233 
yield to the molten mass a quantity of soda greater than that 
possessed by the granites of the principal chain. 
‘In illustration of the foregoing generalization, I offer 
analyses of granites from the following localities :— 
GRANITIC CHAIN. 
. Dalkey, county of Dublin. 
. Fox-Rock, county of Dublin. 
. Three-Rock Mountain, county of Dublin. 
. Enniskerry, county of Wicklow. 
. Ballyknocken, county of Wicklow. 
. Kilballyhugh, county of Carlow. 
. Blackstairs, county of Wexford. 
. Ballyleigh, county of Wexford. 
maT nonrFrwnre 
ISOLATED GRANITES. 
. Cushbawn, county of Wicklow. 
. Croghan Kinshela, county of Wicklow. 
. Ballymotymore, county of Wexford. 
. Ballynamuddagh, county of Wexford. 
m wd — 
“« It will be seen, on reference to the Ordnance Map, or any 
good map of Ireland, that the localities selected extend from 
the north td the south of both the granite series; and on re- 
ference to the Geological Maps of Wicklow and Wexford, it 
may be observed by those unacquainted with the geological 
structure of this part of Ireland, that the granites of the second 
group examined are taken from four distinct and distant iso- 
lated patches of granite. 
‘« In order to investigate the relative proportions of quartz, 
feldspar, and mica, of which these granites were composed, I 
used the following method, which appears to be as simple as 
any that has been proposed for such a purpose. 
“¢ Let the per-centage of silica in the granite be divided by 
the atomic weight of silica, and let the quotient be denoted 
by a.” 
