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The Dockum series, of Upper Triassic age, overlies much of the oil-producing area in the southern part of the Permian basin, in West Texas and southeastern New Mexico. In the area south of the 33d parallel the Dockum consists of red and non-red conglomerate, sandstone, and shale beds of terrestrial origin. An examination of the series in well samples shows that it is composed of two formations. The names Santa Rosa and Chinle, as used for the Triassic of central New Mexico, are extended to include the equivalent formations in the Texas section. A critical study of the means used for separating the Red-beds of the Triassic and Permian shows that the gravel and non-lithified shales of the Triassic and the thick beds of very fine sandstone and hard shale of the Permian are t e most prominent features.

By comparing the Upper Permian stratigraphy of West Texas and Oklahoma it is found that the Whitehorse of Oklahoma is equivalent to the lower evaporites of the southern basin and that the Permian of the Oklahoma Quartermaster is equivalent to the Yates sand. Formations above the Yates in the southern basin are younger than any of the Oklahoma or Kansas Permian.

The marked Cretaceous surface structure overlying arched Permian limestones in the Yates area in eastern Pecos County, Texas, was developed by salt solution rather than folding. The solution was active in two stages. In the first, salt was removed from the crest of the dome and the hole left by this solution was filled with clastics. Cretaceous beds were laid down flat over this clastic plug. Post-Cretaceous solution developed a ring syncline around the plug and produced the present surface structure.

The Delaware basin is a strongly negative structural depression in western Texas and southeastern New Mexico. The early history of the basin was part of that of the western mid-Paleozoic Tobosa basin (Fig. 1). Its history as a separate basin began with the rise of an Early Pennsylvanian median ridge in the Tobosa basin. During the Pennsylvanian and Permian 20,000 feet of sediments accumulated in the deep Delaware basin trough. These basinal sediments consist largely of clastics in contrast to the thinner equivalent carbonate sections deposited on the surrounding shallow shelves. Water depth was a controlling factor in this facies distribution pattern. Clastic supplies were limited and throughout its history waters in the Delaware basin were deep. Only near the end of the ermian, when the basin filled with evaporites, did the surface of sedimentation reach sea-level. Formation of a late Paleozoic geosyncline, which includes the Delaware basin, was associated with high-angle faulting rather than crustal folding. Exploration has not proceeded far enough to justify discussion of local structures within the Delaware basin.

The Yates pool in Pecos County occurs on a structural and depositional "high." Porosity in the top of the "Big lime" was developed during periods of subaerial exposure. The oil originated from accumulations of organic material in the deep Crockett County basin east of the pool.

Bedded dolomites in the Permian Basin were formed by the alteration of metastable limestones by hypersaline brines refluxing from evaporate lagoons. The hot, heavy, highly alkaline, carbon dioxide-free, magnesium-supercharged brines displaced connate waters to provide both a chemically favorable environment for magnesium-calcium exchange and a vehicle for removing displaced calcium. Fossil lagoonal brines and fillings of halite and anhydrite in the dolomite pores offer proof of the brine invasion. Sedimentary dolomites in other areas are commonly associated with evaporites, and for these dolomites a similar origin is postulated.

The thick series of redbeds along the eastern edge of the southern Permian basin is divided into groups and formations that can be recognized both on the outcrops and in the subsurface. Gradations between nearshore, marine, and retricted sea deposits are recognized and described, and unconformities in the section are traced out into the basin. The Triassic-Permian boundary line is re-defined as occurring between the top of the newly defined Dewey Lake redbeds and the base of the overlying Tecovas silts.

It has been stated that no commercial accumulations of petroleum have been found in areas where the controlling structure is a simple terrace in the reservoir sand. That is, in all pools located on apparent terraces, trapping is caused by buried closure or by variations in the porosity of the reservoir rock.(FOOTNOTE 3) In most instances, this is undoubtedly true. However, pools are known in which open terraces are the only causative structures for retaining the oil in place. The Wheat pool is believed to be an example of this type. A description of the geology is followed by suggestions as to the possible origin and maintenance of such an accumulation.

The Ochoa series includes the uppermost Permian deposits of the southwestern United States. Most of the rocks included in the series are poorly exposed unfossiliferous evaporites. The well known subsurface section in and around the Delaware basin is described and illustrated by cross sections. A short chapter discusses theories on the origin and distribution of the characteristic evaporites.

The writers advocate the classification of the American Permian as a system composed of four series, named, from oldest to youngest, the Wolfcamp series, the Leonard series, the Guadalupe series, and the Ochoa series.