The key to the Mid Argyll Group research is the historical figure of Donnchadh Mac Eáin. As Captain White, who did the survey of Donnchadh's burial slab in 1875, pointed out when speaking about the slab, it is one of the few burial slabs that can be linked to a historical figure.
To quote Captain White, 'The writing in this case is tolerably perfect, and there is no difficulty in reading the initiatory words, ''Hic iascet Duncanus." Now, in 1479, King James III granted to Colin, Earl of Argyll, the lands of Gareald, Craigenewir (in the vally of the Add) and Tangladlew (within the barony of Glassary), resigned by Duncan Makcane. With the aid of this information, if we turn again to the inscription, the following, I think, can be deciphered-- Hic iacet Duncanus Roy M'Allan -- and at the top of the slab the name 'Lachlan.' This appears to be one of those rare instances where we are enabled to identify a mediaeval tombstone in the West Highlands with a substantive individual of whom there is documentary record.'
Captain White was correct Donnchadh appears is the Scottish crown records and the Argyll records. He is the vector. Through him we can follow his descendants and those of his three brothers, Dónall, Eáin Riabhach, and Giolla Chríost.
In most of the 1400s and 1500s records that Donnchadh and his descendants appear, they continue the use of the Mac Eáin surname. Usually is found put into Lallans, but sometimes left in a Gaelic spelling.
It is interesting that we know so much about Donnchadh as his House, at Dunemuck, was not the head of the clan, it was his older brother Dónall who was the Taoiseach of the Dunadd Mac Lachlainns. The House were Dónall of Dunadd, Donnchadh Mór of Dunemuch, Eáin Riabhach of Killiemuchanock, and Giolla Chríost of Creig an Tairbh.
As the research progresses I will post more of these brothers and their descendants from the primary sources. Luckily the habit of writing a man's Derbfine name was often followed in the Argyll records, so that we not only get the man's name, but his line of descent, usually for four, sometimes three, generations.