Rock asphalt is present in great amount in the Anacacho limestone and is associated with many igneous intrusive rocks. The intrusions are either later than or contemporaneous with the oil source strata and the asphalt-bearing rock. It is suggested that the oil was originally in bituminous shales older than the intrusive rocks and was distilled and caused to migrate to higher levels as a consequence of intrusive processes and effects. At least, it is certain that large amounts of asphalt and tar now occur in close juxtaposition to the igneous masses, which certainly left intact a large quantity of the oil originally present in the intruded strata.

Some of the known occurrences of hydrocarbon, methane, and other combustible gases in craters during the hottest and most active phases of vulcanism are cited. Probable lack of a sufficient supply of oxygen may be the reason these gases are not consumed in the intense heat of active vulcanism. Hydrocarbon gas and methane may be derived from bituminous and carbonaceous sediments intruded by molten rocks, perhaps from carbonaceous rocks, by combination with highly heated and dissociated water vapor. Carbon dioxide and carbon monoxide may have their source in intruded limestones and other calcareous rocks. Oil and gas under these conditions perhaps are characterized by some percentage of sulphur or sulphur compounds.

A discussion of the dates of Balcones faulting is included.