l)r Hibbert's Observations on Vitrified Forts. 287 



my own experience, I do not hesitate to say, that some few of 

 these forts are not ill calculated to favour the deception. In 

 a hasty survey which I took of the hill of Finhaven (the first 

 vitrified fort I examined) I saw, like Mr Pennant, an apparent 

 crater-formed cavity, filled with fused materials, occurring in 

 such an abundance as to render unsatisfactory any explanation 

 which has been hitherto given of the artificial mode in which 

 vitrification to this immense extent must have been produced. 

 But my illusion was short-lived ; — in the examination of a se- 

 cond example it was instantly dispelled. 



2dly, The theory, that vitrification teas artificially induced., 

 as a cement for the consolidation of ramparts of loose stones. 



In the year 1777, the validity of the volcanic theory was 

 first opposed in a pamphlet published by Mr John Williams, 

 mineral surveyor and engineer for the forfeited estates of Scot- 

 land. 



This author, in advocating the artificial origin of vitrified 

 forts, first assured himself, on the authority of a late eminent 

 chemist, that many varieties of the rocks of Scotland were with 

 little difficulty fusible. Dr Black's letter to him on this sub- 

 ject may perhaps be worth cjuoting : " There are in most parts 

 of Scotland different kinds of stones which can, without much 

 difficulty, be melted or softened by fire, to such a degree as to 

 make them cohere together. Such is the greystone, called 

 whinstone, which for some time past has been carried to Lon- 

 don to pave the streets. Such also is the granite or moorstone, 

 which is applied to the same use, and pieces of which are plainly 

 visible in some specimens of those vitrified walls which I receiv- 

 ed from my friends. There are also many limestones, which, in 

 consequence of their containing certain proportions of sand and 

 clay, are very fusible ; and there is no doubt that sandstone and 

 pnddingstone, when they happen to contain certain properties 

 of iron mixed with the sand and gravel of which they are com- 

 posed, must have the same quality. A pnddingstone composed 

 of pieces of granite must necessarily have it. There is abun- 

 dance of one or other of these kinds of stone in many parts of 

 Scotland ; and, as the whole country was anciently a forest, 

 and the greater part of it overgrown with wood, it is easy to 



NEW SERIES, vol.. v. NO. II. OCTOBEB 18U1. T 



