SOUTHERN PACIFIC LINES 
103 
For several miles near Danube siding the railroad is margined by a 
dike or levee of earth to protect the tracks from washouts. 
The 
erosion and flood-water conditions in the valleys of the arid regions 
are somewhat peculiar. 
Most of the infrequent rain falls in heavy 
Fault 
| Lobo siding 
Horizonte! scale 
eae scale 
Nee near i 
FicureE 16. across the 
Horn Mountains near their north end. 
500 Feet 
, Sandstone 
—Sect Van 
Cox); Cpl, Paksina limestone; sch, Carrizo Mountain schist; Qal, alluvium; oe ae rock 
showers, or ‘‘cloudbursts,” 
which quickly flood the drainageways 
I 
with a swiftly moving body of water sufficiently powerful to ro 
containing, according to Baker, Enal- 
laster texanus, Exogyra quitmanensis, 
Gryphaea marcoui, Requienia, and Tylo- 
stoma. The Edwards limestone is thin 
in the Van Horn Mountains, apparently 
comprising only 25 feet of beds at the 
south end of the range, near Chispa 
Summit. It is a massive bluish rock 
grading down into some slabby beds 
supposed to represent the Comanche 
Pea Walnut clay. The repre- 
sentative of the Georgetown in this area 
consists of nodular limestone and marl 
underlain by a bed of brown sandstone 
and capped by a heavier-bedded lime- 
stone, in all about 500 feet. In expo- 
sures 9 miles southwest of Lobo siding 
there have been collected from this 
formation, according to Baker, Pervin- 
quieria graysonensis, P. wintoni, Holas- 
ter simplex, and Holectypus limitis. At 
the fault 3 miles west of Chispa Sum- 
mit the sandstone noted above lies on 
Edwards limestone and is overlain by 
nodular impure blue-gray limestone of 
Georgetown age, which carries Enallas- 
calvini, Holect - planatus, Kingena 
is, Neithea terana, Cypri ia 
terana, and Gryphaea corrugata. These 
are overlain by b: nes 
slab 
and shales of the Eagle Ford formation, 
which are highly fossiliferous at Chispa 
Summit, where besides the characteris- 
Hemiaster | 
tie Inoceramus labiatus many fine am- 
monites have been collected. These 
include, according to Adkins, Mantelli- 
ceras M. couloni (D’Orbigny), Ro- 
maniceras cumminsit Adkins, R. loboense 
Adkins, Coz 
Hoplitoides? mirabilis Bése, Neocardio- 
ceras septem-seriatim (Cragin), Scaphites 
ff. S. africanus Pervinquiére, S. aff. S. 
asia Sowerby, and Metsctgehaiiae 
3 ds). 
under 
shales with thin limestone layers equiv- 
alent to the Austin chalk, and these in 
th 
Es 
la delawarensis, as~ 
and many others—a fauna which is re- 
garded by Stanton as lying between the 
— and the Austin limestone. A 
of a tooth of ——— 
“mortont Agnasis waa as found, 
