Dr. F. H. Hateh—L. Silurian Felsites of SE. Ireland. 547 
Notes on the foregoing Groups. 
Group I.—1. (I. 113.)—Half a mile south-east of Cairn on Castletimon Hill, 
Co. Wicklow. Sheet 130. 7 
Compact grey felsite, of irregular fracture. Under the microscope shows felsitic 
(cryptocrystalline) structure, but with frequent patches of more coarsely crystalline 
(microcrystalline) matter. No porphyritic crystals. 
2. (I. 172.)—One mile west of Great Newtown Head, Co. Waterford. Sheet 179. 
Compact brown felsite, of irregular fracture. Under the microscope shows a cloudy 
unindividualized substance, containing a number of ill-defined spherular clots, mostly 
aggregated in strings. These bodies have no radially fibrous structure, presenting 
between crossed Nicols a speckled or dappled depolarization instead of the character- 
istic black cross, and cannot therefore be regarded as true spherulites. They doubt- 
less represent, however, some incipient form of crystallization. The remainder of 
the ground-mass shows a confused, patchy deyitrification, The rock contains no 
crystals and is probably a devitrified pitchstone, 
3. (I. 110.) —Castletimon-ford, right bank, Co. Wicklow. Sheet 130. _ ‘ 
Compact, grey, mottled felsite, fracturing easily; the joint-faces stained with 
oxide of iron. 
Felsitic or cryptocrystalline structure with an occasional porphyritic crystal of 
non-striated felspar (orthoclase). Between crossed Nicols the devitrification of the 
ground-mass shows itself in the presence of innumerable minute spherular bodies, 
each giving a black cross. Chlorite is present in scattered scales. 
4. (I. 111.)—Castletimon-ford, left bank, Co. Wicklow. Sheet 139. 
Very compact, light grey felsite; brittle and splintery, fracturing easily along 
joints, the faces of which are stained yellow with oxide of iron, resulting from the 
decomposition of pyrites which occurs in small quantities in this rock. 
Under the microscope the structure is truly felsitic or eryptocrystalline, there being 
no porphyritic crystals present. 
Group II.—5. (I. 81.)—Quarry on road from Woodenbridge to Aughrim, 14 mile 
north-west of Woodenbridge, Co. Wicklow. Sheet 139. 
Compact grey felsite, spotted white with small crystals of felspar. Iron pyrites 
in disseminated specks. 
Under the microscope: Cryptocrystalline ground-mass, embedding numerous por- 
phyritic crystals of striated felspar. The twinning is on both types (pericline and 
albite). Microperthite structure is occasionally shown. 
6. (I. 126.)—Kilmacrea Wood, 12 mile north-west of Redcross, Co. Wicklow. 
Sheet 130. - 
Compact, grey, mottled felsite. 
Under the microscope: Structure varying between cryptocrystalline, in which the 
constituent granules are not distinctly separable, and microerystalline in which each 
granule can be clearly distinguished. Here and there occur a few larger grains of 
quartz and felspar, but not sufficiently separated from the ground-mass to constitute 
a true porphyritic structure. 
7. (I. 169.)—Boulder on coast, near Annstown, Co. Waterford. Sheet 178. 
Compact dark grey felsite, well banded (fluidal structure). 
Under the microscope: Felsitic ground-mass with confused and patchy devitrifi- 
cation. Hmbedded in the ground-mass are large porphyritic crystals of quartz and 
felspar, the former corroded, the latter presenting both single and double twin- 
striation. 
8. (I. 109.)—One mile south-east of Ballynacor Cross-roads, Co. Wicklow. 
Sheet 130. 
Compact back felsite ; fracture irregular. 
Under the microscope: Confused felsitic ground-mass, depolarizing in patches, 
with isolated porphyritic crystals of striated felspar. 
Grove III.—9. (I. 83.)—Quarter-of-a-mile east of Coatsbridge, on the road 
from Woodenbridge to Aughrim, Co. Wicklow. Sheet 139. 
A grey almost phanerocrystalline felsite, with slight parallel structure (probably 
secondary and due to the earth-movements that have affected this region). 
Viewed between crossed Nicols the ground-mass has an intricate mosaic-like 
