184 ON THE REVOLUTIONS 



with no case deviating; more than 10° or 12° from that average 

 on either side *. 



Specimens. 



I shall now describe the situation of fifteen specimens around 

 Corstorphine Hill, denoted in Plate IX. by the number of 

 each inclosed in a little circle. 



No 1. The first is upon the rock at Craigleith, part of which 

 is now worked as a quarry. It is a very complete and firm 

 sandstone, and, as I have already mentioned, stands up, in the 

 course of our supposed stream, to the height of forty or fifty 

 feet, having a long projecting tail to the eastward, similar, on 

 a small scale, to that of Edinburgh. It has likewise, on its 

 western side, an excavation similar to that which forms the 

 North Loch, but on a proportionally small scale. 



This rock had lain bare, and open to the day on its wester- 

 ly front, and it everywhere presents to view, where not con- 

 cealed by the rubbish of the quarry, that rotundity of form 

 which might be expected in such a situation, though, by its ex- 

 posure 



* I am aware, that the usual mode is to describe the direction of a current at 

 sea, by stating the point towards which it flows. But my object, on this occa- 

 sion, being to trace the origin of these currents, I have been induced to follow an 

 opposite mode, and in general to denote the course by the point from whence 

 the stream has been supposed to flow. In the following descriptions, the prin- 

 cipal object of which is to mark the place of each specimen, I have frequently 

 omitted the direction, in order to avoid interruption. But these directions have 

 been carefully observed, and may be seen by turning to the page at the end of 

 this paper, where they are a]l placed in one column, each opposite to the name 

 of the spot, and to its number. 



