431 
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 vuigata) 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. 
Ist. 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. 
2Qndly. 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 confltient 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 
to the action of the weather, or water, or to original iene in 
the composition: of the stone. 
_ A paper ‘‘ On Moss Agates and other Siliceous Bodies,’ by John 
Scott Bowerbank, Esq., F.G.S., was then read. : 
In a paper “On the Origin and Structure of Chalk-flints and 
* See Bulletin Geol. Soc. France, vol. x. p. 434, 1839. 
