I believe the history of Wild Mountain Thyme is that Francis McPeake wrote the song (in its three-verse-and-a-chorus version) trying to remember BRAES OF BALQUIDDER

I've heard various fourth verses added to the original, but none of them seem to have stuck. One, written by Steve Suffet (from memory - it may have mistakes):

"With my collie I did stroll
All upon the blooming heather
But my collie didn't piddle
Though we walked for half an hour
Will ye go, Lassie, go..."