EVIDENCES OF THE GEEAT EEOSION. 
69 
the full extension of the Eocene as having a very high degree of proba- 
bility, but falling short of certainty. , 
II. The foregoing argument is strongly sustained and supplemented 
by the displacements. If it be true that the Grand Canon district received 
between the close of the Carboniferous and the close of the local Eocene 
10,000 feet of deposits averaged over its entire surface, it follows that at 
the latter epoch the summit of the Carboniferous lay at least 10,000 feet 
below sea-level and was much more nearly horizontal than it is at present. 
And if such was its position and configuration, the great faults and dis- 
placements which traverse it must be of Tertiary age, and there must have 
been an enormous amount of uplifting, ranging from 12,000 to 18,000 feet, 
in various portions of the district. These are some of the consequences of 
the great denudation. If by independent evidence they shall appear to be 
true — to have really happened — the original inference will be much 
strengthened ; but if they fail, the original inference will be greatly dam- 
aged, if not exjfioded. For it may be remarked that every true deduction 
runs off into important consequences, and (in geological reasoning, at all 
events) derives its strongest support from its congruity with a vast system 
of facts. We shall soon find by independent evidence that the inference 
of the great denudation agrees rigorously with the above mentioned con- 
sequences. 
It is first necessary to find the configuration and position of the sea- 
bottom on which the Mesozoic sediments were deposited at each and every 
epoch of that age. This problem looks very large and formidable, but an 
approximate solution is right at hand. During the entire age the surface of 
deposition was always very near the sea-level. The proof of this is 
abundant and clear. Throughout the entire Plateau Province the strata 
are all shallow water deposits. Fossil forests, ripple-marked shales, fre- 
quent unconformities by erosion without discrepancy of dip, cross-bedded 
sandstones, occasional retirements of the waters, all mark very shallow 
water in the Permian, Trias, and Jura; while coal, carbonaceous shales, 
abundant remains of land plants indicate the same for the Cretaceous. 
And, finally, the absence of all traces of appreciable displacement except 
along the coasts combines to prove that the Mesozoic beds were deposited 
