ON THE CONSTITUTION OF THE GRANITES OF DONEGAL. 61 
VIII. Poison Glen.—Coarse-grained granite. 
(a). Quartz; conspicuous, grey. 
(b). Feldspar ; pink, in large crystals (4 in. by 4 in.), transparent, 
bright calespar lustre, set in a paste of quartz and pinkish 
feldspar. 
(c). Mica; an occasional speck of green mica, probably not } per 
cent. 
IX. Doocharry Bridge——Medium-grained granite, tending to become por- 
phyritic. 
(a). Quartz. 
(6). Feldspar ; orthoclase, pink, in 3 in. crystals. 
(c). Feldspar ; oligoclase, grey, in } in. crystals. 
(d). Mica; black, in small grains or specks, and in small quantity. 
X. Barnesmore Gap.—Coarse-grained reddish granite, of platy structure, 
one-inch slabs. 
(a). Quartz; very prominent, grey, occupying a surface only infe- 
rior to the red feldspar. 
' (0). Feldspar; pale red, uniform in texture, with some well-deve- 
loped cleavages, not very brilliant. 
(c). Mica; green, very compact, with few leaves, passing into 
chlorite-earth : this chloritic earth covers the joint-surfaces 
2, in. to 7; in.), and is visible in all such partings. It is 
very difficult to distinguish the green mica from hornblende, 
XI. Arranmore Island.—Porphyritic granite; feldspar predominating. 
(a). Quartz ; easily visible, abundant, grey. 
(b). Feldspar ; reddish, in distinct crystals (4 in. by } in.), cleavage- 
planes distinct, with bright lustre, semitransparent. 
(c). Mica; black; when seen on the edge, it resembles hornblende, 
of which, however, there is not a particle in the rock: facets 
of mica difficult to see, but having a very brilliant reflexion ; 
subordinate to both the quartz and feldspar. 
XII. Tory Island—Coarse granite, almost entirely composed of quartz and 
feldspar, platy structure, one-inch slabs. 
(a). Quartz; conspicuous, crystals (4 in.), grey. 
(b). Feldspar; uniform red, with cleavage-planes of dull lustre, 
orthoclase. 
(c). Mica; greenish, sometimes white, in occasional very small 
plates. 
XIII. Ardara.—Coarse-grained gneissose granite :— 
(a). Quartz; small grains. 
(6). Feldspar; pink orthoclase 
(c). Feldspar; grey oligoclase 
(d). Mica; black, in large quantity, giving a gneissose appearance 
to the rock. 
Sphene occurs disseminated in small crystals. 
} in lumpy masses. 
XIV. Dunlewy.—Consists of quartz and feldspar intimately blended together 
and very similar in colour, whitish grey. In this paste are nume- 
rous crystals of feldspar (orthoclase) with definite (4 in.), lustrous, 
smooth faces, Also occasional stains of greenish mica, looking like 
