206 /:'. M. Ki/ndle—StraUgraphic Relations of the 



Structural Featu res. — The Devonian limestone forms the 

 floor of the Devonian shales everywhere in Ohio to the east of 

 a line running from Columbus to Sandusky. The most import- 

 ant factor bearing on the area] distribution of these shales is a 

 northern axis or branch of the great Cincinnati geanticline 

 which rims north past Dayton between Toledo and Sandusky 

 and pitches northward on reaching Lake Erie. Away from 

 this axis the Devonian limestones dip to the eastward and 

 southeastward. So far as drill records afford data this declin- 

 ation is always easterly bnt at a somewhat variable rate, rang- 

 ing throughout eastern Ohio between 15 and 10 feet per mile. 

 This easterly declination of the Devonian limestone appears 

 to be a joint product of the Cincinnati uplift and the great 

 downwarp trough in which the sediments comprising the west- 

 ern part of the Allegheny Mountains were deposited. Near 

 Pittsburg the drill has shown that the Devonian limestone 

 lies more than 5000 feet below sea-level. The great thickness 

 of the Devonian and Carboniferous shale and sandstone series 

 in eastern Ohio doubtless has a direct casual relation to the 

 depth of this limestone floor. Its depression was doubtless in 

 progress during much of this cycle of deposition, which in parts 

 of western Pennsylvania dumped a thickness of more than one 

 mile of sediments upon the sea floor during middle and late 

 Devonian time. Owing to the great thickness of the Devo- 

 nian shales in western Pennsylvania and eastern Ohio as com- 

 pared with their slight thickness farther west, the inclination 

 of the upper beds of this series cannot be expected to coincide 

 with that of the limestone floor. If we take the thickness of 

 the Chagrin and its underlying shales near the northeastern 

 border of Ohio in Ashtabula County at 1800 feet, and at Cleve- 

 land 900 feet, which are close approximations to the actual 

 thicknesses of these formations at these two localities, the top 

 of the Chagrin and adjacent beds, if the formation were depos- 

 ited on a horizontal sea floor, should dip to the west at 16 feet 

 per mile owing to the excessive thickness of the beds at the east. 

 Whether horizontal or inclined to the eastward, as at present, at 

 the close of Chagrin deposition, the Devonian limestone, which 

 is the basal formation of the Devonian shales, could not possibly 

 have had the same declination as the upper surface of the Cha- 

 grin. It is the failure of Mr. Ulrich to recognize this fact that 

 has led him to use different declinations of the shale and lime- 

 stone as an argument for distinct marine basins for the Chagrin 

 and the Cleveland. It is a simple mechanical fact due solely to 

 differences in thickness of the Devonian shales at the eastern 

 and western ends of the northern Ohio section, and has no 

 bearing on the question of distinct marine basins of sedimen- 

 tation for the different members of the Ohio shale. The gen- 



