8 J. Rofe — On Lithodomous Perforations. 



upwards, -wliich is contrary to the habit of the PJiolades, as they 

 bore downwards, and make their holes pyriform to fit their shells ; 

 but these at Birkrigg, as well as those in the Boulonnais, at Tenby, 

 and at the Ormeshead, are of a great variety of shapes, and seem, in 

 some cases, to have had several inhabitants at once. Nor are the 

 holes at all similar (except at the opening) to those made by any of 

 the Pholades. 



Even supposing the holes might be similar to Pliolas borings, it 

 is scarcely possible to believe that thin and esjDosed ridges of lime- 

 stone, like those in question, would not have been weathered and 

 denuded so as to have destroyed every trace of such comparatively 

 superficial apertures, during the many ages which must have passed 

 since their elevation ; that being probably anterior to the Glacial 

 period, or, if since that period, they must have been denuded of the 

 glacial drift or Boulder-clay then left on them without being them- 

 selves materially acted upon. 



We may now consider the action of snails, which appear to 

 abound wherever these borings occur, and which are very fre- 

 quently found, alive or dead, in the holes. M. Constant Prevost, 

 who, many years since, found excavations in the hard crystalline 

 marble of Monte Pelegrino, near Palermo, did not hesitate to 

 ascribe them to the Helices which he found in them, and most of 

 the authors above alluded to mention the presence of snails, or their 

 shells, in the holes ; and although finding a snail in a hole cei-- 

 tainly is no proof that it made the hole, still, when snails are 

 repeatedly found in holes made in situations which they usually 

 frequent, it is strongly suggestive of their agency ; and when we 

 have reason to believe that they have the power of making them, I 

 cannot think we can be wrong in giving them the credit. At first 

 it may excite surprise that a snail should have power to drill into 

 a hard Crystalline Limestone Eock, but we do know that the 

 Gasteropods are furnished with a lingual band of teeth which " can 

 be used like a file for the abrasion of very hard substances. With 

 them the limpet rasps the stony nullipore," and " the whelk bores 

 holes in other shells." ^ M. Bouchard watched these excavations in 

 the " Bois des Eoches" for many years with great care, and from 

 time to time measured their progress, which left in his mind no 

 doubt of the fact that they were made by the snails ; but assuming 

 that to be so, the question suggested itself — How do they work 

 upon the rock, mechanically or chemically, or by both means ? 

 M. Bouchard advocated the chemical theory, and has made obsei"va- 

 tions on the mucus or slime which the snail leaves in its trail, and 

 which he believed has corrosive action, although he could find no 

 trace of any free acid in it. This action of the slime ajjpears to me to 

 be veiy doubtful, as there is no trace of any corrosive action on the 

 polislied surface of rock at Birkrigg, above alluded to, and which 

 must have been repeatedly passed over by the snail in going to and 

 from its hole. Miss Hodgson states (in the Geologist, vol. vii. p. 43) 

 that she tried the fluid secreted by the snail when crawling, and 

 ' Dr. S. P. Woodward; Manual of the Mollusca, p. 27. 



