178 ON THE REVOLUTIONS 



ence of an agent, unless it can be shewn, that its action has a 

 tendency to produce the alleged result. If it has a tendency to 

 produce a different result, that difference would be augmented 

 in proportion to the duration of the action. Now, the diurnal 

 operations are everywhere found in the act of corroding and 

 altering the forms here alluded to * ; but they are nowhere seen 

 to produce them. This class of facts, on the other hand, all 

 conspire in giving probability to the hypothesis of a diluvian 

 wave, which affords an easy explanation of all the large features 

 of this country. 



An important principle of the theory of running streams 

 must here also be considered, namely, that the shape assumed 

 by such a stream flowing through sand or other loose matter, p 

 bears a distinct relation to the magnitude of the stream ; the 

 radius of curvature of its bendings being in proportion to that 

 magnitude. Thus, all the water collected from this neighbour- 

 hood, is capable of producing no more than a paltry brook, 

 as appears from the Water of Leith, which we see meander- 

 ing between two of the ridges just mentioned. This meander- 

 ing course, suits the diminutive size of the brook ; whereas 

 these ridges being straight, or, mathematically speaking, having 

 a curvature whose radius is of infinite length, we are led, by a 

 very obvious analogy, and in concurrence with what has been 

 observsd in other parts of the globe, to believe that a cause 

 very different from any now in activity, and far more power- 

 ful, has exerted its influence upon this spot ; that a stream 



has 



* As is very apparent upon some of the ridges last mentioned, as we see on 

 the road to Dalkeith, just as we leave Edinburgh. Some ravines there present 

 themselves in front, and on the right hand, descending the northern side of the 

 ridge, and denoting a genuine diurnal action, in obedience to the mere action of 

 gravity. 



