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



between joints, cut across at large angles with the trend of the 

 bedding. No contrast could be more striking ; on the one hand we 

 have a gradual passage from bedded metamorphic strata into granitic 

 rocks, where the bedding becomes fainter and fainter, and can at last 

 only be detected by the closest observation, and the line along which 

 this passage takes place maintaining a steady course parallel to the 

 trend of those rocks, which still retain their bedding ; on the other 

 hand, a sharp change from bedded to unstratified crystalline rocks, 

 and the line along which this change takes place, winding over the 

 country and cutting at all possible angles across the strike of the 

 bedded rocks, and dykes running out in numbers from the crystalline 

 mass. 



I have incidentally mentioned the glaciation of the district. 

 Except where weathering may have effaced them, there are every- 

 where superb traces of wide-spread ice-action. 



The Granite Hills, the highest of which, Slieve Snaght, is 2240 

 feet above the sea, are everywhere moutonneed up to and over their 

 summits. The coarse nature of the rock, however, and its rapid 

 weathering, has not allowed of the preservation of scratches to show 

 the direction of the flow. 



To the south-west of Dunlewey, however, is a tract of quartzite, 

 and the scorings on this hard rock have been beautifully preserved. 

 The direction of all that I saw was nearly magnetic east and west ; 

 they show a total disregard to the surface of the ground, running 

 across ridges up and down hill, and sometimes barring a precipice 

 with horizontal scratches, where its face happens to be parallel to 

 their trend. The grooves are extremely regular, and where the ice- 

 marked surface rock has broken up under the action of the weather 

 a very singular effect is produced ; for so true are the flutings on the 

 rouncled surfaces of each moutonneed boss that, as one stands among 

 the fragments M^hich have split off, one could almost fancy oneself 

 amidst the fallen columns of a ruined Grecian temple. Fig. 2 will 

 give some notion of these fluted surfaces. 



Whether the ice passed over Errigal, the highest point (2466 feet), 

 it is impossible to say ; for the rapid weathering of its well -jointed 

 quartzite has long ago effaced any marks that may once have been 

 there, ^ The low country of mica- schist is everywhere moutonneed, 

 but, like the granite, shows no scratches. 



Lakes are abundant; many certainly, and probably all, lie in 

 rock-basins ; and those that are grown- or silted-up quite equal in 

 number those that still remain. Fig. 3, which is on a true scale, 

 shows a very common arrangement of these lakes. The faces A 

 and B are often very nearly plane surfaces, when not covered by 

 debris, so steep and smooth that it is all but impossible to stand on 

 them ; and seen from a distance they glitter in the sun, when wet, 

 like polished glass ; they plunge straight down in many cases into 

 the lake. At the other end smoothed rock-surfaces rise at a low 



1 Mr. Campbell metitions a doubtful ice-marked patch at the summit. "Frost 

 and Fire," vol. ii., p. 56. 



