SOUTHERN PACIFIC LINES 143 
From Deming the railroad line goes slightly south of west on a 
tangent 37 miles long over a great desert plain, with a rise of only 
250 feet in 33 miles to the Continental Divide. 
At Tunis siding Black Mountain seems near on the north, showing 
in cross section its eastward-dipping cap of black basalt about 250 
feet thick, lying on volcanic ash and sand of which 500 feet is exposed, 
cut by rhyolite. Still nearer, to the south, is the craggy butte known 
as Red Mountain, so named from the pinkish tint which it shows in 
some lights. It consists of nearly white felsitic rhyolite, apparently 
lying on agglomerate. Probably this igneous mass was extruded in 
a highly viscous condition, so that it piled up thickly without extend- 
ing far beyond its present area. It is regarded as of Tertiary age. 
The Snake Hills, a group of low mounds in the plain 3 miles south 
of Red Mountain, consist of the upper member of the El Paso lime- 
stone and the lower member of the Montoya limestone. 
North of Gage are some conspicuous rounded and pointed buttes 
known as the Grandmother Mountains, composed of felsitic rhyolite 
similar to the rock of Red Mountain and doubtless 
G ‘ j 
oe extruded at the same time. Other buttes farther 
Elevation 4,590 feet. 3 . ‘< 
Population 20.* north include Cow Cone, which also is part of a large 
pipe Be coreg 129% mass of felsitic rhyolite. In the distance to the north 
! are the mountains in which lies Silver City. South 
of Gage are the Victorio Mountains, which present many features of 
geologic interest. The main ridge consists of a sheet of hornblende 
andesite about 200 feet thick underlain in part by a thin sheet of 
rhyolite. It dips 20°-25° NNE. In the hills just south of this 
ridge there are, in succession, the El Paso, Montoya, Fusselman, and 
Gym limestones. Devonian, Mississippian, and Pennsylvanian time 
apparently is not represented. Figure 34 shows the principal features 
in both parts of the uplift. 
®° The Gym limestone, about 300 feet 
stone. There are various unconformi- 
a crops out in a zone about 2,000 
ide marked by knobs on the 
pe side of the range. It appears to 
The Gym is overlain unconformably by 
700 feet of shale and sandstone, mostly 
dish, which resembles the Lobo for- 
mation (Triassic?) but may be much 
conglomerate are included which con- 
tain boulders of seremee and near the 
top some greenish quartzite carrying 
pebbles of fossiliferous Paleozoic lime- 
ties in the succession, but all the strata 
have practically the same attitude. 
are several faults and some 
obvious overlaps. The F 
estone carries an interesting fauna 
of Niagaran corals and lies on cherty 
beds of Montoya limestone with Rich- 
mond fossils. The Montoya includes 
a prominent eae member. There 
several intruded dikes, mostly of 
es v.08 alt amount of mineral- 
ization has occurred along the fault in 
the west side of Mine Hill, but the 
mining operations on this zone ap- 
parently did not yield a return suffi- 
ciently satisfactory to warrant ex- 
tensive development, 
