EVIDENCES OF THE GREAT EROSION. 
65 
period of erosion should be proportional to the amount of relief in the pro- 
files of the country. But in the Plateau Country, and especially in the 
Grand Canon district, these reliefs are very great. It is a region of giant 
cliffs and profound canons, and, as will ultimately appear, it has been so 
during a very long stretch of geological time. The thickness of the strata 
removed from it is only proportional to the values of those conditions which 
favor rapid erosion. In the foregoing discussion it may appear that the 
area of denudation in the Grand Canon district, though large, and the 
thickness of the strata denuded, though very great, are not so excessive as 
to impose such a heavy burden upon the credulity as the first announce- 
ment of the figures portended. 
We may now proceed to examine the evidence upon which the infer- 
ence of so great a denudation is founded. In this discussion three classes 
of facts will be utilized: 1st, the stratification; 2d, the displacements; 3d, 
the drainage. Each, by itself alone considered, might be deemed insuffi- 
cient; but when they are all placed in their natural relations to each other, 
they form a compact and self-consistent w'hole which is quite convincing. 
I. In drawing inferences from the stratification, the geologist is obvi- 
ously bound to presume that the beds cut off in the terraces, and in the long 
line of the Echo Cliffs, extended originally without a break, until they 
reached some locality where the conditions of deposition failed. There are 
two, and only two, cases to be considered. The first case is that in which 
the extension is towards the shore-line of the sea in which the strata were 
deposited. At the shore-line of course the strata ended. The second case 
involves their extension away from shore-lines, in which event they thin 
out seaward, and either vanish entirely or dwindle to a merely nominal 
volume. It becomes essential therefore to ascertain something about the 
situations of the shore-lines of the sea in which the Mesozoic strata were 
deposited. 
In the preceding chapter I have frequently alluded to the littoral belt 
of strata situated in southwestern Utah and Nevada. These strata are the 
continuations of those which form the terraces and the entire sedimentaiy 
masses of the High Plateaus. In Mesozoic time the Great Basin area of 
Nevada and western Utah was a large mainland, and the littoral belt 
6 G 0 
