382 
granite, that is, of a mechanical and very variable mixture of 
quartz, felspar, and mica; and he admits that potash always 
appeared amongst his results. But its quantity, relatively to 
the soda, is, he contends, so small, that he is of opinion it 
should be referred exclusively to the mica, and that the fel- 
spar containing no alkali but soda must be viewed as an al- 
bite. This argument I cannot but consider as somewhat too 
circuitous to be altogether satisfactory. The investigation may 
be conducted in a much more simple manner, and it appears to 
me that mineralogists will probably not feel themselves safe in 
adopting the conclusion which Sir Robert Kane has drawn 
until it is supported by the results of experiments made di- 
. rectly on the felspars themselves. 
Sir Robert Kane explained, in reference to Dr. Apjohn’s 
observations, that he had never denied that orthose or potash 
felspars were found in certain localities of the Dublin and 
Wicklow range, and that Killiney was certainly one of those, 
as was sufficiently well known and indicated by the presence 
of other minerals rich in potash as the Killinite itself, of 
which portions were actually attached, as Dr. Apjohn admit- 
ted, to the specimen of felspar selected by Professor Apjohn 
for examination. But from Dr. Apjohn’s own analyses of the 
other specimens, it was evident that as they were taken more 
in the granitic mass, the soda element first equalled the potash, 
and then preponderated in the granite of the Three Rock Moun- 
tain. Hence Dr. Apjohn’s analyses did not impugn the truth 
or accuracy of Sir Robert Kane’s idea,—that the predominant 
character of the granitic district of Dublin and Wicklow was 
the presence of soda felspars. This idea was founded not merely 
on the results of the analysis of the waters, read at the last 
meeting of the Academy, and which in itself Sir Robert Kane 
did not consider very important, but was the result of'a widely- 
spread series of observations which, on another occasion, Sir 
Robert Kane hoped to be able to bring before the Academy. 
