GEOLEX

Summary of Citation: Baltimore

Publication:
Williams, G.H. and Darton, N.H., 1892, Geologic map of Baltimore
   and vicinity: U.S. Geological Survey, Map to accompany "Guide
   to Baltimore".

Usage in Publication:
Baltimore gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Named	Piedmont-Blue Ridge province	Gneiss

Summary:
Name Baltimore gneiss or gneisses used on this map to include gneiss overlying Cockeysville marble and the hornblende gneiss underlying Setters quartz schist. Text says Baltimore gneisses embrace a great variety of types. The gneiss that overlies Cockeysville marble is in Wissahickon formation.

Summary of Citation: Baltimore

Publication:
Williams, G.H. and Clark, W.B., 1893, Maryland, its resources,
   industries, and institutions; geology: Maryland Board of
   World's Fair Managers, p. 55-88, Prepared for the Board of
   World's Fair [Chicago, 1893] Managers.

Usage in Publication:
Baltimore gneisses

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Piedmont-Blue Ridge province

Summary:
No certain traces of clastic origin have ever been detected in Baltimore gneisses, although their sedimentary character may be inferred from their rapid alternations of beds of different composition, and from the nature of other rocks intercalated in them, like the marbles and quartz schists.

Summary of Citation: Baltimore

Publication:
Mathews, E.B., 1904, The structure of the Piedmont Plateau as
   shown in Maryland: American Journal of Science, 4th series,
   v. 17, p. 141-159

Usage in Publication:
Baltimore gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Piedmont-Blue Ridge province

Summary:
Unit is a highly crystalline banded gneiss. All workers in the area agree that it is Precambrian. Usually in eastern MD it is separated from other metamorphosed sedimentary rocks by igneous masses, but in the vicinity of Baltimore and in the Philadelphia area, as shown by Dr. Bascom, these banded gneisses immediately underlie the quartzite.

Summary of Citation: Baltimore

Publication:
Knopf, E.B. and Jonas, A.I., 1923, Stratigraphy of the crystalline
   schists of Pennsylvania and Maryland: American Journal of
   Science, 5th series, v. 5, no. 33, p. 40-62

Usage in Publication:
Baltimore gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Piedmont-Blue Ridge province

Summary:
Baltimore gneiss is restricted to sedimentary gneiss, and the intrusive gneiss is here named Hartley augen gneiss. The Baltimore unconformably underlies Setters formation.

Summary of Citation: Baltimore

Publication:
Knopf, E.B. and Jonas, A.I., 1929, Baltimore County report
   [Maryland]: Maryland Geological Survey County Report, 420 p.

Usage in Publication:
Baltimore gneiss

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Piedmont-Blue Ridge province

Summary:
Early Precambrian Baltimore gneiss consists of biotite and hornblende gneiss that shows some cataclastic deformation. Varies in appearance from a heavily bedded, granitoid gneiss of white or gray color to a thinly layered ribbon gneiss of alternating light and dark bands. [Type locality information supplied in this report.]

Summary of Citation: Baltimore

Publication:
Bascom, Florence and Stose, G.W., 1932, Description of the
   Coatesville and West Chester quadrangles [Pennsylvania-Delaware]:
   U.S. Geological Survey Geologic Atlas of the United States,
   West Chester-Coatesville folio, no. 223, 15 p.

Usage in Publication:
Baltimore gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Piedmont-Blue Ridge province

Summary:
Baltimore gneiss includes a nongraphitic facies and a graphitic facies. Latter was formerly treated as a distinct formation and called "Pickering gneiss," but this name is now abandoned, as the rocks are only a graphitic facies of Baltimore gneiss. Assigned to Archean. [In 1934, the USGS decided to adopt Pickering for the Precambrian sedimentary rocks associated with Franklin Limestone (a white coarsely crystalline limestone or marble, more or less contemporaneous with Pickering Gneiss), with which it is found interbedded as well as apparently overlying.]

Summary of Citation: Baltimore

Publication:
Jonas, A.I., 1932, Structure of the metamorphic belt of the
   southern Appalachians: American Journal of Science, 5th
   series, v. 24, no. 141, p. 228-243

Usage in Publication:
Baltimore gneiss

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Piedmont-Blue Ridge province

Summary:
Baltimore gneiss, on which the rocks of Glenarm series were deposited is now exposed only in southeastern MD and PA, as far as known.

Summary of Citation: Baltimore

Publication:
Jahns, R.H. and Griffitts, W.R., 1953, Outlying deposits in
   Virginia, IN Mica deposits of the southeastern Piedmont: U.S.
   Geological Survey Professional Paper, 248-C, pt. 4, p.
   C171-C202

Usage in Publication:
Baltimore gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Piedmont-Blue Ridge province

Summary:
Unit is geographically extended into Anna River area of VA, where it forms a well-defined belt on east side of area. West of gneiss is Wissahickon schist.

Summary of Citation: Baltimore

Publication:
Crowley, W.P., 1976, The geology of the crystalline rocks near
   Baltimore and its bearing on the evolution of the eastern
   Maryland Piedmont: Maryland Geological Survey Report of
   Investigations, no. 27, 40 p.

Usage in Publication:
Baltimore Gneiss

Modifications:	Geologic Province:	Dominant Lithology:
Revised Principal reference	Piedmont-Blue Ridge province

Summary:
Author proposes to redefine the type locality of the Baltimore Gneiss as the outcrops along Towson Run and Bellona Avenue to Towsontown Blvd in Towson and Cockeysville quads. [According to the Code, type localities may not be redefined. Therefore, this locality is considered to be a principal reference section.] Outcrops along Jones Falls and Gwynns Falls, generally considered to be the type locality of the Baltimore Gneiss, are younger than and texturally different from the rocks known as Baltimore Gneiss in the cores of anticlines lying unconformably beneath the Glenarm. At least 95 percent of the exposed Baltimore Gneiss consists of quartzo-feldspathic gneiss of granodioritic to granitic composition. Remaining five percent consists of amphibolite. The Baltimore is intruded by the Slaughterhouse Gneiss (new) and the Gunpowder Gneiss. Detailed mapping has led to the recognition of four reasonably distinct subdivisions: a layered gneiss member, an augen gneiss member, a streaked-augen gneiss member, and a hornblende gneiss member. All four units probably fall within the time range of 1.1 to 1.0 b.y. (late Precambrian). Type localities of these four unnamed members are given in the Appendix.

Summary of Citation: Baltimore

Publication:
Rankin, D.W., Stern, T.W., McLelland, James, Zartman, R.E. and
   Odom, A.L., 1983, Correlation chart for Precambrian rocks of
   the Eastern United States, IN Harrison, J.E., and Peterman,
   Z.E., eds., Correlation of Precambrian rocks of the United
   States and Mexico: U.S. Geological Survey Professional Paper,
   1241-E, p. E1-E18

Usage in Publication:
Baltimore Gneiss*

Modifications:	Geologic Province:	Dominant Lithology:
Overview Isotopic dating	Piedmont-Blue Ridge province	Gneiss

Summary:
Baltimore Gneiss from several domes has yielded ages of 1 to 1.2 b.y. Consists foliated granitic rocks, augen gneiss, layered gneiss, and minor amphibolite. Crops out in cores of a number of foliation folds (mostly domes) in area of Baltimore, MD, and West Chester, PA. U-Pb discordia curve on zircon 1180+/-25 m.y. in the Towson dome and 1080+/-20 m.y. in the Phoenix dome. Rb-Sr of 1028+/-40 m.y. in the Phoenix, Towson, and Woodstock domes and 980 and 1060 m.y. in the Chester prong and Avondale anticline.