To these general objections we may add some of a local nature. No marine remains exist in Glen Roy, nor arc there any indications of those deposits of calcareous sand or of mud, which must have existed at the bottom of such a bay of the ocean, and in which the sea must have rested so long. Those lochs which really do belong to the sea are proved by the sounding line to contain such deposits; while, where the water has been compelled to retire in consequence of the lateral increase of the land, the allu vial lands, now laid dry, contain decided traces of their marine origin. This is remarkable in that low tract which lies between Campbeltown and Al achrianish Bay, and which once rendered the hull of Cantyre an island ; and it is even more conspicuous in Isla, where a deep maritime deposit forms the neck of land which now sepa rates Lochindaal from Loch Gruinart. If, as we formerly attempted to show, Glen Roy was once dry even before it became the receptacle of a lake, the difficulties here stat ed on this hypothesis become still greater. But they are already insuperable, and we shall therefore make no scru ple in rejecting that, which appears to us among the most gratuitous and untenable of all the theories which have been proposed on this subject. We admit, that the na ture of the barriers and their changes forms the most diffi cult part of Dr. Macculloch's Theory ; but that which on this view is merely a matter of difficulty, may, on the pm: sent one, be considered as fairly impossible.
If we have thus brought to a conclusion the history of the principal facts, and the reasonings which belong to this subject, there is yet ground for some useful and interest ing remarks on the surrounding state of the country, as connected with these revolutions. \Ve shall make these as brief as possible.
If the great Caledonian glen was once occupied by the sea, as is commonly supposed, the present land, which forms its bottom, and which is now elevated about ninety feet above the level of the water, must have been deposit ed by rivers, or other analogous causes, and the whole of it must be alluvial. By some partial accumulation of these, have also been formed the dams which separate the several lakes from each other, and from the sea. It is plain, indeed, that these alluvia are slowly augmenting, and at some future, if far distant period, the effect will be to fill up all the lakes, and reduce the whole to a dry glen, conducting rivers to the northward and southward. Thus, the first process here must have been that of accumulat ing alluvia, or raising the level of the bottom ; while, at the same time, the destruction of the barriers of Loch Spean required a reverse operation. These are not, how ever, incompatible under conceivable circumstances, but we cannot spare any space to enter on many more of these abstruse discussions.
But there is a consequence much more puzzling than even this, to be deduced from some of the phenomena of Glen Roy, and which, being of a general nature, was re served to this place. In many places the lines enter into the furrows on the faces of the hills for a certain space, without being prolonged all through them. It is evident, from an examination of these furrows, that they have been formed by the water courses which still occupy them. But as they bear the marks or the lines through the outer, or most ancient part only, it is plain that these lines are posterior in time to that early part of the furrow, or bed of the torrent, which bears their marks, and anterior to the deeper part, where these are wanting. But if we now conceive the water of the lake to have stood at the height of the upper line, it is evident that the furrow gene rated by the lateral torrent could not have been formed at that level, and so far below it also, as is necessary to ad mit the depositions of these lines, or shores, on its sides; still less to have continued and repeated the same opera tions at the lower levels. The descent of the torrent must have ceased as soon as it met the lake, and there fore, those parts of the furrows which are of higher or equal antiquity with this lake, as that is determined by the presence of the lines, could not have been formed by such torrents. It seems, therefore, necessary that such parts of the furrows as bear the marks of the lines, should have existed even under the waters, or before they were accumulated in the valley ; while the bottoms of the same channels, which now bear no marks of this nature, have been produced by the corrosive action of the same tor rents since the drainage of the waters.
• We arc aware that this is a piece of delicate reasoning, and some of our readers may possibly think that it is over refined. But if it be just, there roust have been lateral water courses in Glen Roy, flowing down the hills far to wards the bottom of the present valley, and in times more ancient than the formation of the lines. They were, there fore, more ancient than the lake itself; or there was a pe riod prior to the state of a lake, in which Glen Roy was a dry valley, or at least a lake of less depth than the most ancient one. For this end we should also require the for mation of a barrier, as well as its subsequent removal ; and that within a period subsequent to that at which the present distribution of hill and valley was made, and, therefore, in times comparatively modern.
Some other geological inferences of no small import ance may be made from the appearances that have thus been described, and without the necessity of adverting to the precise nature of the actions which produced them, or even with the admission that any of the rejected hypo were the true one.