} 
4 
: 
| 
| 
239 
‘* From the foregoing Table it appears, that the granite of 
Cushbawn cannot be -considered as a ternary compound of 
quartz, feldspar, and margarodite, and in fact it contains a 
sensible quantity of a mineral which is either hornblende or 
chlorite. Calculating the per-centages of quartz, feldspar, and 
mica of the two granites, which may be represented as com- 
posed of these minerals, we find— 
TaBLe VI.—Per-Centages. 
LocaLiry. Quartz.| Feldspar. Mica. 
Ballymoty,. . .| 3°08 96-02 0-91 
Ballynamuddagh,| 9°62 84:05 579 
«¢ Whatever doubt may be attached to the preceding cal- 
culations, owing to the hypothesis on which they are of neces- 
sity founded, no such doubt or uncertainty can belong to the 
results of direct experiment, contained in Tables I. and IV., 
which have a positive value, independent altogether of the in- 
ferences which may be deduced from them. From these Ta- 
bles I deduce the following as the average composition of the 
_ granites of the main chain and of the isolated granites :— 
Taste VII.—Average Composition of Granites. 
Main Chain.| Isolated. 
Silieas.) Ai Libs 2 72°305 71:430 
Alumina, .. .| 14251 13°045 
Peroxide of Tron, : 2-299 4-470 
EAMG, Se one. 1815 2-778 
Magnesia, .... 0-119 0°595 
Potash, 3n fey 4:822 1-940 
NOUR, (as op eens 2-967 3°982 
Loss by Ignition, .| 0°899 1:240 
Wolo: swe ake 99°477 99-480 
*¢Qn examining Tables I. and IV., several interesting dif- 
- ferences present themselves in the composition of the two 
