AT ST. ERTH, :!fEAE LAXd's EXD, CORXWALL. 71 



(which were evidently denizens of a warmer sea than that which now 

 washes the shore of Cornwall), may have been due to the changes 

 consequent on the incoming of the major glaciation. 



The fossiliferous clay is of a nature difficult to work for extraction 

 of shells, and the occurrence of specimens, even to the smallest and 

 most unrecognizable fragments, is, except in the case of one or two 

 species, unfrequent ; but by the cooperation of Mr. Cornish and the 

 Yicar of St. Erth, I am having consignments of it forwarded me, 

 by which I hope to extract a more extensive collection of the 

 Mollusca of this deposit, by which the inferences as to its age and 

 relation to other deposits may possibly be modified. Eventually I 

 hope to be able to figure and describe these Mollusca. 



Mr. Robert Bell has aided me most materially in searching the 

 collections, recent and fossil, in the British Museum for anything 

 that would throw the light of identity on the more obscure, and on 

 the apparently new forms that the deposit has yielded (which my 

 invalid condition precluded me from doing myself), as well as by his 

 own Recent and Pliocene collections, and knowledge of Recent and 

 Pliocene Mollusca. The publication in 1882 of the third part of 

 Prof. Bellardi's MoUusca of the Tertiaries of Piedmont and Liguria 

 containing the very numerous fossil forms of the genus Nassa * that 

 occur in these Tertiaries has been very opportune. Dr. J. Gwyn 

 Jeffreys has also had most of the shells before him for examiaation, 

 from me ; and for his aid in the determination of some of the very 

 minute species, I have to express my thanks. 



Angular stones occur occasionally in the clay along with the 

 shells, but I have not met with one more than 3 inches long or more 

 than between 2 and 3 cubic inches in solid dimensions, and they 

 are mostly very much smaller than this. With the exception of some 

 which do not exceed the size of a swan-shot, I have only met with 

 one rounded pebble, about the size of a filbert. The average quantity 

 of the angular fragments, so far as I have encountered them, is about 

 1 lb. to 1 cwt. of the clay. They seem to indicate that, notwith- 

 standing the southern character of the Mollusca, ice must have 

 drifted over the strait during winter, but I have not detected any 

 glacial striae in the fragments. 



* In connexion with the age of the St. Erth bed, as affected by the propor- 

 tion of forms in it not known liting, it is proper to point out that the propor- 

 tion of Nasscs not known liying is quite a fallacious guide ; for while of Mio- 

 cene and Pliocene Mollusca, other than this genus, more than half the Miocene 

 and three fourths of the PHocene are known liying, Prof Bellardi.in this work, 

 figures, or describes, forms of JSassa (of which more than two thirds are ranked 

 as species), to the niunber of 145 from the Middle, 130 from the Upper Miocene, 

 61 from the Lower, and 64 from the Upper Pliocene of Italy. Of these he regards 

 none of the Lower, and but one of the L^pper Pliocene, 4 of the Lower, and 5 of 

 the Upper Pliocene as living species, — the living species, 5 in all, being N. 

 mutabilis, Linne, in 3 vars. : N. gihhosula, Linne, 3 vars. ; N. reticulata, Linne, 

 in 2 vars. ; N. incrassata, Miiller, in 4 vars. : and IS. semistriata, Brocc, in 4 



