SOUTHERN PACIFIC LINES 81 
re is a striking exposure on the north side of the track just 
beyond Comstock in which Del Rio yellow clays are capped by Buda 
limestone, as shown in Plate 11, B. The Del Rio 
Comstock. clay at all places contains thin layers of hard, dark 
Elevation 1,546 feet. limestone carrying an abundance of Exogyra arietina, 
aaa en ee mites, the characteristic fossil. 
A short distance beyond milepost 416 (3 miles 
beyond Comstock) the outcrop of Eagle Ford limestone begins, and 
this formation caps the rolling country about Rona and Viaduct. 
From the highlands in this vicinity there are excellent views of the 
Burro Mountains, in Mexico (State of Coahuila), 15 miles or more to 
the south. The Eagle Ford beds in this region are impure slabby 
limestones of pale-reddish tint, highly characteristic in aspect. They 
are beautifully layered and in places show crumples and faults. From 
Viaduct siding the railroad descends across the Eagle Ford beds and 
Buda limestone and reaches the platform of massive Georgetown 
limestone, in which the canyon of the Pecos River is cut. Underlying 
the Georgetown is the Edwards limestone. (See pl. 12, A.) The 
railroad crosses this impressive canyon on a bridge 2,184 feet long 
(middle span 185 feet), built in 1890, noted for its idiaht (321 feet) 
and the view that it affords. The uéjleanal when first constructed, 
went west from a point near Comstock and, deflecting to the left, 
passed into the canyon of the Rio Grande to cross the Pecos River 
at its mouth; thence it climbed from a side canyon of the Rio Grande 
to the present site of Shumla. It was on this part of the line that 
construction from the east and from the west made their junction on 
January 12, 1883, at a point 24 miles west of the Pecos Bridge, or 8 
miles east of Shumla. 
The Pecos River rises in the high ridges of the Sangre de Cristo 
Mountains, a part of the Rocky Mountain system, in north-central 
New Mexico, and empties into the Rio Grande about 4 miles below 
the railroad bridge, a short distance below the Pecos Bridge on High- 
way 3. Its length is about 600 miles. The portion of the State 
lying west of the stream is called trans-Pecos Texas. Apparently the 
first white man to visit this section was Cabeza de Vaca, in his 
wanderings across Texas in 1528 to 1536. In 1541 the Pecos was 
crossed far above this point by Coronado on his expedition in search 
of the city of Quivira. He noted in the region many buffalo but 
only a few roving Indians. Later the Pecos was crossed by Espejo 
on his return trip into part of the region discovered by Coronado, and 
he called it Rio Vaca (Cow River). In 1590 Castafio de Sosa chris- 
tened it the Rio Salado because he found it salty in places. West 
Texas was the home of the Apache Indians and later of their bitter 
enemies, the Comanches, who came down from Wyoming about 1700. 
The Indians obtained food and clothing from the buffalo, great herds of 
‘ which roamed the plains, blocking caravans and even railroad trains. 
