OF NORTH AMERICA 
29 
Carboniferous beds in discordant stratification!),, and that they are below the Jurassic rocks which 
form the summit of the immense table-land called the Llano-Estacado. 
From your specimens, 1 perceive the Trias is composed principally of red friable sandstone, 
with red and gray clay; in a word, it is variegated, with interposition of beds of gray sandstone, 
of dolomite or magnesian limestone ; and finally it contains an immense mass of white gypsum , amor- 
phous or crystallized, having the same structure and texture as the Triassic gypsum of France and 
Germany. Salt springs and saline efflorescences are also found in this formation. The character- 
istics of the American Trias are very easily recognized at first sight. It has red rocks, giving 
a reddish aspect to the whole country, with grayish- white bands of gypsum. All the water run- 
ning through or springing from this formation is red and brackish; and one may say, without he- 
sitation, that everywhere to the east of the Rocky Mountains there is a lied river or Vermillion river, 
or Salt Fork or Rio Colorado. These rivers run through, or have their source in, the Triassic 
rocks. 
Your road was upon the Trias, from the time that you quitted the banks of the Clear Water 
Fork of the Rio Brazos, until you reached the base of the Llano Estacado, at the source of the Rio 
Colorado of Texas. 
For the construction of a railroad the rocks of the Trias present great facilities. They fur- 
nish sandstone, plaster, or gypsum; excellent hydraulic lime from the magnesian limestone; and, 
finally , they are very easy to work , and at the same time firm enough to form excavations or em- 
bankments. Also numerous springs issue from the beds of red clay, and give water in abundance. 
At the foot of the Llano Estacado, in following the ravines where the headwaters of the Rio 
Colorado flow, and at Big Spring, is found a sub-chalky whitish limestone, containing fossils, such 
as; Exogyra Texana, Ostrea vesicularie var. Aucella Rosm., Ostrea anomiaformis , which indicate that these 
rocks belong to the group of the Marly Chalk of the Cretaceous formation. It is probable that 
these strata of Marly Chalk are found again along the Rio Colorado, and are in continuous rela- 
tion with those of the bluffs in the environs of Austin, New Braunfelds. Fredericksburg, and the 
Rios Guadalupe and Biedernales, etc. 
') I have ascertained, bv direct observations, tlie superposition and the concordance of stratification 
between the Carboniferous rocks and the New Red Sandstone at Tigeras, Antonio and San Pedro, in 
the Sierra de Sandia (Rockv Mountains); at the Pueblo de Pecos and near Santa Fe; on the two de- 
clivities of the Sierra Madrc, near the Agua Fria, as w^ell as at several [loints of the lesser chain of 
the Sierra of Mogoyon. Lastly I recognized very distinctly all along the western declixity of Mount De- 
laware in following the Topofki creek, an affluent of the Canadian river, that the beds of the New Red 
Sandstone arc superposed in discordant stratification upon the Lower Carboniferous or Mountain Lime- 
stone which has been very much broken and upheaved before the epoch of the New Red Sandstone. 
Mr. Dawson has proved {On the New lied Sandstone of Aova Scotia; sec: Quart. Journal of the Geol. Soc. 
of London ; 1847.) that in Nova Scotia the New lied Sandstone is superposed upon the Carboniferous 
rocks, only he did not find it covered by the Jurassic rocks as I did in the Rocky Mountain region. 
On the rest of the Atlantic Coast as well as at Lake Superior, the New Red Sandstone lies directly upon 
the gi'anite, and other eruptive and metamorphic rocks. It is probable that it will at some future day 
be found, between the Sault S" Marie and S' Joseph's island resting on the Lower, or perhaps even on 
the Middle Silurian. 
