I have just returned from Scotland and spent some time in the areas frequented by the Galloways (my mother's ancestral line). Apparently, the Galloways were "septs" of the clan MacFarlane, i.e., they were a tribe associated with that clan. I have read elsewhere that they were a clan unto themselves (you can find some info on that via the web) and associated with other clans. I have a map showing the Galloways among the MacFarlanes in the areas just north and west of Glasgow, Scotland.
My ancester James Galloway left Scotland, via Liverpool to the Port of Philadelphia, in 1638. After more than 20 years of searching, I still cannot find his origins. Not much written or saved sometimes among the highland clans.