the Granites of the Dublin and Wicklow Mountains. 117 



at about equal distances in a line stretching forty miles from 

 Dublin, I subjected them to careful analysis, and furnished the 

 results to the Academy, and also to your valuable Journal. 

 These results leave nothing to be wished for as far as the second 

 question is concerned, as in every case the specimen appeared to 

 be true orthose, resembling in every particular those which are 

 to be found in Killiney and Dalkey. 



In the last Number of your Journal I perceive that a commu- 

 nication has been made by Professor Haughton, in which he 

 gives a number of analyses of rock specimens taken from diflPerent 

 localities in this range ; his results appear to be altogether in- 

 consistent with the opinion expressed by Sir Robert Kane as to 

 the character of the felspars of these mountains, and therefore, 

 of course, with the extended series of analytical investigations of 

 rock specimens on which Sir Robert Kane stated that he founded 

 his opinion, and which, although now nearly three years have 

 elapsed, he has never produced. 



Professor Haughton has, in the course of his research, dis- 

 covered a most interesting fact as to the character of these gra- 

 nites, namely that in every specimen taken from the range itself 

 the potash predominates over the soda, while in the outlying 

 granitic protrusions, the soda prevails, thus indicating a curious 

 constitutional difference, which may, and probably does, accom- 

 pany a difference of age in these rocks hitherto undiscovered. 



As to Mr. Jenning's interference in this discussion, he has 

 not, in my opinion, contributed much to either side ; nor do I 

 think he understands the question in all its bearings. In the 

 course of this article it has been stated, that, at the very outset 

 of the discussion, analyses of felspars were produced and relied 

 on by Dr. Apjohn, in which the proportion of the alkalies was 

 nearly equal ; it will therefore appear that the production of a 

 single additional, and that but a partial analysis, confirming, so 

 far as it goes, Dr. Apjohn^s result, cannot throw much new light 

 on the question at issue. 



Immediately after the meeting of the Geological Society, at 

 which I obtained a part of the specimen furnished by Mr. Jen- 

 nings, I made the following analysis : — 



Silica 70-32 



Alumina .... 16-12 



Peroxide of iron . . 3-20 



Lime 1-34 



Potash 4-65 



Soda 3-39 



Loss by ignition . . 0-96 



99-98 



