12 RIO GRANDE COAL FIELDS OF TEXAS. [bull. 164. 
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 t Colorado, viz, uppermost Cretaceous and transitional Cre- 
taceo-Tertiary. The second area is situated in the Vieja Mountains, 
in 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, Geo7iomitestenuirachisIjx., which also occurs in the u 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. 
