Showing papers in "The Journal of Geology in 1939"

Creep of Rocks

Abstract: "Creep" is the name applied to the slow deformation of solids under small loads acting over long periods of time. Two types of apparatus have been developed for the purpose of investigating the creep of rocks in response to stresses below the "elastic limit," as ordinarily defined. The present paper describes results obtained with these instruments during runs of various duration, up to 550 days. It is found that in many cases there is measurable flow at stresses below the "elastic limit." An empirical law has been derived which resolves this deformation into two types of flow, termed "elastic flow" and "pseudoviscous flow." The creep characteristics of several materials at room temperature and atmospheric confining pressure are described. Preliminary experiments on creep at high pressure and on creep by recrystallization are reported.

Preferred Orientation of Pebbles in Sedimentary Deposits

Abstract: Pebbles from glacial till, from an outwash terrace, and from a beach show characteristic preferred orientations. Methods used in collecting and measuring the pebbles are described, and the importance of two distinct concepts in orientation analysis is stressed: (1) the dip direction and dip of the longest axis and (2) the orientation of the maximum projection plane of the pebble. Methods of plotting the data are discussed, including conventional petrofabric diagrams, polar co-ordinate charts, and histograms based on azimuthal and dip frequencies. The principles of statistical analysis of the data by radius-vector summation and by conventional moment analysis are developed. The latter affords numerical data suitable for comparative studies of size, shape, and other attributes with preferred orientation, and permits the development of isopleth maps showing areal variations of preferred orientation.

Viscosity of Lava

Abstract: Palmer, by assuming that the Alika flow of Hawaii when liquid was turbulent, found that its viscosity was 15 times that of water. Becker, who also assumed turbulent motion, found that the viscosty of the 1840 flow of Hawaii was 60 times that of water. Dimensional analysis, however, proves that these flows moved with laminar motion and therefore the viscosities computed by Becker and Palmer are in error. By using the Jeffreys formula, the viscosity of the Alika flow is found to have been about 287,000 times the value calculated by Palmer. The specific gravity, the thickness, and the gradient of the last 6 miles of the Mc-Cartys flow are known. If it is assumed that the viscosity was similar to that of the 1887 flow of Hawaii, the velocity in this area, calculated by the Jeffreys formula, is 4.8 miles per hour. This figure, together with a consideration of the flow mechanism of the flow, indicates that it covered the last 6 miles in about 12 hours. The volume of the last 6 miles of the flow is known, and, a...

Some Types of Bedding in the Colorado River Delta

Abstract: The subaerial portion of the Colorado River Delta may be divided on the basis of texture and structure into three principal areas. The upstream area is one of deposition during periods of low-river stage only, and its deposits are almost exclusively fine sand, showing in vertical section intricate patterns of small-scale cross lamination formed by current ripples. The middle area is the principal site of deposition today and is characterized by many local deltas built up on the general plain. During low-river stages mud alone is deposited here, but with higher waters the mud is carried beyond and fine sand is deposited. The mud is structureless or flat bedded; the sand shows cross lamination either of the ripple variety or of a type comparable to the foreset beds of a simple experimental delta. The lower part of the delta, including the estuary, is entirely of mud today due to recent severance of direct connection between the river and the sea. The deposits are uniformly flat bedded except where erosion c...

Triassic Fault-Line Deflections and Associated Warping

Abstract: Associated with major faults in the Triassic areas in the eastern United States are some well-known warped structures in the relatively downthrown blocks. Much of the warping appears to be related to deflections of the fault lines. Adjacent to salients- fault-line deflections whose outlines are convex toward the dropped blocks-occur anticlinal warps; adjacent to re-entrants occur synclinal warps. The theory is proposed that, during faulting, irregularities of fault surface have caused differential movement, resulting in warping. The salients are lag points, where movement of the downthrown blocks has been least; the re-entrants are advance points, where movement has been greatest. Tentative explanations are offered for a number of the individual structures. An attempt is made to test the theory by examining part of a Triassic area in which a fault-line boundary has not previously been described. In addition, some data from other areas, outside the Triassic, are included as partially supporting evidence.

The Miocene Humboldt Formation in Northeastern Nevada

Abstract: The Humboldt formation of northeastern Nevada consists of 5,800 feet of continental deposits which range in grain size from coarse fanglomerate to fine shale and in composition from lake deposits of limestone and oil shale to stream-laid conglomerate, sandstone, and mudstone interbedded with fine pyroclastics of water-laid and air-borne types. These beds may be divided into three members: (1) a lower member, mostly lake beds; (2) a middle member characterized by ash and tuff beds; (3) an upper member, mostly stream-laid deposits. Vertebrate and plant remains indicate a late Miocene age and an environment more humid than the present. The formation occupies basins separated by northward-trending fault-block mountains. It was originally deposited in a large irregular depression or a series of connected intermontane basins, which have become basins of sedimentation through warping or faulting. In the area considered, some of the basin and mountain blocks have been outlined by faulting during deposition of the...

Volcanic Centers of the Sunlight Area Park County, Wyoming

Abstract: The Sunlight area is located in the northern Absaroka Mountains of northwestern Wyoming. The rocks are dominantly Tertiary pyroclastics and basalt flows which rest on flat-lying Paleozoic limestones. The pyroclastics were thrown out from a large number of vents in explosive eruptions and were later modified by mud flows. Two major volcanic centers and one small explosive vent have been found in the Sunlight area. Intrusions of stocks, laccoliths, plugs, cone sheets, and radial dike systems are closely related to the volcanic centers. The radial dikes were formed by magma moving horizontally outward from the intrusive centers in vertical cracks. The Sunlight centers are similar in many respects to the Scottish Tertiary volcanoes. The rock types in general show a normal differentiation series from olivine gabbro and basalt through diorite and andesite to sodic syenite and trachyte. Several unusual orthoclase-bearing basalts, known as the absarokite series, are also present.

Multiple Alpine Glaciation in the Leavenworth Area, Washington

Abstract: In this area there is evidence for three successive Pleistocene glaciations, each of which was less extensive than the preceding one. The first two glaciations were separated by a long interval. The third is fairly well established as a distinct event but may possibly represent a phase of the preceding stage. In any case the third glaciation is undoubtedly equivalent to all or to part of the Wisconsin stage.

Mass Transportation of Sediments on Subaqueous Terraces

Abstract: Sand ridges having a steep slope on one side and a gradual slope on the other occu on some subaqueous terraces in Lake Michigan which have a plentiful supply of sand The origin and behavior of these ridges is explained in connection with one class c beach cusps. A similar subaqueous mass movement of sand on a larger scale is describe! as it occurs off a large cuspate projection such as a cape. An understanding of the be havior of subaqueous dunes is important in explaining the common occurrence of cross bedding, the preservation of ripple marks and other bottom irregularities, and the em bedding in sediments of organic remains and other objects.

Physiographic Subdivisions of the San Luis Valley, Southern Colorado

Abstract: The San Luis Valley in south-central Colorado has heretofore been considered a single physiographic unit. In this paper are described five distinct geomorphologic subdivisions of the valley together with the fundamental geologic history which gave rise to the characteristics of each subdivision.

Structural Features of a Landslide near Gilroy, California

Abstract: Structures produced by plastic flow in a recent large landslide near Gilroy, California, are strikingly similar to certain structures produced on a larger scale in the deformation of rocks. Fracture patterns along strike-slip faults, and successive normal faults due to tension and rotation, are especially well displayed. Well-defined grabens were formed where the slide overrode small hills. Local compression has produced fractured anticlinal ridges. Relations of these structures to the slide's movement and to the original topography are discussed with the aid of detailed maps.

Loch Borolan Laccolith, Northwest Scotland

Abstract: The scattered literature relating to this eruptive mass has been brought together and condensed into a connected account. The main part of the mass has the form of a laccolith which appears to rest on a floor of limestone. The silica content of the rocks decreases progressively from the top to the base of the laccolith, and the rocks near the base develop melanite, diopside, and nepheline. The variety known as "borolanite" contains also what appear to be pseudomorphs after leucite. Fundamental problems of petrogenesis are involved in the interpretation of the evidence.

An Exhumed Erosion Surface in the Jemez Mountains, New Mexico

Abstract: The plateau-like surface of San Pedro Mountain in the northwestern part of the Jemez Mountains of New Mexico is a remnant of an exhumed erosion surface. It is overlain in places by a thin veneer of chert, here named the Pedernal chert, with underlying gravel. The chert and gravel are a part of a thin wedge of Tertiary beds which thickens eastward and extends across the northern spurs of the Jemez Mountains. The rocks of the wedge are correlative with the El Rito formation, Abiquiu tuff, and Santa Fe formation, found in the Rio Grande depression east of the border faults of that trough. The stratigraphy and structure of the Tertiary sedimentary rocks of the wedge reveal in some detail the history of the deformation of the Rio Grande depression. The mountains formed during the Laramide revolution were reduced in early Tertiary time to a low-lying erosion surface or peneplain. A slowly subsiding basin then formed and was maintained until late Tertiary time, when it was broken by the normal faults which now b...

Modes of Retreat of the Pleistocene Ice Sheets

Abstract: The Pleistocene ice sheets receded by melting, evaporation, and calving in the marginal belt, while the ice surface in the interior was lowered by evaporation and outflowage of ice. The wastage decreased from the edge toward the center. The zone of melting ranged perhaps from 25 to 100 or more miles in width. For the most part the retreating ice sheets had a firm, continuous, gently to steeply rising edge; but especially in transversal valleys, separated by high ridges, there was formed a belt of stagnant ice, rarely, if ever, as much as 10 miles broad. Contrasting of "downwastage" with "recession" has no physical basis.

Gravitational Accumulation of Olivine during the Advance of Basaltic Flows

Abstract: Late Tertiary basaltic flows in southeastern Oregon show locally a surface depletion and a basal concentration of olivine above a chilled basal zone containing scattered phenocrysts of that mineral. Field and laboratory evidence indicates that the mafic grains gradually accumulated in a manner somewhat analogous to the deposition of sand at the delta of a river.

Properties of Saturated Aqueous Solutions of Potassium Chloride at Temperatures above 250° C.

Abstract: Equilibrium pressures of the three-phase system-steam, solid KCl, and saturated aqueous solution-have been determined between 250° and 600° C. A maximum pressure of 225 atm. is found at 565o C. This maximum is evidence that critical phenomena do not occur in aqueous solutions saturated with solid KCl. The specific volume of solid KCl and the apparent volume of water in the saturated solution were also determined. From the measured volumes and certain assumptions about other properties of the system, the specific volume of the liquid phase and the volume change and latent heat in the reaction: Steam + Solid KCl $$\rightarrow$$ Saturated liquid solution, were evaluated.

"Lyell" Gully, a Record of a Century of Erosion

Abstract: Sir Charles Lyell, when he visited the United States in 1846, published a description and a woodcut of a gully which he observed near Milledgeville, Georgia. Several photographs and statements give subsequent information on the gully since 1846. Similar gullies are widespread in the Piedmont area, many of which have been studied by the writer. An accurate survey and detailed study of the gully using physiographic evidence, the age of old pine trees in the gully, and the details of Lyell's description make it possible to reconstruct the conditions of 1846 and to interpret the changes since that date. As the gully was 20 years old when Lyell saw it, there is thus a documented history of over no years of erosion.

Late Quaternary Upwarpings of Northeastern North America

Abstract: The crustal upwarpings upon decrease and removal of the load of the last Labradoran ice sheet appear to have occurred spasmodically and intermittently during ages of several hundred to a few thousand years' duration, separated by somewhat longer ages of quiescence. The most important uplifts took place prior to, and during, the first stages of the glacial lakes Algonquin and Iroquois, during the Champlain Sea age, and during the early and the late Postglacial. With the exception of that during the Nipissing age, the long quiescences were caused by increase of the ice or by a balance between supply and wastage; and, when established, they prevailed until the accumulating stresses had increased to the yielding point. The most important quiescences were those during the deglaciation of New England (perhaps regionally equal uplift); during the three-outlet stage of Lake Algonquin, Lake Iroquois proper, and Lakes Vermont and Frontenac; during the Ottawa Sea (possibly some land sinking); and during the Nipissin...

Frozen Ground in Siberia

Abstract: Permanently frozen ground underlies 3,728,900 square miles of Soviet territory, largely in eastern Siberia. Ice is not always present, but temperatures remain below 0° C. to depths down to 890 feet. In some places unfrozen layers are found between frozen ground. Most frozen ground has acquired its low temperature from the atmosphere.

The Howell Structure, Lincoln County, Tennessee

Abstract: A small area of highly disturbed, contorted, and brecciated strata centering at Howell, in north-central Lincoln County, Tennessee, has been mapped and studied in detail The salient structural feature is a circular area of intensely deformed Black River and Trenton rocks, which have been uplifted approximately 100 feet above their normal positions This circular area is composed of jumbled blocks of limestone imbedded in a matrix of shatter breccia The major deformation is believed to have been post-Trenton and pre-Fernvale in age Overlying the shattered strata is the Fern vale formation, the relative thickness and lithology of which point directly toward deposition in a graded crater The Fern vale shale unit shows moderately high dips This partial disturbance of the Fernvale possibly indicates a mild renewal of the forces which caused the major deformation The younger Silurian and Mississippian formations are relatively undisturbed A magnetic survey indicates a "closure" of 335 gammas, 1 3/4 miles

A Phytosaur in Union County, New Mexico with Notes on the Stratigraphy

Abstract: A skull of the phytosaur Machaeroprosopus, discovered in the Sloan Canyon formation, confirms the Triassic age of the rocks lying beneath the Exeter (Jurassic) in the valley of the dry Cimarron River of Union County, New Mexico, and Cimarron County, Oklahoma. The underlying red beds, the Sloan Canyon formation, and the Sheep Pen Canyon formation form a continuous and conformable succession of strata in this region, and the conclusion is drawn that these three units should be included in the Dockum group.

Detailed Geological Mapping and Fault Studies of the San Jacinto Tunnel Line and Vicinity

Abstract: In driving the 13-mile San Jacinto Tunnel on the Colorado River Aqueduct water was tapped in a fault intersected a short distance from the Potrero shaft. A geological investigation was made in an effort to determine whether additional faults were present in the mountain mass to be penetrated by the tunnel. The use of aerial photographs facilitated structural studies and geological mapping of the area. During the course of this survey, a number of faults were identified which were expected to be sources of difficulty in driving this tunnel. The geological features involved in a change in the alinement of the tunnel and the location of an additional access to expedite the completion of the tunnel are herein described.

The Status of Cephalaspis Schrenckii Pander from the Upper Silurian of Oesel

Abstract: Cephalaspis schrenckii Pander is a Silurian ostracoderm generically distinct from both Cephalaspis and the forms to which the term Tremataspis is usually applied. Under strict application of taxonomic law this species is the genotype of Tremataspis. This would result in confusion; it is advocated that the rules be suspended and C. schrenckii be made the type of a new genus, Witaaspis.