198 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 6, 



from which we deduce 



A = 0-291 

 H= 0-133. 



Referring to the analysis of the anorthite, it is easy to see that its 

 atomic weight is 



46 X 3 + 51-4 X 2 + 27*1 x 2, 



or exactly 295 ; from which, multiplying by the value of A just 

 found, we have, finding the hornblende by difference, — 



Mineralogical Composition of altered Granite^ 



Anorthite =85*84 

 Hornblende = 14*16 



10000 



On comparing this result with that obtained in page 195 from 

 the granite before it is metamorphosed, it is interesting to observe 

 that the total quantity of hornblende remains almost unaltered, and 

 that the effect of the addition of the limestone to the melted granite 

 has been to convert the quartz and orthoclase into anorthite. In 

 this operation, the alkalies of the orthoclase have disappeared ; the 

 lime, being a more fixed base at high temperatures, has altogether 

 displaced the alkalies ; showing on a grand scale, in the great labora- 

 tory of Nature, an experiment, which is in daily use on a small scale 

 by chemists, for the determination of the amount of alkaline consti- 

 tuents in an earthy mineral. 



III. Granites of the Newry District. 



The Newry district of granite extends, as already described, N.E. 

 and S.W. about thirty miles, from Slieve Croob to Forkhill. My 

 examination of the granites of this chain is incomplete, but interest- 

 ing, so far as it has extended, as proving in this district the existence 

 of the two types of potash- and soda-granite, which I have established 

 in the granites of the south-east of Ireland. 



Taking a nearly N.S. line through Newry, from Goragh Wood on 

 the north, through the Wellington Inn on the south to Jones- 

 borough, I have obtained the following results : that on this line 

 there is soda-granite to the north of Newrj^, and potash-granite to 

 the south ; I am not prepared to say that the potash- and soda- 

 granites are confined to the limits here indicated, nor do I know 

 the relations between them ; but I hope shortly to be in a position 

 to state more precisely the exact connexion between these two varie- 

 ties of granite in this district. 



Potash-Granites of the Newry District, 



To the south of Newry much of the granite has the character of 

 the medium-grained granite No. 1 of the Carlingford district, of 



