SOUTHERN PACIFIC LINES 
115 
uplifts limestone of Trinity age in Triple Hill. There are two other 
conical masses of rhyolite a short distance north and northwest of 
the large one, but they are of much less height.” 
Just north of Sierra Blanca is a long ridge of limestones and sand- 
stones of Trinity age penetrated by small bodies of intrusive rocks and 
apparently cut off on the east side by a fault. 
north to Triple Hill. 
This ridge extends 
South of Sierra Blanca are other high ridges of the same limestones 
and sandstones.™ 
FIGURE 22.—Section von the southern edge of the baaers ner to Eagle Flat, east of the Sierra 
eee a, Tex. ae B. King. K, Sandston 
Ho oneyaay ( Cam brian); 
— _ — Phe seein. Cp, bape gees 
ud 
(Per 
ing — ye at peat (b); A 
There has been Br a in obtaining an adequate water supply 
for Sierra Blanca, but in 1930 a well about a mile east of the town 
struck water, apparently either in a sandstone low in the Trinity 
8 The rock of Sierra Blanca and the 
similar smaller cones is classed 
rhyolite, as it is composed mainly of 
quartz, ortho sete and sodie plagio- 
clase. The phenocrysts are orthoclase, 
oligoclase, and small 
and hornblende. 
_—- is a porphyritic rock composed 
y of sodie plagioclase and horn- 
blenda with phenocrysts of oligoclase 
and hornblende in a groundmass of 
a small disk-shaped fossil ¢ 
of the upper part of the Trinity group. 
A mile southwest of Sierra Blanca the 
limestone has been metamorphosed 
by intrusive sills, and secondary 
minerals, such as garnet, hematite, and 
specularite, have been developed. The 
strata (Cox) underlying the limestones 
sandstones with thin limestone 
members at intervals, passing into 
medium-bedded gray limestones with 
interbedded sandstones, in 
all 750 feet thick. In the 
3 to 5 miles south of Sierra Blanca the 
cap of Finlay limestone is underlain 
by 1,000 feet of limestones, sandstones, 
and conglomerates, some thin bedded, 
of the Cox formation. At the north- 
east base of the ridge just south of 
Sierra Blanca are sandstones with a 
few interbedded limestones, ig? Cox. 
(Baker.) 
The large mesa 5 miles south of 
Etholen is capped by massive limestone 
about 200 feet think: with a thick 
quit Other fossils in this 
miata necordiing to Baker, are 
