‘… and mossed trees in the goyals.’
A dialect word for a trench or ravine, also spelled goyle or or goile and presumably related to ‘gully’.
Source: Henry Williamson, Tarka the Otter: His joyful water-life and death in the two rivers, illus. C.F. Tunnicliffe (Harmondsworth: Puffin Books, 1976 (1927)), p. 162