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 Eobert 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. 



