The evidence of language will be found sufficient to show not merely the common origin of the Welsh and Irish, but also to fix a much more recent date for their separation than that which has been assigned by Lhuyd. It will thence appear that the Irish are descendants of Colonists of the Welsh or British race, not of a distinct Celtic sept, and that the commencement of the separate existence of the Irish nation must be referred to a comparatively recent date, propositions of much interest, of which the proofs about to be advanced will probably be deemed to be at once clear and simple. Lhuyd’s reasoning in favour of his theory, that the Irish or Gael existed in Britain as a separate Tribe, prior to the arrival of the Britons who fought against Cæsar, the ancestors of the modern Welsh, is founded on a false analogy not unnatural to a first inquirer. The proposition that the most important local names in every country for the most part consist of terms belonging to the language of the very first inhabitants, is one of which I conceive the truth will be evident. For a proof of this principle, I may refer to Chalmers’(52) admirable analysis of local names in the Lowlands of Scotland, where, in spite of a succession of Conquests, and the utter extinction in that part of Britain of the language of the original inhabitants, viewed as a vernacular dialect, Welsh and other Celtic names are still preserved, after the lapse of ages, for the most prominent features of the country. This result, it may be observed, is one that flows from the very nature of things. Even the most fierce and ruthless invaders are compelled to hold sufficient intercourse with the first population to enable them to learn the proper names of their localities, and these names, from obvious motives of convenience, they almost universally adopt. Now, had Lhuyd shown that the most ancient Local names in Britain are _exclusively_ Irish, there can be no doubt that, consistently with the principle just noticed, his theory would have been supported by the facts to which he adverts. But the most ancient local names in Britain are not _exclusively_ or _principally_ Irish; in an equal number, perhaps in a majority, of cases they are Welsh.