button. I COBRASION OF THE COLORADO. 159 



distance, as the river runs, of about 1,050 miles, is about 5,150 feet, or 

 very nearly five feet to the mile. The fall through the Grand Canon is 

 on an average 7.5G feet to the mile. Taking the several divisions of the 

 Grand Canon, the declivity may thus be tabulated: 



Declivity of the Colorado in the Grand Canon. 



Fall in 

 Subdivisions. ,„ „ liW fiwt feet per 



mile. 



From Little Colorado to Kaibab division 0.0 60 6.25 



Kaibab division 700 12.07 



Kanab division 



Uinkaret division 



Sbeavwits division 



Distance 



Fall in 



in miles. 



foot. 



0.G 



60 



58 



700 



47.0 



240 



19.2 



100 



84 



540 



>. 01 

 5.21 

 6.43 



Totals i a** 1,040 7.56 



The Marble Canon, with a length of 05.2 miles, has a descent of 510 

 feet, or an average fall of 7.82 feet per mile. When compared with the 

 declivities in the middle and lower courses of other large rivers, that of 

 the Colorado in the canons is seen to be very excessive. It falls about 

 as many feet as the others fall in inches. The flow of other large rivers 

 which are usually considered swift is calm and easy in comparison with 

 the rush of the waters of the Colorado. 



There is another factor which would be fatal to corrasiou in other 

 rivers, but which in this one greatly augments its corrasive power. Not 

 only are few rivers so swift, but fewer still are so continuously turbid 

 and so heavily charged with sediment. Rarely is the river clear, even 

 in the droughts of midsummer. Immense quantities of sand and clay 

 are swept along at all parts of the year. Ordinary rivers, and even 

 most of the exceptional ones, would be gorged with such quantities of 

 sand, and instead of corrading would have their energies fully taxed in 

 carrying the load which the Colorado bears easily. This sand is the 

 tool which it employs for its work, and it uses it with great effect. 

 Though the river is heavily loaded, it is still underloaded, and has great 

 power to corrade.* 



To show how efficieut the corrasive action may become under ex- 

 tremely favorable circumstances, we may cite the case of some of the 

 great hydraulic mines in California. In these mines powerful streams 

 of water are discharged against the gravel banks, and the spent water 

 is gathered into a brook which finds its way over the " bed-rock" into a 

 tunnel, and finally escapes into some deep natural gorge below the level 

 of the workings. As the water flows away it carries with it all the 

 debris washed from the banks, whether coarse or fine. In the well- 

 known Bloomfield mine I saw a gash in the solid basaltic bed-rock 12 

 feet in depth, which I was assured had been cut by the escaping water 

 and gravel in a period of about sixteen months. The actual ruuni ng 



* The details of corrasion in the canon will be much more fully discussed in the 

 monograph on the Grand Canon District. 



