30 GRANITIC ROCKS OF OTHER COUNTRIES [Ch. 111. 



porated as to constitute an apparently homogeneous mass, 

 much resembling some varieties of trap ; and in other places 

 it verges towards clay-slate in aspect and texture, as at West 

 Aston and Rockstown. This granite acquires also, in some 

 instances, a syenitic character, containing small crystals of 

 hornblende, as in Carrigmore ; and, in the western end of the 

 Dunganstown range, it passes into true felspar porphyry, 

 exhibiting a fine granular or compact ash-grey base of felspar, 

 in which are inlaid small brilliant crystals of hornblende and 

 glassy felspar.* There are few parts of this granitic region 

 in which shorl, tourmaline, and garnets may not be casually 

 found, but it is only casually, and in such small proportion 

 that they must be considered as merely adventitious." 



Thus we learn, that mica is the characteristic mineral of 

 this part of Ireland ; so that the granitic rocks are, in a great 

 measure, constituted of varieties of true granite. The peculiar 

 kind of rock accompanying these, in the southern portion of 

 this district, appears to be a kind of eurite ; for the descriptions 

 of Mr. Weaver very accurately correspond with the Cornish 

 species of this rock. 



The association of these varieties in irregular and alter- 

 nating beds, is also another analogy between this mass of 

 granite and that of Cornwall ; and we must not omit to men- 

 tion another circumstance, which furnishes an additional 

 feature of resemblance. " The granite, in the east of Ireland," 

 says Mr. Weaver, " abounds in contemporaneous veins of 

 granite, and also of quartz ; which, however, are not quite so 

 frequent. The former vary from the smallest to a very large 

 grain, and in width from that of a thread to two feet. There 

 is no glen, in which the rock is at all denuded, in which they 

 may not be studied to advantage, and nowhere more so than 

 among the sublime scenery of Glendalough. At the head of 

 the glen the granite forms mural precipices, in which may be 

 seen numerous veins of granite and quartz, several of which 



* Geol. Trans., vol. v. pp. 168, 169. 



