JOHNSON: GRAND CANON DISTRICT. 143 
the Colorado. Erosion, guided by this joint structure gives a sharp, 
pointed form to spurs and pinnacles in the face of the cliffs. At other 
places we observed evidence of local faulting cutting obliquely across 
the cliff-line, but these did not seem to be related to the oversteepened 
sloi)es. It seemed to us that the influence of the crossbedding and 
jointing on erosion might account for the peculiar form of the cliffs. 
East Kaibab ]Monocline. 
The East Kaibab Monocline (fig. A, E. K.) is a great fold which 
carries the Carboniferous limestone of the ^Marble Platform upward 
toward the west to an elevation from 2,500 to 4,000 feet higher, where 
it forms the surface of the Kaibab Plateau, or "Buckskin ^Mountains," 
as the plateau is locally called. The monocline is in part double, and 
as one views it from the east he can distinctly see the up-arched lime- 
stone rising from 1,500 to 2,000 feet above the desert level of the 
Marble Platform, then continuing westward across a great bench or 
terrace from two to four miles wide, from the western side of which it 
rises in another arch to the summit of the plateau. To the north and 
to the south he can see the lower fold swing gradually westward until 
it merges with the upper, and the ascent from the INIarble Platform to 
the summit of the Kaibab is made in a single great arch. As a rule the 
monocline is free from faulting, but several miles south of House Rock 
Ranch (fig. A, H. R. R.) we observed several minor faults, apparently 
trending with the strike of the fold. 
The Kaibab Plateau is higher toward the south than farther north, 
and it is near the highest part of the plateau that the Colorado River 
has cut its way through the fold which rises across its path. It is 
evident that the river could not have accjuired such a course under the 
present surface conditions of the region, and it was partly to account 
for the river's course at this particular point that Button proposed the 
theory of antecedence. He believed that the river acquired its present 
course, and removed the ]\Iesozoic beds from much of the district 
before the fold developed. At a comparatively recent period the great 
monocline was gradually raised above the river's path, but so slowly 
that the river was able to cut down as rapidly as the rocks were uplifted, 
and so to maintain its course. At this same general period the Echo 
Cliffs ^Monocline, and the great faults farther west, were believed to 
have been developed. 
