ON THE CONSTITUTION OF THE GRANITES OF DONEGAL, 69 
FELDSPAR SECTION. 
Ortnoctase. Of a pinkish colour, very abundant in gneiss along the 
southern edge of the granite, about Lough Errig* and Glenleheen*; at 
Lough Barra; also in veins in the granite at other localities, especially at 
Pollnacally*, and near Lettermacaward; at Breaghy Head; white in Glen- 
veagh*; at Knockastoller; crystallized specimens occur with the beryls at 
Sheaskin na Rone*, and also in the neighbourhood of Lough Nambraddan*, 
near Fintown. 
In a quartz vein, with chlorite and micaceous iron, at Croaghonagh* 
Quarry, near Lough Mourne. 
Oxieocrasr. Abundant in granite, accompanying orthoclase, throughout 
the county, especially at Annagary* ; in gneiss at Glen*, near Creeshlagh* ; 
in syenite, at Black Gap*, near Pettigo, and at Ballykillowen* ; at Knader, 
near Ballyshannon. 
Note.—The veins of greenish oligoclase and black mica, containing molyb- 
denite and copper-pyrites, which were discovered by the Rev. S. Haughton, 
occur at Garvary Wood, near Castlecaldwell, county of Fermanagh, about two 
miles from the border of the county Donegal. 
Lasraporire. Opalescent feldspar, supposed to be labradorite, occurs in 
boulders of granite in the Gweebarra valley, and along the shore of the Rosses. 
Aventurine feldspar.—Was found by Sir C. Giésecke in the Doochary dis- 
trict. 
Pircustonz. Dykes of this rock, some of which are amygdaloidal, pene- 
trate the granite of Barnesmore*, and are also found in other parts of the 
county. 
Frtstonz. Felstone porphyry occurs in a columnar dyke in granite be- 
tween Tordhu and Cladaghillie, in Arranmore*, 
Hattoysirze. At Drumsallagh. : 
MICA SECTION. 
Waurre Mica. This occurs in considerable quantities in the granite, toge- 
ther with black mica. It is common at Sheaskin na Rone*, near Dunglow, 
with the beryls; also at Ballaghgeeha Gap*, Dooish Mountain; in gneiss 
(speckled) at Breesy Mountain* ; at Madavagh, near Lettermacaward. 
Brack Mica. This occurs in small plates throughout the whole area of 
the granite, and also in the gneiss on its flanks, especially at Glen*, near 
Creeshlagh. It is also found in nests in the granite, as is the case at Newry ; 
also in syenite and hornblende rock, but sparingly, at Kilrean*, near Ardara. 
Large crystals are found in quartz at Annagary*; also at Ballaghgeeha 
Gap*, Dooish Mountain, and at Doochary Bridge. 
Green Mica, produced by weathering from the foregoing, is found in a 
remarkable granite-vein which penetrates the gneiss near the Black Gap*; 
also radiated, on quartz, near Rockhill. 
Cutorire. In quartz at Malin*; with orthoclase and quartz at Lough 
Mourne* ; at Killybegs* ; Ards, 
Hyprovs Sizicates, 
TALC SECTION. 
Tarc. At Crohy Head*, crystallized, with iron pyrites; Foxhall; Glen- 
keeragh ; at the Reelan Bridge. 
Soarstonz. At Crohy Head*; at the mill, near Gartan Abbey* ; at Ards; 
at Glinsk, in Ross Guill. 
Porstonr. Called ‘“‘Cambstone” in the neighbourhood, at Convoy*; at 
Leaght, parish of Donaghmore ; near Killygordon; at Culdaff *, 
