Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/378

 Greece holes of various sizes bored to different depths by the combined action of vegetation and atmospheric influences. In some cases these holes were large enough to receive the arm, and were two or three feet in length.

3. On the Origin of the Parallel Roads of Glen Roy. By James Nicol, Esq., F.R.S.E., F.G.S., Professor of Natural History in the University of Aberdeen.

The general characters and appearance of these celebrated roads are so well known as scarcely to require to be mentioned. Running apparently with perfect horizontality and complete parallelism along the two sides of a long Highland glen, turning up every lateral valley and encircling every hill, they form a spectacle altogether unique in this country, and which, when once seen, can never be forgotten. Their mode of origin, on the other hand, still remains one of the open, undecided questions in Scottish geology. Various theories have been proposed, each enjoying popularity for a time, but no one permanently remaining master of the field. The horizontality, parallelism, and general character of the lines leave no doubt that they have been formed by water standing at the level of each line or road for a very considerable period, and then suddenly subsiding to the level of the next lower road. Thus far all recent observers seem agreed. But fresh water and salt — mountain loch and sea-firth — have still each their own supporters ; and some who once advocated the one of these views, may now be found supporting the other. It is thus evident that no facts very decisively in favour of either theory have yet been adduced. But that such facts do exist I hope to be able to show in the following observations, and thus to contribute some evidence tending to decide this question.

As the general aspect and characters of these lines or roads are so well known, and have been so often and accurately described, I shall abstain from referring to them as far as possible. My remarks also have reference to the rival theories generally, and not to any special view or defence of them, and I have therefore avoided all reference to the writings of former observers, and all criticism or remark on their arguments. With very few (and these easily understood) exceptions, the facts stated are only such as I have personally verified during my repeated visits to the country where the lines occur.

Two rival theories as to the cause and origin of these lines at present prevail among scientific men. One party considers them ancient sea-margins, left behind as the land rose, or, as it may be otherwise expressed, when the sea retired. The other party ascribe them to fresh-water lakes which formerly filled the valleys and were drained at intervals, as the barriers, of ice or detritus, that shut in these lakes, were suddenly dissolved or broken down. I adopt the first or marine theory, and therefore am not much con-