MESOZOIC FOEMATIONS. 
7 
ain axis. It forms the culmination of the Sierra Madre, and extends south¬ 
ward as far as my examination was carried. 
The first and most northern section was carried across the flank of the 
mountain twelve miles south of the entrance of the canon of the Gallinas 
Creek. The oldest beds of this section form a plateau surrounded by 
■ greater elevations, from which it is separated on the south and east sides at 
least by deep ravines. The walls of these are composed of a deep-red marl 
of the Trias, capped by the usual heavy bed of gray sandstone. The 
north side of this plateau is bounded by an abrupt precipice of Jurassic 
strata, the red below, yellow in the middle, and the bed of snowy gypsum 
on top; the relations of the Triassic and Jurassic here being precisely as 
described above at the entrance of the Canon Cangilon. The sandstones of 
Cretaceous No. 1 are observed on both east and west flanks of this open 
anticlinal; on the eastern side, without the intervention of the gypsum-bed. 
The yellow bed is also deeply scored, and in some places isolated, showing 
that a stronger eroding action had been at work on this side than on the 
west, prior to the deposit of the Cretaceous No. 1. Immediately to the 
west of the plateau, a more elevated wave is also covered with the Jurassic 
beds; the entire summit of the mountain for many miles being composed 
of the gypsum. This soft material is worn into innumerable gullies. It is 
separated from the plateau by a gorge which is the seat of a fault. The 
Triassic plateau has evidently been thrast upward to the level of the yellow 
beds of the Jurassic at this point; the fault thus amounting to not more than 
three hundred feet. But the Jurassic beds dip southward, forming the 
descending slope of a longitudinal wave of their axis of elevation. As the 
Triassic is level at the point of descent of the Jurassic gypsum to the val¬ 
ley-level, the fault amounts to a thousand feet. At the junction of the two, 
the evidence of faulting is to be seen in the vertical escarpments of the 
middle bed of Triassic sandstone, which is here on edge, with the deep-red 
marls on both east and west sides of it. The gypsum does not descend 
southward to the valley-level, however;' the end of the anticlinal having 
been cut transversely by a line of drainage, marked in summer by a deep 
arroyo. Immediately to the west, the sandstone of Cretaceous No. 1 forms 
the usual line of hog-backs; but at this point it does not lie immediately on 
