282 PROCEEDINGS OF TFE GEOLOGICAL SOCIETY. [May 12, 



Greece holes of various sizes bored to different depths by the com- 

 bined 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 Okigiit of the Parallel E-oads of Glen Rot. By James 

 NicoL, Esq., E.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 horizontahty 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. Yarious 

 theories have been proposed, each enjoying popularity for a time, 

 but no one permanently remaining master of the field. The hori- 

 zontality, 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 sud- 

 denly 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 sup- 

 porting 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 observa- 

 tions, 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 under- 

 stood) 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- 



