AQUEOUS AGENCIES. 25 



level strata, which have been cut into by the Colorado and 

 its tributaries in such wise that the whole river system of 

 the country runs far below the general level. The Grand 

 Canon of the Colorado is 300 miles long and 3,000 to 

 6,000 feet deep, and all its tributaries come in by side 

 canons of almost equal depth (Fig. 7). 



FIG. 7. View of Colorado Canon and its tributaries, with erosion-columns and 

 mesas in the distance. 



Besides this prodigious stream cutting, the general rain- 

 erosion has been here upon an equally grand scale. Many 

 thousands of feet have been carried away over the whole 

 area of about 100,000 square miles or more. This is shown 

 by the isolated peaks and tables of level strata scattered 

 about, and still better by the succession of cliffs shown in 



