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An inventory of geologic mapping in the continental United States shows the areal extent of published geologic maps, differentiated by scales, and gives the results of calculations of the approximate number of square miles geologically mapped in each State on several scales, with separate figures for the maps published since 1919. Several graphs compare the progress of geologic mapping in the different States and in different countries.
The lavas of the Hawaiian Islands range from mafic picrite-basalts and melilite-nepheline basalts to salic trachytes. Olivine basalt, by far the most abundant type, is regarded as representing the parent magma of the Hawaiian province. Closely associated with the olivine basalts are basalts, and picrite-basalts with many large phenocrysts of olivine. Further differentiation results in eruption of andesine andesite, oligoclase andesite, picritebasalt with abundant large augite phenocrysts, and more rarely trachyte. Following a long period of quiescence there have been erupted on some islands nepheline basanite, nepheline basalt, melilite-nepheline basalt, “linosaite,” and a third type of picrite-basalt. The mineral and chemical composition of the various rock types, and their distribution on the individual islands, are described. Starting with olivine basalt as the parent magma means of deriving the other rock types are considered. It is concluded that crystal differentiation has been the principal process, although assimilation of limestone may also have been important. The parts played by gaseous transfer and selective remelting are difficult to evaluate, though both probably operated to some extent. Comparison of the types of igneous rocks in the Hawaiian province with those recorded from other Pacific islands shows that the rocks throughout the true Pacific Basin are, for the most part, closely similar, and suggests essential uniformity of parent magma and petrogenic processes throughout the Pacific Basin.
This paper presents four terrain diagrams, on a scale of 1:1,000,000, which cover all the Philippine Islands. The diagrams were prepared during World War II by the Military Geology Unit of the U. S. Geological Survey for the Chief of Engineers, U. S. Army. Terrain features shown on the diagrams owe their individuality to the nature of the rock formations and the tectonics. Mountain areas are made up of pre-Tertiary basement rocks, and of Tertiary and Quaternary volcanics; Tertiary and Quaternary sediments from the lowland areas. The mountain areas of basement rocks are geanticlines or horsts, and the lowland areas of Tertiary sedimentary rocks are downwarps. A striking tectonic feature, which has strongly influenced the terrain, is the Philippine fault zone, a belt of dislocation which extends southeast from Luzon to Mindanao.
Broad paleostructural development in south-central Pennsylvania and Maryland was similar to that of central and eastern New York during the deposition of lower Middle Ordovician beds. Thick marine limestones of the easternmost belts of outcrop in the Cumberland Valley indicate the southward extension of the Champlain miogeosyncline. Thin and, in part, coarse-textured limestones in belts of outcrop just west of the Cumberland Valley indicate the extension of the Adirondack arch. Intermediate correlation shows the development of a relatively shallow platform east of the Adirondack arch and marginal to the Champlain miogeosyncline during part of the Bolarian (Kay, 1947) and Trentonian epochs. Detailed description, definition and correlation of the stratigraphic units are presented. The Pinesburg and Fannettsburg members (new) of the Shippensburg formation (redefined), the Housum and Kauffman members (new) of the Mercersburg formation (redefined), the Oranda formation (Cooper and Cooper, 1946) and the lower Martinsburg exhibit westward thinning by overlap or convergence or both from Champlain miogeosynclinal sections in eastern belts to sections on the Adirondack line in Path Valley. The Doylesburg member (new) of the Shippensburg is believed truncated to extinction southeastward from Path Valley by pre-Mercersburg regional unconformity. Argillaceous material in southeasternmost exposures of Oranda begins the Middle Ordovician transgressive clastic deposits resulting from the Vermontian disturbance. Correlations indicate Shippensburg is post-middle Chazyan to pre-Chaumont in age, Mercersburg is Rockland and Kirkfield, Oranda is Shoreham, and lower Martinsburg is Denmark.
A terminology is suggested to aid the field geologist in describing the structures of stratified and cross-stratified rock units. Qualitative terms describing the character of rock layering are stratification, stratum, cross-stratification, cross-stratum, set, coset, and composite set. Quantitative terms applying to the thickness of stratification are very thick-bedded, thick-bedded, thin-bedded, very thin-bedded, laminated, and thinly laminated. Quantitative terms applying to the thickness of units into which the rock splits are massive, blocky, slabby, flaggy, shaly, platy, and papery. A classification of cross-stratification is suggested, based primarily on whether the lower bounding surface of a set of cross-strata is one of erosion or nondeposition and, if erosional, whether it is plane or curved. Features of secondary importance in this classification are the shape of set of cross-strata, the attitude of the axis, the symmetry of the cross-strata with respect to the axis, the arching of the cross-strata, the dip of the cross-strata, and the length of individual cross-strata.
During the night of March 1 and 2, 1951, an inconspicuous group of hot springs and small mud volcanoes in northeastern California burst into spectacular eruption, unequalled by other known mud volcanoes. The eruption cloud of steam, gases, and mud particles rose several thousand feet in the air and distributed fine debris to the southeast for a distance of at least 4 miles. More than 20 acres of the hot-spring area was intensely disturbed and greatly modified by the eruption, estimated to involve at least 6 million cubic feet or 300,000 tons of mud. Several days after the eruption, the area was barely active. The eruption appears to be unique in the history of the springs.
The isotopic compositions and concentrations of lead and uranium have been determined in some separated minerals and the composite of a granite from Monmouth township, Haliburton County, Ontario. The chemical and mass spectrometric methods that were used are described. The age of the zircon from the granite is 1050 million years. Much of the lead, uranium, and thorium exists in chemically unstable and presumably interstitial phases of the granite. A comparison of the observed amounts of uranium, thorium, and lead in the various minerals with those amounts that should have been present, had these three elements existed within the minerals as closed systems, shows a non-balance of these elements in every case. It appears that the granite as a whole has closely approximated a closed system since it was formed with respect to uranium and its decay products, but has been an open system with respect to thorium and its decay products. Interpretations concerning the relationship of these data to lead ores are discussed.
Alluviation along the North and Middle Loup rivers in Valley County, Nebraska, produced a series of alluvial silt beds on which are developed five interstadial soils of Brady (?), Cary and Mankato (?), Mankato (?), early Recent and late Recent age. No deposits of Illinoian age were found and in at least one place the Brady (?) soil is superposed on a gleyed horizon developed on the Sappa formation, which overlies the Grand Island formation. Post-Yarmouth erosion removed the Sappa formation and part of the Grand Island formation at most places. The characteristic Sangamon soil was not developed on uneroded remnants of the soil of Yarmouth age because of a wet, poorly drained environment. A large collection of molluscs obtained from this gley soil supports stratigraphic evidence indicating a Yarmouth age. Alluviation during the glacial substages of Wisconsin time and soil formation during the interglacial substages were uninterrupted by erosion until after development of the soil of Mankato age. The Wisconsin deposits were dissected to below the Brady soil in places, and the resulting gullies were filled with later alluvium. The late Recent fill terrace lies 15 feet below the top of the late Wisconsin terrace. Subsequent cutting and filling in late Recent time produced another terrace 11 feet below the older terrace. The modern gully was cut during the last century.
Precambrian rocks are exposed throughout an area of about 7500 square miles in northern Michigan. Of this area, approximately 3300 square miles is underlain by relatively unmetamorphosed Upper Precambrian (Keweenawan), about 2700 square miles by metamorphosed Middle Precambrian (Huronian), and about 1500 square miles by metamorphosed Lower Precambrian (“Archean”). Flat-lying or low-dipping strata of Paleozoic age overlap the Precambrian along the east margin of the area. The metamorphism, which is shown most clearly by mineralogic changes in the Hu-ronian sedimentary rocks, especially in the iron formations and the graywackes and slates, and in the post-Huronian basic intrusive rocks, occurred during a post-Huronian-pre-Keweenawan interval of orogeny and minor granite intrusion. At least one earlier period of major, intense metamorphism of pre-Huronian age (Algoman?) is recognized. In near-by areas of Wisconsin and Minnesota, a later thermal metamorphism is related to the intrusion of the upper Precambrian Duluth gabbro and equivalent masses;it is restricted to the immediate vicinity of the gabbroic bodies. Zones of metamorphic intensity delineated by chlorite, biotite, garnet, staurolite, and sillimanite isograds or their equivalents are partly or completely developed around four nodes, two of which lie in immediately adjacent parts of Wisconsin. The zones range in width from less than a mile to about 30 miles, and metamorphism of low grade is areally dominant over that of intermediate and high grade. The principal iron-ore deposits of the region—the “soft ores”—are restricted to the lower metamorphic zones, whereas the material considered suitable as low-grade concentrating ore (“taconite”) is restricted to the areas of high-grade metamorphism. The influence of metamorphism on grain size appears to be the controlling factor. Analysis of thermal gradients inferred from the metamorphic zonation indicates that the heat required for metamorphism must have been derived from subjacent bodies of magma, but the metamorphic patterns show no clear relation to regional structure or to the exposed granitic intrusions of the same orogenic cycle. The granite is most abundant in the areas of strongest metamorphism, but field evidence shows that most of the masses were intruded after the metamorphism. Field evidence also shows that deformation and metamorphism are independent variables in the orogenic scheme for this particular region.
No abstract available.
Patches of Buffalo till record the earliest glaciation in the southwestern Wind River Mountains. In places, these rest in youthful valleys cut in high gravel terrace. Two other younger and lower terraces are both topographically and stratigraphically associated with Buffalo till, which may indicate that the Buffalo advance was compound. The pattern of well-preserved moraines shows that during both Bull Lake and Pine-dale time the west-central portion of the range was covered by a mountain icecap from which piedmont glaciers flowed to the floor of the Bridger Basin. In the southern part of the range the glaciers were confined to valleys. Bull Lake stage is clearly double; two large, weathered, and modified moraines are present in several valleys. Each is associated with an extensive outwash plain and valley train. The Pinedale stage is recorded by massive, fresh, slightly modified moraines behind which are many recessional moraines. Extensive outwash aprons lead outward from the massive Pinedale moraines, and a small lower terrace can be traced through the main Pinedale moraine to the recessional loops. In several upper valleys well-formed slightly weathered small moraines of the Temple Lake stage occur within 2 miles of cirque head-walls. A terrace below the younger Pinedale outwash is correlated with the Temple Lake stage. In sheltered cirques, small very fresh moraines, probably from the Little Ice Age, occur upstream from the Temple Lake moraines and a few yards from existing small glaciers. The sequence of glacial deposits in this region is typical of many ranges in the Rocky Mountain region. Outwash terraces of the Bull Lake, Pinedale, and Temple stages have been traced down the Big Sandy valley nearly to the Green River and down the Sweetwater valley to the North Platte. Thus the Green-Colorado and Platte-Missouri drainages are linked across the Continental Divide by means of traceable outwash deposits. Eolian action was pronounced in the Eden valley during Bull Lake, Pinedale, and post-Pinedale time, and in the East Fork valley during Pinedale time. Frost action features record two phases of intensity in areas formerly covered by Pinedale glaciers: an earlier phase synchronous with the Temple Lake advance, a later during the Little Ice Age. Pollen profiles in the Eden valley show a climatic change during post-Pinedale time, notably a grass maximum which was probably contemporaneous with the Temple Lake advance and the occupation of the Finley site by Early Man.
Silt mantles the upland slopes and ridge tops throughout the unglaciated interior of Alaska, reaching maximum thickness along the north side of the Tanana River Valley. The silt is probably loess deposited during glacial advances by south winds blowing from the glaciated Alaska Range across outwash plains in the Tanana Valley. In the Fairbanks area, where it is best exposed, the upland silt is 1–80 feet thick on tops of low hills, 50–150 feet above the valley floor. It is 10–100 feet thick on middle slopes of higher hills and thins to a few feet on the higher slopes of ridges 800–2000 feet above the valley. Much silt has been reworked and moved by stream erosion into valley bottoms where it forms a fill 10–300 feet thick. The upland silt is well sorted. The texture and mineral composition are uniform throughout the Yukon-Tanana upland, whether the silt overlies schist, chert, granite or basalt. The silt stands in sheer cliffs and is massive, showing little or no stratification. During the past 50 years, fluviatile, marine, estuarine, lacustrine, residual, and eolian hypotheses have been proposed to explain the origin of the upland silt. The fluviatile marine and estuarine hypotheses never had strong support, but the lacustrine concept was popular in the early part of the century. Most of the upland silt is considered to be wind blown, derived from glacial outwash because: (1) it occurs as a surficial mantle (2) it is lithologically independent of the underlying material, (3) stratification is indistinct or absent, (4) it is associated with sand dunes and ventifacts, (5) it contains fossils of air-breathing land animals, (6) the sorting and texture are similar to upper Mississippi Valley loess and wind-blown dust, (7) the grains are angular and relatively fresh, and (8) loess is being deposited in the region today.
Mihara Yama is the active central cone of O Shima Volcano on the island of O Shima, Tokyo Prefecture, Japan. The outer slopes of O Shima Volcano compose most of the island. Their crest is a somma, about 600 km in altitude and 3 km in diameter, which encloses a caldera. Mihara Yama rises from the southern part of the caldera to an altitude of 755m. It is a truncated cone with a crater 800 m in diameter. Before the eruption in 1950 the crater contained an inner pit approximately 300 m in diameter and 165 m deep. Mihara Yama erupted on July 16, 1950, after 10 years of quiescence. Activity continued until September 24. Eruption resumed on February 4, 1951, and continued until April 2, after which activity was intermittent until the eruption ceased on June 28. In 1950 molten basalt was ejected explosively accompanied at times by flows. Two successive cinder cones formed from the accumulation of ejecta, some of which were hurled as high as 500 m. Lava filled the inner pit and crater, and a small amount overflowed into the caldera. About 52,000,000 metric tons of material was erupted. In 1951 six successive small cones developed. Beginning February 21 the principal cone formed. Lava overflowing the crater rim solidified mostly as aa and covered nearly 2 square km of the caldera floor. The intermittent activity during the final 3 months consisted of nine brief periods of eruption, a few of which were relatively violent. Between eruptions and especially after the final eruption the crater floor subsided. In 1951 about 20,000,000 metric tons of material was erupted.
In the Blue Ridge Province of northern Virginia, Maryland, and southern Pennsylvania the established lower Cambrian beds are underlain by a thick sequence of greenstone and interbedded sedimentary rocks known as the Catoctin formation. In an effort to determine the thickness of the formation, its relationship to overlying and underlying rocks, and the original nature of the lavas from which the Catoctin greenstone was derived, an area near Luray, Virginia, was studied. There the Catoctin formation lies unconformably on granitic rocks. Its basal sedimentary layer ranges from a few inches to 150 feet thick and contains pebbles of underlying plutonic rocks. The erosion surface beneath the Catoctin is irregular, and in several places hills up to 750 feet high were buried beneath the Catoctin lavas. No important time break is indicated between the deposition of the Catoctin formation and of the overlying Cambrian sediments, and the Catoctin may be early Cambrian. Mineralogy, chemical composition, and primary structures indicate that the original Catoctin lavas were basaltic in composition and were probably normal plateau basalts. Columnar joints, amygdules, sedimentary dikes, flow breccias, low-dipping primary joints, and other primary structures are well preserved, and the flows in this area are believed to have been subaerial.
Beds composed of oölites or of shell fragments are more soluble than beds of fine-grained or earthy limestone. Vertical crevices are most likely to develop where joints traverse the more soluble beds; bedding-plane crevices in the same beds are likely to form directly above shale partings that are somewhat thicker than average. In the Hopkinsville quadrangle 80 per cent of the wells drilled in limestone of Mississippian (Carboniferous) age obtain adequate water supplies for home or farm needs, because of the extensive development of the bedding-plane crevices. Data from 146 wells reveal a fairly uniform distribution of crevices to an average depth of about 80 feet; the frequency of crevices declines rapidly at greater depth. A rapid increase in mineral content of water below 100 feet signals a decrease in rate of circulation that must be attributed to a decrease either in number of or size of crevices, or to a combination of both. Ratio between the lowering of water level in observation wells and the gaged stream discharge during rainless periods (base flow) gives a storage coefficient of 0.005—that is, 0.5 per cent of drainable open space in creviced limestone. The average seasonal range of fluctuation of the water table is about 13 feet; thus the ground-water reservoir stores less than an inch of water in the interval between high and low water levels.