556 A. H. Green — Geology of Co. Donegal. 



them, and the strike of these planes was everywhere parallel to 

 that of the undoubtedly bedded rocks which I had left to the west. 

 The rock, however, could scarcely, perhaps, be fairly called granite ; 

 rude foliation was discernible ; it was rude, but perhaps enough to 

 justify any one, who disliked the idea of bedded granite, in calling 

 the rock gneiss. 



With my suspicions excited by what I had seen, I started next 

 up the Poisoned Glen, determined to go well into the heart of the 

 granitic district, and see how far these glimmerings of bedding could 

 be followed. 



I crossed, as before, the mica-schist with its limestone, the same 

 alternations of that rock with bedded granitic gneiss, and noted the 

 same gradual decrease in number and thickness of the bands of 

 mica-schist, and their final disappearance altogether. Scrambling 

 up the steep southern end of the glen, I found myself in a region 

 strikingly granitic both in its physical features and in the minute 

 character of its rocks. In spite of the universal glaciation, which 

 had smoothed and rounded off every hill-top and edge, atmospheric 

 wear, acting on a very characteristically jointed structure, had begun 

 to produce Tors, which any geological artist would pronounce 

 eminently granitic in their outline ; and in the rock itself I could 

 detect nothing deserving the name of foliation. Here for a while 

 I was undecided. This rock might have been once bedded, but its 

 metamorphism has been carried so far as to destroy all traces of 

 bedding ; or, on the other hand, we may have here an intrusive 

 igneous mass, which has produced the metamorphism of the rocks 

 to the west. 



I sat down to take breath and think. Casting my eyes over the 

 country I saw the hills everywhere traversed by a set of divisional 

 planes ranging parallel to one another, and to the general strike of 

 the rocks I had crossed in coming up, and dipping at high angles 

 towards the south-east. If I had not known what rock I was 

 standing on, I should without hesitation, from an instinctive feeling 

 which every field-geologist will understand, have called these planes 

 of bedding. But they might be joints. This doubt was soon 

 settled. I was sitting on a smoothed moutonneed boss, the wetted 

 surface of which laid bare the structure of the rock as clearly as if 

 it were an artificially polished section. I then saw that this granite 

 was made up of a number of layers of different thicknesses, and 

 differing from one another in composition, grain, and other mineral 

 peculiarities, and that these layers had the same high dip towards 

 the south-east, and exactly the same strike across the country as the 

 larger divisional planes I had noticed just before. The layers of the 

 boss had so exactly the look of a group of alternations of coarseish 

 and more finely grained sandstones with sandy shales, such as any 

 section in ordinary Carboniferous rocks would furnish, that I could 

 have no doubt that they were true laminae of deposition ; and hence 

 the conclusion was obvioiis that the larger divisional planes were 

 main planes of bedding. I spent the rest of the day on the granite 

 hills, and found numberless other ice-cut sections of the highly 



