BEN-NEVIS. 



351 



such cases, owes its property to the circumstance 

 of being equally poised on a projecting edge or 

 corner of its base. This projection penetrates the 

 earth to a small depth, before it reaches the 

 harder ground, or probably the rock, on which 

 it stands. It is evidenty a rolled mass that had 

 sunk into the soft soil, by which its equilibrium 

 is no doubt assisted. A man's force impressed up- 

 on it, makes a point on its summit describe an 

 arch of a few inches. 



The vitrified fort on Dundgairdghall, lies a- 

 bout four miles up Glen-Nevis, on the west side. 

 It stands on a summit 1100 or 1200 feet above 

 the level of the river ; and its dimensions seem, as 

 nearly as I could judge, to be ninety feet by forty 

 within the walls, which are raised on the edge of 

 the steep, and, till this day, are very distinct. On 

 the description of what is already so well known, 

 I shall dwell no longer than to say, that the vi- 

 trified stone appears to have been the particular 

 felspar, (having veins of greenstone, or rather fel- 

 spar and hornblende, with iron-pyrites), of which 

 the neighbouring rocks are composed, and which 

 might melt into the different -forms of slag, pre- 

 sented by the specimens. Whatever hypothesis 

 may be adopted to account for the vitrification of 

 such forts, the position of Dundgairdghall suffi- 

 ciently corresponds with the opi ion of Sir George 

 Mackenzie, lately delivered to the Royal Society 

 on this subject. It had probably been the signal- 

 post or watch-tower of Inverlochy Castle, once 



