To account for the vitrification appearing all round the area, we have only to refer to our supposition of a system of signals, and the shifting of the wind rendering it neces sary to change the side on which the fires were to be light ed. The vitrified masses appear in many instances to have been displaced ; and one fact occurred to our notice which ascertains this displacement beyond a doubt. On search ing below a mass, the vitrified side of which was consi derably inclined, we observed some melted matter that had run down and consolidated in the form of stalactites. Had this mass been in its original position, these would have been perpendicular ; hut they were at right angles to the inclined vitrified surface. Many fortuitous circumstances may have contributed to produce the present irregular ap pearances. It cannot be doubted that the rampart was ori ginally formed with as much regularity as the nature of the materials would allow, both in order to render it more du rable, and to make it serve the purposes of defence. For we must believe, that so important a station as one for sig nals, was rendered sufficiently strong to resist the attacks of an enemy. We do not, however, consider that any ap pearance on Knock Farril indicates the fusibility of the stones having been used for consolidating the ramparts.. Dr Anderson was mistaken when he stated, in the 6th vol. of the ?rchxologia, that the vitrifications arc to be seen only on the outside of the ramparts of Knock Farril. He men tions, however, the fact, that on the hill called Top of A'oth, in Aberdeenshire, the vitrification is only on the inside ; which is a very satisfactory confirmation of the idea that it has been produced by signal fires. Had the outside of the rampart on Top of Noth been vitrified, we might have been warranted in concluding that fire had been used to strengthen it. Had the inside been vitrified with this view, it is impossible to conceive that no attempt was made to cement the outside also ; since in every structure for de fence, however rude, we find the strongest, and not, as in this instance, the weakest, part opposed to the approach of an enemy. On some hills, places apparently intended for defence have been found, where there are no appearances of vitrification. In such instances it is probable that the stones will be found not to be of an easily fusible nature ; if in reality, no vitrification can be found, on accurate search being made. This last remark is occasioned by the disco very of a mass of vitrified stones on the hill of Dun Jardil, one of the stations along the great chain of lakes, which escaped the notice of Mr Tytler, but was found by Mr Nimmo, civil engineer, and late rector of the academy at Inverness.
The following considerations seem to support the idea of such high situations being chosen expressly for signal stations. Such hills only, as command an extensive view of the sea, or adjacent country, have been selected.
Each hill is in sight of one or more similar stations, as far as has yet been observed, with the exception of Dun Creich, which seems to have been devoted exclusively to the use of the extensive valley in which it is situate ; though hereafter others may be discovered to be connected with it.
There is a regular chain from Knock Farril and Craig Phadrick, along the great valley of Lochness to the west coast ; and others are in sight towards the east. So that, on the appearance of an enemy on either side of the island, the whole country from coast to coast could be informed, probably within the short space of an hour.
Such is the situation of vitrified forts exclusively ; for they are not seen in any but commanding situations ; while many spots more convenient, and better adapted in every respect for defence, are often to be found in their vicinity, or at no great distance.
In the statistical account of the parishes of Boleskine and Abertarf, the hill of Dunardile, or Dun Jardil, mentioned by Mr Tytler, is noticed ; and it is added, " that a similar tower is in the same direction, contiguous to the house of Invergarry ; and that the tradition of the country is, that those hills were watch towers for giving signals upon the approach of an enemy by large fires.",
It is about seventeen years since the writer of this article suggested to several persons whom he accompanied in their visits to Knock Farril, which is near his country residence, the idea of vitrified forts having been signal stations ; but this he believes was not new, though he had not before seen or heard it stated. The opinions which were at that time entertained were, that fire had been used for the purpose of cementing the walls, by fusing the materials of which they were composed ; and that the vitrifications had been caused, not in the erection, but in the destruction of the buildings, of which we now sec only the ruins.
The first of these opinions, started by Mr Williams, was supported by Dr Anderson ; and if we consider barely the possibility of forming walls which shall be cemented by the fusion of a part of the materials, there appears no reason whatever to doubt it.
But it is not whether a wall can or cannot be constructed of fusible materials, which is the question ; but whether the appearances which now present themselves justify the as sumption that they had such an origin. We have already shewn that the people, who had seen the possibility of heat being applied successfully to cement a wall on the hill of Dun Creich, had not availed themselves of what must have been long apparent to them. No wall, or part of a wall of a uniform thickness or height, has ever been seen vitrified on both sides, or throughout, so as to indicate a regular mode of procedure in its formation. We find, indeed, a general regularity in the form and manner in which the ramparts are laid down, and which has been guided by the shape of the hills : but nothing else than irregularity in the mass of which they are formed. We speak of all those we have seen, and of a variety of descriptions which we have read. We often find masses of melted matter of a breadth far exceeding what can be imagined the limits of a wall ; and we find them, too, as on Craig Phadrick, on the brink of inaccessible pre..apices, whet e no wall was necessary. When a breadth of vitrified stones extending 40 feet is mentioned, it instantly occurs as being very unlikely that the labour of constructing such a wall was thrown a way, since one half the thickness is far beyond the strength ne cessary for a rampart. There is little difficulty in comely ing how signal fires, kindled sometimes in one place, some times in another, and varying in magnitude as occasion re quired, might spread over a surface of forty feet. The shift ing of the wind, and the violence with which it blows on the tops of such hills, was.sufficient to put those who had the charge of making signals, on some contrivance to pre vent the wood from being dispersed, and themselves from being annoyed ; and thus the ramparts of loose stones which they had raised to defend themselves from being surpi iced, may have become stronger without their having had any intention of making them so. It is nevertheless by no means unlikely, that in some cases, the fusible nature of the stones might have been taken advantage of ; but there is nothing, which we have been able to discover, to justify the idea that a regular method for raising walls and cementing them by fire, was ever in use. On the hill of Dun Jardil, Mr Tytler could discover no marks of vitrification; yet such maths were discovered by Mr Nimmo, on the only part of the hill where signals could be made, so as to connect the great chain of posts extending from coast to coast ; and along this chain it has been found necessary to make use of hills on both sides of the valley, in order to complete the com munication. Here, then, is another instance in which the fusibility of the stones has not suggested the idea of strengthening walls by means of fire. But we have said enough on this part of our subject.