The Barrilla Mountains, in the northeastern part of the Davis Mountains of Trans-Pecos Texas, are composed of Tertiary volcanic materials. Five tuffs and five lava flows, 1500 feet thick occurring throughout the mountains, persist in thickness and lithologic characteristics. Their upper surfaces show little erosion. The lavas are chiefly Silicic and soda rich. The volcanic succession is underlain by a Tertiary sandstone above Upper Cretaceous marine formations.

The geographic distribution, lithology, thickness, and paleontology of the subsurface Woodford in the Permian basin are described and illustrated. On the basis of conodonts and spores, the Woodford is assigned to the Upper Devonian and correlated with the Ready Pay member of the Percha shale in New Mexico, Woodford and Chattanooga of Oklahoma, Kansas, and Arkansas, and tentatively correlated with the Upper Devonian parts of the Caballos novaculite and Arkansas novaculite of Texas and Arkansas.