GLACIAL SUCCESSION IN EUROPE. 145 



the occurrence of a few forms, which are common to the Forest -bed and the underlying 

 Crag, does not necessarily prove that the two faunas occupied adjacent districts. Mr 

 Eeid, indeed, admits that some of the marine shells in the Forest-bed series may have 

 been derived from the underlying Crag. Were the marine equivalents of the Forest>bed 

 forthcoming we might well expect them to contain many Crag forms, but the facies of 

 the fauna would most probably resemble that of the existing North Sea fauna. Again, 

 the appearance in the Weybourn Crag of a few southern shells common to the Forest- 

 bed, does not seem to prove more than that such shells were contemporaneous somewhere 

 with an Arctic marine fauna. But it is quite possible that they might have been carried 

 for a long distance from the south ; and, even if they actually existed in the near 

 neighbourhood of an Arctic marine fauna, we may easily attach too much importance to 

 their evidence.* I cannot think, therefore, that Mr Eeid's conclusion is entirely satis- 

 factory. After all, the Cromer Forest-bed rests upon the Weybourn Crag, and the 

 evidence as it stands is explicable in another way. It is quite possible, for example, that 

 the Forest-bed really indicates an epoch of genial or temperate conditions, preceded, as it 

 certainly was eventually succeeded, by colder conditions. 



If it be objected that this would include as interglacial what has hitherto been regarded 

 by most as a Pliocene mammalian fauna,t I would reply that the interglacial age of 

 that fauna has already been proved in Central France. The interglacial beds of Auvergne, 

 with JSlephas meridionalis, rest upon and are covered by moraines, J and with these have 

 been correlated the deposits of Saint-Prest. Again, in Northern Italy the lignites of Leffe 

 and Pianico, which, as I showed a number of years ago, § occupy an interglacial position, 

 have likewise yielded Elephas meridionalis and other associated mammalian forms. 



* The inference that the Forest-bed occupies an interglacial position is strengthened by the evidence of certain 

 marine deposits which immediately overlie it. These (known collectively as the Leda-myalis bed) occur in irregular 

 patches, which, from the character of their organic remains, cannot all be precisely of the same age. In one place, for 

 example, they are abundantly charged with oysters, having valves united, and with these are associated other species of 

 molluscs that still live in British Seas. At another place no oysters occur, but the beds yield two Arctic shells, Leda 

 myalis and Astarte borealis, and some other forms which have no special significance. Professor Otto Torell pointed 

 out to Mr Reid that these separate deposits could not be of the same age, for the oyster is sensitive to cold and does 

 not inhabit the seas where Leda myalis and Astarte borealis flourish. From a consideration of this and other evidence 

 Mr Reid concludes that it is possible that the deposits indicate a period of considerable length, during which the depth 

 of water varied and the climate changed. Two additional facts may be noted : Leda myalis does not occur in any of 

 the underlying Pliocene beds, while the oyster is not found in the Weybourn and Chillesford Crag, though common 

 lower down in the Pliocene series. These facts seem to me to have a strong bearing on the climatic conditions of the 

 Forest-bed epoch. They show us that the oyster flourished in the North Sea before the period of the Weybourn Crag 

 — that it did not live side by side with the Arctic forms of that period — and that it reappeared in our seas when favour- 

 able conditions returned. When the climate again became cold an Arctic fauna (including a new-comer, Leda myalis) 

 once more occupied the North Sea. 



+ Elephas meridionalis is usually regarded as a type-form of the Newer Pliocene, but long ago Dr Fdchs pointed 

 out that in Hungary this species is of quaternary age : Verhandl. d. k. k. geolog. Beiehsanstalt, 1879, pp. 49, 270. 

 It matters little whether we relegate to the top of the Pliocene or to the base of the Pleistocene the beds in 

 which this species occurs. That it is met with upon an interglacial horizon is certain ; and if we are to make the 

 Pleistocene co-extensive with the glacial and interglacial series, we shall be compelled to include in that system some 

 portion of the Newer Pliocene. 



% Julien, Des Phe'nomenes glaciaires dans le Plateau central, &c, 1869 ; Boule, Revue d'Anthropologie, 1879. 



§ Prehistoric Europe, p. 306. Professor Pence writes me that he and the Swiss glacialist, Dr Du Pasquier, have 

 recently examined these deposits, and are able to confirm my conclusion as to their interglacial position. 



