80 MB SMITH on an undescribed Vitrified Fort, 



brown glass, either run into considerable masses, or into veins 

 alternating with the strata of quartz, which has become granular 

 like freestone : occasionally the vitrified matter forms a white 

 enamel. 



I know not whether any more easily fusible substance has 

 been used as a flux, but I could not observe any appearance of 

 breccia, which Dr MACCULLOCH, in his paper on Vitrified Forts, in 

 the second volume of the Transactions of the Geological Society, 

 states to have been generally used for that purpose. 



Within the walls the flat surface of the rock is exposed at 

 A (Plate IV). Near it, at B, there is a small hollow, which was per- 

 haps a well or cistern : at C there is an appearance of a ditch, 

 which, if artificial, was probably intended to strengthen the de- 

 fence on that side. 



There are some peculiarities in the situation of this fort 

 which appear to me decisive of the question which is still agi- 

 tated whether the vitrification is the effect of accident or design. 

 Those who advocate the former opinion have supposed that they 

 were produced by ancient volcanoes, by destruction by fire, or 

 more recently, by the repeated action of signal fires. It is quite 

 unnecessary to say any thing here as to their volcanic origin ; * 

 and I think it proved by the experiments of Dr MACCULLOCH, 

 that, from the intensity of heat required to melt the most fusible 



* Since this paper was written, the theory of their volcanic origin has been revived 

 by Dr HIBBERT, in consequence of an examination of the Fort of Finhaven, in the 

 county of Forfar. I have not seen that fort, but I cannot imagine that it will ap- 

 ply to the one in question, which is of a regular form, and placed on the flat surface 

 of a primitive rock. Neither can it be accounted for by supposing that volcanic pro- 

 ductions have been brought from a distance for the purpose of building, because 

 both from the size of the vitrified masses, and from the downward direction in which 

 the fused matter has run, we must conclude that the vitrification has taken place af- 

 ter the walls were built. 



