408 PEOCEEDIlirGS OF- THE GEOLOGflCAL SOCIETY. [June 18, 



Table IY. — Chemical Composition of Donegal Granites. 



No, 



I. 



II. 



III. 



IV. 



V. 



VI. 



VII. 



VIII. 



IX. 



X. 



XI. 



XII. 



XIII. 



XIV. 



XV. 



Ardmalin 



Unismenagh 



Glen 



aien 



Glenveagh 



Glenveagh 



Poison Glen 



Poison Glen 



Doocharry Bridg( 



Barnesmore 



Arranmore 



Tory Island 



Ardara 



Dunlewy 



Anagarry 



w. 



70-00 

 65-80 

 68-96 

 58-44 

 69-36 

 68-00 

 68-20 

 70-64 

 72-24 

 73-60 

 68-80 

 69-20 

 55-20 

 75-24 

 73-04 



■73 



16-36 2-80 

 12-80 16-64 

 17-40 2-52 

 2000 6-44 

 16-00 3-03 

 16-80 13-68 

 15-96 ;3-69 

 15-64 2-64 

 14-92 il-63 

 13-80 12-00 

 16-40 2-60 

 16-40 :2-09 

 19-28 ,6-08 

 13-36 0-60 

 15-20 ... 



n3 



.1 



0-08 

 0-18 



2-05 

 0-30 

 0-65 

 1-00 



0-23 



0-65 

 1-00 

 0-46 



1-12 

 2-92 

 2-80 

 4-72 

 2-29 

 4-05 

 2-92 

 2-47 

 1-68 

 0-79 

 1-75 

 1-03 

 5-08 

 2-25 

 1-60 



^ 



0-71 

 1-78 

 0-41 

 1-57 

 0-54 

 0-95 

 0-78 

 0-15 

 0-36 

 0-50 

 0-85 

 0-85 

 3-66 

 0-14 

 0-07 



4-13 

 4-16 

 3-03 

 3-81 

 4-17 

 4-32 

 3-75 

 3-81 

 3-51 

 4-29 

 3-78 

 4-20 

 4-63 

 4-86 

 2-88 



4-66 

 4-40 

 5-25 

 2-82 

 4-47 

 2-04 

 4-14 

 4-53 

 5-10 

 5-22 

 5-31 

 5-22 

 3-17 

 3-27 

 7-32 



9S 



0-32 



0-96 



1-20 



0-64 



o 



99-86 



99-88 



100-37 



99-85 



100-16 



100-49 



100-44 



99-88 



99-99 



100-20 



100-14 



99-99 



99-16 



99-72 



10011 



I. Ardmalin, near Malin Head. — Coarse-grained granite, composed of 



(a). Quartz ; very conspicuous {^ in. crystals). 



{h). Red orthoclase felspar {^ in. crystals). 



(c). Green mica ; in small nests, resembling chlorite. 



II. Unismenagh, near Dunaff Head. — Mediiim-grained granite, containing — 



(a). Quartz ; not very visible. 



{b). Pink felspar ; probably orthoclase (f in. crystals). 



(c). Grey felspar ; probably oHgoclase (|- in. crystals). 



{d). Black mica ; -^-^ in. crystals ; occasionally passing into a dark 



blackish-green mica, in small nests, and resembling a mixture of 



chlorite and hornblende. 



III. Glen. — Coarse-grained gneissose granite, containing — 



(a). Quartz ; scarcely visible, broken, transparent, grey. 



{b). Red felspar ; probably orthoclase, forming large crystals (partly 



made up of pink translucent felspar, with bright reflexion), dull 



waxy lustre, opaque, 

 (c). Whitish translucent felspar ; probably oligoclase, and quite distinct 



from {b). 

 {d). Green mica ; abundant in streaks, alternating, as in gneiss, with 



crystalline sheets of red and pink felspar. 



IV. Glen. — Gneissose coarse-grained granite, apparently in beds in the granite 



No. III., and containing — 

 (a). Whitish felspar ; anorthic, semiopaque, and sometimes in macles, 



probably oligoclase (crystals \ in. by \ in.). 

 (5). Jet-black mica ; in great abundance, probably equal to the felspar, 



which occurs in rounded masses imbedded in the black mica, 



which itself occurs in streaks as in gneiss. 



V. Glenveagh. — Beautiful, coarse-grained, porphyritic granite: — 



ia). Felspar; conspicuous, pink (crystals ^in. to fin.), orthoclase. 

 (6). Quartz ; inconspicuous, grey, transparent, with rounded angles. 

 (c). Mica ; jet-black, abundant in minute grains ; the black mica and 

 pink felspar give character to the rock. 



