David Miln«, Esq., on Polished and Striated Bocks. 156 



These observations of Sir James Hall have lost none of their in- 

 terest by the lapse of time. On the contrary, their importance with 

 reference to geological speculations, has vastly increased, — Jlrsty by 

 the discovery that the same phenomenon occurs in multitudes of other 

 places throughout this country, and in others; and, secondly, by 

 the vain, at all events diversified, attempts to assign an adequate and 

 probable cause for the phenomenon. 



Sir James Hall suggested the notion of a tremendous wave which 

 swept over the country ; and in this suggestion most people were con- 

 tented to rest, until the theories of Glaciers and Icebergs came into 

 fashion ; and, supported as they have been by philosophers of great 

 talent and reputation, the question as to the origin of the polishing 

 and scratching which exists on the surface of rocks, now forms one of 

 the most difficult and controverted in modern geology. 



I do not wish, however, to be understood as stating, that in all 

 the cases where the phenomenon occurs, geologists are completely 

 baffled as to a probable explanation. In Switzerland, for example, 

 it is now generally allowed, that the smoothed and striated appear- 

 ances presented by the rocks situated in its valleys, and even con- 

 siderably beyond them, are to be explained by the action of glaciers 

 moving over them. An attempt has been made to extend this ex- 

 planation to Scotland ; but, with the exception of Professor Forbes's 

 Memoir on the Cuchullin Hills of Skye, I must say, that none of 

 these attempts ever brought conviction to my mind. The proposal of 

 those who first searched the country in quest of moraines, was to 

 cover the whole of Scotland, lowlands as well as Highland glens, with 

 sheets of ice, which, moving forward even on plains the most level 

 and the nearest to the sea, ground down the rocks, and occasionally 

 rutted them with the loose blocks encased in the body of the glacier ; 

 and, so far as I can learn, this theory is not yet abandoned. Pro- 

 fessor Forbes, on the other hand, has limited his glacier views, in 

 so far as yet made known, to the explanation of polishing and scratch- 

 ing in valleys and the mouths of valleys, which have not only a con- 

 siderable slope, but are connected with ranges of hills having a con- 

 siderable height. 



In such cases as these, there is not much difficulty in applying the 

 glacial hypothesis. Bat when the phenomenon occurs where there 

 are no valleys at all, and where, if a glacier existed, it must have 

 moved in a way entirely different from what the scratches indicate, 

 then arises the problem, as to the solution of which geologists are by 

 no means agreed. 



I have been led into these preliminary remarks, to shew the great 

 geological value of the discovery recently made on the west side of 

 Arthur Seat. In forming a part of that magnificient carriage-drive 

 which is to encircle the hill, the work-people came upon those rocks, 

 a description of which will occupy the chief part of this paper. The 

 value of the discovery is great for two reasons : In the first place, 



