143 
which the granite contained, and that the felspar was almost 
exclusively an albitic or soda felspar, containing only in some 
cases a small quantity of replacing potash.” 
Rey. Mr. Haughton stated, with referenee to Mr. Gal- 
braith’s communication, that he had himself made a chemical 
examination of some specimens of mica from the Wicklow and 
Dublin granites, with reference to some remarkable differences 
in their optical properties, and that he had found in these 
micas, as Sir Robert Kane himself had observed, a prepon- 
derance of potash over soda, on an average of about 15 to 2. 
This result seemed to Mr. Haughton to render very difi- 
cult of satisfactory explanation the result of Sir R. Kane’s 
unpublished analyses of granites, in which he found a great 
preponderance of soda; for if the micas contain potash to 
soda in the proportion of 15 to 2, and the felspar, as Mr. 
Galbraith had just demonstrated, contain potash to soda in 
the proportion of 9 to 2, Mr. Haughton confessed himself 
unable to understand how a rock made up of such minerals 
could contain a great preponderance of soda. He quite 
concurred in Mr. Galbraith’s wish, that Sir R. Kane would 
favour the Academy with his promised analyses. 
Dr. Apjohn remarked, that in his opinion Mr. Galbraith’s 
analyses were conclusive as to the relative quantities of potash 
and soda in the Dublin and Wicklow felspars, and were quite 
coincident with the opinions which he had himself previously 
expressed upon this subject. He further observed, that he 
objected to the use of the terms orthose and albite, as distin- 
guishing between potash and soda felspars, as both alkalies 
might and did occur in both minerals in varying proportions. 
The true distinction, in his opinion, between these minerals 
was crystallographic, the former always occurring in the fifth, 
and the latter in the sixth system. 
Mr. Mallet mentioned a fact which had come under his 
observation, which confirmed in a remarkable manner the.re- 
02 
