STEWART OF ATHOLL -Conacher, Cruickshank(s), Duilach, Garrow, Gray, Larnach, MacGarrow, MacGlashan
MacGlashing is not listed.
I checked "Surnames of Scotland" by George Black. It does not list MacGlashing in the etymology of the name MacGlashan. I suppose the spelling could have been "corrupted" and not hit the Scottish records at all.
Chair, Genealogical Committee
Clan Stewart Society in America, Inc.http://www.clansstewart.org