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because it agreed with the evidence of their senses. At 

 this stage of the inquiry some one might propose that the 

 question of a flood origin for the channels could he settled 

 at once by an actual examination of the mighty streams 

 of the Mississippi and the Amazon. The argument would 

 be much as follows : — " The waters of the ordinary Amazon 

 are much greater than the mightiest floods ever experienced 

 along the Thames, therefore, if floods have done the work 

 of forming the channels, then an examination of the mighty 

 Amazon or Mississippi should settle the question." The 

 explorers would then examine the normal flow of these 

 giant streams ; they would see the water winding lazily 

 along the broad reaches and lying almost stagnant in places, 

 and even along the more swiftly moving portions upstream 

 they would see that the pebbles and boulders were not 

 moved by the streams. Upon their return they would 

 report that the flooded Thames could only move similarly 

 to the low-level Thames, because the mighty Amazon 

 moved in a similar way. Then the observers would become 

 divided into two camps — first, those whose keen insight 

 had shown them the presence of peculiar profiles apparently 

 intimately related to the flood limits of the streams, but 

 who nevertheless could not explain the mechanical diffi- 

 culties, and second those who simply denied the hypothesis 

 of channel formation by streams. And this would be an 

 expectable consequence. Nevertheless their methods 

 would be unscientific, because in the first place they would 

 have failed to perceive the complex relation of the increase 

 of stream velocity to its increase of corrasion, and in the 

 second place they would have confused the normal Missis- 

 sippi (or Amazon) with the same stream in flood, simply 

 because the normal Mississippi (or Amazon) was of much 

 greater volume than the Thames in flood. The latter error 

 would be serious because it failed to convey the truth that 

 the Thames in flood made its own channel; could the 



