235 
feldspar, and mica; as combinations of other minerals might 
equally well represent the analyses; but on the hypothesis 
that the granites are composed of these three minerals, they 
give their per-centages with a close degree of approximation ; 
and further, if the equations cannot be satisfied with positive 
values of Q, F, M, it may be considered as proved that the 
granite under consideration cannot be simply a compound of 
quartz, feldspar, and margarodite. 
“It is to be observed, that if a granite be composed of four 
or more minerals, it is not possible to find by the process 
just described the per-centages of each mineral, because, in 
this case, the number of unknown quantities is greater than 
that of the equations from which they are to be calculated. 
“«‘ The following Table contains the analyses of eight gra- 
nites taken from north to south along the principal granite 
chain, and the notes appended contain a few interesting parti- 
culars respecting each granite :— 
Taste I.—Analyses of Granites from Principal Chain. 
fu Perox-) Mac- | Pot- Loss 
Locauirizs. Silica. aoe ie oF "Lime. Mag- ash, | Soda. by Ie- Torats,| 
1. Dalkey,. - . .| 70°38] 19-64 | 3°16| 2°84} 0°53} 5°90) 3-13 | 1:16| 99-74 | 
2. Fox-Rock, . .| 73:00 | 13-64 | 2°44| 1-84] 0°11] 4-21] 3-53 | 1-20} 99-97 | 
3. Three-Rock, . .| 70-28 | 16-44 | 2°60] 2°04) Trace] 5-79 | 2°82 | — 99-97 | 
4. Enniskerry, . .| 74:24 | 13.64 | 1:40] 1-48| Trace] 3°95| 2:72 | 1:20| 98-63 
5. Ballyknocken, -| 70°82 | 44-08 | 3°47] 2°65 | 0°31} 4°64) 2°31 | 1°39} 99-67 | 
6. Kilballyhugh, -| 73°24 | 45-45 | 1°60) 0:99 | Trace] 4°59} 3-08 | 1°20 /100-15 | 
ie Blackstairs, - «| 73°20 | 45-48 | 1°72] 0-96 | Trace] 4°80) 3°18) — | 99:34 
8. Ballyleigh, . .| 73-28} 19-4 | 2°00] 1-72 |Trace! 4-70| 2-97 | 1-04] 98°35 | 
“No. 1. Dalkey.—Specific gravity, 2°647 ; a fine-grained 
granite, containing black and transparent mica. This granite 
cannot be a ternary compound of quartz, feldspar, and marga- 
rodite. ‘This granite was used in the construction of Kings- 
town Harbour. 
