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‘*¢ Tn regard to the constituents of the rock which occurs in the 
several lines and positions above mentioned, it may be stated that 
the granite of the western, or principal range, consists of white feld- 
spar, gray quartz, and white, or greenish, or yellowish-white mica, 
which latter sometimes passes into talcose mica, the prevailing ac- 
cidental minerals being schorl and common garnet. 
‘** The granite of the first or most western detached range, that 
commences north-east of Rathdrum, and terminates at Conna Hill, 
consists for the most part of constituents similar to those of the 
great or principal range, viz., white feldspar and white mica, though 
red feldspar and black mica do occur north of West Acton in Wick- 
low county. But the constituents of the granite hills, south-west of 
Oulart, and also of Camaross Hill and that of the Carnsore district, 
all in Wexford, differ from the former, and consist of red feldspar, 
gray quartz, black mica, and hornblende. Some time since it oc- 
curred to me that possibly these newer granites might be distin- 
guished from the older by the occurrence of potash in the one, and 
soda in the other; but this is merely surmise, not being aware of 
any analysis having been made. 
‘“«*T am, my dear Sir, faithfully yours, 
‘“¢* RICHARD GRIFFITH. 
“** Rev. Professor Haughton, 
““< Trinity College, Dublin.’ 
“Such being the state of geological knowledge on this 
subject, it dccurred to me that it might be useful to direct at- 
tention to a distinction of a chemical character which appears 
to exist between these two groups of granites—a distinction 
to which I have been led in the course of a series of analyses of 
Irish granites, in which I have been for some time engaged. 
The distinction to which I have alluded is the following. The 
granites of the main chain contain more potash than soda, 
and vice versd, the granites to the east of the chain, which are 
isolated from it and from each other, cantain more soda than 
potash, —showing that the circumstances, unknown to us, 
under which the isolated granites were formed, were such as to 
