258 MR. GARDINER AND PROF. REYNOLDS ON [May 1902, 
Dayia navicula. Chonetes striatella, too, as remarked by Salter,’ 
is here most common in beds of Wenlock or Llandovery age, as at 
Poulnakeragh and north of Carrigard; while in Britain it is a 
characteristic Ludlow fossil. In this district it occurs in beds ot 
Ludlow age on the north-western slopes of Croaghmarhin. 
With regard to the general facies of the Silurian fossils from Ae | 
locality Mr. Reed writes :— 
‘The lack of cephalopods, the great poverty of crinoids, and the scarcity of 
trilobites and gasteropods may be noticed. The trilobite Encrinwrus Stokesi 
appears to me to differ from the typical specimens of H. punctatus from 
the Wenlock rocks of England; but it may prove to be only a local variety 
of the latter species. Horiostoma is the most abundant genus of gasteropods. 
and Encrinurus of trilobites. The only peculiar species from these Silurian 
beds of the Dingle district appears to be Spirifer bijugosus, and it is a 
generally abundant form.’ 
Rhynchonella nucula occurs from the top of the Ludlow to the 
Jower part of the Wenlock (as, for example, at the base of Clogh 
Point). 
V. PETROGRAPHICAL DeralIts.? 
(a) The Lavas. 
These, which are invariably rhyolitic in character, form the most 
remarkable of the volcanic rocks of the district. They are fine- 
grained white, pale-grey, or purple rocks, with a groundmass which 
under the microscope is generally seen to be mainly cryptocrystal- 
line, though commonly with microcrystalline or micropeecilitic 
patches and bands which are elongated in the direction of flow, 
and often merge imperceptibly into the surrounding cryptocrystal- 
line material. None of the rocks show vesicular structure, and the 
phenocrysts, which are almost always felspar (generally orthoclase), 
are never very abundant, and are often completely absent. Pheno- 
crysts of quartz are never met with. The prevailing eryptocrystal- 
line character of the groundmass is probably due to devitrification. 
The rhyolites may be divided into the following groups :— 
(1) Nodular rhyolites ; 
(2) Banded-rhyolites ; and 
(3) Rhyolites not showing nodular or banded structure, 
(1) Nodular rhyolites.—The best examples of these rocks 
occur on the east side of the inlet. of Foilminnaun, north of Mull 
Cove (band A 5) and in the thick band of rhyolite (C7) which 
forms the greater part of the promontory of Poulnakeragh or 
Foilwee. The Clogher-Head rhyolite is also sometimes nodular, as 
too is that seen south of the village of Carhoo, The mass exposed 
on the foreshore of the south side of Ferriter’s Cove is another 
example of a rather coarsely nodular rock. The nodules in all these 
1 Brit. Assoc. Rep. 1857 (Dublin) Trans. p. 89. 
2 We are much indebted to Mr. Alfred Harker for help in the determina- 
tion of some of our rocks. 
