MARL SERIES—SALIFEROUS SANDSTONES. 91 
Defiance nearly the whole of the upper part of the Marl series is represented by a great stratum 
of pink, soft, calcareous sandstone. 
Below these indurated marls is exposed some four hundred feet of buff, orange, purple, lilac, 
olive, green, and blue marls, with strata of gypsum and magnesian limestone. This series 
closely resembles that in the mesa wall bounding the valley of the Little Colorado, between our 
Camps 89 and 90, and is undoubtedly its exact equivalent. The beds of dolomite are less 
numerous here than there, but are in the same manner most characteristic of the lower part of 
the section. Silicified wood also occurs abundantly along the same horizon, and is profusely 
scattered over denuded surfaces. The Marl series is here susceptible of division into two groups, 
but, as before remarked, their lithological differences are rather in degree than kind, and 
are not constant. 
Beneath the variegated marls nearly a hundred feet of red and green foliated sandstones and 
shales are exposed, which form the upper member of the red sandstone group. These strata here 
exhibit nearly the same characters as on the banks of the Little Colorado, where I first observed 
them. At Fort Defiance, Bear Spring, Agua Azul, and many other points on our route, the 
exposures form the same geological horizon as at Navajo valley; and while the correspondence 
between all its different portions is such as to render the work of identification both easy and 
sure, the features presented by the last-mentioned group are peculiarly constant wherever it is 
visible. 
From Camp 101 to Fort Defiance we were constantly travelling on the red saliferous sand- 
stones. The general surface gradually rises, but less rapidly than the geological substrata. 
The upper part of the valley traversed by the Pueblo Colorado creek is excavated in the 
upper member of the sandstone group. Going east from this point we saw no more of the 
variegated marls till we had crossed the valley in which Fort Defiance is located. Gradually 
descending in the geological scale, we passed through the upper members of the red sandstone 
group, and, as we approached the crown of the arch formed by the strata, we found the surface 
rock to be a reddish, compact, cross-stratified sandstone, also belonging to the Saliferous series, 
but much harder than any portion of that group exposed on the Little Colorado, and doubtless 
somewhat changed by the proximity of the igneous rocks below. The limit of the rise in the 
strata was reached near Camp 102, at an elevation of nearly 7,000 feet above the sea level. 
From this point they pitch to the east at an angle of 10° to 15°, which brings in review within 
a few miles all the strata above the Carboniferous limestone we had up to that time observed. 
