812 THE GEOGRAPHICAL SIGNIFICANCE OF FLOODS, 



able only to partly override these boulder-heaps, without moving 

 them. 



(d) Schofield's Creek . — The marvellous work effected 

 along this small watercourse during a severe thunderstorm has 

 been described elsewhere by the writer (1,6, p.504). 



These examples could be multiplied almost indefinitely by the 

 reader. In all, the wonderful similarity of forms produced to 

 those existing in glacial caiions is most pronounced. 



The Action of Great Floods generally. 



The chief phases of flood-action have been described elsewhere 

 by the writer(l,a,pp.34-41). Several additional facts of observation 

 may be here noted, since to those unaccustomed to the phenomena 

 of great floods, much difficulty attends the conception of ratio of 

 work to increase of velocity as observed by streams. One easily 

 repeats the formula "Power of transportation varies as the sixth 

 power of the velocity," but the significance of this law can only 

 be properly appreciated by the individual through personal 

 observation. In this connection Dr. W. G. AVoolnough, of 

 Sydney University, described to the writer a most severe rain- 

 storm in Fiji during which boulders w^ere swept along a creek 

 bed with such force as to leap high out of the water. In such 

 cases, also, whole masses of water are sheared and driven high 

 above the flood-level. Again, the placid water above the Niagara 

 or Zambesi Falls is the same water which, a little later, rushes 

 in its mad career below the falls. The former may be considered 

 the normal stream, the latter a furious flood, and this simply by 

 reason of greatly increased velocity. In the ordinary stream it 

 is the volume of the flood which produces the increased speed, 

 whereas at Niagara and the Zambesi it is the steepened grade 

 which accelerates the velocity. 



Again, during floods torrent-narrows are also scoured, and the 

 debris sw^ept thence into valley-divergences. Shearing and 

 eddying of water-masses, as also the scouring of stream-narrows, 

 find their analogies in glacial action. As such shearing and 

 eddying are at a maximum during the period of greatest efliciency 



