Their capricious arrangement, if considered as works of art, is equally an argument against the notion of their having been intended as roads. Equally impossible is it to assign any reason for their numbers, when no obvious purpose is held out, or for the various irregularities to which they are subject ; or, lastly, for the extraordinary range of ground which they cover. It is almost super fluous to add to these, the uncalled for nature of an ar rangement so rigidly mathematical, although it were pos sible to admit, which it is not, that the engineers of these days could have constructed works which, for their diffi culty and expence, would alarm even those of our own times. Lastly, we may add on this head, that they are everywhere interrupted by torrents, yet are deficient in bridges, or the traces of such buildings, without which their purposes must have been entirely defeated.
As it is thus plain that they could not, at any rate, have been roads of communication, it has been said that they were constructed for the buntings of these imaginary he roes or kings. Those who have discovered this solution, seem to be less acquainted with the chace of the deer than a Highlander ought to be. They could have been of no use, either for the purpose of deer-stalking, as it is called, or for watching and shooting them in their passage. The reasons must be apparent enough to all those who either are acquainted with this variety of the chace, or will be stow a thought on the subject ; nor is it worth our while to enter on them more particularly.
To get rid of this difficulty, it is said that they were used as a decoy, and that they were staked in on each side, so as to prevent the deer which had once entered from escaping. That such stakes should have been pre served for so many centuries, is not one of the least won derful facts. This notion is, indeed, too absurd to deserve a serious examination, and seems to have been the last effort of those who were driven from all their other holds. Fortunately there arc the remains of a real decoy for deer, still existing in Rum, which seems to have consisted of two stone walls, commencing in the hills, and gradually con tracting till they terminated in a tall circular enclosure, in which the deer were at length confined and killed. The superfluous number of parallel roads for any purposes of this kind, as well as their mathematical arrangement, need scarcely be added to the preceding objections to a theory so very preposterous that we almost repent having bestow ed so much time on its refutation.
Having thus got rid of all artificial causes, we must turn our attention to the discovery of natural ones, and these must obviously have consisted in the action of water in some manner. We think, ourselves, that the mode of ac tion of this cause can be assigned with great certainty ; al though we have not succeeded in explaining all the cir cumstances requisite to its action, or the exact nature of the consequences which have attended it. But as other views, different from ours, have been entertained by some philosophers, and as these are attended with geological consequences of some interest, we shall give an account of these, together with the objections by which these theories are invalidated.
As Mr. Playfair considered these parallel roads to be really artificial works,* Sir James Hall attributed them to his favourite system of debacles. Having remarked that, where a torrent hurries along mud and stones, it leaves their traces at the highest point of its past elevation, so he imagined that the lines of Glen Roy were the traces of huge deluges, or torrents on a larger scale, which at dif ferent elevations had held their courses through this and the adjoining valleys. Lord Selkirk, on the other hand, who visited them about the same time with the two last named philosophers, though be also, like Sir James Hall, considered them owing to the action of water, conceived that they had been produced by the gradual operations and descent of the rivers, which, in cutting their way down wards, and shifting their positions laterally, had left these traces. Thus he considered them as of the sante nature as the terraces so generally formed on the margins of rivers; while, from the frequent coincidences of both these appearances in Glen Roy itself, he considered this opinion as fully established. In Dr. Macculloch's theory, the lines are considered to be the shores of lakes which once occu pied those levels, and their present appearances are attri buted to the drainage of these lakes at different intervals of time. We shall examine the arguments that relate to these different opinions.
In examining the hypothesis which attributes them to debacles or large torrents, we shall pass over any inqui ries about the general principle, and grant, what we have some doubts of, that such phenomena have been genetal or frequent. We must here recall the general disposition of these lines to our readers, that they may the easier un derstand the following arguments. They are found in Glen Roy, at its eastern extremity, commencing near that summit which is the common origin of the Spey and the Roy, the one running eastward and the other westward. In their progress to the west, they increase in number, and in the perfection of their forms and markings, main taining the same level throughout ; while the bottom of the valley descends with a rapid declivity to its junction with that of the Spean. One of these lines, the lowest, ascends the valley of the Spean, surrounding Loch Lag gam and entering into Glen Turit, and finally terminating in the broad common valley of the Roy and Spean, on the south side, as it does on the north also ; the former being continuous with the same line on the one side of Glen Roy, and the latter being, in the same way, a prolongation of the other. The upper lines of Glen Roy enter partially into Glen Turit, as well as into other smaller ramifications of the principal valley, and one line is also found occupy ing a similar position in Glen Gloy.