Perforatio7is in Carboniferoits Limestone. 119 



theory that the Co. Meath, and with it the site of the village 

 of Nobber, were submerged beneath the sea at a compara- 

 tively recent period, I venture to think that, nevertheless, the 

 perforations in question are not due to the action of Plwlas, 

 or any other marine mollusc, and in this view I am supported 

 by Prof. Sollas. 



It may not be out of place to refer here to a discussion 

 which was continued for several 3^ears between 1869 and 1872, 

 in the Geological Magazine. Lithodomous perforations, exactly 

 similar to those described above from various parts of Ireland, 

 were discovered in the Carboniferous Limestone of the Great 

 Orme's Head in Wales by Mr. R. D. Darbishire. He con- 

 sidered them to have been formed by a species of Pholas, 

 probably P. crispata. Prof. Bonney, in reply to several articles 

 on the same subject, figures a number of sections of the 

 supposed pholas burrows which show clearly that they could 

 not have been produced by that or any other marine mollusc. 

 Moreover, in a great many of the holes he found living 

 specimens of Helix aspersa, and he comes to the irresistible 

 conclusion that the perforations "are not the weathered 

 burrows of departed Pholades, but have been, and are being 

 hollowed out by Helices, the principal, if not the only agent 

 being Helix aspersa.''^ 



But not alone in England have these perforations in the 

 Limestone been observed and recorded. In a paper entitled 

 "Observations sur les Helices Saxicaves du Boulonnais" M. 

 Bouchard-Chantereaux describes similar excavations at great 

 length. He watched them for many years with great care, 

 and measured their progress from time to time, which left in 

 his mind no doubt of the fact that they were made by snails. 

 He found that if he removed the snail, whilst in the act of 

 perforating the limestone, the exudation from the mouth 

 reddened litmus paper, showing the secretion was then of an 

 acid nature. It is probable, therefore, that the perforating 

 action is mainly a chemical one, though the mechanical action 

 of the snail's tongue, which is like a little rasp, must assist it 

 in the work to some extent. 



Helix aspersa is a very common snail in most parts of 

 Ireland, and I believe, considering the evidence we have 

 before us, that the burrows in the Carboniferous Limestone 

 discovered by Mr. Smith in the Co. Meath are not only due to 

 the action of that mollusc, but are being produced by it at 

 the present day. 



The perforation in the stone from the harbour-bed at West- 

 port, sent by Mr. McBride, is undoubtedly due to the action 

 of a species of Pholas. 



