WHITE MESA, MOQUI COUNTRY. 87 
structure and age to be matters of conjecture until it shall be reached by some more fortunate 
explorers. 
Rising, as it does, so distinctly from the mesa of Lower Cretaceous rocks, but two formations 
are left in the series of which it could be composed, Upper Cretaceous and Tertiary. The 
lithological characters of both these groups of rocks are frequently such as to exhibit snow- 
white sections similar to that described. The upper members of the Cretaceous group, the 
‘‘ White chalk,’’ or Crate blanche of European geologists, compose the white cliffs.on the southern 
coast of England, which afford an exact counterpart in appearance to that under consideration. 
It is also true that the materials composing the strata of the different Tertiary basins in the 
country bordering the Rocky mountains on the east are frequently nearly as white as chalk. 
In the order of succession of the different formations the White chalk or Upper Cretaceous, in 
the ascending series, immediately follows the group forming the base upon which this white mesa 
rests; yet this proves nothing, for it happens that the fresh water Tertiaries are not unfrequently 
found occupying basins in the Lower Cretaceous strata, and such is the case with those passed 
over on our route. From these facts it will be seen that nothing but an actual examination will 
clear this subject of all doubt. 
There are some reasons, however, why we should suspect this white mesa to be Upper 
Cretaceous rather than Tertiary, and these are, first, that all the Tertiary rocks of the Rocky 
mountain country, as far as they have yet been examined, are of fresh water or estuary origin, 
have been usually deposited in basins of less extent and depth than would be indicated by this 
great plateau, which has evidently been greatly reduced in dimensions by the erosion it has 
suffered; second, the materials composing the Tertiary strata found on the great central plateau 
are generally soft, and yield readily to the action of the elements, presenting rounded and 
unbroken outlines or pinnacles and deeply channelled surfaces, the results of erosion. On the 
contrary, the Upper Cretaceous strata, as they appear in several points on our route, holding 
precisely the relative position of the white mesa to the Lower Cretaceous sandstones, consist of 
a series of shales and limestones, which, though dark internally, weather to an almost chalky 
whiteness, and yet are as resistant to atmospheric erosion as any other sedimentary rocks. 
Judging from the view we had of it, we regarded the white mesa as continuous with the 
high mesa bordering the Colorado, which has about the same altitude. If so, the strata com- 
posing it must occupy a very large area north and west of our Camp 96, one almost too large 
to accord with the supposition that it is of Tertiary age. 
NAVAJO COUNTRY. 
The route from the Moqui villages to Fort Defiance, though leading through a more fertile 
region than that last traversed, one abounding in picturesque and beautiful scenery, and every- 
where exhibiting magnificent exposures of its geological structure, added little that was 
absolutely new to our former experience. 
Its general structure may be given in a few words. The Lower Cretaceous mesa occupies the 
greater part of its surface, but near Fort Defiance we approach the eastern border of the great 
basin of the Little Colorado, and the strata all begin to rise rapidly on to the first of the lines 
of upheaval, which complicate the structure of so large an area eastward of this point. A few 
miles west of Fort Defiance the culminating point in this ascent is reached, and thence all the 
formations pitch rapidly toward the east. In this vicinity the profound erosion they have 
suffered has cut through and locally removed the entire mass of Lower Cretaceous rocks, as 
well as the variegated marls below, and has reached and laid bare the lower and harder portion 
of the red sandstones. These are here considerably affected by the proximity of the igneous 
axis of the line of elevation. They have been much hardened and brought to resemble, in 
color and consistence, the light red sandstones of the carboniferous series west of the Colorado. 
Tertiary rocks.--Fer twenty miles after leaving Walpi, the most eastern of the Moqui 
