But there are tracts in the Book of Leinster (compiled A.D.

1130), and in the Book of Ballymote (compiled A.D.

1391), which are of the highest authority.

O'Curry is of opinion, that those in the Book of Leinster were copied from the Saltair of Cashel and other contemporaneous works.
The historical use of these genealogies is very great, not only because they give an authentic pedigree and approximate data for chronological calculation, but from the immense amount of correlative information which they contain.

Every free-born man of the tribe was entitled by _blood_, should it come to his turn, to succeed to the chieftaincy: hence the exactitude with which each pedigree was kept; hence their importance in the estimation of each individual; hence the incidental matter they contain, by the mention of such historical events[78] as may have acted on different tribes and families, by which they lost their inheritance or independence, and consequently their claim, however remote, to the chieftaincy.
The ancient history of a people should always be studied with care and candour by those who, as a matter of interest or duty, wish to understand their social state, and the government best suited to that state.