Geological Society. 459 



GEOLOGICAL SOCIETY. 



May 19th, 1841. — A paper " On the Agency of Land Snails in cor- 

 roding and making deep Excavations in compact Limestone Rocks," 

 by the Rev. Professor Buckland, D.D., F.G.S., was first read. 



During the meeting of the Geological Society of France at Bou- 

 logne, in September 1839, Dr. Buckland's attention was called by 

 Mr. Greenough to a congeries of peculiar hollows on the under sur- 

 face of a ledge of carboniferous limestone rocks. They resembled 

 at first sight the excavations made by Pholades, but as he found in 

 them a large number of the shells of Helix aspersa, he inferred that 

 the cavities had been formed by snails, and that probably many ge- 

 nerations had contributed to produce them*. 



A few years since, the Rev. N. Stapleton informed the author that 

 he had discovered at Tenby, in the carboniferous limestone on which 

 the ruins of the castle stand, perforations of Pholades 30 or 40 feet 

 above high-water level ; but having recently examined the spot, Dr. 

 Buckland ascertained that these excavations were the work of the 

 same species of Helix as that which had formed the cavities in the 

 limestone near Boulogne, and he found within them specimens of 

 the dead shells as well as of the living. The mode of operation by 

 which the excavations were made, he conceives, is the same as that 

 by which the common limpet {Patella vulgata) corrodes a socket in 

 calcareous rocks, and he is of opinion that the corrosion is due to the 

 action of some acid secreted from the body of the limpet or helix. 



That the perforations, both at Boulogne and Tenby, were not the 

 work of Pholades, Dr. Buckland says, is evident, 



1st. From their size and shape, which, instead of the straight and 

 regular form accurately fitting the shell of the animal by which each 

 hole was perforated, are tortuous, irregularly enlarging and contract- 

 ing, and rarely continuous in a straight line. The holes moreover 

 are often separated by only a thin partition, or are confluent. 



2ndly. Because they are wanting on the upper surface of the 

 projecting ledges of limestone, whilst on the sides and lower sur- 

 faces of the ledges they are excavated to considerable depths. 



The above reasons, Dr. Buckland says, against the excavations 

 having been made by any marine lithophagous animal, are favour- 

 able to the hypothesis which refers the production of them to snails. 

 These animals, he observes, could find shelter only on the margin 

 and lower surface of the projecting rock, and the irregular form of 

 the confluent cavities correspond with that of the clusters of snails 

 in their ordinary latitat and hybernation ; and if to these reasons be 

 added the fact of finding both living and dead shells in the excava- 

 tions, the evidence, the author conceives, is decisive as to the agency 

 of snails in producing the phenomena under consideration. 



In conclusion, the author offers some remarks on the means by 

 which these hollows have been corroded having been overlooked, 

 in consequence, he suggests, of their having been probably referred 



* See Bulletin Geol. Soc. France, vol, x. p. 434, 1839. 



