Hiya Jim,
I have a copy of "Prisoners of the '45, Cromarty's Regiment" a booklet in the records at the Ullapool Museum, extracted from a larger book, perhaps the one you found your data on Alexander in, it has 225 people listed, mostly from Cromarty's, and a few from Glengarry's whose residence looks to have been in Lochbroom Parish.
"Mickle" I take for "muckle", meaning big or large, "Strath" was a wide and long valley.
Though there are other big straths in Scotland my guess is your Alexander was from the one in Lochbroom, given Cromarty recruited a large part of his regiment in the area.
You wrote:
I believe Alexr. to be my ancestor. We also believe, according to family lore, that he was a marchent, a Jacobite, fought at Culloden Mor and was deported to the colonies on the ship Gildart, which left Liverpool 5 May 1747 to the colonies.
The Regiment fought in a number of battles in the Rebellion, then were ordered north to Sutherland and Caithness, with a side trip to Orkney, to recruit, and attempt to recover a ship load of gold from the French that had been captured by the Hanoverians there. They captured Dunrobin Castle in the last siege battle that has been fought on the mainland of Britain.
They were ordered south to Inverness where a major battle was expected, and set out the day before the Battle of Culloden... the officers tarried at the Castle, the privates, likely including your Alexander (and some of my relatives) were captured leaderless on the road, and while the Earl parlayed in the castle one of the Sutherlanders lied to the bodyguards below that the Earl had surrendered and unlocked the gates... If the Regiment had made it to Culloden the result of that battle might have been different.
The note I have on Alexander says he was noted as held at Inverness in June, 1746, then on the prison ship Alexander & James, then on the prison ship Liberty, then at the Prison of Medway. Also has a slightly different date for his "Transportation" than you have, 20 March, 1747.
Lochbroom was mostly MacLeods and MacKenzies, but there was always a healthy sprinkling of MacDonalds; Achadh a Donnell, later Dundonnell, was south-west of the big strath, and the mountainous area between Glen Achall and Strathcanaird north-west of the big strath is mostly Ben Donald, those place names indicating the great age of the family in the area.
Hope that is some help,
Donald.