to the Ohio Shale Problem. 159 



graphic sequence and correlation of the Devono-Waverleyan 

 black shale series in Ohio, Indiana, Kentucky, and Tennessee. 

 The first departure concerns the stratigraphic position of the 

 Chagrin formation (Erie shale of Newberry) with respect to 

 the Huron shale of the Ohio geologists. Beginning with New- 

 berry in 1870 and continuing to the present day, all geologists 

 who have worked on this part of the Ohio section have placed 

 the Chagrin above the Huron. I insist that this relation of the 

 two formations has never been established, and that most prob- 

 ably the opposite condition obtains ; in other words, that the 

 Huron is younger, and not older, than the Chagrin. Incident- 

 ally it will appear that the beds beginning with the concre- 

 tionary Dinichthys herzeri zone (which usually forms the lower 

 part of the Huron) and ending with the top of the Cleveland 

 shale, constitute a single broadly conceived and diastrophically 

 unbroken formation, or a group of three lithologically distin- 

 guishable members, which overlaps eastwardly over the edge 

 of the westwardly diminishing wedge of Chagrin shale. It will 

 appear, further, that these oppositely directed overlaps are 

 explained on the ground of continental tilting by virtue of 

 which the marine waters in which the Chagrin and other late 

 Devonian deposits in eastern Ohio and contiguous areas were 

 laid down, invaded from the north middle Atlantic, while those 

 making up the Huron-Cleveland, or Ohio shale, group invaded 

 from the Gulf of Mexico. 



The second difference concerns the equivalents in the north- 

 ern Ohio section of the Chattanooga shale of Tennessee and 

 Kentucky. Formerly the " Black shale " in these southern 

 states was rather generally regarded as corresponding approxi- 

 mately to the Genesee shale of New York. Later it was learned 

 that, in the Ohio valley at least, this shale comprises a continu- 

 ation of the Cleveland shale, and as the latter was known to 

 overlie beds with a Chemung fauna, it at the same time became 

 obvious that, while the basal part of the Ohio shale, as it was 

 then commonly named, might be of Genesee age, its top could 

 not be older than late Chemung. Finally, after Foerste and 

 Morse* had shown that the black shale of south central Ken- 

 tucky is not limited above by the top of the Cleveland, but 

 that its upper part includes an hiatus which opens northwardly 

 from the vicinity of Irvine to make room for a wedge of Bed- 

 ford sftale and Berea sandstone that finally expands to a thick- 

 ness of 118 feet at the Ohio, the way had been paved for a 

 revised conception of what the Chattanooga shale might really 



* Jour. Geology, vol. xvii, pp. 164-167, 1909. 



