GLACIAL DAMS, LAKES, AND WATERFALLS. 389 



and breaking up the foundations of its own dam. With the 

 depression of the dam the level of the lake also fell. Possibly 

 the change was gradual, and the dam and the lake went gently 

 down together. Possibly, but not probably, this was the case. 

 Far more likely is it that the melting was rapid, and that it 

 sapped the strength of the dam faster than it lowered the 

 water. This will be more probable if we consider the immense 

 area to be drained. The catastrophe was then inevitable — the 

 dam broke, and all the accumulated water of Lake Ohio was 

 poured through the gap. Days or even weeks must have 

 passed before it was all gone ; but at last its bed was dry. The 

 upper Ohio Valley was free from water, and Lake Ohio had 

 passed away. . . . 



But the whole tale is not yet told. Not once only did 

 these tremendous floods occur. In the ensuing winter the 

 dam was repaired by the advancing ice, relieved from the melt- 

 ing effects of the sun and of the floods. Year after year was 

 this conflict repeated. How often we can not tell. But there 

 came at last a summer when the Cincinnati dam was broken 

 for the last time ; when the winter with its snow and ice failed 

 to renew it, when the channel remained permanently clear, and 

 Lake Ohio had disappeared forever from the geography of 

 North America. . . . 



How many years or ages this conflict between the lake and 

 the dam continued it is quite impossible to say, but the quan- 

 tity of wreckage found in the valley of the lower Ohio, and 

 even in that of the Mississippi, below their point of junction, 

 is sufficient to convince us that it was no short time. "The 

 age of Great Floods" formed a striking episode in the story of 

 the "Ketreat of the Ice." Long afterward must the valley 

 have borne the marks of these disastrous torrents, far surpass- 

 ing in intensity anything now known on the earth. The great 

 flood of 1885, when the ice-laden water slowly rose seventy-three 

 feet above low-water mark, will long be remembered by Cincin- 

 nati and her inhabitants. But that flood, terrible as it was, 

 sinks into insignificance beside the furious torrent caused by the 

 sudden, even though partial, breach of an ice-dam hundreds of 

 feet in height, and the discharge of a body of water held behind 

 it, and forming a lake of twenty thousand square miles in extent. 



