U.S. Geological Survey Home AASG Logo USGS HOME CONTACT USGS SEARCH USGS
National Geologic Map Database
Map showing publication footprint
  • Usage in publication:
    • Ilchester granite
  • Modifications:
    • Named
  • Dominant lithology:
    • Granite
    • Gneiss
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Hobbs, W.H., 1889, On the paragenesis of allanite and epidote as rock-forming minerals: American Journal of Science, 3rd series, v. 38, p. 223-228.


Summary:

Name Ilchester granite introduced in this report for one of the youngest of a series of eruptions in the gneiss and crystalline schist of eastern MD. Described as a medium to coarse grained rock, with a porphyritic aspect caused by the large microcline crystals scattered through the holocrystalline to granophyric groundmass. Occurs at Ilchester. Age is Precambrian(?).

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Ilchester Gneiss
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
Publication:

Hopson, C.A., 1964, The crystalline rocks of Howard and Montgomery Counties: Maryland Geological Survey County Report, 337 p., Reprinted from Cloos, Ernst, and others, "Geology of Howard and Montgomery Counties," p. 27-215


Summary:

Ilchester granite revised as Ilchester Gneiss and mapped along with Leakin Park Gneiss in the Laurel belt of MD. Neither unit is discussed, but shown only on a small scale map.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Map showing publication footprint
  • Usage in publication:
    • Ilchester Gneiss†
  • Modifications:
    • Not used
  • AAPG geologic province:
    • Piedmont-Blue Ridge province
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.


Summary:

Though Hopson (1964) assigned the quartzo-feldspathic rocks in the Laurel belt to two formations, the Ilchester Gneiss and the Leakin Park Gneiss, these rocks are here mapped as one continuous unit intrusive into the Baltimore Mafic Complex and overlying James Run Formation. The formal name Cold Spring Gneiss is proposed.

Source: GNU records (USGS DDS-6; Reston GNULEX).


Search archives

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).

Accessibility FOIA Privacy Policies and Notices

USA Gov U.S. Department of the Interior | U.S. Geological Survey
Supported by the National Cooperative Geologic Mapping Program
Page Contact Information: Personnel
Page Last Modified: Thu 04 Apr 2024 03:22:49 PM MDT