The Yarrow is an upland tributary of the Tweed. Its vale was once 
forested, but was later well-known for the few trees which grew there. 
The ballad 'The Dowie Dens o' Yarrow' (the grieving hillsides of Yarrow) 
is one of those red-blooded-breast and white-faced-maiden stories. The 
song 'Betsy Bell and Mary Gray' is equally jovial, being concerned with 
the isolated death of two girls in times of plague. All good stuff!