Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/388

 a point which shall satisfy the requisite conditions. It is not at present necessary to pursue it further in this direction; we must turn our attention to the lower end of Loch Lochy. Here we find the lake terminating in a wide alluvial plain, the recent increase of which is marked by the depth of peat on its surface; while it communicates by wide openings, as well with the sea at Fort William, as with the wide and open valley in which the western branch of Loch Eil lies. If any probable place can be selected for the barrier to the sea in this direction, it is at the narrowest part of this opening, which lies at Fort William, between the skirts of the range below Ben Nevis and the opposite hills of Ard Gowar. The aspect of the ground, the course of the waters, and the nature and disposition of the rocks, render it difficult to assign any barrier nearer to the opening of Glen Spean. But I have shown that there is another free opening to the sea, from the supposed lake of Glen Roy through Loch Shiel, and Loch Moidart. Another barrier must therefore be interposed in this direction; and thus there will be formed a large lake occupying Glen Roy to some point beyond the present source of the Spey; Glen Spean, with the whole of Loch Laggan, and Glen Gloy; the Great Caledonian Valley, from a point, of which I do not pretend to define the northern limit, to Fort William; Loch Arkeig, and a part of the valley which includes it; and finally the western valley of Loch Eil, to some undefinable point lying towards Loch Moidart and the western sea. The whole of this limit is indeed not demonstrable, but I consider that the similarity, if not the actual community of the lines of Glen Roy and Glen Gloy, does demonstrate that a portion or the whole of Loch Lochy was included in it. Here therefore a serious difficulty arises, although perhaps not greater than that which is afforded by the view of Glen Spean. This is the total absence of all corresponding water marks