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



rocks at this place, I proceed to mention some collateral points, 

 which appear to deserve attention. 



1 . The superficial deposits over these rocks are of two kinds. 



The one lying immediately on them, is a clay of a light brown 

 colour, very stiff and tenacious. In order to be removed, it must be 

 worked with the pick. There are many blocks of stone, of various 

 sizes, interspersed through the clay, some of them rounded, and 

 others angular, the nature of which will be immediately described. 



This stiff clay is not stratified, and it resembles, in many respects, 

 the well-known Till or Boulder clay which prevails over the rocks in 

 the Lothians. The only difference is, that it wants the bluish- 

 black colour which almost everywhere characterises the boulder 

 clay, and that it is not quite so tenacious. 



At Sampson's Ribs, this deposit is in immediate contact with the 

 polished and striated wall faces of the trough or gully, which, in fact, 

 had been filled by it ; and it is to this impervious covering of the rocks 

 that we seem to be indebted for the very perfect preservation of the 

 strise. Many of these striae are exceedingly minute, so that they 

 could have been easily obliterated by weathering ; and from this 

 circumstance, as well as from the aspect of the whole surface when 

 the clay covering is removed from it, the idea is strongly suggested, 

 that little or no time could have elapsed between the formation of 

 the strise and the deposit of this clay bed. 



The largest of the boulders imbedded in this clay which I ob- 

 served, is the one before specially noticed, as having partly choked 

 up or filled the gully at or near its north opening. It was very 

 much rounded, and had an average diameter of from three to four 

 feet. I observed five or six other blocks nearly as large near it, 

 but, generally speaking, the blocks were about half the size of the 

 one now mentioned. 



They were not deposited in any regular order, but just as they are 

 usually seen in the well-known Till or Boulder clay of Scotland. 



Whilst some of them were rounded, others of them were angular. 

 The smallest in size were generally the most angular. 



Multitudes of both classes of boulders were lying in immediate 

 contact with the polished and striated rocks, — not only where the 

 surface of these rocks was horizontal, but where they sloped even at 

 the most considerable angle to the centre of the trough. 



As to the nature of these imbedded boulders, they were of two 

 kinds. Some of them, being very compact and much rounded, had 

 evidently been brought from a distance, an inference confirmed by 

 the fact, that some of them were of rocks, none of which occur at 

 this place or in the neighbourhood of it; others, again, being soft 

 and friable, and consisting of rocks the same as those occurring in 

 the neiorhbourhood. But in both classes, there was no imbedded 

 mass which could be discovered in the clay of a rock precisely the 

 same as that forming the gully itself. 



