Olj
Bedrock
Lake Jackson Pluton
Metasedimentary
Foliated and lineated
Middle Ordovician
albite, quartz, and perthite; phyllite
Green-red
Biotite and muscovite metatonalite, contains inclusions of phyllite
Foliated and lineated biotite and muscovite metatonalite composed of albite, quartz, and perthite; contains inclusions of phyllite from unit OCp. SHRIMP U-Pb single zircon age of 461+-7 Ma
Lake Jackson pluton (Middle Ordovician)
OCp
Phyllite
Ordovician and (or) Cambrian
phyllite
Gray and green
Phyllite and metasiltstone
Phyllite (Ordovician and (or) Cambrian)
Olr
Lunga Reservoir
Sedimentary
Sedimentary mélange that resembles a granitoid
Ordovician
quartz and plagioclase, mica-schist, calc-silicate
Micaceous quartzofeldspathic groundmass of quartz and plagioclase
Micaceous quartzofeldspathic groundmass of rounded grains of quartz and plagioclase supports pebbles and cobbles of clear-milky quartz, mica schist, calc-silicate rocks, mafic and ultramafic rocks
Lunga Reservoir Formation (Ordovician)
CZum
Mafic and ultramafic rocks
Composite masses, relict gabbroic texture
Neoproterozoic and (or) Cambrian
epidote-hornblende gneiss and amphibolite
Green
Epidote-hornblende gneiss and amphibolite
Composite masses of green, medium to coarse grained epidote-hornblende gneiss and amphibolite, locally having relict gabbroic texture. Interpreted to be a large clasts and blocks in the Lunga Reservoi
Mafic and ultramafic rocks (Cambrian and (or) Neoproterozoic)
Ocw
Chopawamsic
Metavolcanic and Metasedimentary
Interbedded and interlayered
Upper Ordovician
Silicic & mafic flows, breccias & tuffs w slate, phyllite, schist, metasandstone
Vesicular and porphyritic silicic, intermediate & mafic volcanic flows, breccias & tuffs interbedded & interlayered w/ volcanogenic sediments metamorphosed to slate, phyllite, schist & metasandstone.
SHRIMP U-Pb age of 454+/-5 My from metarhyolite layer (Horton and others, 1998) and 471 +/- 1.3 My from metarhyolite and 470+/-1.4 My from metabasalt (Coler and others, 2000)
Chopawamsic Formation (Upper Ordovician) Metavolcanic and metasedimentary rocks
Oi
Felsic intrusive (?) rocks
Foliated
Silurian
Biotite metatonalite and hornblende quartz diorite with epidote, sodic plagio...
Foliated, biotite metatonalite and hornblende quartz diorite with epidote, sodic plagioclase, chlorite, actinolite. SHRIMP U-Pb zircon age of 434+/-6 Ma from metatonalite (Horton and others, 1998)
SHRIMP U-Pb zircon age of 434+/-6 Ma from metatonalite (Horton and others, 1998)
Felsic igneous rocks (Silurian)
Ocg
Breccia and greenstone
Chopawamsic Formation (Upper Ordovician) Breccia and greenstone
Oq
Quantico
Layered
Ordovician marine fossils
Dark gray
Slate; graded metagraywacke, quartz-rich layers & tuffaceous metavolcanic rocks
Dark slate, rich in carbon and pyrite that contains layers of graded metagraywacke,  thin quartz-rich layers, and tuffaceous metavolcanic rocks
SHRIMP U-Pb zircon age of 451+/- 6 Ma from metamorphosed lapilli tuff layer in lower part of pelitic sequence which contains Ordovician marine fossils (Pavlides and others, 1980)
Quantico Formation (Upper Ordovician)