On August 11, 1960, sixty oil exploration and research seismograph crews attempted to record two shots detonated in the Texas Gulf Coastal Plain. Shotpoint A was located 16 miles northwest of Cleveland, Texas. Shotpoint B was located 27 miles northwest of Victoria, Texas. The shotpoint line is approximately parallel to the strike of the Cenozoic sediments and the distance between shot points is 260.2 km. More than 3,000 pounds of explosives were placed in five holes at each shot point. The top of the charge was at a depth of 95 feet and the bottom at 250 feet at each shot point. The regional Bouguer anomaly is -25 mgal. The shot instant was keyed to a 140 cps reference signal transmitted by radio station KTRH, Houston, Texas. First and later refracted arrivals were used to determine the velocity structure which was supported by events identified as reflections from the refractors. The results indicate the following thickness-velocity relationships: 2.0 km of 2.3 km/sec material, 5.3 km of 3.94 km/sec material, 12.5 km of 5.38 km/sec material and 13.2 km of 6.92 km/sec material. The Mohorovicic discontinuity is represented by a velocity of 8.18 km/sec and the total crustal thickness is 33.0 km. The geologic identity of the refractors has been interpreted as follows: The 2.3 km/sec and 3.9 km/sec layers represent the Cenozoic and Mesozoic sediments, the 5.4 km/sec layer represents the Paleozoic and Precambrian rocks, the 6.9 km/sec layer represents the transition zone and the 8.18 km/sec zone represents upper mantle material. It is apparent that the Texas Coastal Plain has been growing outward over the oceanic area for long geologic time and that this outward growth has been accompanied by a thickening of the transition zone (6.9 km/sec layer). The behavior of the transition zone is believed to be intimately connected with the regional tectonics of the Texas Coastal Plain-Llano area.

Extended reconnaissance over 700 square miles of the Pahranagat, Alamo and Hiko Ranges has revealed that more or less continuous emission of fissure type nuees ardentes has been punctuated by periods of fluvio-lacustrine deposition of reworked volcanic ejecta. Use of the exceptional value of ignimbrites as stratigraphic-structural datum planes, and the presence of fresh water limestones and water-laid tuffs, demonstrate that the nuees were extruded over deformed Paleozoic rocks during Oligocene-Miocene time under conditions of gentle topography and at least greater humidity than exists today. Furthermore, the volcanic rocks themselves were extensively faulted as part of the formation of the Basin and Range structures.

Abstract Not Available.

Cylinders of sand crystals, composed of single crystals of calcite that poikilitically enclose detrital grains, and calcite-cemented sandstones from the Tensleep (Pennsylvanian, Wyoming) and Supai (Permian, Nevada) formations were experimentally deformed dry at confining pressures of 1--5 kilobars and temperatures of 150°--300°C. Thin sections of the undeformed and deformed specimens were studied microscopically to gain a better understanding of the behavior of sandstones in simulated tectonic environments. The calcite and the detrital grains (quartz, feldspar, and others), which have radically different physical and mechanical properties, are shown statistically to have deformed with respect to the principal stresses across the boundaries of the whole specimens rather than with regard to local stress concentrations at grain contacts.

Three major rivers supply the bulk of the clay mineral matter to the northeastern Gulf of Mexico. The type of clay supplied is a function of the clay minerals in the soils of the source basins and appears to be largely climatically controlled. The westernmost major river, the Mississippi, is supplying a very large amount of richly montmorillonitic clay. In an easterly direction kaolinite gradually becomes more abundant in the soils and rivers; and the Apalachicola River, at the eastern extremity, is contributing a clay mineral suite very rich in kaolinite with much less montmorillonite. The Mobile River is geographically and clay mineralogically midway between the Mississippi and Apalachicola rivers. As clay from the Mississippi and Apalachicola rivers enters saline water, a very slight relative increase in the proportion of kaolinite to montmorillonite occurs. As yet this slight increase has not been explained satisfactorily. In the Apalachicola River, it may be the product of a minor size separation combined with a loss of swelling properties by some of the stripped mica portion of the clay. This slight change, which may be in part a response to changing chemical environment, is of a much smaller order of magnitude than the river to river change in the relative abundance of montmorillonite and kaolinite. The relative magnitude of the two effects should be kept in mind in deciphering paleogeography on the basis of clay minerals. Once the clays have been delivered to the Gulf of Mexico, the distribution of that portion of the clay not flocculated by the saline waters at the river mouths is governed first by the shallow water, wind-driven currents, and then by the semipermanent oceanic currents. The eventual distribution of the clays follows a gradational facies pattern in which the sources of supply and the distributional directions are clearly evident. When viewed in regional aspect, the study of clay mineral distributions in ancient unmetamorphosed sediments should form a valuable adjunct to conventional paleogeographic methods.

In spite of the extensive micropaleontological literature, there has been little systematic study of the second most stratigraphically useful microfaunal group---the ostracoda---from the type areas of the Jackson group. Many ostracodes have been described from the Jackson or its age equivalents in adjacent states, but for some reason those from the type sections of the Jackson have been neglected. It is the essential purpose of this paper to rectify this neglect and to provide another link in the chain of studies of the important Jackson faunal groups in the eastern Mississippi embayment.

Abstract Not Available.

The Cretaceous Dakota Sandstone is a land-derived, relatively unfossiliferous lithogenetic unit which occurs over a large part of the western interior of the United States and Canada. Its thickness over most of this area does not exceed 600 feet. In many places it disconformably overlies a former land surface comprised of a variety of formations and rock types, from Precambrian granites to Late Jurassic mudstones. Above the Dakota, and conformable with it, is a marine black shale whose name and age vary from place to place. Thus the Dakota records the passage of an ancient shoreline over a large part of the western interior of the North American continent, the last large-scale invasion of the craton by marine waters. The purpose of this study is the reconstruction of sedimentary environments and determination of geologic history from deposits of the Dakota Sandstone in northwestern Colorado. Close study should reveal the presence of several continental, marginal, and marine deposits within the unit.

The massive, white, dense siliceous rocks forming the prominent relief of the Ouachita Mountains and the Marathon Basin have been the subject of recurrent speculation for 100 years. Although this thin siliceous sequence is exposed in only two areas, it nevertheless has received international attention as a classical example of siliceous sedimentation. The white rocks were named novaculites in 1819 (Croneis, 1930) from their exposures in the core of the Ouachita Mountains; however, the name has since become a stratigraphic term to include the entire siliceous sequence which is underlain and overlain by varicolored sandstones, shales and limestones.

The purposes of this investigation were to determine the effect of chemical weathering on the distribution of thorium and uranium in a single weathering profile, and to investigate the distribution of these elements in a single, well-defined, and extensive shale body. Particular objectives were to determine the manner in which thorium and uranium may occur in source rocks and in sediments, particularly shales, and to relate the variations in the distribution of thorium and uranium in a shale to the fundamental geological processes. For these purposes 13 samples were collected from a Pennsylvanian weathering profile and more than 150 samples from the Upper Cretaceous Mancos shale. Most of these samples have been analyzed for thorium, uranium, and potassium by radiometric and chemical methods.