610 Mr. J. Beete Jukes and the Rev. Samuel Haughton on the 



Composition of the foregoing Granihs — continued. 



No. 9. Camaros Hill. This rock appears to contain only two minerals; it weathers into a 

 compact yellowish-white felspar, and has a general resemblance to the granite of 

 Croghan Kinshela, No. 4 ; it is composed, apparently, of — 



1. Felspar of yellowish waxy lustre; facets abundant, not very numerous, set in a 



paste of yellowish felspar and greenish-black hornblende, intimately mixed. 



2. Hornblende in dots, specks, and streaks, mixed with felspar paste. 



3. No quartz visible. 



Of these isolated granitic patches, the most important, taking into account 

 both area and elevation, are Croghan Kinshela and Camaros Hill CNos. 4 and 9). 

 It is remarkable that these are the only granites that retain the predominance 

 of potash over soda, that characterizes the granite of the main chain ; and it is 

 worthy of remark, that even in Croghan Kinshela, where the central main mass 

 of the hill retains the character of the original granite that produced it, yet the 

 granite of the summit of the mountain, No. 5, shows a deviation from the mean 

 type of the granitic chain, as great as is presented by any granite in the whole 

 south-east of Ireland. Such an anomaly as this is found nowhere in the gra- 

 nitic chain, where even at Poulniounty, Enniskerry, Three Rock, Dalkey, and 

 other localities within a few yards of the metamorphic slate, the granite of the 

 chain retains its physical and chemical character, uninfluenced by the neigh- 

 bouring rocks. On the contrary, in the outlying granitic patches no two 

 granites are alike ; some have more alumina ; some, more iron ; some, more 

 lime and soda ; but all differ from each other, and that within the space 

 of a few hundred yards or feet. It would be a hopeless task to investigate the 

 law of composition of rocks so changeable in their character as the granitic 

 island patches of Wexford and Wicklow, and the conclusion is forced upon us 

 irresistibly, from the facts observed, that the only mode of accounting for such 

 a diversity of composition is to assume an equally diverse composition in the 

 aqueous rocks they came in contact with, which have changed and metamor- 

 phosed the granite of the main chain into compoimds, which, though they are 

 still genuine granite, deviate from it so far as to render it difficult to determine 

 the law of their changes. 



3. Origin of the Outlying Granitic Tracts. — It is nearly certain tliat the iso- 



