166 David Milne, Esq., on Polished and Striated Bocks. 



vium in its original state. Immediately over the basis of the marked 

 rock surface, there lies a sloping mass of recomposed diluvium, — that 

 is, mixed up with sandy and other stuff, as well as boulders of green- 

 stone, mica-schist, &c. Over its surface lie horizontal beds of im- 

 pure sand and peaty matter, the deposit of a lake now degenerating 

 into a morass. 



At Blackford Hill there was, till lately, a considerable surface of 

 smoothed and striated rock, of which an account will be found in a 

 Memoir published by me on the Mid-Lothian Coal-fields. 



On the knoll occupied by Craigmillar Castle, there were similar 

 dressings seen, as I am informed by Mr Jardine, when the rock 

 was quarried a number of years ago. In several places near the 

 castle, the conglomerate rocks are much rounded, and the bared sur- 

 faces all towards the north-west, but no furrows are at present dis- 

 cernible. 



3. The next circumstance, which I deem worthy of notice here, 

 is the rounded form or shape of the rocks on the N W. side of Samp- 

 son's Ribs, and the comparatively sharper or more angular forms of 

 the rocks on the S. and SE. sides of the same hill, 



II. Having described the most important facts connected with 

 the appearances of smoothing and rutting on the rocks of Arthur 

 Seat, and on others in the neighbourhood, I proceed to the more diffi- 

 cult question, What is the agent which has produced them ? 



1. In the first place, it appears clear, from some of these facts, 

 that an immense volume of water has passed over the country— at 

 or immediately after the period that these rocks were smoothed and 

 striated. 



There are two points involved in this proposition, first, the passage 

 of the water ; and, secondy the time when the rocks were so operated 

 on. 



(1.) As to the first point," no doubt can be entertained. The ac- 

 cumulation in Sampson's Ribs gully, of limestones, coal, sandstones, 

 felspar, porphyry, greywacke, and other rocks, which do not belong 

 to this neighbourhood, and must have been brought from a distance, 

 is one unequivocal proof of this. 



The deposit of gravel and sand at Windygowl, about a quarter of 

 a mile to the eastward, is another clear proof of the existence of 

 running water at that level. 



Nor would it be difficult to adduce indications of water currents at 

 a still higher level on Arthur Seat. Mr Maclaren* gives an account 

 of rolled blocks and boulders in places adjoining this gully, and from 

 300 to 400 feet above it. 



And that the water which flowed at this high level must have had 



* Geology of Fife and Lothians, p. 4) 



