55 



a sort of huge bed dipping at a moderate angle witli the horizon 

 from N\V. to SE., and probably thinning out in the latter direc- 

 tion. In confirmation of this view, it is stated that the junction of 

 the hyperstheno and claystone occurs at a height of 2050 feet on 

 the northern slope of the CuchuUins, all below being common trap ; 

 but the junction descends to the very bottom of Glen Sligachan 

 near Loch-na-Nain, which is little elevated above the level of the 

 sea. The hypersthene appears to have a decidedly slaty structure 

 parallel to this bed, which, with its singularly intractable nature, and 

 its resistance to weathering, occasions the jagged forms for which it 

 is so celebrated. The author believes that it has a triple cleavage, 

 one parallel to the bed and two perpendicular to it ; and that the nu- 

 merous claystone veins which traverse the mass of hypersthene up 

 almost to the very summit, have, likewise, a threefold direction 

 parallel to these cleavages. The author thinks that the posteriority 

 of the hypersthene to the neighbouring rocks is probably deducible 

 from the facts which he mentions. 



The second part of the paper refers to what he considers unequi- 

 vocal traces of glacier-action in many directions around and amongst 

 the Cuchullin Hills. Those are principally — 



(1.) Furrowed and striated rocks and roches moutonnees, undis- 

 tinguishable in kind from those in the Alps, and, if possible, ren- 

 dered more remarkable from the unparalleled hardness and toughness 

 of the rock operated on, and the palpable incongruity which these 

 forms present to those natural to the hypersthene rock. These fur- 

 rows are to be seen parallel to the direction of the different ravines 

 of the Cuchullin Hills, and that at all points of the compas.s, thus 

 radiating from this little mountain group as a centre, and clearly 

 localizing the cause — the wonderful mechanical cause — which has 

 produced such a phenomenon : which, when the nature of the rock 

 is taken into account, must be considered as one of the most wonder- 

 ful instances of abrasion of which the world presents an example. 



(2.) Coupled with this is the transportation of angular blocks of im- 

 mense mass, transported over chasms, and lodged high and dry in 

 fantastic positions on ledges of rock, and on the summit of the ice- 

 worn domes of smoothed hypersthene. These phenomena, so well 

 seen at Coruisk, and so graphically described, though unexplained 

 or misunderstood, by Dr MacCuUoch, are in all respects analogous 

 to the blocs perches of the Alps. Of banded and ti-rminal moraines 

 'examples are pointed out in radiating directions, east, north, and 



