Leabhar na nGenealach, was reprinted, and published in a five volume edition in Dublin in 2004 as The Great Book of Irish Genealogies.
In the words of Nollaig Ó Muraíle: " ... who or what prompted Mac Fhirbhisigh to undertake the compilation of Leabhar na nGenealach?
As to the question of why he wrote Leabhar na nGenealach, Mac Fhirbhisigh himself stated it was his intention to "... do mhórughadh glóire Dé agus do ghéunamh iúil do chách i ccoithchinne / to increase the glory of God and to give knowledge to everyone generally".
That it seems to be a book written for all the peoples of Ireland is indicated by the following: "Na slioinnte, iomorra, da suarraighe atáid, ní fuigfeam dar ndeóin éanghloinneadh aca gan a aireamh ó a cheap fén / of the surnames, moreover, however undistinguished they may be, we do not willingly leave a single one of them without reckoning it from its own stock".David Sellar, who was the Lord Lyon King of Arms in Scotland, stated that it dates from 1585 to 1670.
The díonbhrollach describes the contents of the book, including: It is customary for great lords that, when their families and kindreds multiply, their clients and their followers are oppressed, injured and wasted.
[translation by Thomas Charles Edwards in Early Irish & Welsh Kinship, p. 221]Begins with the following introduction: "Senchus genealach gabháltas uasal Éreann agus Albansgot go ccraobhsgaoileadh a ccineadhach ó créudthós na n-aimsior n-aicsidhe gus aniú (mar ghebh mid / The history of the genealogies of the invasions of the nobles of Ireland and of the Scots of Alba with the genealogical branchings of their races from the beginning of visible times until today, as we find, according to the order".
The Leabhar Oirghiallach is in many instances very obviously drawn from versions of the Books of Lecan and Ballymote, yet once again there is unique material concerning Clann MacDonnell, a gallowglass family.
Other sources for the remaining subjects include: Senchus fer n-Alban; the Book of Uí Maine, from sections now missing; Amhra Colm Cille; Opus chronologicum by Ubbo Emmius; versions of De Shíl Chonairi Móir, De Maccaib Conaire, the Duan Albanach; the poem 'Saor do leannán, a Leamhain' by Muireadhach Albanach Ó Dálaigh (fl.
The only source explicitly named – though he refers vaguely to other books – is once called Leabhar Buidhe Lecan Mec Fhirbhisigh, now lost.
This book outlines the history and genealogical ramifications of the descendants of Íor son of Míl Espáine, known as the Síol Ír.
Mac Fhirbhisigh added "a great amount of additional material ... both in the margins and interlineally ... those inserted between the lines are variant readings, some of them of considerable interest, deriving as they do from quite a different recension of the work; ... represented by just one manuscript older than LGen, namely RIA B iv2."
As Mac Fhirbhisigh intended to merely summarise material, he did not reproduce the original texts, which were extracts from Saltair Chaisil, written in Latin.
This was a fabrication, based on the Plunkett's status in the late 16th century, claiming them as descended from King Donnchad mac Briain, who died in Rome in 1064.
As did Geoffrey Keating, Mac Fhirbhisgh reserves doubts on this, though pointing out that it should not be discounted merely because of Donnchad's age, as "there is no period in a man's life in which he may not beget."
Given that Galway was within days of plague, famine and siege, O Muraile expressed the wish "for the merest hint by Mac Fhirbhisigh of what conditions were like in the stricken city while he was penning his list of Irish kings!"
It finishes with a dedication and note by Mac Fhirbhisigh: Ad maiorem Dei gloriam, DF do theagair agus rus graif for Iuil, 1653 / To the greater glory of God.
By Saturday 5 May, he had completed some 45% of the surviving material, and would appear to have finished prior to returning to Dublin and working for Sir James Ware.