S792» ajitiquities in Scotland. 273 



vitrify the whole mafs that was on fire at the time ; 

 but as onlj a small part of the tuel in a lime kiln is 

 on fire at one time, the fire ascending gradually as 

 the fuel is consume'd, from the^bottom to the top, if 

 the weather was calm the day after a high wind, 

 the fuel burnt them much more slowly ; so that the 

 pare of the stone immediately above the vitrified 

 layer was not sufficiently burned. Thus it happened 

 that the irregularity of the weather produced the 

 disagreeable effects already described. In like man- 

 ner might the fuel that was applied for the purpose 

 of vitrifying these walls, be alternately blown up in- 

 to a melting flame, by the force of a high wind one 

 day, and sufFered to burn slowly during a succeeding 

 calm day, or more, so as to act then with so little 

 force upon the stones, as not to melt them at all. 

 According to this hypothesis, it would seem pro- 

 bable that the fuel had been here intermixed with the 

 stones in building the v/all, which does not seem to 

 have been the case with any of the others I obser- 

 ved. But on this head, the facts are not so clear as 

 to enable us to speak with certainty : probable conjec- 

 ture is all that can be here ofiered. 



On the whole, respecting these structures, the on- 

 ly particular that seems to be with undeniable cer- 

 tainty ascertained is, that they are not volcanic pro- 

 ductions, but clearly works of art, that have been 

 calculated for some sort of defence against the at- 

 tacks of afsailing foes. J. A. 



VOL, X. ■ N N f 



