718 KEPOBT — 1887. 



10. TJie Pliocene Beds of St. Erth, Cormvall. 

 By RoBEET Geokge Bell, F.G.S. 



Since the publication of the paper read before the Geological Society of London 

 in February 1886 a good deal of work relating to the geological surroundings 

 and to the special fauna of the deposit has been undertaken. Considerable excava- 

 tions were made, and much examination given to the sands and clays, with the re- 

 sult that the section given in p. 202, ' Quarterly Journal of Geological Society, ' for 

 May 186G, was completely verified. 



The clay deposit is not, however, vmiformly fossiliferous, nor is it uniform in 

 the distribution of its fossil contents as a rule. Cerithium is found in great num- 

 bers at the base of the blue clay, while the larger Nassas and Turritellas are 

 generally distributed in that bed. A great feature of interest is the large number 

 of the smaller species of moUusca, especially of Gasteropods, which embrace more 

 than three-fourths of the total amount. 



Of these small shells the genera Rissoa and Odostomia are the most plentiful, 

 in species and numbers ; about twenty species of the former (including the Hydrobias) 

 and eighteen of the latter genus are present, some being living inhabitants of the 

 British and Mediterranean seas, while others appear new to science, and will have 

 to be de.scribed. The Trochi are nearly all extinct, three only being Crag and 

 livino- forms. Of Nassa about eight species are present, Axkxsa serrnta being by far 

 the most common ; it is nearly identical with the general form of Nassa reticosa, 

 Sowerby, so plentiful in the coprolite pits of the Boyton district in Suffolk ; there 

 are also other well-known Crag species of this family. 



The carnivorous Gasteropods are, however, not otherwise plentiful; one should 

 be noticed, a large fragment of Buccinum undatum, but no traces of Fusus anti- 

 qum or F. gracilis ; all the Pleurotomas are scarce except P. bi-achy stoma, and 

 here are two species of Pisania or Lachesis ; all these last are southern forms. 



Of the bivalves not much cau be said ; few species were obtained, and these 

 mostly in a fragmentary condition. It is still a difficulty to afford an adequate 

 explanation of this fact, for while the deposit of clay is so well calculated to pre- 

 serve the shells, as is shown by the perfect state of the univalves, the bivalves (if we 

 except the oysters and some minute species) have universally suffered. Some expla- 

 nation other" than that of the physical character of the deposit must be sought for, 

 and none has yet appeared sulhciently satisfying 



The opinion expressed in the earlier reports upon this deposit, as to the southern 

 facies of Its fauna, has been amply justified by fresh researches ; a large quantity 

 of the fossiliferous clay has been carefully washed and examined, and no trace of 

 northern forms, except i?i<mrtHWi iindaf.itm, and the two small species noticed in the 

 paper previously referred to, has been found, while greatly increased evidence 

 confirming what has been already said is present. Had there been any connection 

 with northern seas or colder waters, it would be difficult to understand the entire 

 absence of those forms of Pleurotoma (Bela) so abiuidant in the Boreal seas of 

 the Crag period and the present age, as well as the equally characteristic bivalves, 

 Astarte and Cypriua. 



Some conflict of opinion exists upon the depth of water in which the St. Erth 

 clays were deposited. 



In a letter to Nature, of August 12, 1886, a very competent authority on 

 Pliocene phenomena, Mr. Clement Eeid, F.G.S. , gave it as at least forty or 

 fiftv fathoms, founding his view on the evident fact of its deposition in still 

 water, which he maintains could not be found in a district exposed to Atlantic 

 swells at less depth. To this the writer must take serious exception. Undoubtedly 

 the clays exhibit an entire absence of such a disturbing cause as the influence of 

 o-reat wave action, but it remains to be proved that such a great depression as Mr. 

 Reid describes did occur at the western end of Cornwall, and as far as I have been 

 able to observe there is little indication of such a fact. Some depression, of course, 

 must have happened, sufficient to submerge the low-lying land near St. Erth, 

 causinsj a strait or gulf, dividing the Land's End from the main eastern portion of 

 the county. 



