Note B — THE PARALLEL ROADS OF GLEN ROY, IN SCOTLAND.

Having enumerated the characteristic features of the glacial phenomena in the preceding pages, I throw into this note some explanation which may render my views of the parallel roads more intelligible, not to interrupt again the exposition with details. It would be desirable, however, that the reader should first make himself thoroughly familiar with the localities concerned, before proceeding any farther. I would therefore state here, that, in the wood-cut opposite, G. R. indicates the valley of Glen Roy, with the three parallel roads marked 1, 2, 3. Glen Spean is designated by G. S., and the river flowing at its bottom by S. Loch Laggan, out of which the River Spean rises, is marked L. G. indicates Glen Gloy, a little valley to the northwest of Glen Roy, with a single terrace. Loch Treig is designated by T., Loch Lochy by L. O., Loch Arkeig by A., and Moeldhu Hill by M., while E. indicates Loch Eil. The Great Glen of Scotland, through which the Caledonian Canal runs, extends in the direction of L. O. and E. The position of Ben Nevis is designated by N. The dotted area between N. and M. marks the place occupied by the great glacier of Ben Nevis, when it extended as far as Moeldhu; while the close continuous lines in front of Loch Treig indicate the direction of the glacial scratches left across Glen Spean by the glacier of Loch Treig, when it extended as far as the eastern termination of the two upper terraces. It ought to be remembered, in this connection, that the bottom of the valley of the Spean, as well as that of Glen Roy, is occupied by loose materials, partly drift, that is, materials acted upon by glaciers, and partly decomposed fragments of rocks brought down by the torrents, greatly impeding the observation of the polished surfaces. The river-bed is cut through this deposit, and here and there through the underlying rock. Besides the parallel roads, there are also peculiar accumulations of loose materials in Glen Roy and Glen Spean, more particularly connected with the lowest terrace, which Mr. Darwin and Professor Jamieson have shown to be little deltas formed during the existence of the lake of Glen Roy at the bottom of the gullies intersecting the shelves of the upper roads. The outlet for the water at the period during which the second terrace was formed, not known when I visited Glen Roy, has been discovered by Mr. Milne-Holme, and also observed by Professor Jamieson. During the formation of the upper terrace, the waters escaped through the westernmost tributary of the River Spey, in the direction of the northeast corner of the wood-cut, and during that of the lowest terrace, at the eastern end of Loch Laggan, also through the valley of the Spey. The state of preservation of the parallel roads is such as to prove that no disturbance of any importance can have taken place in the country since they were formed. Far from believing, therefore, that these remarkable shelves are ancient sea-beaches, I am prepared to maintain, that, had the area occupied by them been submerged only for a few days, under an ocean rising and falling for several feet with every tide, no vestige would have been left of their former existence.