830 THK GEOGRAPHICAL SIGNIFICANCE OF FLOODS, 



The one marked difference is the wonderful disparity in size 

 existing between water- and ice-formed contours. 



Now in roadside gutters and other small stream-examples 

 these peculiar contours are known, by direct observation, to 

 originate in flood-water thrusts : in the cases of the great river- 

 valley, the shoreline and the glacial canon, we infer a similarity 

 of origin for their similarly situated contours. And the reason- 

 ing is equally sound when applied to the case of the larger forms, 

 for in addition to the similarity of contour-shape and location 

 for both large and small examples; in addition also to the fact 

 that floods occur in the cases of seawaves and ice, and that the 

 peculiar shoreline and fiord contours under consideration do not 

 rise above the highest floodmarks, the dimensions of the forms, 

 in all instances, possess the most intimate relations with those of 

 the heaviest floods. Thus the basins of roadside gutters rarely 

 exceed a few feet in depth, while those of fiords and lakes in 

 regions of former intense glaciation, besides being similarly 

 situated to those of roadside gutters, may be thousands of feet 

 in depth and many miles in length. Apparently, then the deduc- 

 tion is legitimate that all the forms have a similarity of origin, 

 namely that of flood-stream action. 



The apprehension of this truth is of the utmost significance. 

 For since direct observations have shown that the striking 

 irregularities of ordinary stream-developed channel-contours 

 result from severe flood-action, and that lesser flood-action is 

 confined, in the main, to working over the storm debris with 

 aggradation of the larger channel-base irregularities, then a 

 similar condition of afi'airs must also obtain along Amazonian or 

 Mississippian channels, shorelines, and regions of former intense 

 glaciation. 



1. Shorelines. — Since, for wa\ es of translation and for currents, 

 power of transportation increases so amazingly with but moderate 

 increase in velocity, the heavier material moved by the " great 

 storm of the century" cannot be handled by succeeding gales of 

 less velocity. Only with the visit of an equally strong wind can 

 this heavy material be forced into activity, so that cliffs and rock- 



