90 GEOLOGY 
The upper member of the Marl series at Camp 100 is a soft, fine-grained, nearly pure white 
calcareous sandstone, very similar to that already noticed in the description of the section at 
Camp 92. 
NAV&JO VALLEY AND CANON BONITO. 
Ascending the mesa east of Camp 100, we travelled upon its surface, with nothing new in our 
experience, for twelve miles, when we reached the brink of the wall limiting a larger, richer, 
and more beautiful valley than that last described. Thisis one of the favorite grazing grounds 
of the Navajos, and the green plain below us, as far toward the north as the eye could reach, 
was dotted with their herds and flocks. The walls bounding Navajo valley are generally abrupt, 
frequently perpendicular, and exhibit the brilliant and varied colors characteristic of the Marl 
series composing them. Toward the south they approach each other to form what has been 
most appropriately named Cafion Bonito. 
The strata have here a strong westerly dip, and the Cretaceous rocks have so nearly run out 
that they only appear capping the western wall of the valley where it is highest. In the first 
arm of this great valley which we entered the upper and middle portions of the Marl series are 
fully exposed, while its eastern branch, through which flows a permanent stream, is cut down 
to the middle of the underlying red sandstones. 
— wet “A Sag — 
ae a SS y re : 
; SSNS ‘LANA RMA A TRO ee = Fh il php ye ay 
thy 
~ —— a le ae 
Fig. 25.—MAssEs OF WHITE CALCAREOUS SANDSTONE SHAPED BY EROSION, NEAR CAMP 100. 
The upper portion of the Marl series here, as in the region immediately south of the Moqui 
villages, is composed of strata of greater individual thickness and more indurated than those 
below. They consist of soft, thick-bedded, calcareous sandstones, pure white or nearly blood- 
red. The colors and consistence of this portion of the series are, however, by no means con- 
stant. As we have seen, at Camp 92, soft green and red marls overlie white calcareous sand- 
stone, and represent the green and purple calcareous sandstones of Camp 91; while at Fort 
