10 
MESOZOIC FOEMATIONS. 
an angle of 20° and 25° to tlie south, marking the terminus of another 
longitudinal wave of the axis, of which the one immediately to the north 
ha« already been described. The valley caused by this descent is the 
drainage-level of the Upper Gallinas Creek, which issuejj from the mount¬ 
ains at this point. This locality is instructive as furnishing the third 
example of the fault existing between the Triassic and Jurassic. The 
Triassic sandstone is also faulted at several points at right angles to the 
principal fault, as seen in the north and south escarpment. The fragments of 
the fractured sandstone bed strew the west slope of the Triassic mountain, 
and disappear in the red marls. 
From this depression, the mountain rises gradually, first in a lower 
ridge, and then to the long and regular crest of the Nacimiento Mountain. 
The axis of this new elevation forms an open angle with that of the range 
of the Gallinas proper, running northeast and southwest, the consequence 
of which is a change of strike of all the elevated beds on its flanks. The 
Cretaceous hog-backs make a very regular angle in their direction; its 
apex being the point of change of axis at the cove I have described above 
in detail. At the same time, the hog-backs approacli nearer to the mount¬ 
ains, and the variegated and gypsum beds of the Jurassic are not seen. 
J'he southward route passed over the divide which separates the drainage 
of the Gallinas from that of the Puerco. South of this divide, the Creta¬ 
ceous beds, including their highest members, Nos. 3 and 4, disappear on 
the sides of the Nacimiento Mountain. The mountain itself is the feld- 
spathic porphyry of the true Rocky-range axis, which, rising through the 
Mesozoic beds which cap the northern part of the Sierra Madre, forms its 
most elevated portion. At the village of Nacimiento, the red Triassic beds 
are visible on the rnountain-side, and its upper sandstone dips south as well 
as west from an elevated position. The range extends south from this point 
as far as my observation reached. The valley is occupied, in localities near 
the mountains, with the red feldspathic gravel usual along the Rocky ranges. 
Some of the Mexicans spoke of copper-mines, with ancient stone buildings, 
in the ravines of the Nacimiento. 
I conclude this chapter by a little further allusion to the Cretaceous 
Jiog-]jacks, of wliicli tlie most important is that formed by No. 3. At one 
