262 Dr. Mac CaLLOCii on the Viti-'ified Forts of S> coil and. 



probably not considerable. Nor indeed would a work which was 

 intended for defence from within admit of a greater height of wall 

 than five feet, or that over which a man might look, a height which 

 is equal to that of the ancient British field works, if this may be 

 determined from some of the perfect fragments which remain in 

 Cornwall. 



Of one of the most remarkable of these, I have given an account 

 to the Antiquarian Society. It is the fort known by the name of 

 Castle an Dinas, in the parish of Ludgvan, in that county. Here 

 the altitude of the work is determined by the perfect finish of part 

 of the remaining wall, which consists of well-fitted dry masonry, 

 the strength and solidity of which show that it was not a temporary 

 enclosure, but a sort of citadel, or work of permanent defence. 

 The wall is here only five feet high, and from this I am inclined to 

 conjecture that the vitrified forts did not exceed this height. Nor 

 indeed are the accumulated ruins about them sufficient to give rea- 

 son for suspecting that they ever were of a greater elevation. It is 

 deserving of remark, that the vitrification of the outer work is not 

 so complete as that of the inner ones. 



Before examining the materials of which the wall is composed, 

 it is necessary to mention the mineralogical nature of the rock on 

 which it stands, and that of the immediate vicinity. The hill of 

 Dun Mac Sniochain is formed of limestone, lying in schistus, similar 

 to that which constitutes the neighbouring island of Lismore. The 

 schistus and the limestone alternate, but the latter is the predominant 

 rock. The hill itself is perfectly insulated in a great alluvial plain. 

 To the west this plain is bounded by the mountains of Benediraloch, 

 which descend abruptly into it, approaching at their nearest point 

 within half a mile or less of the fort. These mountains are formed 

 of the old rocks common to this country, granite, gneiss, mica-slate. 



