This Saint is a vague sort of a figure. W J Watson, in "A History of the Celtic Place-names of Scotland" (1926) suggested two possibilities: ...Baetan Maccu Cormaic, abbot of Cluain mad Nois who died on March 1, A.D. 664, or to Abban Maccu Cormaid, Oct. 27, of Magh Arnaide... (page 283) It seems that today, the consensus is that this Cormac/Charmaig/Chormick was indeed, the latter: ABBAN MACCU CORMAIC. He was most likely a son of Cormac, King of Leinster.
"ABBAN" means "abbot." "Maccu" means something like "the family, tribe of", and has today transmogrified into the more familiar, "mac O'". Thus, our man was of the tribe of Cormaic.
This Cormaic probably died about 620 CE. He founded several churches on mainland Ireland, expecially in modern County Wexford. His principal community was at what is today known as "Adamstown" (originally, 'Abbanstown').
"Keills" indicates that this chapel was a centre of Christian activity. That is, "Keills" is derived from the word "little cells" or "cenaculae." As to the Eilean Mor establishment, it is assumed that it was the monks' place of retreat from the busier main centre at Keills itself. According to Campbell, the island was turned into an Inn by the 18th century, and visited by John Paul Jones during the American War of Independence. At the south end of Eilean Mor, there are remains of a small cave, probably a place for solitary meditation. Eilean Mor is now owned by the Scottish National Party, in large part through the efforts of Marion Campbell of Kilberry.
The drawings on this page were made by the indefatigable Captain T. P. White, and published in his book, "Archaeological Sketches in Scotland: Knapdale and Gigha", now sadly out of print and very rare.
This sketch of the Keills Cross appears in Ian Fisher's "Early Medieval Sculpture in the West Highlands and Islands" (RCAHMS), on page 47. The photo I took of this cross appears as part of the banner on the front page of knapdalepeople. As you can see in that photo, its surface is very worn, making it difficult to see the original detail . So, the accompanying sketch will give you a much better feel for the carving's sophistication and beauty.