330 



rock of Slieve Donard is similar in character but somewhat more coarsely 

 crystalline. Another specimen from an unknown locality in the Mourne 

 Mountains furnishes a magnificent illustration of micro-pegmatitic structure. 

 In the absence of white mica as an original constituent and in the mutual 

 relations of the quartz and felspar the granite of the Mourne Mountains 

 possesses affinities with the Dimetian granites of Wales and with the 

 Eskdale granite in the Lake District. In the occurrence of drusy cavities 

 containing white orthoclase and smoky quartz it resembles the granite 



of Arran. 



I. II. III. IV. 



Si0 2 66-25 ... 68-97 ... 43-42 ... 75.00 



A1A 17-35 ... 19-23 ... 19-00 ... 13-24 



Fe 2 3 .-. 17-64 ... 2-52 



CaO 1-25 ... 1-21 ... 1-81 ... 0-69 



MgO 0-05 ... 0-24 ... 0-54 



K 2 11-22 ... 1-56 ... 8-77 ... 4-33 



Na 2 3-05 ... 8-71 ... 3-66 ... 3-07 



Loss 0-30 4-30 0-80 



99-47 99-92 99-14 99-65 



I. Orthoclase from granite of the Mourne Mountains average of three analyses by 

 Dr. HATJGHTON. 



II. Albite from same rock. 

 III. Mica from same rock. 

 IV. Bulk analysis of the rock. 



The granites of the Carlingford district, according to Dr. HAUGHTON^ 

 belong to two varieties ; the one composed of quartz, felspar and greon 

 mica, the other of quartz, felspar and hornblende. The granites of the 

 Newry district are also divided by Dr. HAUGHTON into two groups ; the 

 potash-granites and the soda-granites. The latter appear to have affinities 

 with the diorites. A felsite dyke traverses the granite of Newry Quarry. 



I. II. III. IV. 



Si0 2 70-48 ... 71-41 ... 63'34 ... 74'20 



A1A 14-24 ... 12-64 ... 15-28 ... 10-84 



Fe 2 3-72 ... 4-76 ... 6-88 ... 1-88 



CaO 1-48 ... 1-80 ... 4-34 ... 2-84 



MgO 0-40 ... 0-63 ... 2-48 ... tr. 



K 2 4-26 ... 5-47 ... 2-67 ... 3-12 



Na,0 8-66 ... 3-03 ... 3-68 ... 4-77 



Loss 1-59 1-01 0-83 



99-83 99-74 99-68 98-48 



Sp. Gr. 2-593 2-632 2-713 



I. Medium-grained granite from base of Slieve-na-glogh, Carlingford. 

 II. Fine-grained granite from Grange Irish, Carlingford. 



III. " Soda-granite " from Newry district mean of two analyses. The "potash-granites " 

 of this district resemble in composition the medium-grained granite of Slieve-na-glogh. 

 FV. Felsite dyke in Newry Quarry. 



