(The). Not the wood where rooks do congregate, but the misty or dark wood. The verb reek (to emit vapour) had the preterite roke, rook, or roak; hence Hamilton, in his Wallace, speaks of the “rooky mist.”
Light thickens, and the crow Makes wing to the roaky wood.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894