first of these includes a number of isolated or limited districts in New Mexico, to which belong the Cerillos, Bernalillos, and Fort Bayard fields, which are probably of the same age as the so-called " Laramie" coals of Colorado, viz, uppermost Cretaceous and transitional Cretaceo-Tertiary. The second area is situated in the Vieja Mountains, the vicinity of San Carlos, Texas. These coal beds are of Pierre age. The third area occupies the interior portion of the Rio Grande Plain, and extends from the Santa Rosa Mountains of Mexico to beyond Eagle Pass, Texas. Mines are worked in it near Eagle Pass, Texas, and near San Felipe, Sabinas, Fuente, and Porfirio Diaz, in Mexico. The coal of this area is of Fox Hills age. Associated with it is a fossil plant, Geonomites tenuirachis Lx., which also occurs in the "Laramie" coal of New Mexico. The marine fauna is equivalent to that of the Ripley and Navarro beds of the Gulf region and to that of the Fox Hills beds of the Rocky Mountain section. The fourth area is the, coal field adjacent to Santo Tomas, Texas. These coals are usually lignites of Eocene age.

In addition to the districts mentioned adjacent to the valley of the Rio Grande, allied beds are found in the Trinidad-Raton district of Colorado and New Mexico and in the White Oaks district of the Sacramento Mountain region of New Mexico.