742 THE POPULAR SCIENCE MONTHLY. 



great size. None of the tributaries of the river, either from the 

 north or the south, flow through regions more recent than the 

 Carboniferous, with the exception of the lower parts of the Ohio 

 itself and of the Tennessee, which border on the Quaternary. The 

 lowest formation in the valley is the Cincinnati, which is just 

 touched at a single point, and only for a short distance, about 

 twenty miles above the city. 



It may be stated, then, that since the close of Carboniferous 

 time the river has flowed mainly in the same channel. The vast 

 antiquity of the river is thus easily established, and the existence 

 of the wide valley, with its broad bottom lands, is readily ac- 

 counted for. The story of the river during the long period of 

 pre-glacial time would be simple. For ages its waters were prob- 

 ably poured directly into the Gulf of Mexico, an arm of which 

 extended northward into the continent at least as far as the pres- 

 ent site of Cairo, Illinois. In later time the Mississippi-Missouri 

 began the formation of a delta, which, gradually extending, has 

 left the Ohio a tributary merely of the mighty " Father of 

 Waters." As ages passed away it smoothed its rocky bed, and 

 cut deeper and deeper between the hills, until at last there came a 

 time in the history of the earth which man has called the " Gla- 

 cial period." It was an age of intense cold when a mantle of ice 

 and snow covered all the New England States, New York, part of 

 Pennsylvania, of Ohio, of Indiana, and Illinois, and thence ex- 

 tended northwestward to Dakota and the Rocky Mountain region. 

 When the period was at its height, and the maximum limit of the 

 ice-sheet had been reached, the course of the Ohio River became 

 seriously affected. 



Profs. G. F. Wright and H. Carvill Lewis, Mr. Warren Up- 

 ham and others, have shown that, at the period of the greatest 

 extension of the ice, a portion of it crossed the Ohio River in the 

 vicinity of Cincinnati, and extended southward for some miles 

 into Kentucky. The course of the river as it now exists was 

 blocked for a distance of probably fifty miles, or from near Point 

 Pleasant, twenty miles above Cincinnati, to the mouth of the Big 

 Miami, thirty miles below. 



Investigations into the topography and surface geology of the 

 region about Cincinnati reveal the existence of an ancient chan- 

 nel of the Ohio which divided into two branches.* One was on 

 the eastern, the other on the western side of the city, and the two 

 united just north of the city and continued to Hamilton, twenty- 

 five miles. Here the old stream was joined by what is now the 

 Big Miami, and the united rivers then turned southwestward and 



* See a paper by the writer in the Journal of the Cincinnati Society of Natural His- 

 tory, vol. xi, pp. 96-101. 



