COMPARISON OF VARIOUS DEFENSIVE STRUCTURES. 



103 



southern extremity, where the ground is most precipitate, we meet with three 

 hues of ramparts, which intersect the area of the camp, through two of which 

 there is an opening : the eastern point was fortified by a raised mound." — {lb. Vol. 

 IL, p. 101.) 



The singular vitrified forts of Scotland, are suggested in this connection. They 

 appear to have been composed of loose stones, which, by some process of vitrifi- 

 cation, were made to present the outward features of sohd rocks, and have long 

 perplexed antiquarians. Some have attributed the vitrification to lightning, others 

 to accidental conflagration, while a few, more daring in their speculations, have 

 considered them the craters of extinguished volcanoes ! It has also been supposed 

 that vast defences of wood once surrounded and surmounted the ramparts, by the 

 casual burning of which they were vitrified. There is, however, every reason to 

 believe, that this feature was the result of design, although it is not easy to explain 

 how it was produced. Dr. Anderson, in a communication to the Society of Anti- 

 quarians, in 1777, gives an account of a remarkable work of this description, called 



Knockferral, in Ross-Shire. It is placed on a high ridge of an oblong shaped hill, 

 very steep on three sides, the walls being raised on the edge of a precipice all 



