28 = W. P. Jenney—Notes on the Geology of Western Texas. 
Il. The Llano Estacado, or Staked Plains. 
A great deal has been written about this desert, which 
stretches north and south nearly 350 miles, and, from the head 
waters of the Rio Colorado and its branches westward, from 50 
to 150 miles, to the Rio Pécos. Its underlying strata were an- 
Reenter to be Triassic and Jurassic by Jules Marcou, but are 
now well known to be of Cretaceous age. A finesection of the 
Llano is expiked at Castle Cafion, near Horsehead Crossing of 
the Pécos: the strata, beginning at the base, are arranged as 
1. A coarse red sandstone without fossils, but probably of 
Triassic age, 50 feet expose 
. Soft caleareous brown sandstone, with fragments of. fossil 
tate hs bed is 50 feet in thickness and probably of Creta- 
ceou 
3. “Soft ‘yellow limestone, 450 feet in thickness, containing an 
abundance of well known Cretaceous fossils, including Gryphea 
Pitcheri, Hxogyra Texana, E. Arietina, Arcopaqra Tecana, Ammo- 
nites Pedérna alis, and several species of Cardium, Nerinea and 
Pecten. 
4. Compact yellow limestone. 30 or more feet in thickness, 
wanting at Castle Cafion, but forming the tops of the highest 
hills on the Llano, and also found on the tops of the mountains 
in Jones County. 
The characteristic fossil of this bed is the Caprina crassifibra, 
which is very abundant; the bed is, I think, equivalent to the 
identical with those from bed 8. Similar ae to that of the 
ano were found at Fort Chadbourne, in the neighboring 
mountains, which were identical both in the nieeaeerient of the 
strata and in the fossils from the different beds. 
In Mason County, underneath the limestone and red sandstone, 
there is a metamorphic sandstone resting unconformably on 
micaceous gneiss. The hardness of the upper layers of limestone 
has greatly protected this formation from denudation, and given 
the “mesa” character to the hills, as the bedding is almost 
mation was piaueh more extensive, and that the noe ing hills 
and ranges of low mountains which are found east of 
been subsierget and in some es wave-worn cavities peat 
at the same height along their sides. 
