Named Marshall granite for Marshall, Fauquier Co., VA. Consists of pink to green granite and quartz monzonite. It is intrusive into the Lynchburg gneiss, Lovingston granite gneiss, and Catoctin greenstone. Unit is assigned to the Precambrian.

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

Marshall Granite of Jonas (1928) adopted as Marshall Metagranite for use by USGS in northern Virginia. Mostly fine-grained, dark gray, gneissic granite; dominant minerals are quartz, plagioclase and potassium feldspar; minor minerals are epidote, sericite, and biotite. Zircons have yielded a 207Pb/206Pb age of 1010 Ma. Oldest rock in quadrangle.

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

The Marshall Metagranite is divided into two units in the mapped area, a fine- to medium-grained metagranite and a coarse-grained metagranite. The fine- to medium-grained unit is light-olive-gray to light-brownish-gray, massive, monzogranite composed of 22 to 28 percent quartz, 33 to 34 percent orthoclase, microcline, and microperthite, and 38 to 44 percent oligoclase and albite. The coarse-grained metagranite is light-olive-gray to light-brownish-gray monzogranite with orthoclase and sausseritized oligoclase porphyroblasts. The Marshall Metagranite is of Middle Proterozoic age.

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

Biotitic Marshall Metagranite from the Rectortown quad, southwest of the map area, yielded a U-Pb zircon age of 1055 +/-5 Ma (Aleinikoff and others, 1993, GSA Abstracts with Programs, v. 2 no. 2, p. 2). Has been traced from map area south to its type area in Marshall quad (Burton and others, 1992, USGS Open-File Report 92-716; and P.T. Lyttle, 1991, oral commun.). Report includes geologic map, cross sections, and correlation chart.

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