542 Geological Society: — Mr. Bowerbank 



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 

 to the action of the weather, or water, or to original irregularities 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 

 Greensand Cherts*," Mr. Bowerbank inferred that the sponges from 

 which he conceives those bodies originated, differed from recent kera- 

 tose sponges only in having possessed numerous siliceous spicula. 

 Since that paper was read, the author, however, has found in true 

 keratose sponges from Australia f, as well as in the sponges of com- 

 merce from the Mediterranean and the West Indies J, siliceous spicula 

 in great abundance. All discrepancies, therefore, between the extinct 

 and modern types of a portion of the animals under consideration, he 

 says, is now removed. In these prefatory remarks, Mr. Bowerbank 

 likewise states that there is at present only one known species of 

 recent sponge (S. fistularis) the fibre of which is truly tubular. 



The author then proceeds to detail the evidences of the existence 

 in moss agates from Oberstein and other parts of Germany, as well 

 as from Sicily, and in green jaspers from India, of the remains of 

 sponges, in the following order : 1st, the proofs of the fibrous struc- 

 ture ; 2nd, of the preservation of gemmules ; and 3rd, those of the 



* See Geol. Trans., 2nd Series, vol. vi. Part 1. 1841. Proceedings, 

 vol. iii. p. 278, 1840. [and Phil. Mag., Third Scries, vol. xviii. p. 220.] 

 t Annals of Nat. Hist., April 1841. 

 X Microscopic Journal, vol. i. No. 1, p. 8, 1841. 



