800 THE GEOGRAPHICAL SIGNIFICANCE OF FLOODS, 



the subject under discussion. Between the periods 1874 and 

 1883, the scientific epics of Dutton,(10) Gilbert,(17,a,&) and 

 Powell(33) were produced. So clear is Gilbert's statement con- 

 cerning flood-action that one marvels at the persistence of the 

 glacial controversy. 



For the benefit of all, Gilbert's(17,a,pp.S9-90) grand announce- 

 ment is here reproduced. 



" The explanation of these inequalities depends in part on a 

 principle of wide application, which is on the one hand so 

 important and on the other so frequently ignored that a para- 

 graph may properly be devoted to it, by way of digression. 

 There are numerous geologic processes in which quantitative 

 variations of a causative factor work immensely greater quanti- 

 tative variations of the eflfect. It is somewhat as though the 

 effect was proportioned to an algebraic power of the cause, but 

 the relation is never so simple .... and it gives to the 

 exceptional flood a power greatly in excess of the normal or 

 annual flood. Not only is it true that the work accomplished in 

 a few days is greater than all that is accomplished during the 

 remainder of the year, but it may even be true that the effect of 

 the maximum flood of the decade or generation or century sur- 

 passes the combined effects of all minor floods. It follows that 

 the dimensions of the channel are established by the great flood 

 and adjusted to its needs. 



" In littoral transportation the great storm bears the same 

 relation to the minor storm and to the fair-weather breeze. The 

 waves created by the great storm not only lift more detritus 

 from each unit of the littoral zone, but they act upon a broader 

 zone, and they are competent to move larger masses. The 

 currents which accompany them are correspondingly rapid, and 

 carry forward the augmented shore-drift at an accelerated rate. 

 It follows that the habit of the shore, including not only the 

 maximum height of the beach line and the height of its profile, 

 but the dimensions of the wave-cut terrace and of various other 

 wave-products presently to \>e described, is determined by and 

 adjusted to the great storm. 



