nuTTox.) 



PERSISTENCE OF RIVERS. fil 



take account of "purposes" or "design," but seeks its explanations in 

 11 natural " causes alone. It asks by what natural processes were those 

 gorges made? 



The answer it finds is, that the rivers themselves scoured them out, 

 and that secular decay has widened them somewhat. A reader not 

 versed in geology might be led to ask a further question. How can a 

 river attack a mountain wall, or even a gentle declivity, and quarry 

 though it a pathway giving a continuous descent for the flow of its 

 waters ? The reply is that no river ever does that. To understand how 

 it all came about we must go back to the beginning. The rivers were 

 born with the country itself. The land emerged from the sea; and 

 when it emerged the rains or melting snow sought whatever channels 

 were determined by the slight inequalities of the newly-risen surface 

 and flowed seawards. These lofty ridges, gashed with noble ravines, 

 had then no existence. The rivers are older than the mountains. As 

 time ran on the mountains grew upward, athwart the courses of the 

 streams. But a flowing river has a power to fight for and maintain its 

 right of way, which becomes apparent only when we have carefully 

 studied and analyzed it. This power is inherent in the descent of its 

 waters— is literal water-power. The weapons or tools are thesand, gravel, 

 and silt which the waters carry, and which act after the manner of a 

 sand-blast, except that in the sand-blast the grit is impelled by air or 

 steam, while in the river it is impelled by water. This power, inherent 

 in the fall, increases rapidly as the fall increases. When the declivity 

 is feeble the power to grind down the channel— to "corrade," as Pow- 

 ell terms it— is correspondingly feeble, or even annihilated. When a 

 barrier like a ridge rises across the track of a stream the declivity is 

 increased at that point. Increased velocity and corrasivo power is at 

 once developed in the stream, and it cuts down the barrier. Perhaps 

 a lake may be formed above the barrier, but its outlet will be cut down 

 and the lake drained. 



In a low country the slopes are, with rare exceptions, feeble, and this 

 corrasive power by which the stream maintains its locus is in such conn 

 tries correspondingly feeble. Here we may expect to find many cases 

 where streams have been deflected largely from their courses; but in a 

 high country the reverse is the case. In a region newly risen from the 

 waters the positions of the streams may be very inconstant; but as the 

 elevation increases they gradually fasten their grip upon the land and 

 hold it. 



It would be difficult to point out an instance where a great river has 

 ever existed under conditions more favorable to stability of position 

 than those of the Colorado and its tributaries. Since the epoch when 

 it began to flow it has been situated in a rising area. Its springs and 

 rills have been among high mountains, and its slope since the earliest 

 period of its history has always been great. The relations of its larger ^ 

 tributaries have, in these respects, been the same; and indeed the river 



