Ch. VII.] THE GRANITIC AND SCHISTOSE ROCKS. 133 



by Mr. Weaver, in his account of the east of Ireland : " In 

 a ravine, which marks the northern face of Crogan Moira, 

 we may observe that the granite acquires more and more of a 

 quartzy nature as it approaches the mica-slate, becoming 

 almost slaty-quartz at the point of contact ; while the mica 

 slate itself abounds in beds of quartz of variable thickness, 

 and the granite is traversed in all directions by contem- 

 poraneous veins of quartz of greater or less magnitude, and 

 also by veins of granite." * 



In the Island of lona, according to Dr. Macculloch, a few 

 rocks of red large-grained granite occur on the shore below 

 the Bay of Martyrs, and are in contact with the schist. The 

 latter rock, at a distance from the granite, is described as a 

 black compact clay-slate, occasionally containing hornblende, 

 and sometimes mica, and seems to hold an intermediate place 

 between clay-slate and gneiss : but when in contact with the 

 granite, it puts on a remarkable appearance, displaying exter- 

 nally a singular mixture of black and red. It is very hard, 

 and its fragments are as sharp-edged as siliceous flint. In 

 many places this schist loses its black colour and becomes 

 grey ; in others it is mottled with red felspar, and interspersed 

 with quartz, which minerals increasing in quantity, the slate 

 appears to be on the very verge of passing into the granite 

 with which it is nearly in contact, the sea, in this place, pre- 

 venting the actual contact from being examined; else it is 

 probable that a still more perfect series of this transition 

 might be observed. The junction of argillaceous schist with 

 granite is not rare in Scotland ; but this is the only instance 

 seen by Dr. Macculloch, in which the interference of the latter 

 is of such a nature as to produce the appearance of a real 

 transition from the one to the other rock.f 



In the Island of Mull, says the same author J, a long and 

 interesting line of the junction of granite and the primary 



* Geol. Trans., vol. v. p. 152. f Western Islands of Scotland, vol. v. p. 15. 

 | Idem, vol. i. p. 554. et seq. 



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