A BRIEF HISTORY OF THE OHIO RIVER. 745 



The investigation of this matter was made the subject of a special 

 paper by Prof. E. W. Claypole, and from his pamphlet we glean 

 some interesting facts. 



Lake Ohio, as this body of water produced by the ice-dam was 

 called, extended four hundred miles up the valley and was in 

 places two hundred miles broad. Its waters covered the present 

 site of Pittsburg to a depth of three hundred feet. Backing up 

 the Monongahela River, it carved the terraces already mentioned, 

 so that these represent the shores of this ancient lake in the 

 mountains of Pennsylvania. Its northern boundary was formed 

 partly by the ice wall itself and partly by the irregular outline of 

 the high land it could not overflow. A few isolated patches pro- 

 jected as islands above its surface. On the south, long fiords ex- 

 isted in place of the former tributaries, and from the lower end of 

 one of these was the probable outlet for the water. This, how- 

 ever, is still a mooted question, and though it is probable that 

 much found its way through a low pass in the water-shed be- 

 tween the valleys of the Licking and the Kentucky Rivers, it is 

 also likely that a part followed the foot of the ice and reached the 

 Ohio Valley again some thirty or forty miles below the present 

 site of Cincinnati. 



How long Lake Ohio was in existence it is, of course, impossi- 

 ble to say. Various facts, however, indicate a life of many hun- 

 dreds, perhaps thousands of years. So long as the dam existed, Lake 

 Ohio held its own ; but, when the ice began its retreat, the fate of 

 the lake was sealed. As year after year the foundations of the 

 dam were weakened, the pressure of the water was with greater 

 and greater difficulty withstood. The heat of summer sapped its 

 strength, but this was again renewed by the winter's cold ; but, 

 when the cold of winter was insufficient to supply the waste of 

 summer, the end was really at hand. As Prof. Claypole says : 

 " 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 when 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 and 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." 



This conflict of ice and water must have been frequently re- 

 peated, for the cold of winter would have repaired the damage 

 of the summer ; so that year after year, for how long one can 

 not tell, the conflict was renewed. Says Prof. Claypole : " This 



* Lake Age in Ohio, p. 16. 

 tol. xxxtiii. 52 



