Dr. Mac Culloch on the Vltrijled Forts of Scotland. 26o 



The walls of the fort are found on examination to consist partly 

 of the old rocks before enumerated, and partly of that which I have 

 now mentioned. Gneiss, quartz, granite, mica-slate, clay-slate, pud- 

 ding-stone and pyritical slate are seen entangled together, with a very 

 small proportion of the particular rock on which the fort itself is 

 founded. The source whence these rocks were derived is evident, 

 with the exception of the pyritical slate, which I could not trace in 

 the neighbourhood. 



T have now to enquire what motive could induce the builders of 

 this work to reject the stone which lay at their feet, and to fetch 

 from such a distance the large quantities required to raise their walls. 

 It is particularly remarkable, that although the plain and shore are 

 covered with fragments, yet these are almost entirely fragments of 

 the primary rocks. I state this for the purpose of obviating a sup- 

 position that may be adduced to nullify the argument which I am about 

 to derive of a previous intention in the builders to vitrify their work, 

 from their having neglected to use that rock on which the building 

 was erected, and which was not adapted for the purposes of vitrifi- 

 cation. It might otherwise be suggested that they collected the 

 loose rolled stones of the plain, as being ready broken to their hands. 

 But besides that the pudding-stone is rare among these fragments, 

 the pieces of the wall which have not felt the fire are angular and 

 not rolled stones, showing pretty clearly that they were not collected 

 on an alluvial plain, but broken from the rocks where they were 

 formed. 



Now, in the walls, tlie pudding-stone which we shall presently 

 find to be the only vitrifiable ingredient, predominates to such a de- 

 gree as to occupy the greater part of it. Hence it appears at least 

 a probable conclusion, that the builders were acquainted with the 

 effect of fire in destroying limestone, and that intending to erect a 



Vol. II. 2 l 



