454 On the Natural Causes which operate 



Jevel than that of the country through which the valleys 

 have been cut ; and were they all filled up, there would still 

 be a sufficient fall in the country for the streams to flow the 

 same wav : and as water, when left to itself, by its fluidity 

 and gravitation constantly seeks the lowest place, we may 

 always be assured that the conrse which the stream has 

 taken is the lowest descent of the country in that direction. 

 With these circumstances in view, let us select any indi- 

 vidual stream, and suppose all its valleys to be filled up by 

 replacing the very materials of the strata formerly carried off, 

 thereby restoring the country to its pristine state before the 

 valleys were excavated; and then, by attending to the course 

 of the stream from its source, we shall acquire a clear and 

 porrect conception of the manner in which the valleys were 

 oripmally formed. The old channel being in the lowest fall 

 of ti.e country, the stream will still flow in the same direc- 

 tion, but it wijl be on and over the newly restored mate- 

 rials, which we have supposed to be replaced ; and it will 

 first pass over that portion which has filled up the first val- 

 ley, until it arrives at what was the lower end, which being 

 now a declivity, it will be precipitated into the hollow 

 below. In that hollow or flat the water will spread itself 

 out into a lake, wider or narrower in its dimensions ac* 

 cording to the form and bearing of the ground; and the lake 

 continuing to fill, the water will rise over the level of the 

 materials which filled up the second valley, and running on 

 to where was the lower end, it will again descend the 

 declivity into the hollow below, and will accumulate and 

 spread itself until it again rises over the third valley, and 

 descend again at the lower end; and in this manner it will 

 continue its course, falling down every declivity which it 

 reaches, and accumulating into a lake wherever the nature 

 of the ground obstructs it, until the water reaches over the 

 level oi the obstructing rise ; and the stream in this stage of 

 its course will consist of a chain or streams, waterfalls and 

 lakes, from its source to the channel of the next stream, or 



ot these., its if, the grandreceptacle of the whole. Let us 



nov\ attend to what will take place at the several falls. There, 

 in -every instance where the stratum is not an indurated rock, 



the 



