The Clarksville North and Boydton 7.5 minute quadrangles include an area of about 260 square kilometers in southeast-central Virginia from about 9 km to about 21 km north of the Virginia -North Carolina State line, mostly north of and along a ponded part of the Roanoke River and it minor tributaries that form John Kerr Reservoir. Informal units of isoclinally folded greenstone and underlying phyllite are mapped in a structural recess in the southeastern part of the Boydton quadrangle and are tentatively correlated across strike with the Late Proterozoic Virgilina Formation and Aaron Formation of the Virgilina copper district in the western part of the slate belt. The phyllite unconformably overlies dominantly felsic volcanic and volcaniclastic rocks, mapped in eleven informal units in the central and eastern parts of the Boydton quadrangle, and tentatively correlated with the Hyco Formation of the Virgilina copper district The oldest felsic volcaniclastic unit, very coarse-grained lithic-crystal metatuff, lies along the axis of an upright to slightly eastwardly-overtumed isoclinal anticline identified by topping sense from relict bedding and repetition of stratigraphic units about its flanks in the central and eastern parts of the Boydton quadrangle. Rocks on the west limb of the anticline are breached by the Clarksville batholith in the western parts of the Boydton quadrangle and in the Clarksville North quadrangle.The Clarksville batholith is a zoned pluton. Mapped phases, from oldest to youngest, include: metagabbro, foliated biotite quartz diorite, foliated biotite granite dated as Late Proterozoic, and foliated porphyritic granodiorite.The magmas were probably fed from a deeplyrooted (12 km) funnel-shaped core, associated with a 10 milligal regional gravity anomaly centered near the southwest comer of the Boydton quadrangle. Granodioritic crystal-mush magma, that developed an inward-dipping flow-foliation, surged through an earlier-crystallized carapace of finer-grained foliated biotite granite, invading the country-rock probably about 600 million years ago. The bodies of metagabbro and foliated biotite quartz diorite are now in pods and lenses marginal to the porphyritic granodiorite core. They were also early crystalline phases as evidenced by their being cross cut by granite and granodiorite.

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