Guest John Spence,
Yep I know it's a Scots song but the last time I looked Scotland was firmly anchored to the top of Northern England.
Without wishing to ignite a whole Scots/English debate there were most likely better lines of communication between Dumfries & Galloway and N England, road and coastal craft, than there were to Glasgow and Edinburgh.
When Rabbie stood on the coast looking south he was looking at the lumpy bits of England. Most of the dialect developed as Scots, Welsh and country people came together in the mill towns