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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 73 records · Page 4Linked to original sources
USGS1963

Early pennsylvanian currents in the southern Appalachian Mountains

Measurement of more than 1200 cross-beds in lower Pennsylvanian sandstones of the southern Appalachian Mountains reveals a broad pattern of sediment transport to the southwest and west. Most of the sand appears to have been derived from the east and to have moved south-westward parallel to the axis of the Appalachian geosyncline. The pattern has a similar alignment to that in the Illinois basin, but it is at right angles to earlier Paleozoic dispersal directions in the Appalachian geosyncline. Little or no sand has been contributed from the Cincinnati arch. The cross-beds are in sheetlike sandstone formations; the sandstone is conglomeratic, contains plant impressions, and is composed of lenticular, channeling, quartzose sedimentation units. The variation in thickness and lateral persistence of sedimentation units is also reflected in a moderate variability of mean cross-bedding directions between adjacent formations, and even within the same formation. Cross-bedding variability between adjacent units is thought to be due to regional changes in the position and orientation of channel-way systems from deposition of one sandstone formation to the next. Changes of cross-bedding azimuths within the same formation may result from channel curvature of local meanderlike deposits or from channel migration as the sands coalesced into a blanket deposit.

Kentucky, Tennessee, Alabama, Georgia↗
USGS1905

Report on progress of investigations of mineral resources of Alaska in 1904

During the last two years the United States Geological Survey has met the demand of the mining public for early publication of economic results by issuing an annual bulletin entitled "Contributions to Economic Geology." Though these volumes have made no attempt to treat exhaustively any of the subject discussed, and while many of the included papers have been but the barest outlines, they have met a cordial reception from those interested in developing the mineral resources of the country. Among the many papers in these bulletins were a number devoted to the mineral deposits of Alaska. In view of the rapid extension of the Alaskan work of the Geological Survey and its segregation in a distinct division, it has seemed desirable to issue a separate publication containing the papers summarizing the previous year's work.

Alaska↗
USGS2000

Cambrian Pelecypoda (Mollusca)

The record of Cambrian bivalved organisms that have been placed in the Mollusca includes undoubted pelecypods and other bivalved shells. This record is reviewed herein. Additional topotype material of Delgado's (1904, Communicacoes da Commissao do Servico Geologico de Portugal 5:307-374) Lower Cambrian specimens from Portugal shows that they are distorted brachiopods. Restudy of Zhang's (1980a, Bulletin Chinese Academy of Geological Sciences, Series 8, 1:1-19; 1980b, 26th International Geological Congress 4:121-129) type specimens from the Lower Cambrian of China shows that most of them are also brachiopods. New specimens of Tuarangia MacKinnon indicate that this genus is a Middle-Upper Cambrian pelecypod.

American Malacological Bulletin↗