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Volume 25 Issue 9 (September 2015)

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Article, pp. 4-7 | Full Text | PDF (1.2MB)


1973 Geology Article Covers Baltimore Gneiss Geology

As GSA looks ahead to GSA 2015 in Baltimore, Maryland, USA, on 1–4 November, we reproduce here the first Geology * journal article published on the structural geology of Baltimore and its surrounds. The study by Michael W. Higgins, George W. Fisher, and Isidore Zietz also gives a sense of the geologic mapping there as it examines the extent of the Baltimore Gneiss.

Two of the authors cited in this paper have major GSA awards named for them. Florence Bascom, the first woman hired by the USGS (1896) and the first woman vice president of GSA (1930), was well known for her geologic mapping; thus, GSA’s newest award has been named for her: “Geologic Mapping Award in Honor of Florence Bascom.” Randolph W. “Bill” Bromery†, GSA’s first African-American president (1989), established the “Randolph W. ‘Bill’ and Cecile T. Bromery Award for Minorities” in 1999.

Would you like to know more about the early science and history of Baltimore? Have a look at this 1892 open-access (thanks to the Internet Archive Digital Library) Guide to Baltimore with an Account of the Geology of its Environs, by the American Institute of Mining Engineers.

*Geology, v. 1, p. 41–43, doi: 10.1130/0091-7613(1973)1<41:ADOABG>2.0.CO;2. All GSA journals and books are posted online at www.gsapubs.org.

†Bromery’s GSA Presidential Address is online at gsabulletin.gsapubs.org/content/102/3/405.full.pdf.


GEOLOGY Rerun: Aeromagnetic Discovery of a Baltimore Gneiss Dome in the Piedmont of Northwestern Delaware and Southeastern Pennsylvania

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Michael W. Higgins1*, George W. Fisher2, Isidore Zietz3

1 U.S. Geological Survey, Beltsville, Maryland 20705
2 Johns Hopkins University, Baltimore, Maryland 21218
3 U.S. Geological Survey, Silver Spring, Maryland 20242


In the central Appalachian Piedmont the “basement complex” is an assemblage of 1,100- to 1,300-m.y.-old gneisses, migmatites, and amphibolites that crops out in “domes” mantled by younger metasedimentary rocks of the Glenarm Series. Aeromagnetic data and reconnaissance fieldwork indicate that a previously unknown Baltimore Gneiss dome, here called the Mill Creek dome, is present in southeastern Pennsylvania and northwestern Delaware. The discovery of previously unknown domes of Baltimore Gneiss has bearing on the thickness, structure, and regional relations of the Glenarm Series.

Original Geology manuscript received 26 Feb. 1973; manuscript accepted 3 July 1973.