| ae GEOLOGY. 
At the mouth of Cottonwood Fork the same rocks are still better shown. The banks of the 
stream are there composed of reddish shaly sandstones, the more solid portions closely resem- 
bling the red sandstone of New Jersey. From this rock, about fifty feet below its upper 
surface, issue copious salt springs, the water of which collects in several natural reservoirs, 
and is covered with a sheet of salt resembling ice. This salt is very palatable, and apparently 
quite pure. Above the sandstone is the conglomerate first noticed at Camp 88, here having a 
thickness of thirty or forty feet, then purplish shales, above which are greenish brown sand- 
stones, which form the summit of this series. Over the sandstones are beds of brown, blue, 
purple, lilac, red, and cream-colored marls, with bands of magnesian limestone, the base of the 
series of variegated marls hereafter to be described. Thin layers of gypsum occur locally in all 
the members of the saliferous sandstones, being most noticeable in the middle portion, at the 
ruined pueblo between Camps 88 and 89. I had no means of measuring accurately the aggregate 
thickness of this group of rocks, but have estimated it, on the Little Colorado, at about seven 
hundred feet. Further eastward | think it is considerably less. 
PAINTED DESERT. 
After crossing the Little Colorado at Camp 85, a detachment of our party struck northward, 
to regain the line of exploration abandoned on account of the impassable cafions of Cascade 
river. Ascending the mesa wall which bounds the valley north of our crossing place, we 
entered a region to which the above name was appropriately given, as indicative of its bar- 
renness and desolation, as well as of the peculiar scenery which it exhibits. Although com- 
pelled by the want of water to retrace our steps before we had penetrated this district to any 
great distance, such is the nature of the surface, the atmosphere so clear, our view so entirely 
unobstructed, that we were able to determine its geological structure at least fifty miles beyond 
the point where we turned back. Subsequently, when on the high mesa at the Moqui villages, 
we obtained a nearer view of the region we then saw in the distance north of us, which fully 
confirmed the impressions we then received, and showed that the peculiar physical aspect and 
geological structure of the Painted Desert prevail over a wide belt of country bordering the 
Little Colorado on the east, and extending at least as far northward as our Camp 73. 
Fig. 18.— esa WALIS OF RED SANDSTONE.—PAINTED DESERT. 
All this area is occupied by the mesa of which the edge forms the eastern boundary of the 
valley of the Little Colorado. It is traversed by a series of broad valleys of erosion, which 
seem to have been formed by a more abundant supply of moisture than now falls upon this 
surface. These valleys are bounded by abrupt and usually perpendicular walls, composed of 
the blood-red strata of the saliferous sandstones and the variegated marls which overlie them. 
imabe process of erosion many buttes and pinnacles have been left standing, which, by their 
forms ¢ colors, closely imitate upon a colossal scale the structures of human art. The geo- 
ica “horizon i is here precisely the same as that of much of the country lying between the 
: sissippi and the Rio Grande, of which the peculiar scenery, so frequently described by 
- travellers, seems also to be very similar to that of the region under consideration. 
_ Variegated marls.—This formation composes the mppor portion of the mesa when unbroken 
