CHAPTER VII. 
GENERAL DESCRIPTION OF THE GEOLOGICAL FORMATIONS. 
GYPSUM FORMATION—CRETACEOUS, TERTIARY AND VOLCANIC. 
GYPSUM FORMATION SUPPOSED TO BE TRIAS BY MR. MARCOU.—ABSENCE OF FOSSILS.—CALLED GYPSUM FORMATION BY PROFESSOR 
HITCHCOCK.—EXTENT AND BOUNDARIES OF THE FORMATION.—LITHOLOGICAL CHARACTERS.—SECTION AT PYRAMID MOUNTAIN.— 
GYPSUM.—EXTENT AND LOCALITY OF THE DEPOSITES.—MOST ABUNDANT EAST OF THE MOUNTAINS.—DOLOMITE EAST AND WEST OF 
' THE MOUNTAINS.—THICKNESS OF THE GYPSUM FORMATION.—DISTURBANCES OF THE STRATA.—UPLIFTS NEAR SAN ANTONIO DUE 
TO TRAP DYKES.—EXTENDS IN NEARLY UNBROKEN STRATA FROM THE EAST TO THE WEST SIDE OF THE MOUNTAINS. — PROBABLE 
AGE OF THE FORMATION AND ITS REPORTED SYNCHRONISM WITH THE TRIAS OF EUROPE.—CRETACEOUS FORMATION.—POINTS AT 
WHICH IT IS IDENTIFIED BY FOSSILS.— ÜRETACEOUS AGE OF THE LLANO ESTACADO.—OF THE PLATEAUX WEST OF THE SIERRA 
MADRE.—EXTENT OF THE CRETACEOUS ALONG THE ROUTE.—MINERAL CHARACTERS. —THICKNESS. —DISLOCATIONS.—MOUNTAIN 
RANGES OLDER THAN THE CRETACEOUS.—SUBMERGED IN PART BY THE CRETACEOUS SEA.—REPORTED JURASSIC AGE OF THE 
LLANO.— TERTIARY.— POST-TERTIARY. —ALLUVI 
GYPSUM FORMATION. 
RED SANDSTONE AND CLAY CONTAINING GYPSUM. 
The descriptions of the geology along the route have shown that for a great part of the dis- 
tance a remarkable series of strata of red sandstone, red marls and clays, containing an abund- 
ance of gypsum, were found in all the valleys of erosion. These strata were considered by Mr. 
Marcou as the equivalents of the Triassic formation of Europe, and he records his observations 
under that name in his notes, and describes the series in his preliminary report, or Resumé, as 
the Trias or New Red sandstone, and forms the whole group into three divisions corresponding 
to the divisions adopted by European geologists. 
As no fossils have been found in the strata, and as the line of separation between them and 
the underlying Carboniferous, and the Cretaceous above, has not yet been traced satisfactorily 
and does not appear to be well defined, I do not attempt to assign their age, but adopt for them 
the name Gypsum formation for purposes of description until further examinations shall deter- 
mine to what geological period they can, with propriety, be referred. This name was proposed 
by President Hitchcock for similar strata, an extension of the same series of deposites, found along 
the Red river by Captain Marcy, in his exploration of 1852. No fossils having been found, he 
was not able to determine the age of the formation; and as it was characterized by an abundance 
of gypsum, the above name was adopted for those portions of the strata which contained it in 
abundance, and the term Red Clay formation for those where the red marls and clays were pre- 
dominant. In the following descriptions the term Gypsum Formation will refer to all the red 
Strata of sandstone and marl containing gypsum, which are above the rocks containing fossils 
of carboniferous age, and below those in which cretaceous fossils abound. It is therefore possible 
that a portion of each of these two formations may be included in the descriptions. 
Extent and boundaries of the formation.—The strata of red sandstone and clay were first met 
on the western side of Delaware mountain, or about two hundred miles west of Fort Smith. 
They continue along the valley of the Canadian and False Washita westward to the Albu- 
querque mountains, where the carboniferous rocks rise through them, and form the crest of the 
mountains. The strata do not appear to rise high up the slope of the mountains, or as high as 
