24 Cincituiati Society of Natural History. 



during this epoch probably a thousand feet of sediment were de- 

 posited ; for, aUhough but httle remains of it now, we must re- 

 member that the land has been exposed for countless ages to the 

 degrading and denuding agents of air and water, so that at the 

 close of this final period of subsidence came the last one of eleva- 

 tion, and the land rose above the surface of the water until it 

 stood one thousand, and perhaj)s fifteen hundred feet above the 

 level of the surrounding sea. 



It is noteworthy that the beds of barren shales are found just 

 below the level of the second beach, and the inference is that they 

 were deposited at a period when the sea bottom was stationary, and 

 that it was at the close of this period that the land appeared above 

 the sea level. Finally, Prof. Orton says, that the Cincinnati axis 

 underwent oscillations of level, and the facts above given tend to 

 show plainly this was the case. 



Having now discussed tlie aspect and geological position of 

 the rocks found in the immediate vicinity of Cincinnati, and hav- 

 ing seen them raised finally in perfect horizontality above the 

 ocean level, let us examine the agencies which have been in 

 action so long as to change in a wonderful manner the whole ap- 

 pearance of the surface since the time when it emerged as a long 

 ridge with gently sloping sides above the waters. 



No sooner is an area of land exposed to the atmosphere than 

 denudation begins. I'here is an immediate tendency to degrade 

 the summit to the level of the sea, and so actively is the work 

 carried on that it is simply a question of time how soon even, a 

 high mountain range is reduced to the ocean level. The 

 newly elevated island of Cincinnati was no exception to the gen- 

 eral rule, and although it was not extensive enough to possess any 

 large rivers, the ordinary aerial agencies of air and water would be 

 sufficient to accomplish a great deal in a long period of time. A 

 little furrow in a sloping bank, made by a rivulet, soon becomes 

 by the addition of other rivulets a rapid torrent, and gradually in- 

 creases' in size, volume and power. It sweeps more and more 

 sediment down its sloping channel, and at last casts its burden 

 into the "ocean to be there spread out in even sheets upon the 

 ocean floor far from land. 



No more striking example of the erosive power of water 

 acting through long periods of time can be seen than in our 

 Western territories in the great Colorado River Basin. Here the 



