366 RAMBLES OF A GEOLOGIST. 



ing, as he premised, a large portion of the ramparts composed 

 of wood, had succeeded in setting them on fire. This hypo- 

 thesis, however, seems quite as untenable as that of Pennant. 

 Fires not unfrequently occur in cities, among crowded groupes 

 of houses, where walls of stone are surrounded by a much 

 greater profusion of dry woodwork than could possibly have 

 entered into the composition of the ramparts of a hill-fort ; 

 but who ever saw, after a city-fire, masses of wall from eight 

 to ten feet in thickness fused throughout ? The sandstone 

 columns of the aisles of the Old Greyfriars in Edinburgh, 

 surrounded by the woodwork of the galleries, the flooring, 

 the seating, and the roof, were wasted, during the fire which 

 destroyed the pile, into mere skeletons of their former selves ; 

 but though originally not more than three feet in diameter, 

 they exhibited no marks of vitrescency. And it does not seem 

 in the least probable that the stone-work of the Knock Far- 

 ril rampart could, if surrounded by wood at all, have been 

 surrounded by an amount equally great, in proportion to its 

 mass, as that which enveloped the aisle-columns of the Old 

 Greyfriars. 



The late Sir George Mackenzie of Coul adopted yet a fourth 

 view. He held that the vitrification is simply an effect of 

 the ancient beacon-fires kindled to warn the country of an 

 invading enemy. But how account, on this hypothesis, for 

 ramparts continuous, as in the case of Knock Farril, all round 

 the hill 1 A. powerful fire long kept up might well fuse a 

 heap of loose stones into a solid mass ; the bonfire lighted on 

 the summit of Arthur Seat in 1842, to welcome the Queen 

 on her first visit to Scotland, particularly fused numerous de- 

 tached fragments of basalt, and imparted, in some spots to 

 the depth of about half an inch, a vesicular structure to the 

 solid rock beneath. But no fire, however powerful, could 

 have constructed a rampart running without break for seve- 

 ral hundred feet round an insulated hill-top. "To be satis- 



