pg 027: A Partial report on the geology of western Texas, consisting of a general geological report and a journal of geological observations along the routes traveled by the expedition between Indianola, Texas and the valley of the Mimbres, New Mexico, during the years 1855 and 1856; with an appendix giving a detailed report on the geology of Grayson County Publication 1308351

of the Llano Estacado, may have been obtained from the rocks of the Upper Cretaceous Group.

Finally, among the host of fossils obtained from the Secondary Strata of Texas, New Mexico, and the adjacent Indian Territory, we are not aware that a single one has been found that is positively identical with either Triassic or Jurassic species of Europe. The Ostrea subovata (0. Marshii, Marcon) and Gryphœa Tucumcarii, mentioned by Mr. Maroon as occurring along the Canadian, were probably obtained from the Upper Cretaceous, as they occupy this position in other parts of this region.

The mere lithological character of these strata, so much relied upon by that author, cannot be taken as evidence of their being the equivalents of the Triassic and Jurassic Systems of Europe, though it is true they somewhat resemble the latter in mineralogical composition; but from the same kind of evidence we might, with equal propriety, regard them as being parallel with the Permian of Russia, the Tertiary of Auvergne, or the Carboniferous of Nova Scotia.

ECONOMICAL GEOLOGY.

BUILDING MATERIALS.

As a general rule the rocks of this formation possess very little firmness or durability, and are, therefore, but poorly adapted for building purposes or works of internal improvement. In some localities, however, the sandstone is moderately firm and resisting, and might, in the absence of better materials, be used for construction.

GYPSUM.

This mineral, on account of its economical value and enormous development upon the Plains, is of far more importance than any rocks we have considered. The Gypsum Field of the West, the great extent of which was published in 1852, shortly after the return to the States of the Red River Expedition, is believed to be the largest in the world, and will hereafter prove an inexhaustible source of wealth to the State of Texas and adjacent Territories.

The exact limits of the gypsum cannot at present be very accurately determined. It is well known to occur in great abundance at several points north of the Arkansas River, and on that stream it is mentioned by Col. Long and others. Thence southward it has been traced through the regions watered by the Canadian, Red, Big and Little Witchita, Brazos, and Pecos Rivers to within a few miles of the northern base of the Limpea "

Reports of Capt. R. B. Marcy, Lieut Simpson, and Mr. Marcon.