380 
From these results, and the assumption that the alkalies 
are derived exclusively from the disintegration of the adjacent 
granite, Sir Robert Kane went on to infer “that the felspar 
of our Dublin granite is, on the whole, a soda or albitic felspar, 
although, in particular spots, orthose or potash felspar may be 
found.” And in the succeeding paragraph of his paper he ob- 
serves, that he found this conclusion corroborated by the re- 
sults of numerous analyses of the granitic rocks of the same 
locality. 
Having been present when this paper was read, I certainly 
felt, relying merely on my memory at the time, that the 
statement, alleging potash to be absent from the Dublin fel- 
spar, or to be but casually present, and only in insignificant 
quantity, was not in accordance with my experience. I have 
had this mineral frequently analyzed as an exercise for pupils 
in my laboratory, and, while recollecting that soda was inva- 
riably found in it, I had also very distinctly on my mind that 
the potash often preponderated, and was never present in very 
small relative quantity. Upon referring to my notes, and 
instituting some fresh analyses for the express purpose of 
throwing light on this question, I find that the impressions I 
previously entertained are in accordance with my experiments ; 
and as the point under consideration is one of some practical 
and scientific interest, [am anxious to be permitted to put on 
record, through the Academy, the evidence in reference to it 
which I have obtained. The following Table includes two 
complete analyses of felspar, for some time in my possession, 
and three partial analyses, made within the last fortnight, for 
the sole purpose of determining the relative quantities of the 
potash and soda. The composition of the Mourne felspar has 
no immediate bearing upon the question under discussion, 
and is given merely for the purpose of showing that a variety 
of this mineral, generally considered as a true albite, includes 
a large relative amount of potash. 
