SCHISTOSE KOCKS OP NORTHERN DONEGAL. 225 



with the trend of the schist within the granite of Barnesbeg Gap. 

 The litholo^ical evidence is decidedly against the creation of two 

 formations. The hornblende-schist of the so-called Lanrentian is 

 specifically the same as that above the limestone, and cannot be 

 distinguished in hand-specimens from rocks on the other side of the 

 granite, near Creeslough, which are placed by Prof. Hull in the 

 Lower Silurian. The lead-coloured schist, too, may be matched 

 over and over again in the supposed newer series on both sides of 

 the granite promontory. It should also be observed that these 

 schists, hornblendic and micaceous, are fine-grained and thin-bedded, 

 thus differing widely from the massive gneisses of the Laurentian, 

 whether in Scotland, the Malvern Hills, or the Wrekin. On the 

 whole, I can see no reason of any serious weight for separating the 

 schists in or near the granite from the ordinary schistose rocks of 

 the region. 



Fig. 2. — Section West of OroagJi. 



N.W. S.E. 



Sch G 



Gr. Granite. Gf. Foliated Grranite. 



Section ivest of Croagh (fig. 2). 



Coming to the western side of the granite promontory, we find a 

 second junction between the granite and the schists on the main 

 road west of Croagh Hill. The breadth of the granite, where it is 

 crossed by the road through Barnesbeg Gap towards Creeslough, is 

 about three miles. Approaching the western margin of the pro- 

 montory from the east, we observe that the foliation in the granite 

 becomes very marked. In one spot there is a clear dip to the S.E. 

 at 80°. This rock is mainly composed of felspars, one of which is 

 orthoclase, and black mica. The foliated structure is seen, not only 

 in a linear arrangement of the mica, but also in a distinct striping 

 of light and dark bands, corresponding in direction with the strike 

 of the mica, the dark colouring being due to the abundance of that 

 mineral. 



A few yards beyond we come to the junction. The rock next to 

 the granite is a thin-bedded, flaggy, grey schist, containing a whitish 

 mineral, which Prof. Bonney is disposed to think hornblendic. I 

 would suggest that the occurrence of this mineral may be due to the 

 presence of granite in the vicinity of limestone, of which there are 

 signs near at hand. A granitoid material is also seen to penetrate 

 a rock which Prof. Bonney considers pyroxenic. I am inclined to 

 regard this as a case of intrusion of granite in limestone, with sub- 

 sequent chemical reactions. In Prof. Bonney's opinion, some of the 



