In 1728, William Byrd, the wealthy, English-educated master of Westover plantation, undertook a journey with a troop of commissioners, surveyors, and woodsmen to determine the exact boundary between North Carolina and Virginia. Byrd was not only an indefatigable explorer but also an amateur naturalist and diarist of considerable skill. He recorded the journey in two classics of colonial literature-- The History of the Dividing Line and The Secret History of the Line--which showcase in varying measure his keen observations of natural phenomena, his erudition, his predilection...