CHANNEL KEPT OPEN. 289 



" Then I don't see," said John, when Lawrence had ar- 

 rived at this point in his explanation, "how any channel is 

 left for the passage of the water." 



" There is something very curious and remarkable about 

 that," replied Lawrence. " You see that the tendency to 

 deposit is greatest where the water is most nearly in a 

 state of repose, and least along the line of swiftest motion. 

 Where this line of swiftest motion would be would depend 

 much upon the conformation of the shores, but it would in 

 general tend to pass somewhere through the middle of the 

 lake. Of course, as the progress of the deposition goes on 

 nearer the shores and in all the stiller portions of the 

 water, the space which the whole volume of the water will 

 have for its flow will be more and more contracted, and 

 the current along it will become swifter and swifter, and 

 thus, as the channel becomes contracted and defined, there 

 will be an increasing force in the flow of the water to keep 

 it from being closed entirely. 



" At last," continued Lawrence, " things would come in 

 such a case into a state of equilibrium that is, the tenden- 

 cy of the sediment to subside through the water by its 

 weight, and to be borne onward by the swiftness of the 

 current, would balance each other, and the channel of the 

 river would then become in some measure permanent as to 

 its size that is, as to what is called the area of its section, 

 only now, instead of forming a lake, it would flow mean- 

 deringly through a level plain, over which every freshet 

 .vould deposit a fresh layer of fertilizing soil, until it was 

 raised far above the level of the ordinary flow of the 

 river." 



Lawrence went on farther to explain that this process of 



filling up all the natural depressions in the land through 



which rivers flow, and which originally formed the beds 



of lakes, had been going on for thousands of years, and 



N 



