CHAPTER LV. 



REVIEW OP THE G^EOLOGICAL STRUCTURE OF OHIO. 



BY J. S. NBWBEERY. 



LOWEE SILURIA.N SYSTEM. 



THE CINCINNATI AKCH. 



During the first two years of the existence of the Geological Survey, 

 much attention was given to the Cincinnati arch, and its structure and 

 age were then, for the first time, accurately determined. These are dis- 

 cussed at some length in the first volume of this report, and it is there 

 stated that this arch is a great fold of the strata raised at the close of the 

 Lower Silurian age, when it formed two islands, one in Tennessee, the 

 other in Kentucky and Ohio, around which the more recent rocks were 

 deposited on a sloping shore. It was also shown that no evidence exists 

 that these islands have ever been completely submerged since the close 

 of the Lower Silurian age, and it was suggested that the broad, depressed 

 areas of Silurian rocks, which now mark their sites, were produced by 

 the solution and removal by atmospheric water of the limestones of 

 which they were composed. 



Some doubt has been expressed by Prof. E. T. Cox, the able State Geol- 

 ogist of Indiana, whether the theory of the history and structure of the 

 Cincinnati arch, given in our report, is the true one, and he advances 

 the view that it should be rather regarded as a mass of the Lower Silu- 

 rian limestones which formed a highland of the ancient continent, sub- 

 sequently submerged, and receiving on its top and sides the sediments 

 that compose the more recent groups of rocks. In answer to this theory, 

 it may be said that, whatever it may seem to be in Indiana, the Cincin- 

 nati axis in Ohio is unmistakably an anticlinal ridge, of which the arched 

 strata of the Cincinnati group form the core, the more recent formations 

 resting on these, and dipping away on either side. 



That the Cincinnati arch formed an elevated ridge, which separated 

 depressed areas through the Upper Silurian, Devonian, and Carbonifer- 

 ous ages, is demonstrated by the thinning out on its flanks of the Clinton 

 Group, the Corniferous Limestone, the Waverly, and the Coal Measures. 



