1898] Grand Canyon of the Colorado 



its weird magnificence, and its sublime supremacy the 

 world knows. But it impressed me also through its 

 infinite laziness. For while the rest of the earth's Primeval 

 crust has been repeatedly folded and racked by peace 

 gigantic forces, this isolated district rested undis- 

 turbed in the sun beneath a warm and shallow sea 

 for a million years and more. Thus during geologic 

 ages its sand and clay were slowly piled up, layer 

 on layer, until at last the emergence of the Sierras 

 dragged it too above the Gulf. Forces of erosion 

 then began to work, and the river swept away - 

 as sleepily most of what the sea had before laid 

 down, leaving only scattered flat-topped buttes or 

 mesas, to testify to former levels of the ancient plain. 



Two miles of vertical depth above the present Erosion 

 canyon rim were thus washed away. 1 But at that * co miles 

 dim point in time and space, general erosion was 

 sharply checked, the flinty limestones of the sub- 

 carboniferous interposing their firm resistance to 

 the gnawing, sprawling stream, and forming the 

 upper stratum of the present Coconino plateau. 

 The river now had to get down to business in order 

 to break through the flinty crusts; this once ac- 

 complished at the area of deepest current, it began 

 to narrow its bounds. Growing then progressively 

 deeper and swifter, it made relatively quick work of 

 a mile of secondary rocks, and dropping persistently 

 from stratum to stratum is at present engaged in A tough 

 tearing away the earth's granite core at the bottom ' ob 



- a tough job in which it has already made some 

 progress. 



1 According to Clarence E. Dutton, "Tertiary History of the Grand Can- 

 yon," 1882, the area of maximum denudation is from 13,000 to 15,000 square 

 miles, and the average thickness of the strata removed about 10,000 feet. 



C 623 n 



