96 GEOLOGY. 
stones of the same formation. Above these, generally forming a distinct and more remote wall, 
are the cream-colored strata of the Lower Cretaceous series. In places we descended through 
the red and green shales and sandstones of the Saliferous group, and came upon the coarse 
sandstones and conglomerates which overlie the Carboniferous limestone. The dip of these 
strata is nearly northeast, and our route lay so closely along their strike that they seemed to 
be almost horizontal. 
In all this region a fact was observed, to which our attention was first called on the banks of 
the Little Colorado, viz: that the lower hills and the bases of the highlands are covered with 
dead cedar trees, an apparent indication of the increasing dryness of the climate. The timber 
in this country is confined to the more elevated surfaces, where the precipitation of moisture 
is greatest, and the belts of deadened trees, certainly untouched by fire, prove that the condi- 
tions favorable to the growth of arborescent vegetation are becoming restricted to narrower 
limits. This fact is mentioned merely as being confirmatory of the conclusion drawn from other 
data, that the amount of rain on the table-lands west of the Rio Grande is now much less than 
formerly. 
CAMPBELL’S PASS. 
Here, almost unconsciously, we crossed the divide between the waters of the Pacific and 
those of the Atlantic. No mountain chain or line of upheaval marks the summit, and the mesa 
of the Lower Cretaceous sandstones, and that of the variegated marls, stretch over from one 
side to the other, without break or interruption, except such as have been produced by erosion. 
On reaching the summit we obtained a fine view of Mount Taylor, (or San Mateo,) some forty 
miles distant. This mountain has an elevation of 11,000 feet above the level of the sea. It some- 
what resembles, in form, as in all other respects, San Francisco mountain, but its base is broader, 
and, as a consequence, its apparent altitude is less. The summit is irregular, and contains a 
crater. By the Mexicans it is sometimes called El Tintero, or the Inkstand, from its general 
form, and the depression which is said to exist in its summit. 
After passing the divide our descent was more rapid than had been our ascent on the 
western slope, and we soon struck a flowing stream, the headwaters of the Rio San José, which 
we followed from this point to its intersection with the Puerco. Some ten miles from the 
summit of the pass we began to meet with fragments of scoria, and then reached masses and 
streams of lava poured from Mount Taylor, by which all the country adjacent to it has been 
This lava is undistinguishable from that of the San Francisco mountain, and we here 
had a . repetition, in all their details, of the magnificent volcanic phenomena there displayed. 
At Agua Azul the stream we were following has cut down through all the red sandstone series, 
and has exposed, over a considerable area, the Carboniferous limestone, here brought up by an 
arching of the strata. This limestone is blue, gray, and pink; portions of it cellular and cherty. 
It contains many fossils, among which are Productus, Nautilus, Bellerophon, Allorisma, etc. I 
have regarded it as identical with that holding the same relative position on the Little Colorado, 
and as representing the summit of the Carboniferous formation. 
The series of strata exposed in the descent from the top of the upper mesa at Campbell’s 
Pass to Agua Azul is as follows, the thickness given being estimated, and not measured: 
1. Cretaceous sandstones, shales, and lignites, forming first and highest mesa---- 700 feet. 
2. Soft red, white, and green calcareous sandstones or indurate marls, Marl series- 600 feet. 
3. Variegated marls, with silicified wood and bands of magnesian limestone, Marl 
DAMES cei ives oe Ck wey Re ee) ets ca SEU ee Cs AS 150 feet 
£ Red and green foliated deciles and shales, Salt group-----. ss+seseeeeees 120 feet. 
5. Coarse sea or drab sandstone and conglomerate, Salt group ---- +--+ sees eres 250 feet. 
6. Red, blue, and white shales, Salt group---... Se ee eee ee eee 150 feet. 
I> emma blue, gray, and pink, Carboniferous. 
