But some collateral evidence on this subject more than meets the difficulty. "In the Durham MSS. of Nennius, apparently written in the twelfth century, there is an interpolated passage, stating that the spot in question was in the Scottish or Gaelic language called _Cenail_. Innes and others have remarked the resemblance between this appellation and the present Kinneil; but no one appears to have noticed that _Cenail_ accurately represents the _pronunciation_ of the Gaelic _cean fhail_, literally _head of wall_, _f_ being quiescent in construction. A remarkable instance of the same suppression occurs in _Athole_, as now written, compared with the _Ath-fothla_ of the Irish annalists. Supposing, then, that _Cenail_ was substituted for _peann fahel_ by the Gaelic conquerors of the district, it would follow that the older appellation was _not_ Gaelic, and the inference would be obvious."[7] In thus making _pen val_ a Pict gloss, I by no means imagine that any of the three forms were originally Keltic at all; since _val_, _gwal_, _fhail_ all seem variations of the Roman _vallum_, at least, in respect to their immediate origin. Still, if out of three languages, adopting the same word, each gives a different form, the variation which results is as much a gloss of the tongue wherein it occurs, as if the word were indigenous. Hence, whether we say that _pen val_ are Pict glosses, or that _pen_ is a Pict _gloss_, and _val_ a Pict _form_ is a matter of practical indifference. The _Vallum Antonini_ was a work of man's hands, and its name is of less value than those of natural objects, such as _mountains_, _rivers_, or _lakes_. Nevertheless, these latter have been examined: thus the _Ochel_ Hills in Perthshire are better explained by the Welsh form _uchel_ than by the Gaelic _nasal_. But the most important word of all is the first element of the words _Aber_-nethy, and _Inver_-nethy. Both mean the same, _i.e._, the _confluence of waters_, or something very much of the sort. Both enter freely into composition, and the compounds thus formed are found over the greater part of the British Isles as the names of the mouths of the larger and more important rivers. But it is only a few districts where the two names occur together. Just as we expect _a priori_ _aber_ occurs when _inver_ is not to be found, and _vice versâ_. Of the two extremes Ireland is the area where _aber_, Wales where _inver_ is the rarer of the two forms; indeed so rare are they that the one (_aber_) rarely, if ever, occurs in Ireland, the other (_inver_) rarely, if ever, in Wales. Now as Ireland is Gaelic, and Welsh British, the two words may fairly be considered to indicate, where they occur, the presence of these two different tongues respectively.