BY E. C. ANDREWS. 813 



of a river-flood, we may extend the same reasoning to the ice- 

 flood; and thus conclude that great ice-shearing and canon- 

 scouring should mark the period of greatest glacial intensity. 



On the other hand, the great flood is after all but a study in 

 limitations, for at its very height it aggrades as well as corrades. 

 It cuts vigorously on one side and forms deposits opposite the 

 cutting curve. So does the glacier. But in the latter case the 

 flood was not confined to the cailon base. At times the whole 

 lower cailon might form its cutting side, and the aggrading por- 

 tion might have to be sought high up on the canon sides or in a 

 marked valley-divergence. 



Recession of high-tvater mark. — With the least recession of the 

 flood comes the dropping out of the heaviest boulders, that is, 

 those which for their moving taxed the utmost strength of the 

 giant. The subsiding water now no longer possesses the energy 

 — gravitative thrust — to use the reversed grades as bridges for 

 transportation of stream debris : forthwith it commences to build 

 out deltas into the depressions. 



Action of smaller floods. — The smaller flood works over the 

 material left by the great flood, and provides therein for itself a 

 channel similarly shaped to that of the maximum flood. This 

 follows immediately either from direct observation or from a 

 study of the mechanics of flowing water. It cuts basins and 

 other channel-contours now not in rock but in storm-debris, as 

 its strength is incompetent to deliver blows equally telling with 

 those of its predecessor. The largest flood-boulders are not 

 shifted, but merely overriden wholly or in part. 



It cannot, however, too frequently be stated that smaller floods 

 are quite capable of accomplishing peneplanation themselves, but 

 the great flood is of such common occurrence that the forces of 

 weathering have not time enough — during interflood periods — in 

 which to promote rock-decay whereby the smaller flood might 

 accomplish rock-basining. 



5. Shoreline forms. — The recent '' incisive " account of shore- 

 lines by Gulliver,(18) as also the classics of Gilbert(17,a,c) and 

 others enable us to perceive the similarity of shoreline and 



