David Murison

“...the prose tradition had died two centuries before and the recreation of a full canon of all-purpose Scots was beyond even Scott's skill, nor did he attempt it, except, perhaps in the magnificent Wandering Willie's Tale. He took the only course open to him, of writing his narrative in English and using Scots only for those who, given their social class, would still be speaking it: daft Davie Gellatley in Waverley, the gypsies and Dandie Dinmont in Guy Mannering, the Headriggs in Old Mortality, Edie Ochiltree and the fisher-folk of Musselcrag in The Antiquary, Andrew Fairservice in Rob Roy, the Deanses in The Heart of Midlothian, Meg Dods in St. Ronan's Well, and so on.

The procedure gave reality to the Scots characters whose ways and ethos it was Scott's main purpose to portray, and the author in his best English, which lumbered along rather badly at times, did little more than lay out the setting for the action and act as impressario for the characters as they played their roles...

...Scott's felicity in conveying character and action through their Scots speech inspired his imitators for the next hundred years - Susan Ferrier, Hogg, Macdonald, Stevenson, Barrie, Crockett, Alexander, George Douglas, and John Buchan. The tradition of narrative in standard English and dialogue in various degrees of dialect has been the usual procedure since.”
― David Murison, Grampian Hairst: An Anthology of Northeast Prose