History of Scottish Gaelic
All surviving dialects are Highland and/or Hebridean dialects. Dialects of Lowland Gaelic have become defunct since the demise of Galwegian Gaelic, originally spoken in Galloway, which seems to have been the last Lowland dialect and which survived into the Modern Period. By the 18th century Lowland Gaelic had been largely replaced by Lowland Scots across much of Lowland Scotland. According to a reference in "The Carrick Covenanters " by James Crichton, the last place in the Lowlands where Scottish Gaelic was still spoken was the village of Barr in Carrick: only a few miles inland to the east of Girvan, but at one time very isolated. Crichton gives neither date nor details.
Saint Mary's Gaels
""The Gaels are an ethno-linguistic group which spread from Ireland to Scotland and the Isle of Man. Their language is of the Gaelic (Goidelic) family, a division of Insular Celtic languages. The word in English was adopted in 1810 from Scottish Gaelic Gaidheal (compare Irish Gaedhealg and Old Irish Goídeleg) to designate a Highlander (OED). Gael or Goídeleg was first used as a collective term to describe people from Ireland; it is thought to have come from Welsh Gwyddel (Old Welsh Goídel), originally "raider", now "Irish person". Many people who do not speak Gaelic consider themselves to be 'Gaels' in a broader sense because of their ancestry and heritage.""