(a) The _Chronicon Scotorum_ is an abridgment of Tigernach. This was disputed by its editor (Hennessy, Rolls series), but has been established by Dr. MacCarthy,[333] who has at the same time shown the incompetence of the abbreviator (MacFirbis). For the fifth century its value consists in showing what entries were to be found in Tigernach. (4) The _Annals of the Four Masters_, a chronicle in Irish from the earliest times, compiled in Donegal by O’Clery and three others in the seventeenth century, has some value for the early Middle Ages, because it preserves notices derived from older chronicles that are not extant. But its dates are untrustworthy because the compilers had no skill in chronological computation. This has been shown by Dr. MacCarthy (_op. cit._ p. 370 _sqq._). One of their sources was the _Annals of Ulster_, which supplies a means of correcting their mistakes. Among their other authorities were the _Book of Clonmacnois_ (Tigernach?) and the _Book of the Island of Saints_ (in Lake Ree). From these compilations it might be possible to reconstruct the common annalistic structure on which they are based; with the help of the chronological tracts and poems which are contained in the _Book of Leinster_, the _Book of Ballymote_, etc. It is clear that for such a reconstruction the _Annals of Ulster_ would supply the clearest traces of the plan. The Irish seem to have had a special taste and faculty for chronological computations,[334] and in the early part of the seventh century, if not sooner, they were laying the foundations for national Annals on the model of the Roman Annals. In the _Annals of Ulster_ a number of entries, ranging from A.D. 467 to A.D. 628, are justified by references to the _Liber Cuanach_. Zimmer, with great probability, identifies Cuana, the author of this lost work, with Cuana mac Ailcene, a king of Fermoy, whose death is noted in _Chron. Scot._ and in _Annals of F. M._ under A.D. 640.[335] The references under the year 482 show that the _Book of Cuana_ dealt with (the chronology at least of) the pre-Christian period. The authorship of a south Irish prince is consistent with the circumstance that many of the entries in question relate to the affairs of South Ireland.[336] For chronological studies I may refer also to the evidence of Tírechán, on which I have dwelt in _Eng. Hist. Rev._ April 1902, 244-5.