From Alan James – 25 July 2020
I think the puzzle may be the other way about – why were those names spelt that way? As I say in my note, if Creoch was craobhach, ‘eo’ seems to be an attempt to represent the sound spelt ‘ao’ in modern Sc G, i.e. a secondary vowel (not a diphthong) fairly close to French ‘eu’ or German ‘ö’, plus the weak medial vowel of the second syllable. That combination could go either way in Scots to [iəx] or [oəx] (the schwa should be superscript, just a weak glide vowel on to the [x])
Further to what’s in my note: the place in Old Luce that Maxwell spelt Crows, MacQueen (and current OS maps) Crews, when Luce Abbey was dissolved, 1574, was Creauchchis; MacQueen derives it from craobhach, Maxwell from cruadhach, and both reckon Cruise in New Luce has the same origin either way. But MacQueen agrees with Maxwell that Crouse in Kirkinner is cruadhas, Maxwell spells that as Crows, but on Pont/Blaeu it’s Kreochs! And there’s also Croys in Kirkpatrick D, which Maxwell brackets with Crows, along with Croase in Co. Wexford.
So I think the ‘eo’ spelling began with late medieval/ reformation scribal attempts to transcribe a sound which wasn’t close to anything in their phonetic repertoire; it may have stood for various fairly similar sounds in different names, a vowel followed by a weak glide, and this had varied outcomes, though at least in the Glenkens and the Fleet Valley it seems to have emerged as [oə], further west maybe [uə].
Presumably Kirriereoch is riabhach? That makes it a bit of an outsider – it should have been [riəx], perhaps it was retracted to [roəx] under the influence of the other -reoch names in the vicinity.