28 GRANITIC ROCKS OF OTHER COUNTRIES [Ch. III. 



the French geologists ; but Dr. Macculloch regards them all 

 as quartz-rock. Thus, in his account of Glen Tilt, he observes, 

 that the quartz-rock associated with the granite is of a compact 

 and somewhat transparent quartz, containing irregular grains 

 of felspar : it breaks in a flaky manner, and appears to consist 

 of beds which extend along the granitic ridge to Grianan, in a 

 north-easterly direction, and dipping to the westward of north. 

 The granite in this situation is grey, and shows a slight 

 tendency to a foliated structure in the vicinity of quartz-rock ; 

 so that these rocks appear to pass into each other. These 

 beds of quartz-rock occur in many parts of the granitic range, 

 so that it has the appearance of alternating with granite.* 

 Macculloch thinks that these beds of quartz-rock are only 

 superficial and detached portions of the stratified rocks super- 

 imposed on the granite ; but it is more probable that they are 

 members of the granitic rocks : for analogous rocks are de- 

 cidedly so in Cornwall ; and in Ireland they appear to be of 

 the same nature, as will be immediately seen in Mr. Weaver's 

 description of the granitic rocks of the eastern part of that 

 country. 



We are informed by this experienced geologist, that the 

 large tract of granite stretching from the south side of the 

 Bay of Dublin to Blackstairs and Brandon, about twenty miles 

 north of Waterford, is full fifty-nine miles in length, and is in 

 general remarkably pure, and free from minerals not essential 

 to the composition of this rock : its felspar is commonly of a 

 clear beautiful white, or slightly tinged with yellow or grey, 

 very rarely flesh-coloured ; its quartz is mostly grey, and its 

 mica greyish-white, inclining to brown or black. This 

 granite varies much in the size of its grain. The finest- 

 grained variety occurs on the northern foot of Cadeen : it is 

 remarkably close and firm in texture, appearing almost com- 

 pact : it is accompanied, however, with a coarser-grained 

 kind, with which it appears to alternate in layers, as may be 



* Geol. Trans., vol. in. p. 296. et seg. 



