In the Leabhar na h-Uidhre [Lowar na Heera], or Book of the Dun Cow, the existing manuscript of which was transcribed about the year 1100, in the Book of Leinster, transcribed about fifty years later, in the Book of Ballymote and in the Book of Lecan, frequent reference is made to an ancient book now lost called the Cin or Codex of Drom-sneachta. This book, or a copy of it, existed down to the beginning of the seventeenth century, for Keating quotes from it in his history, and remarks at the same time, "and it was before the coming of Patrick to Ireland the author of that book existed."[1] This evidence of Keating might be brushed aside as an exaggeration did it stand alone, but it does not, for in a partially effaced memorandum in the Book of Leinster, transcribed from older books about the year 1150, we read: "[Ernin, son of] Duach,[2] son of the king of Connacht, an ollav and a prophet and a professor in history and a professor in wisdom; it was he that collected the genealogies and histories of the men of Erin into one, and that is the Cin Droma-sneachta." Now there were only two Duachs according to our annals, one of these was great-grandson of Niall of the Nine Hostages, and of course a pagan, who died in 379; the other, who was an ancestor of the O'Flaherties, died one hundred and twenty years later. It was Duach the pagan, whose second son was Ernin; the other had only one son, whose name was Senach. If O'Curry has read the half-effaced word correctly, then the book may have been, as Keating says it was, written before St. Patrick's coming, and it contained, as the various references to it show, a _repertoire_ of genealogies collected by the son of a man who died in 379; this man, too, being great-grandson of that Niall of the Nine Hostages in whose son so large a number of the Eremonian genealogies converge.[3]