AGE OF THE CINCINNATI ANTICLINE 417 



ness due to subsequent erosion, it is not probable that this was the case 

 where the same formations are found directly overlaid b}^ the Black 

 shale. 



This becomes more evident when the demands of a contrary view are 

 considered. If the thinning of the various Silurian formations be due 

 to original deposition, the thinned margins of these formations must 

 represent their extreme limit of deposition on the western flank of the 

 anticline. In that case it will be noted that at many points the bound- 

 aries of several formations occur within a very short distance of one 

 another. Since no case is known in which the margin of an upper 

 Silurian formation extends beyond the margin of a lower formation of 

 this age, it is evident that not only must the Silurian beds have been 

 deposited during a rise of the anticline, but the rise must have been so 

 constant that at no point in the entire field was it possible for any of the 

 Silurian formations to extend beyond the margin of one of the older 

 Silurian beds. When the near approach to one another of the marginal 

 outcrops of the various Silurian formations at man}^^ points is considered, 

 the absence of overlap becomes marvelous, and the possibility of this 

 being due to original deposition incredible. 



If the present thinning of the subdivisions of the Silurian toward the 

 axis of the anticline be due to original deposition, the western flank of 

 the anticline must at some points have been strongly inclined, since in 

 no other manner would it be possible to find such a thick Silurian sec- 

 tion so near to the most eastern edge of outcrop of this age as is found 

 at those localities where the rate of thinning is most rapid. It seems im- 

 possible to believe that no evidences of shore conditions would be found 

 on a shore so highly inclined. Nevertheless not a single Ordovician 

 fossil has so far been found included in Silurian rocks, although Ordo- 

 vician forms are known at various points in Kentucky and Tennessee 

 in the base of the Black shale and in the base of the Devonian limestone 

 where these strata directly overlie or are closely contiguous to Ordovician 

 rocks. No pebbles or ripple-marks or strong lithological changes are 

 noticed pointing to the immediate vicinity of a shore line. The amount 

 of admixture of clayey material in the Laurel bed is much less than 

 might be expected if the Cincinnati anticline was already as well de- 

 veloped in the Silurian age as in times immediatel}^ preceding the depo- 

 sition of the Devonian limestone and the Black shale. 



Moreover, it seems hardly probable that such a rapid decrease of the 

 Silurian beds toward the anticline could take place where these strata 

 are overlaid by Devonian rocks without being accompanied by corre- 

 sponding changes in thickness of these beds where covered by strata of 

 the same general age. 



