SOUTHERN PACIFIC LINES 
101 
Near Quebec siding there are fine views of high ranges from 10 to 
20 miles away. Those to the west are the Tierra Vieja Mountains,”! 
and those to the north and east the higher 
The highest point of the Davis Mountains is Livermore Peak, 
tains. 
its of the Davis Moun- 
named from a major in the United States Army, who first measured 
its height in 1880, when he was returning from a raid on the Apache 
marauders. This peak is 8,382 feet above sea level and is a part of 
a central intrusive mass that extends northwest to Sawtooth Peak. 
The succession of voleanic rocks in this region has not yet been de- 
termined, but it has a thickness of several thousand feet and presents 
a variety of lavas, agglomerates, and tuffs, and numerous feeder dikes 
and stocks by which the volcanic materials reached the surface. 
west from the Finlay Mountains, the 
front of which is conspicuous north of 
Fort Hancock. It is regarded as a for- 
mation of the Trinity group on the 
evidence of the fossils Exogyra quit- 
manensts and Orbitulina terana. The 
Edwards limestone is only 25 feet thick 
in the Van Horn Mountains and about 
Sierra Blanca feb hogar greatly to- 
alone the 
§ the 
Rio Grande. The ‘overlying George- 
town limestone also thickens to the 
southeast and is generally overlain by 
Del Rio clay and Buda limestone. The 
Upper Cretaceous begins with a basal 
sandstone at most places and has a thick 
succession of shales with slabby lime- 
southern and western parts of the Van 
Horn Mountains, at the southeast end 
of the Quitman Mountains, and north- 
west of the Eagle Mountains. Repre- 
sentatives of the overlying Austin and 
resented by 
sandstones and shales with interbedded 
voleanic tuffs and flows, the beginning 
of the great volcanic succession. 
The Tierra Vieja Mountains con- 
age. The lavas range from obsidian to 
a rock of porphyritic character. One 
flow about 300 feet thick of the very 
crest of the mountains, which presents 
a steep front to the west. 
and lava sheets dip to the southeast at 
a low angle, mostly about 4° 
The succession of rocks in the peak 
at the north end of the mountains is 
given by Vaughan as follows (it begins 
a short distance below the great sheet 
of quartz pantellerite) : Feet 
Rhyolite__ 7 ae 
Clay or red sandstone_______ 100 
RhyoliteT_ oo. a 20+ 
Conglomerate and clays_____ 80 
Rhyolite breccia, light colors, 
hard at baseoo So 130 
Conglomeratic sandstone and 
50 
Rhyolite . breccia__-_..._._. 50 
Basalt (black) 65 
Rhyolite and basalt breccia__ 6 
Fine-grained semirgre (tuff?)_ 60 
oe 2 sugserr at 80 
te, EEO eerie 
Ri-paltte, massive, edit tha. 20 
Sands and clays, some con- 
Someries. goci2 2) 4 Br 60 
Sandstone and clays (at base). 40+ 
The sandstones and tuffs at the north 
end and extending along the abrupt 
west front of the Tierra Vieja Moun- 
tains are 
indicate Taylor age, 
