RAMBLES OF A GEOLOGIST. 371 



prominence in the general landscape, had not been selected 

 as beacon-stations. And in the intermediate class of cases 

 we have probably ramparts that were only partially vitrified, 

 because some want of fuel in the neighbourhood had starved 

 the customary fires, or because fires had to be less frequently 

 kindled upon them than on the more important stations ; or, 

 finally, because these hill-forts, from some disadvantage of 

 situation, were no longer used as places of strength, and so 

 the beacon-keepers had no motive to attempt consolidating 

 them throughout by the piecemeal application of the vitrify- 

 ing agent But the old Highland mode of accounting for the 

 present appearance of Knock Farril and its vitrified remains 

 is perhaps, after all, quite as good in its way as any of the 

 modes suggested by the philosophers.* 



I spent some time, agreeably enough, beside the rude ram- 

 part of Knock Farril, in markyig the various appearances 

 exhibited by the fused and semi-fused materials of which it 

 is composed, the granites, gneisses, mica-schists, hornblendes, 

 clay-slates, and red sandstones of the locality. One piece of 

 rock, containing much lime, I found resolved into a yellow 

 opaque substance, not unlike the coarse earthenware used in 

 the making of ginger-beer bottles ; but though it had been 

 so completely molten that it had dropped into a hollow be- 

 neath in long viscid trails, it did not contain a single air- 

 vesicle ; while another specimen, apparently a piece of fused 

 mica-schist, was so filled with air-cells, that the dividing par- 

 titions were scarcely the tenth of a line in thickness. I 

 found bits o schistose gneiss resolved into a green glass ; the 

 Old Red Sandstone basis of the Conglomerate, which forms 

 the hill, into a semi-metallic scoria, like that of an iron- 

 smelter's furnace ; mica into a gray waxy-looking stone, that 



* This mode is described in a traditionary story regarding a gigantic tribe 

 of Fions, narrated in " Scenes and Legends of the North of Scotland," 

 chap. iv. 



