In the inferior strata the most characteristic forms are:

• Ammonites vespertinus (Morton),
• Ammonites Popeanus (B. F. Shumard),
• Turrilites Brazoensis (Roemer),
• Baculites asper (Morton),
• Exogyra costata (Say),
• Exogyra arietina (Roemer),
• Exogyra loevinsculd (Roemer),
• Ostrea vesicularis (Lamarck),
• Gryphoea Pitcheri (Morton),
• Pecten (sp. undt. ),
• Janira quadricostata (Sowerby),
• Inoceramus Cripsii (Mantell),
• Inoceramus mytiloides (Mantell),
• Inoceramus (sp. undt.),
• Pholadomya elegantula (D'Orb),
• Cardium elegantulum (Roemer),
• Cassidulus oepuoreus (Roemer),
• Terebratula Choctawensis (B. F. Shumard),
• Nerinea Texana (Roemer),
• and Trigonia (nor. sp.).

It will be seen from the above list of species that with some few exceptions the fossils of the superior and inferior portions of the Upper Cretaceous strata of Texas and New Mexico are quite distinct. Nevertheless, as we cannot draw a well marked horizon by lithological characters, we have thought proper to make no separation of the strata.

This formation more than any other of the Plains is characterized by lofty and rough precipices and deep and fearful canyons. The elevated plateaus, which sometimes attain an altitude of seven or eight hundred feet, and often are seen stretching across extensive districts of country, present everywhere rough and precipitous cliffs, with sometimes nearly vertical faces, showing almost at a single glance the entire thickness of the formation.

Section No. III, taken from near the headwaters of the Ke-che-ah-que-ho-no, or main fork of Red River, presents a remarkable example of the kind. Here the elevated plateau known as the Llano Estacado terminates abruptly in a line of escarpments from six to eight hundred feet in height. These are for the most part nearly vertical, and extend north and south for a distance of over thirty miles. From their bases there is a descent of about four hundred feet by a succession of abrupt terraces of gypsum, red marly clay, and sandstone, so that we have here in a single locality an exposure of eleven hundred feet of Cretaceous strata.

Section No. IV was taken from near the sources of the main branch of the Brazos River, and exhibits another marked example of the kind. The table land of which this escarpment forms the abrupt boundary has an elevation above the bed of the river of about eight hundred feet, and presents a smooth and nearly flat surface on the top, covered with short yellow moss- like grass and a scattering growth of Mezquite trees. These cliffs are