadily in 

 a westward direction from Cleveland until its base sinks 

 beneath the level of Lake Erie. To this point, however, it has 

 added at least 100 feet to the post-Chagrin series of shales. 

 Considering this fact in connection with the positively estab- 

 lished rapid westward thinning of the underlying Chagrin, it is 

 clear that orogenic movements resulting in reversal of direction 

 of marine transgression had occurred in the interval between 

 the close of Chagrin sedimentation and the beginning of the 

 Olmsted. "When did this reversal take place? May not the 

 point where the Olmsted has attained a thickness of 100 feet 

 mark only the middle or even some later stage in the easterly 

 transgression that was superimposed on the westerly transgres- 

 sion of the Chagrin? That it does not mark the beginning of 

 the reversal is proved to my conviction by the fact that this 

 point is at least 20 miles to the east of the middle of the trough 

 between the Carter and Cincinnati axes in which we may 

 reasonably suppose that post-Chagrin deposition begun. It is 

 quite reasonable then to assume that the Olmsted overlap is 

 but one of the later stages of a marine transgression that began 

 with the earliest of Huron deposition. 



