526 



REV. J. F. BLAKE ON THE 



presence of mica from the coarser varieties of Craig-yr-allor or 

 Holland Arms. This does not appear to reach the coast, nor 

 even to cross the Nebo road. In some parts the felspar is so 

 separated from the darker ingredients in patches as to give the 

 rock the aspect of an impure granite ; and the granite itself, at 

 its purest in this immediate neighbourhood, only differs in having 

 little or no hornblende. Thus, as noted by Mr. xlllport, quoted by 

 Dr. Callaway, there is a passage from one into the other vrhich we 

 have nowhere else seen. There is also here a quantity of indurated 

 rock in which no mica is developed. None of this is ordinary or 

 metamorphosed sedimentary material except, perhaps, the grey 

 gneiss of Dryslwyn. 



The type of granite in the main mass to the north of Nebo is of a 

 different character. It contains no ferruginous ingredient, and its 

 mica is white. It thus corresponds to the granite of the district 

 south of Traeth Dulas ; but when well preserved it is seen to be much 

 coarser in the grain, and its felspars are brownish in tint, giving 

 the rock a peculiar colour. Moreover, where the rock is most 

 massive, mica appears to be absent. This granite is represented 

 in the map as running in several separate tongues; but these 

 tongues must not be taken as actually representing where the 

 granite is, which would be impossible. Thus, in a quarry near 

 Pant-y-bwlet, visited in company with Prof. Green (see fig. 25), the 



Fig. 25. — Quarry near Pant-y-bwlet. 



Granite. 



2. Unstratified material. 



granite is seen to be running in numerous bands of irregular form 

 and in no special direction in the midst of material without 

 character, which may pass under the general name of pelite. The 

 centres of the granite portions are quite clean, but there is no 

 definite boundary between one rock and the other. This behavioiu' 

 of the granite is more interesting than its nature, and we find the 

 same kind of thing wherever a fresh exposure of rock enables us to 

 see the two kinds in conjunction. Thus, at Bryn-fuches and at Ehos- 

 m anarch certain portions of the rock-face might be called granite or 

 other crystalline igneous rock ; but how it ends or where it goes 

 it is utterly impossible to say. The rest is the same unspecialized 

 pelite, which may become micaceous and so appear schistose in 

 places ; so also near the JSebo quarries there is a boss of the 



