814 THE GEOGRAPHICAL SIGNIFICANCE OF FLOODS, 



ordinary stream-channel forms. Consider, in this connection, 

 the subaqueous strip varying, according to the depth of the 

 water, from a mere ribbon to a band several miles in width, 

 and "curving sympathetically" with the shoreline. The main 

 activities are the waves, tides, and resultant currents. On one 

 side the heavy wind limits the seaward extension, while on the 

 other the shoreline acts as a wall to the (shore) stream. The 

 action of this current is to form a bridge alongshore over which 

 to transport material. The heaviest floods (storms) can utilise 

 low flat grades as bridges which succeeding smaller floods (or 

 gales) find too flat, and which straightway they proceed to aggrade. 

 Again, the heaviest "gale of the generation or centur}'^" can 

 work havoc on the cliffs by transport of heavy boulders. With 

 the recession of the great gale these are dropped, and succeeding 

 heavy but weaker gales can merely override, but not move, these 

 boulders. Thus the deadty weapon to the cliffs in the hand of 

 the great gale has become a veritable buttress to the cliffs during 

 the period of lesser winds 



Significance. 



It may seem a simple matter to accept Gilbert's principle, 

 namely, that the great flood accomplishes the main portion of 

 stream-work, nevertheless it is almost safe to state that its 

 proper understanding would lead to results almost, if not quite, as 

 remarkable as those which have followed on the proper apprehen- 

 sion of other fundamental geological conceptions. For the light 

 thrown thus on glacial methods is almost incredible at first glance, 

 while the value of ice-action studies in any discussion as to 

 methods of peneplanation is, in turn, strikingly apparent. And 

 for this purpose, when discussing stream-channel grades, it would 

 appear advisable to consider the channel-contour rather than the 

 surface of the waterbod}^ contained therein. 



Prof. Davis has by letter pointed out to the writer that the 

 term " grade " as applied to streams should have reference more 

 correctly to their surface-levels; for the purposes of this note, 

 however, interest centres around the channel-contours them- 



