70 S. Y. WOOD OIs- A IS'EW DEPOSIT OT" PLIOCEiS'E AGE 



sur les Terrains Cretaces etTertiaires du Cotentin;"' and among these 

 there is nothing hut Ostrea eclulis and nndeterniined single species 

 of Turritella, CeritMum, and Kucula, that even genericallj- occur in 

 the St. Erth deposit. There is a more copious list given in the 

 Geological Magazine for May 1872, hy Mr. Alfred Bell, from an ex- 

 amination of the collection made by Sii^ Charles Lyell from the 

 Cotentin Crag, supx^lemented hy some additions from the authority 

 of M. Hehert ; but there is nothing in that paper to show whether 

 these represent this older '•' Conglomerat a Terebratules," or the 

 newer " Marnes a ]S"assa," and I suspect that Mollusca from both of 

 those beds are mixed up in that list. Erom these " Marnes a Xassa," 

 MM. Yieillard and Dollfus give a more copious list : but there is 

 little in common between it and the list from St. Erth. jSI^one of the 

 St. Erth Kassce, save perhaps N. granulata, nor any of the more 

 remarkable St. Erth shells, are among the species mentioned. 

 Only Ringicula huccinea, Calyjptrcea cJiinensis, Natica miJlepunctaia^ 

 CeritMum reticidatum (scaher), Lucina horealis, Ostrea echdis, and 

 possibly Natica sordida as N. proxima^ Nassa gramdata, Turritella 

 trijdicata as Turritella vermicidaris, and Pectunculus glycimeris as 

 Pectuncidus (species), out of the many St. Erth shells can be recog- 

 nized in it ; and though there are two or three Mediterranean species 

 among them not known in the K'orth-Sea Pliocene, yet the whole 

 fauna is essentially the same as the fauna of that Pliocene, and but 

 subordinately connected with the Pliocene of Southern France or of 

 Italy, which, so far as the evidence serves to show, is just the reverse 

 of the St. Erth fauna. 



We must, as the case at present stands, infer either that Cornwall 

 and N'ormandy, near as tbey are to each other, were at the time of 

 the St. Erth deposit separated by a land barrier ; or else that even 

 the " Marnes a IS'assa " are older, and that the deposit of the 

 JN'ormandy Crag had ceased before the St. Erth deposit began. My 

 present impression is that the latter was the case, for the fauna of 

 the " Marnes a j^assa " seems to me to indicate an age intermediate 

 between the Coralline and Eed Crags, rather than (as it has been 

 supposed) a E,ed Crag age. 



Of whatever age the St. Erth bed may precisely be, however, it 

 seems pretty clear that at the time of its deposition there was no com- 

 munication from the South Atlantic and Mediterranean to the ]N"orth 

 Sea, except round the jSTorth of Scotland ; so that such of the southern 

 species as had not been denizens of the jN'orth Sea during the Older 

 Pliocene, and so lingered on there into the i^ewer Pliocene of the Eed 

 Crag, were prevented by the differences of nine degrees of latitude 

 between Cornwall and the Xorth of Scotland, and the consequent 

 refrigeration northwards of the marine climate, from getting round 

 into the JSTorth Sea. 



A change of conditions evidently took place during the formation 

 of the deposit, by which the blue fossiliferous clay was succeeded 

 gradually by a more tenacious yellow clay, which seems to be destitute 

 of molluscan remains, save some imrecognizable fragments of abivalve; 

 and it is possible that this, and the disappearance of the Mollusca 



