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A.H. Chidester

Publications and source records attributed to A.H. Chidester.

At least 19 recordsLinked to original sources
USGS1974

Geology of the Harper Quadrangle, Liberia

As part of a program undertaken cooperatively by the Liberian Geological Survey (LGS) and the U. S. Geological Survey (USGS), under the sponsorship of the Government of Liberia and the Agency for International Development, U. S. Department of State, Liberia was mapped by geologic and geophysical methods during the period 1965 to 1972. The resulting geologic and geophysical maps are published in ten folios, each covering one quadrangle (see index map). The first systematic mapping in the Harper quadrangle was by Baker, S. P. Srivastava, and W. E. Stewart (LGS) at a scale of 1:500,000 in the vicinity of Harper in the southeastern, and of Karloke in the northeastern part of the quadrangle in 1960-61. Brock and Chidester carried out systematic mapping of the quadrangle at a scale of 1:250,000 in the period September 1971-May 1972; the geologic map was compiled from field data gathered by project geologists and private companies as indicated in the source diagram, photogeologic maps, interpretation of airborne magnetic and radiometric surveys, field mapping, and ground-based radiometric surveys in which hand-held scintillators were used. R. W. Bromery, C. S. Wotorson, and J. C. Behrendt contributed to the interpretation of geophysical data. Total-intensity aeromagnetic and total-count gamma radiation maps (Behrendt and Wotorson, in press a, b), and unpublished data derived from those maps, including the near-surface and the regional magnetic components and aeromagnetic/radiometric correlations, were used in the interpretation.

Harper Quadrangle↗
USGS1963

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

The upper Missisquoi Valley and vicinity as described in this report covers an area of about 250 square miles at the headwaters of the Missisquoi River in north-central Vermont. About 90 percent of the area is forested and the remainder is chiefly farm land. The topography reflects the geologic structure and varied resistance of the bedrock to erosion. Most of the area is on the east limb of the Green Mountain anticlinorium, which is the principal structural feature of Vermont. The bedrock is predominantly sedimentary and volcanic rock that has been regionally metamorphosed. It was intruded before metamorphism by mafic and ultramafic igneous rocks, and after metamorphism by felsic and mafic igneous rocks. The metamorphosed sedimentary and volcanic rocks range in age from Cambrian(?) to Middle Silurian, the intrusive igneous rocks from probably Late Ordovician to probably late Permian. Metamorphism and principal folding in the region occurred in Middle Devonian time. The metamorphosed sedimentary and volcanic rocks make up a section at least 25,000 feet thick and can be divided into nine formations. The Hazens Notch formation of Cambrian(?) and Early Cambrian age is characterized by carbonaceous schist. It is succeeded in western parts of the area by the Jay Peak formation of Early Cambrian age, which is chiefly a schist that is distinguished by the general absence of carbonaceous zones; in central parts of the area the Hazens Notch formation is followed by the Belvidere Mountain amphibolite, probably the youngest of the formations of Early Cambrian age. The Ottauquechee formation, composed of carbonaceous phyllite and quartzite, and phyllitic graywacke, is of Middle Cambrian age. The Stowe formation of Late Cambrian(?) and Early(?) Ordovician age overlies the Ottauquechee and is predominantly noncarbonaceous schist, though it also contains greenstone and carbonaceous schist and phyllite. The Umbrella Hill formation of Middle Ordovician age is characteristically a conglomerate in which the mineral chloritoid is common. The overlying Moretown formation, also of Middle Ordovician age, contains granulite and slate, also greenstone and amphibolite of the Coburn Hill volcanic member. The Shaw Mountain formation, made up of conglomerate, phyllite, and limestone, is the oldest Silurian unit. The Shaw Mountain formation is succeeded by the Northfield slate of Middle Silurian age. The igneous rocks of the region include various ultramafic plutonic rocks, such as dunite, peridotite, and serpentinite, probably of Late Ordovician age; sills and nearly concordant dikes of metagabbro of Late Ordovician age; biotite granite plutons or Middle or Late Devonian age, most notably on Eltey Mountain; and hypabyssallamprophyre, probably of late Permian age. Metamorphic zoning is shown by the distribution of rocks of the epidote-amphibolite facies and the greenschist facies in and near the Green Mountains, and near Coburn Hill and Eltey Mountain. Metasomatism related to regional metamorphism has produced porphyroblasts and quartz segregations in the sedimentary and volcanic rocks, and steatitization and carbonatization of serpentinite. Contact metamorphism has formed rocks of the epidote-amphibolite facies near granite plutons, and probably calc-silicate rock at the contacts of ultramafic plutons. The axial anticline of the Green Mountain anticlinorium and other anticlines and synclines to the east are the major longitudinal structural features of the area. These structures are complicated by transverse folds, particularly a syncline in the vicinity of Tillotson Peak. Early minor cross folds that are best developed in the Hazens Notch formation are believed to be genetically related to the transverse folds. The axial planes of the cross folds are folded about the axes of the later longitudinal folds of the Green Mountain anticlinorium. The longitudinal and transverse fold systems probably formed in the same episode of defor

Bulletin↗
USGS1962

Asbestos in the United States, exclusive of Alaska and Hawaii

The asbestos deposits in the United States (exclusive of Alaska and Hawaii) are shown on the accompanying map. The principal mineralogic types of asbestos (chrysotile and amphibole) are indicated by the shape of symbols, and the relative importance of the deposit is indicated by the size of symbols. The text lists localities by State by numbers that are keyed to the map. Localities are distinguished by name of mine, prospect, or geographic area; their coordinates are given to the nearest minute of latitude and longitude. Geologic relations of each occurrence, if known, are characterized briefly. The text and map were compiled from published and unpublished information, and at least one reference is given for each locality if reports on it have been published. Chrysotile asbestos, a variety of serpentine, occurs chiefly in serpentinized peridotite and is distributed in the United States in two principal belts, the eastern extending from Maine to Alabama, and the western extending from Washington to California, where numerous masses of ultramafic rocks were intruded in Paleozoic and Mesozoic time, respectively. Domestic production from deposits of this type has not been large compared with that of Canada from the extensively developed deposits in Quebec, Ontario, and British Columbia. The principal mine in the United States is located at Belvidere Mountain, Vt. Minor amounts of asbestos have been produced from other deposits in these belts and from scattered occurrences of chrysotile elsewhe,re in a number of States between them. Increased exploration and development activity for short-fiber chrysotile has recently been reported in California. Chrysotile also occurs in bedded limestone, metamorphosed close to intrusions of diabase. The principal occurrences of this type are in Arizona, where small quantities of long-fiber, low-iron chrysotile have been mined from numerous small deposits. Several species of amphibole occur in fibrous forms; in the United States only anthophyllite and tremolite are known to have commercial importance. As both the anthophyllite and tremolite occur in ultramafic rocks, associated greenstone, and amphibolite, the overall distribution of amphibole asbestos in the United States is like that of chrysotile. The deposits are generally small and erratic in distribution.

Mineral Investigations Resource Map↗
USGS1962

Talc and soapstone in the United States, exclusive of Alaska and Hawaii

The locations of talc and soapstone deposits in the United States (exclusive of Alaska and Hawaii) arc shown on the accompanying map. The two types are distinguished by the shape of symbols; the relative importance of the deposits, expressed in broad ranges of tonnage, is indicated by the size of symbols. Two persistent belts in the Southeastern States are shown by patterns, and the locations of the principal deposits within these belts are shown by appropriate symbols

Mineral Investigations Resource Map↗
USGS1959

Steatitization of serpentinite bodies in north-central Vermont

The talc deposits of north-central Vermont are associated with bodies of ultramafic rock, chiefly serpentinite, that are enclosed by metamorphosed sedimentary and volcanic rocks of Cambrian and Ordovician age; these stratified rocks form an essentially homoclinal succession in the east limb of the Green Mountain anticlinorium. The rocks at the localities described here are in the greenschist facies, and show only slight variations in grade of metamorphism between localities. The talc deposits consist typically of a core of serpentinite surrounded by successive shells of talc-carbonate rock and of steatite, next to which the country rock is altered for several inches to chlorite rock (blackwall). The steatite zone is rather uniformly about 3 feet thick, but the talc-carbonate rock and serpentinite zones vary considerably in thickness and are locally very irregular.

Vermont↗
USGS1952

Geologic map of the Barnes Hill talc prospect, Waterbury, Vermont

The Barnes Hill talc prospect is in northeastern Waterbury township, Washington County, Vermont, about 2.2 miles N. 35° E. of the road triangle at Waterbury Center. The deposit occurs in a body of ultramafic rock that crops out between the altitudes of 1,150 and 1,190 feet above sea level, near the crest of a broad, low ridge on a gently rolling upland of low relief. The area surveyed is about 46 acres. It is drained on the east by a small tributary of Thatcher Brook and on the west by Bryant Brook. Thatcher Brook empties into the Winooski River at Waterbury; Bryant Brook flows into the Waterbury River, a tributary of the Winooski River. Most of the area is in open pasture, with a few scattered spruce and hemlock, but along the eastern side of the property there is a dense growth of maple saplings and underbrush.

Vermont↗