EVIDENCES OF THE GEEAT EROSION. 
75 
to meet the Colorado flowing south. We must replace beneath it very 
nearly the same amount of Mesozoic beds as we put beneath the Colorado, 
otherwise we are left without resource. 
Here at the junction the main river turns westward and enters the 
ascending monocline of the Kaibab. The problem has the same aspect as 
at the Echo Cliffs, except that the displacements are increased and the 
consequent amounts of depression required to affect the restoration. The 
argument also is the same. At the axis of the Kaibab the displacements 
reach their maximum. West of this axis the depression required for the 
restoration diminishes as it passes successively each great fault. All along 
the way we may check the argument from the river by the arguments from 
the tributaries. The whole forms a system, and in the treatment and con- 
clusions here adopted everything is self-consistent, and no difficulties arise 
except those which are always inherent in an attempt to bring before the 
mind a picture of concrete facts whose relations are to be discussed. But 
if these can be grasped in their entirety the conclusions drawn from them 
will, I am confident, be deemed unassailable. 
I have thus endeavored to group together diffei’ent categories of facts, 
in order to bring to the fullest possible tests the inference of the great 
denudation of the Grand Canon district. Any deduction if time at all 
must be true in all its consequences. In the evolution of a region all the 
great events are intimately associated, and their consequences reach out 
almost indefinitely. The evolution of the Grand Canon district involves 
many complex operations, and the dominant fact is the great erosion of its 
platform. Every other fact is intimately interwoven with it. In truth it 
is the major premise of the whole discussion, and we cannot therefore be 
too careful in scrutinizing the ground upon which it is based. Thus tested, 
the deduction presents the best possible evidence of verity, which is self-con- 
sistency, and coherence with all the facts to which it may be brought into 
relation. In the course of the argument some data have been, anticipated, 
the evidence of which will appear in subsequent chapters — for example, the 
Tertiary age of the displacements. This and many other facts will appear 
in their proper places. 
It seems proper here to introduce a general consideration which will 
