172 Ulrich — Chattanoogan Series with Special Reference 



quite unnecessary to burden these pages with even a digest of 

 the already frequently published evidence. The only point 

 that might be brought out with profit here is that with the 

 removal of the Chagrin wedge from between the Huron and 

 the Cleveland to a position distinctly beneath the Huron, the 

 paleontological evidence afforded by the upper part of the 

 Chagrin is cleared of the suspicion that it may be a Portage 

 facies of the Chemung fauna and not the Chemung proper. It 

 is to be understood, however, that I have no intention of deny- 

 ing that the Chagrin, providing this formation is interpreted as 

 including all the Neodevonian rocks found outcropping in 

 northeastern Ohio, does not include beds of Portage as well as 

 Chemung age. In fact I believe it does, though I question 

 very much that the Portage, even as a thin wedge, extends as 

 far westward in Ohio as the Chemung. The Genesee, too, 

 I am willing to believe that it once extended as a thin deposit 

 entirely across northern Ohio into the northern Indiana- 

 Michigan basin. This sheet, together with portions of the 

 Olentangy beneath it, which we know to be absent in many 

 sections, would in that case have been rather generally removed 

 by erosion prior to the Huron transgression. However, that 

 is a phase of the general subject that may be readily set aside 

 as having no vital bearing on the problems immediately 

 before us. 



Physical evidence bearing on the relative j)ositions of the Chagrin 

 and Huron formations. 



General discussion. — It has long been known that the Cha- 

 grin thins rapidly in a westerly direction across northern Ohio 

 from the Pennsylvania state line. Newberry originally 

 believed that this formation pinched out also southwardly and 

 that it was confined to the counties near or bordering Lake 

 Erie. This is evident from a statement in his report on Erie 

 county* where he says " it (the Erie shale) probably reaches 

 but a little way back from the lake shore." It was this belief 

 doubtless that led him to assign all of the Ohio shale in cen- 

 tral and southern Ohio to the Huron. Further, it was gen- 

 erally accepted then that the rocks of northern Ohio dipped 

 gradually and continuously eastward from Sandusky, a con- 

 ception that was slightly modified when Newberryf discovered 

 that beginning near the mouth of Rocky River the dip 

 changes from east to west and that it continues westerly to 

 Vermilion River. Finally, as concerns northern Ohio, it was 

 not appreciated that whereas the Chagrin thins westwardly, the 



* Ohio Geol. Survey, vol. ii, p. 188, 1874. 

 f Mon. U. S. Geol. Survey, xvi, p. 127, 1889. 



