1856.] HAUGHTON — GRANITES OF IRELAND. 183 



an igneous focus, different from that of the main chain, and one con- 

 taining more soda and lime. Neglecting the small quantity of mica 

 which enters into the composition of this granite, it may be repre- 

 sented by the mineralogical analysis following : — 



Quartz 1 7'4 per cent. 



Feldspar 82-6 „ 



100-0 



Comparing this result with the mineralogical analysis of the main 

 chain, we observe a deficiency of quartz and an increase of basic earths. 



Second Group of Isolated Granites, 



The second group of isolated granites consists of Croghan Kin- 

 shela, rising to a height of 1985 feet, and Conna Hill. The line 

 joining these hills is N.N.E. and S.S.W., and the greatest length 

 of the granitic outburst may be stated at six miles. The granite of 

 Croghan Kinshela rises through and alters the slate of the district, 

 conyerting it in a great degree into hornblendic and chloritic meta- 

 morphic slate. On the northern slope of Croghan Kinshela are 

 situated the famous gold-mines of Wicklow, which consist of stream- 

 gold brought down from some undiscovered source in the mountains 

 by the floods of winter ; they are still occasionally wrought by the 

 neighbouring peasantry, when other employment is wanting in the 

 district. The granite of Croghan Kinshela differs from all other 

 granites I have seen in the south-east of Ireland in its mineralogical 

 composition. It is, on the whole, a binary compound of quartz and 

 albite, containing variable quantities of chlorite, which is sometimes 

 nearly wanting, at other times present in considerable quantities. It 

 is to be observed, that the quartz occurs in small rounded granules 

 in the rock. The following analysis of a specimen, as free from 

 chlorite as could be procured, will give a good idea of the nature of 

 this rock. 



Granite of Croghan Kinshela. 

 Specific gravity =2'629. 



Per cent. Atoms. 



Silica 80-24 .. 1-744 



Alumma 12-24 



Peroxide of iron .... 0*72 



Lime 0-89^ 



Magnesia trace 



Potash .... 0-40 , 



Soda 5-58J 



100-07 

 From the foregoing analysis we can infer the following mineralo- 

 gical analysis of the granite of Croghan Kinshela. 



Quartz =38 per cent. 



Albite =62 



. 0-247 

 >>. .0-213 



100 



VOL. XII. PART I. O 



