232 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Feb. 22, 



served by him in West Somersetshire in 1866, and stated that in 

 1849 he had himself called attention * to the marks of glacial action 

 shown in the terminal curvatures of slaty rocks in Forfarshire, and 

 suggested that they were to be explained by the progression of a 

 thick covering of ice along the edges of the slaty beds. 



Discussion". 



Mr, GwTN Jeffeets read extracts from the Eev. Mr. Hodgson's 

 ' History of Northumberland ' (published in 1827), in which these 

 borings in limestone were referred to the action of snails. Mr. 

 Jeffreys considered the foot to be the sole instrument employed by 

 the boring Mollusca in excavating their burrows. He exhibited 

 specimens of Lias from Lyme Eegis perforated by PJiolas, and of 

 hard limestone from Malta perforated by Lithodomus, and remarked, 

 in connexion with the notion that asperities on the shell might be 

 boring agents, that the shell of Lithodomus is perfectly smooth. 



Prof. Ramsay mentioned that he had seen Helices taken out of 

 these holes at Tenby by Dr. Buckland, who beheved that the snails 

 effected the perforations by the agency of an acid. 



Mr. Cha.klesworth thought that if so much uncertainty could 

 prevail upon such a subject, it threw great doubt upon some of the 

 grandest generalizations of geology. He referred to the evidence 

 connected with the glaciation of the Great Orme's Head, in which 

 the origin of the perforations under discussion was of much import- 

 ance, Mr. Darbishire maintaining that they were the work of Pho- 

 lades, while Mr. Bonney asserted that they were produced by snails. 

 In the same way the origin of the celebrated borings in the Temple 

 of Jupiter Serapis might be disputed, and the generalization founded 

 upon it rendered doubtful. Mr. Charlesworth noticed the necessarily 

 smaU proportion of borers to the whole snail-population of Britain, 

 and remarked especially upon the absence of perforations in the 

 chalk districts. He considered that repeated observations were ne- 

 cessary before this snail-engineering could be admitted, and sug- 

 gested a systematic course of experiments. 



Mr. Boyd Dawkins suggested that the carbonic acid exhaled by 

 snails in respiration might act upon limestones, and remarked that 

 chalk weathers too rapidly to preserve the excavations. 



2. On the prohable Cause, Date, and Duration of the Glacial Epoch 

 of Geology. By Lieut.-Col. Dkayson, E..A., F.R.A.S. 



(Commuiiicated by Alfred Tylor, Esq., F.G.S.) 



[Abstract.] 



After referring to the evidence of the occurrence of a Glacial 

 Epoch, and to the various hypotheses which have been proposed to 



* Jameson's Edinburgh Jounial, vol. xItI. p. 377. 



