1 INTRODUCTION. 



or table-land, features of this country ? I quote Dr. Ts^'ewleny 



in his own words : 



*' Like the great canons of the Colorado, the broad valleys 



tlie 



'' Aside from the slight local disturbance of the sedimeutair 

 rocks, about the San Francisco mountain — from the spurs 

 the Eocky Mountains, near Fort Defiance on the cast, to tno^e^ 

 of the Corbas and Aztec mountains on the west — the strata 

 the table-lands are as entirely unbroken as when deposits ■ 

 Haying this fact constantly in mind, and examining ^vith a 

 possible care the structure of the great canons wmcii ^ 

 entered, I everywhere found evidence of the exchisive actio 



h 



hounded by high and perpendicular wallsj belong to a vast 

 system of erosion^ and are wholly due to the action of water. * 

 Probably nowhere in the world has the action of this agent | 

 produced results so surprising, both as regards their magnitude 

 and their peculiar character. It is not at all strange that a cause 

 which has given, to what was once an immense plain, under- 

 laid by thousands of feet of sedimentary rocks, confonnaule 

 tlu-oughout, a topographical character more complicated than 

 that of any mountain chain ; which has made much of it 

 absolutely impassable to man/ or any animal but the winged 

 orders of creation, should be regarded as something out of tlie 

 common course of nature. Ilence the first and most plausiul^ 

 explanation of the striking surface features of this region is 

 to refer them to that embodiment of resistless power 

 sword which cuts so many geological knots — -volcanic force. 



^^The great canon of the Colorado would be considered a 

 vast fissure or rent in the earth's crust, and the abrupt 

 termination of the steppes of the table-lands as marking hi^^^ 

 of displacement. This theory, though so plausible, ana so | 

 entirely adequate to explain all the striking phenonienaj toct^' 

 a single requisite to acceptance, and that is truth. 



s 



