SCHISTOSE ROCKS OF NOTITHERN DONEGAL. 227 



we come to the Errigal quartzite. The secondary contortion is at some 

 points very great, and the numerous disturbances render the reading 

 of the ground somewhat perplexing. The schists and limestones 

 are penetrated by several quartz veins and a dyke of dolerite. 

 Similar schists, especially the quartzose and lead-coloured varieties, 

 occupy much of the ground as far west as the sea, and crystalline 

 limestone also occurs near the coast. In fine, I can see no reason 

 whatever for separating the schists east of Errigal from those to the 

 west, and assigning the former to the Lauren tian system. There 

 may be a fault between the Dunlewy schists and the Errigal quart- 

 zite ; but this does not afford sufficient ground for evolving a second 

 formation out of a section which, from Dunlewy to the Atlantic, 

 displays alternations of similar rocks. 



The three sections thus described supply the main evidence which 

 has been relied upon for proving that the granite has resulted from 

 the metamorphism of sediments, that it is associated with certain 

 schists and limestones, supposed to be of the same age, and sepa- 

 rated by a fault on the west and an unconformity on the east, from 

 similar schists and limestones which have been called " Silurian." 

 The facts adduced by me appear to favour the hypothesis that the 

 schists on both sides of the granite are of (approximately) the same 

 epoch, and that the granite has been intruded as an igneous mass. 

 Further evidence of the igneous origin of the granite is supplied by 

 the descriptions which follow. 



Ground round Bunbeg. 



At Dunlewy (fig. 3) the western margin of the granite turns round 

 and strikes to the west for several miles ; but towards the coast the 

 granite projects to the north in a second tongue, near the base of 

 which Bunbeg is situated. The rock about this village is coarsely 

 crystalline, and, so far as I could ascertain, destitute of foliation. 

 Several masses of quartz-schist, some of, perhaps, an acre in area, 

 others mere hand-specimens, are immersed in this granite, which 

 also sends veins into the schist, and sometimes overlies it. Lime- 

 stones also occur, and have undergone great alteration near the 

 igneous rock. A very interesting combination of facts is seen in a 

 low, flat-topped elevation, situated near the " e " of " Bunbeg " on 

 the Ordnance Map. The western escarpment presents a face of 

 bedded limestone, highly crystalline and very full of garnets, some 

 seams being crowded with large, well-formed, brownish-red crystals, 

 while others consist of garnet-rock. The bed at the base of the 

 section, in presumed proximity to the granite, is a melange of 

 minerals, amongst which Prof. Bonney recognizes garnet, more than 

 one member of the hornblende group, and perhaps staurolite. I 

 have little doubt that these minerals are produced by the contact of 

 the granite. Eock is covered between the limestone and the eastern 

 end of the monticule. Here quartz-schist crops out in a low cliff, 

 at the top of which a vein of granite is very clearly seen to pene- 

 trate and overlie the schist. As the limestone and schist both dip 

 at a low easterly angle, there is probably a fault between them, 



