Abstract: The Bannock overthrust in southeastern Idaho and northcentral Utah was originally described by Richards and Mansfield (1912) as a single large thrust fault that formed at the close of the Laramide orogeny and was folded by renewed compression near the end of Pliocene time. Later Mansfield expanded and revised his interpretation of the Bannock overthrust so that at least the northern part of the overthrust was thought to be a thrust zone in which the individual faults originated in a folded sole thrust. Detailed mapping in areas critical to Richards and Mansfield's interpretations has shown that the faults thought by them to be parts of one large thrust are separate faults, and that, although some of the thrust surfaces are curved, they were not folded in Pliocene time but probably were folded during a late stage of the thrusting. Extensions of the Bannock thrust to the north, south, east, and west based upon extrapolation of a single large folded thrust surface are not warranted. The Bannock overthrust is reinterpreted as a westward-dipping imbricate thrust zone possibly several tens of miles wide extending at least from southwestern Montana to north-central Utah. It is recommended that the name "Bannock overthrust" no longer be used, and that this zone of imbricate thrusts in the southeast corner of Idaho be called the Bannock thrust zone. The thrusts range in age from Late Jurassic to post- Early Cretaceous and are progressively younger from west to east; strong regional compressive forces do not appear to have been active in the area as late as Pliocene time. The upper plates of the thrusts moved to the northeast in response to an unknown force. Steep eastward-trending tear faults formed during thrusting probably in response to differential movement among the eastward-moving thrust plates. In Tertiary and Quaternary time ...
From page 127: For the last few years Mr. Henry E. Lee, of Rapid City, S.Dak., has been sending me selected material from the lower part of the Lance formation of Harding County, S.Dak., the exact locality being what is locally known as the Jump Off, an erosion basin of the headwaters of the South Fork of the Grand River, 10 miles north of the East Short Pine Hills. 1 The matrix is a soft gray friable sandstone, and consequently only the coarser, more resistant plants are preserved. In view of the coarseness of the matrix the preservation is excellent, although usually the finer details of venation are obscure. In the sands overlying the plant beds are thin seams of impure lignite.
From introduction: The fossil plants described in the present report were collected at the north end of Grand Coulee during the summer of 1927 by Messrs. T. A. Bonser, F. A. Roberts, and Walter Bruce, of Spokane, and F. W. McCann, of Coulee City. The locality is in the big bend of the Columbia River near the northern boundary of Grant County, Wash., about 85 miles west of the plant-bearing Latah sediments around Spokane. The outcrop in Grand Coulee is about the same distance east of the crest of the Cascade Mountains, about 100 miles northeast of the plant beds at Ellensburg, which are of approximately the same age, and some 200 miles west of beds in Idaho yielding a similar flora and assigned to the Payette formation by Knowlton and others.
Abstract: The author describes 75 species of plants from the Miocene of about 30 localities in Idaho. These plants represent 40 genera in 28 families and 17 orders, and the most common types are species of Acer, Quercus, Populus, Betula, and Laurus. There are 2 ferns, 3 monocotyledons, and 70 dicotyledons, 18 of which are no longer present in the northwestern United States. There are some xerophytic types, but the majority are mesophytic, possibly indicating a mixture from different altitudes. The beds are correlated with the Latah formation and considered to be of upper Miocene age.
From introduction: The geologic record of the Tertiary period in the Green River Basin of southwestern Wyoming consists, in a broad way, of two quite different parts. The history of the first part, lasting through the Eocene epoch and perhaps on into the early Oligocene, was recorded in a thick series of sedimentary rocks of fluviatile and lacustrine origin. The history of the second part was recorded chiefly by successive stages of stream planation and stream trenching, but also in part by fluviatile sedimentation and, in certain localities, by glacial deposits. The first part of the record is virtually continuous, though its interpretation is by no means simple and obvious. The second part of the record is distinctly fragmentary, and the evidence the fragments provide is difficult to evaluate and to integrate.
Abstract: The identification of new collections of fossil plants from the Green River formation of middle Eocene age made it necessary to reexamine the megascopic types of the Green River flora. This study resulted in the reassignment of some species and the rejection of such species as were based on fragmentary, indefinable specimens. The recent collections yielded 22 new species. Exclusive of the microscopic forms of thallophytes and pollens, the flora now numbers 135 megascopic species that are considered to be recognizable and distinctive. The new elements found in the flora do not alter the previously expressed opinion that the megascopic Green River flora lived in a warm-temperate well-watered environment.
From introduction: The history of glaciation in Alaska offers a fascinating field for study. Because of the remarkable development and easy accessibility of valley and piedmont glaciers in the coastal mountains, Alaska has long been popularly conceived as a land of ice and snow, a concept that is only slowly being corrected. To the student of glaciation, however, Alaska affords a unique opportunity to observe the formation, movement, and dissipation of the many living glaciers, to examine the results of glacial erosion on a gigantic scale, and to discover and work out the sequence of Pleistocene events as shown by the topographic forms in both glaciated and unglaciated areas and by the deposits left by ice and water during earlier stages of glaciation.
From introduction: In the following report the species of Foraminifera found in the Miocene of the Coastal Plain region of the eastern United States from Florida to Maryland are described and recorded. Numerous papers have been published on this region, some of which, however, are largely lists. Where the original material on which a paper was based has not been available for the present study, the records have been omitted, as it is very difficult to place the species in their proper position without seeing the actual specimens.
From abstract: The thesis of this paper is that the anhydrite cap rock of salt domes originated by the residual accumulation and consolidation, on top of a salt stock, of sedimentary anhydrite freed from the salt by solution of the top of the stock. This hypothesis is compared with that of origin from a bed of sedimentary anhydrite supposed to have overlain the salt of the salt stock in depth and to have been forced up on top of the stock as it rose. The strongest basis for the hypothesis of residual accumulation is the presence, between the anhydrite cap rock and the top of the salt stock on many salt domes, of a flat solution surface, the "salt table," decapitating anhydrite-bearing folds in the salt. The paper considers other general geologic evidence and internal petrographic evidence with a view to ascertaining to what extent they confirm or at least fit this interpretation.
From abstract: The Santa Monica Mountains lie only a few miles northwest of the city of Los Angeles and comprise one of the prominent structural features that adjoin the Los Angeles Basin, one of the most prolific oil-producing districts of California. Even though the eastern part of these mountains may yield no oil, information concerning the rock types, structural character, and detailed geologic history of this area should be of value to petroleum geologists. The area described in this report, which lies between Topanga Canyon on the west and the Los Angeles River on the east, presents a section of varied rock types including coarsely crystalline plutonic rocks, basic and acidic intrusive and pyroclastic rocks, metamorphic slate and schist, and a wide assortment of sedimentary rocks.
From introduction: From the time of the publication of the Leadville monograph 2 by the United States Geological Survey, in 1886, the general geology and stratigraphy of the Mosquito Range around the Leadville and Alma districts have been known. In the recent resurvey of the area, however, it has been found necessary to undertake much more detailed studies of most of the formations. In particular, the sediments of Pennsylvanian age and the overlying red beds have received considerable attention and thought. This study was necessary to determine the amount of displacement along some of the notable faults and the depth to older strata that had contained valuable ore deposits in the larger mining districts. In some places the outcrops appear to have been improperly correlated in the older reports. These were given additional study, and considerable revision of stratigraphic sections has been necessary.
Abstract: This paper describes the mollusks and echinoids found in limestone dredged from ditches along the Tamiami Trail in southern Florida, in the area mapped as "Lostmans River limestone (Quaternary)" by Sanford but included in the Pliocene Caloosahatchee formation by Cooke and Mossom on the evidence of these fossils as identified by Mansfield. The matrix of the fossils is unlike the typical Caloosahatchee formation, which is sandy, but the fauna is closely related to that of the upper part of the Caloosahatchee formation and is regarded as a facies of the Caloosahatchee. The fauna shows considerable resemblance to that of the Imperial formation of California but may not be contemporaneous with it.
From introduction: This report deals with the stratigraphic and ecologic significance of Foraminifera contained in a Tertiary sequence that crops out in the northern part of the Olympic Peninsula, Wash. (pl. 1). The work was done as a part of a program of geologic investigations for oil and gas possibilities conducted by the U.S. Geological Survey.
From introduction: In the spring and early summer of 1950 the writers undertook an investigation of the outcropping Permian rocks in northeastern Arizona, northwestern New Mexico, and parts of southern Utah. This work had as its specific objective the establishing of correlations of Permian rocks in the Zuni uplift, Defiance uplift, and Monument Valley upwarp. The determination of these relations, it is believed, will be of aid in the current activities of the Geological Survey in the Navajo Reservation which have as objectives the investigation of the mineral fuels and water resources of the area.
From introduction: This paper describes a small fossil flora from the vicinity of Leadville, central Colorado. The beds from which the flora was collected have long been referred to as the "Weber formation ", though with considerable doubt on the part of many geologists that all the beds so named in Colorado are correlative with the Weber quartzite of northeastern Utah. In current usage these Colorado beds are designated the " Weber (?) formation."
Abstract: A new genus of the Cycadofilicales, Diichnia, is described from the New Albany shale, of late Devonian age, in central Kentucky. The one known species, which is based on stem material showing internal structure, belongs in the family Calamopityeae. Foundation for the generic segregation is seen in the double leaf truce of the genotype, D. kentuckiensis, in contrast with the originally single trace in other known representatives of the family.
From introduction: The ammonite genus Barroisiceras Grossouvre is noteworthy because of its wide geographic distribution and its apparently small stratigraphic range. It is reported from deposits of Coniacian age in Europe, Africa, South America, and North America. In the North American Upper Cretaceous it is rather rare, authentic species having been recognized hitherto only in the Austin chalk of Texas, in the Coniacian beds of Zumpango del Rio, Guerrero, Mexico, and, with doubt as to the source, in New Jersey. The Texan species, B. dentatocarinatum (Roemer), is by no means an abundant form, though among those described in early work in the region. The Mexican representatives of the genus thus far described include only fragmentary specimens not specifically named. The occurrence ascribed to New Jersey is based on a fragment that seems to belong to Barroisiceras but whose source is very doubtful.
From introduction: The main purpose of the field investigations on which this paper is based was to determine the structure of the mountains. The geologic formations were therefore studied, and sufficient data were obtained to construct a combined areal and structural map.
From abstract: This paper is a continuation of the study of the kaolin minerals, in the first part of which, published in 1931, the kaolin minerals kaolinite, dickite, and nacrite were described. In that paper the application of chemical, optical, X-ray, and dehydration methods to the investigation of clay materials were discussed. The present study shows that halloysite is a fourth mineral of the kaolin group, closely related to but distinct from kaolinite. The chemical, optical, X-ray, and dehydration properties of a representative group of halloysites are recorded, all these being new data determined by the authors on separate portions of single samples whose purity has been carefully tested.
More than nine-tenths of the Upper Cretaceous rocks in northeastern Wyoming are fine-grained shales, mudstones, and calcareous marls. A comparative study of the mineralogy, chemical and mechanical composition, density and porosity, fissility, and lamination of samples of these rocks discloses several relations that throw light on the geologic history and structural deformation of the region, and perhaps on its oil and gas possibilities.
Abstract: By grinding minerals under water it has been found that they yield relative and reproducible measurements of the hydrogenion concentration resulting from their hydrolysis. Many silicate minerals and two glasses have been studied in this way by a colorimetric method of determining hydrogen-ion concentration, and some of them have been studied more quantitatively by means of the hydrogen electrode. The results of these tests are a rough index of the weathering qualities of different silicate minerals. The effect of silicate minerals on underground waters and upon geochemical changes is discussed.
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