Dr. Mac Culloch on the Vitrified Forts of Scotland. 271 



rocks. The pudding-stone of Craig Phadric differs completely from 

 that of Lorn. It contains no fragments of the greenstone amyg- 

 daloid, there being no greenstone beds, in its vicinity, as there are 

 on the Oban coast. The pebbles which it does contain are of quartz, 

 gneiss, granite, and the other associated rocks. The paste which 

 cements them is of a granular texture, entirely and essentially dif- 

 ferent from that of the Lorn pudding-stone, and belonging to a very 

 different class of substances. It is agglutinated by adhesion, as 

 th'^ sandstones are, without a common binding paste; and con- 

 sists of fragments of the same rocks which form the nodules, 

 exhibiting generally a gritty mixture of horn-blende, mica, fels- 

 par and quartz, with a considerable portion of ferruginous fels- 

 par clay. The difference in the vitrification of the wall arising 

 from this cause is obvious, since the scoria of Craig Phadric 

 contain none of that very light and spungy sort capable of floating 

 in water, and which I have shown to arise from the fusion 

 of the calcareous amygdaloid. It differs also in these respects, that 

 it contains no pyritical slate, and that it contains fragments of sand- 

 stone. The heat has operated on these stones so as to roast and 

 crack the quartz, granite, gneiss, mica-slate, common slate, and 

 sandstone, producing appearances similar to those of the specimens 

 in Dun Mac Sniochain. The gneiss only which contains much 

 hornblende, and passes into hornblende- slate, is partially fused. 

 The mica-slate, containing also in some instances layers of horn- 

 blende, has been split in sunder by the vitrification of these laminse, 

 and in other cases it is bent and contorted in a very amusing and 

 instructive manner. But the cementation of the wall is produced 

 by the vitrification of the paste v/hich forms the pudding-stone. By 

 this, not only its own pebbles are united, but the neighbouring 

 stones have been entangled in the general mass. 



It is plain that no additional argument to support the notion of 



