174 Vlrich — Chattanooga n Series with Special Reference 



Oil the west by the outcrop of the Berea, doubtless comprises an 

 average thickness of Cleveland shale. This formation proba- 

 bly extends farther under cover, but, judging from the fact 

 that it pinches out eastward ly from Cleveland before reaching 

 Trumbull County, it is thought unlikely that it is present 

 under any of the eastern range of counties. The Bedford, 

 however, is believed to occur not only in this band but to 

 extend eastward and southeastward beyond the limits of the 

 state. As for the Olmsted and the Huron, the former per- 

 haps, the latter most probably, are thought to be confined to 

 the west of the 8r30 meridian. Huron sedimentation may in 

 fact be limited on the east by the crest of a low axis — the 

 Carter axis — which is indicated across eastern Kentucky in a 

 S. S.W. direction from Carter County, and from the same point 

 in a generalized opposite direction through Ohio to the low 

 arch shown along Lake Erie between Berea and Elyria. 

 The Chagrin, on the other side, probably did not extend far to 

 the west of the present crest of the same low arch. At any 

 rate very convincing evidence must be offered before I shall 

 admit that the Chagrin wedge reaches as far as Huron River. 

 These relations are expressed graphically in fig. 1. 



With the issue thus clearly set forth, namely, that there is 

 no Chagrin shale in Huron County and no Huron beneath the 

 Chagrin under Cuyahoga County, it is obvious that very rapid 

 thinning of these formations must have taken place in the 

 intervening area. The Chagrin, with a thickness of something 

 like 1200 feet, must pinch out in 40 miles, or at the rate of 30 

 feet to the mile. The Huron overlapping eastward must lose 

 approximately 300 feet in less than 30 miles. Is there suffi- 

 cient warrant for such contentions in the records of deep wells 

 in the affected area? 



Comparison of published logs of deep wells in Ohio shows inva- 

 riably a thinning of the shale complex in a westerly and north- 

 westerly direction from Wellsville on the Ohio near the eastern 

 border of the state. It shows, further, that the rate of pinching 

 increases rapidly as it nears the Carter axis. Under Wellsville 

 the shale complex is over 2600 feet thick, the bottom of the 

 well being still in the shale. From this point to Huron River, 

 a distance of something like 112 miles, the shale complex loses 

 about 2000 feet, or nearly 18 feet per mile. To lose the whole of 

 the 2600 feet would require thinning of a little over 23 feet per 

 mile. The latter rate would be more nearly the proper one if 

 we assumed that the shale under the Berea at Wellsville is, 

 with the probable exception of perhaps 100 feet at Bedford, all 

 pre-Huron Devonian. That it is late Devonian beneath the 

 Bedford part is strongly suggested to my mind by the frequent 

 presence of thick beds of red shale (presumably Catskill Che- 



