192 
THE GEAND CAISTON DISTEICT, 
eastern side of the district, and more than 6,000 feet upon the western side. 
And if, as is most probable, there has been a general upward movement 
during Pliocene time affecting all of that portion of the continent the 
change of altitude has been correspondingly greater. The amount of this 
more general upheaval can be deduced for the whole of Tertiary and Qua- 
ternary time, but how much was accomplished before the advent of the 
Pliocene, and how much since, it is impossible to say. 
It is necessary to remark here, that the reference of this divisional 
epoch to the commencement of Pliocene time ought to be considered with 
some qualifications. It should be borne in mind that a strict correlation of 
geological jieriods is here impossible. We have within the district no Plio- 
cene beds and no Pliocene fossils. Nevertheless, events point to that epoch 
as the approximate one, when the present order of things took their forms 
and relations. The error cannot be great. 
With the Pliocene, as thus understood, the Kaibab began to have a 
distinct existence. Probably at this time the great East Kaibab monocline 
began to develop itself It is older than the Hurricane fault, and older than 
either of the displacements which occur between it and the Grand Wash. 
The reasons for assigning an early Pliocene date for the East Kaibab 
monocline may be found in a comparison of the drainage channels. The 
problem is a charming one, carrying the requisite data for a satisfactory 
conclusion, but it is also complex and difficult to present clearly to a reader 
who has not thoroughly traversed the ground and made himself familiar 
with the surface topography of the plateau. Nevertheless, the attempt 
must be made, and if it fails to convey a clear idea of the facts presented, 
and tlierefore fails to convey a clear conception of the interpretation of 
them, it must be attributed to the difficulty which always attends the effort 
to draw a mental picture of a distant region from a merely graphic descrip- 
tion. 
Along the greater part of the length of the Kaibab, and keeping very 
near to the median or axial line of the summit of the plateau, there is a long 
and comparatively narrow valley. The depth of this valley is from 200 to 
400 feet, and its width is from one to two miles. It is seen in the northern 
part of the summit, where it is rather shallower than in the middle portion. 
