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.

The successional mode of speciation of Julian Huxley (1942) may be defined as gradual transformation of one species into a successor species, or several of them, during the course of geologic time without primarily involving geographic, ecologic, or adaptive segregation.

Gravitational observations were made of the pre-Cambrian Coal Creek serpentine mass in Blanco and Gillespie Counties, Texas, the geology of which had been mapped previously.

The magnetic iron-ore prospects of the Llano region of central Texas were investigated in a program which combined dip-needle and gravity-meter surveys by the Bureau of Economic Geology of The University of Texas and the U.S. Geological Survey with exploration by the U.S. Bureau of Mines.

Steeply dipping shales and interbedded sandstones presumably of the Ouachita facies have been discovered along the Colorado River in Burnet and Travis counties, Texas. Previously the Ouachita facies was known in Texas only from bore-hole samples.

The occurrence of sulphur in the vicinity of Rustler Springs in northeastern Culberson County, Texas, has been known since 1854 when, according to Phillips (1902, pp. 13, 71), the mineral was recognized by William P. Blake, a geologist attached to a U.S.