Mr. H. J. Carter on Holasterella and Hemiasterella. 145 
what it gains in the other, viz. in thickness, but averaging 
l-22ncl by 1 -120th inch in its greatest dimensions. It is 
possible that these spicules also may have become thickened 
during fossilization; but even then they have very much the 
appearance of the sausage-shaped form characterizing some of 
the large-spiculed Renierida (group 4, viz. Crassa) of the 
present day, though much thicker than the latter. 
I might also add here that Mr. Thomson has sent me some 
specimens of limestone which came from the Carboniferous 
system of the west coast of Ireland, found on the western side 
of Black Head, County Clare, at the southern entrance of 
Galway Bay. Here he computes the limestone to be about 
3000 feet thick, and overlain inshore by the u Yoredale 
Shales.” 
These specimens are of two kinds—viz. one obtained about 
700 feet from the summit, and the other from the talus of the 
scarp below. 
No. 1 consists of a mass of very small crystals of quartz, 
typical of a stratum 3 feet in thickness, showing by their 
weathered-out rhomboidal cavities in the mass , and their gra¬ 
nular structure, that they have been formed in the limestone, 
now more or less occupying their interstices, while the yeodic 
cavities of the mass are lined by large and more perfect crystals 
of the same mineral. What the origin of this accumulation 
of quartz crystals in the limestone may have been, there is no 
evidence to show, although, by the apparently round and 
pointed form of some of those in the mass , together with their 
rhomboidal excavations, so characteristic of the fossil spicules 
of Hyalonema Smithii (‘ Annals,’ 1878, vol. i. pi. ix. fig. 4 
&c.), it is possible that they may be transformed sponge- 
spicules; and this seems to have been the opinion of Dr. West- 
ropp, late of the Geological Survey of Ireland, who, Mr. 
Thomson states, visited the locality from which the speci¬ 
mens were obtained. But, until th eform of a sponge-spicule 
can be undoubtedly recognized among them, they must remain 
conjectural. Silex, in such a position, is not likely to occur 
without organic origin; and sponges are almost the only or¬ 
ganisms that could supply it. 
Over one portion, the dark brown spherular apothecia of a 
saxicolous lichen sunken into the limestone and occupying 
exclusively the intervals between the quartz crystals, seems 
to point out at once the preference of the lichen for, as well as 
the presence of, the limestone. 
No. 2 represents the typical structure of 11 sheets ” of dark 
limestone about 1^ inch thick and 18 by 12 inches square, 
found among the talus at the foot of the scarp mentioned. 
Ann. & Mag. N. Hist. Ser. 5. Vol. iii. 10 
