Even in the gallic "mac" means "son of" so the clans are based on descent from an original holder of the name.
See http://www.almac.co.uk/stronvar/ferguson/index.htm for more information.
That makes Fergus on its own at best a sept of the Ferguson clan.
[B][COLOR="Red"][SIZE="1"]Reverend Earl Trefor the Sublunary of Kesslington under Ox, Venerable Lord Trefor the Unhyphenated of Much Bottom, Sir Trefor the Corpulent of Leighton in the Bucket, Viscount Mcclef the Portable of Kirkby Overblow.
Cymru, Yr Alban, Iwerddon, Cernyw, Ynys Manau a Lydaw am byth! Yng Nghiltiau Ynghyd!
(Wales, Scotland, Ireland, Cornwall, Isle of Man and Brittany forever - united in the Kilts!)[/SIZE][/COLOR][/B]