The latest examination of Vitrified Forts is contained in a paper by Dr. Edward Hamilton,[103] in which he gives detailed descriptions of two such structures in Arisaig, one of which is situated on a promontory in Loch na Nuagh. It is an irregular oval occupying the whole summit of the promontory, and measuring about 100 feet in length by about 50 feet in breadth. The enclosing wall varies from 6 feet in thickness and 7 feet in height to about 5 feet in thickness and 3 feet in height. In this case also the wall was not vitrified down to the foundation. Underneath the vitrified portion there was a depth of 3 feet of walling formed of water-worn boulders quite unvitrified. The internal part of the upper or vitrified portion of the wall was also unvitrified. From these appearances Dr. Hamilton concludes that the vitrifaction was the result of fire applied to the upper part of the wall externally. ----- Footnote 103: _Archœological Journal_, vol. xxxvii. p. 227. ----- From a consideration of these examples it is evident that the Vitrified Forts do not differ in any essential point of their character from the forts that are not vitrified—if vitrifaction be not a feature in the method of their construction. The results of former investigations have not produced evidence sufficient to carry the conclusion that the vitrifaction was accomplished at the time of their construction, or that it was a method of construction. The determination of this question lies at the end of an exhaustive investigation, and can only be obtained from evidence furnished by the phenomena of the structures themselves.