Named for town of Falmouth in Stafford Co., east-central VA. Includes foliated granitoid and nonfoliated pegmatoid rocks. Forms dikes, sills, and small plutons (granitoid and pegmatoid rocks), all of which were formerly included in informally used Fredericksburg complex of Pavlides and other (1974). Intrudes Po River and Ta River Metamorphic Suites, Holly Corner Gneiss, and Falls Run Granite Gneiss (all in Fredericksburg Complex). Also intrudes Quantico Formation. Age is Carboniferous (340-300 Ma) based on concordant zircon ages and two whole-rock Rb/Sr ages.

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

Falmouth Intrusive Suite, mapped in Stafford, Spotsylvania, and Louisa Cos, is described as fine-grained to pegmatitic granite, quartz monzonite, granodiorite, and tonalite dikes, sills, and small plutons. Predominant minerals include plagioclase, quartz, microcline, biotite, muscovite, hornblende, garnet, epidote, apatite and titanite. Intrudes Cambrian Ta River Metamorphic Suite, Silurian Falls Run Granite Gneiss, Late Proterozoic and Cambrian Holly Corners Gneiss, Ordovician Quantico Formation and porphyroblastic garnet-biotite gneiss (referred to as Po River Metamorphic Suite by Pavlides, 1980). Unit has been dated at 300-325 Ma (U-Pb zircon and Rb-Sr whole rock, Pavlides and others, 1982). Map symbol indicates Mississippian and Pennsylvanian age.

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