GLACIAL DAM.\ LAKES, AND WATERFALLS. 387 



portion of the State which whs glaciated, and which is about 

 twice the extent of the unglaciated portion. Ten feet over 

 the glaciated portion is equal to twenty feet of water over 

 the unglaciated. To this must be added an equal amount 

 from the area farther back whose drainage was then into the 

 upper Ohio. This makes forty feet per year of water so con- 

 tributed to this lake-basin. Furthermore, this supply would 

 all be furnished in the six months of warm weather, and to 

 a large degree in the daytime, which gives the rate above 

 mentioned. 



The breaking away of the barrier to such a body of water 

 is no simple affair. As this writer remarks : 



The Ohio of to-day in flood is a terrible danger to the val- 

 ley, but the Ohio then must have been a much more formidable 

 river to the dwellers on its banks. The muddy waters rolled 

 along, fed by innumerable rills of glacier-milk, and often 

 charged with ice and stones. The first warm days of spring 

 were the harbinger of the coming flood, which grew swifter 

 and deeper as summer came, and only subsided as the falling 

 temperature of autumn again locked up with frost the glacier 

 fountains. . . . The ancient Ohio River system was in its 

 higher part a multitude of glacial torrents rushiug off the ice- 

 sheet, carrying all before them, waxing strong beneath the ris- 

 ing suu, till in the afternoon the roar of the waters and their 

 stony burden reached its maximum, and, as the sun slowly 

 sank, again diminished, and gradually died away during the 

 night, reaching its minimum at sunrise. . . . 



But. with the steady amelioration of the climate, more vio- 

 lent and sudden floods ensued. The increasing heat of sum- 

 mer compelled the retreat of the ice from the Kentucky shore, 

 where Covington and Newport now lie, and so lowered its sur- 

 face that it fell below the previous outflow-point. The waters 

 then took their course over the dam, instead of passing, as 

 formerly, up the Licking and down the Kentucky River Val- 

 ley-. The spectacle of a great ice-cascade, or of long ice-rapids, 

 was then exhibited at Cincinnati. This cataract, or these rap- 

 id-, must have been several hundred feet high. Down these 

 cliffs or this slope the water clashed, meltirg its own channel, 



