Devonian Shales of Northern Ohio. 213 



the base of the Olentangy and the top of the Bedford shale. 

 Others have been assumed as corollaries of the overlap theory, 

 but the mass of evidence already presented against this hypoth- 

 esis removes them from consideration. The Devonian shales of 

 Ohio represent a great series of alternating black and gray or 

 bluish shale, in which the black color predominates to the 

 westward and the gray color to the eastward. This succession 

 of black, blue, and gray shale is broken for the first time by 

 the appearance of red or chocolate-colored shale in the upper 

 part of the Bedford. This earliest appearance in the Ohio 

 section of red and chocolate-colored sediments in the Bed- 

 ford shale indicates a change in the character and conditions 

 of sedimentation of a more profound character than any which 

 had previously occurred in the region since the cessation of 

 limestone sedimentation. This type of sedimentation is termi- 

 nated throughout northern Ohio by a very marked unconform- 

 ity which intervenes between the Bedford shale and the Berea 

 sandstone. The logical place at which to draw the Devonian- 

 Carboniferous boundary in northern Ohio appears to the writer 

 to be the horizon of this unconformity. The fauna of the 

 Bedford shows a Devonian facies with the possible exception 

 of Syringothyris, but this genus can no longer be regarded as 

 strictly limited to the Carboniferous. The " Corry " sand- 

 stone of northwestern Pennsylvania, which follows the Bedford 

 horizon and is the equivalent of the Berea, contains, according 

 to Grirty, a distinctly Carboniferous fauna. This definition of 

 the boundary between the two systems gives as the initial 

 formation of the Carboniferous a coarse sandstone holding an 

 undoubted Carboniferous fauna which follows an unconformity 

 above beds with a fauna which is more Devonian than Carbon- 

 iferous in facies. 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 200. -August, 1912. 

 15 



