122 SUMMAEr. 



The Vertebrata, on account of their more specialised forms, 

 would be likely to change more rapidly than the Invertebrata, 

 and it might therefore be expected that they would be found to 

 yield data for the more definite division of the Pliocene horizons ; 

 but it wiU be obvious from a glance at the table that the mate- 

 rials available from the beds between the Nodule-bed and the 

 Forest-bed are quite insufficient for this purpose. With regard 

 to these two horizons it is interesting to note the great increase of 

 living species, for while in the former they comprise less than 

 9 per cent, of the fauna, yet in the latter they have advanced to 

 nearly 70 per cent. 



This large proportion of living forms in the Forest-bed is, 

 however, to some extent due to the fishes, amphibia,^ reptiles, 

 birds, and small mammals being included, few of which have been 

 obtained from other Pliocene or Pleistocene horizons, and when 

 these are eliminated, leaving only the larger mammals, as in the 

 other horizons, about 40 species remain, of which 50 per cent, 

 are now living. About 80 per cent, of the British Pleistocene 

 mammals are still living. 



The large number of recent species found in the Forest-bed 

 has been looked upon as a reason for including that series of 

 deposits with the Pleistocene rather than with the Pliocene ; this, 

 however, can scarcely be accepted in face of the facts just noticed. 

 Moreover a large proportion of the Deer which were abundant in 

 the Forest-bed times, died out before the deposition of those beds 

 which are generally accepted as of Pleistocene age. And besides 

 this the Forest-bed is linked on to the beds below by several 

 forms which do not pass to the beds above, and although that 

 essentially Pliocene mammal, the Mastodon, is absent from the 

 Forest-bed, yet this does not seem sufficient to outweigh the 

 evidence in favour of placing the Forest-bed in the Pliocene. 

 However, it is not of very great moment whether these deposits 

 are classed with the series just above or those below them ; and 

 happily there is a general agreement that the Forest-bed stands 

 between strata of undoubted Pliocene and Pleistocene age. 



In all the Pliocene deposits there is a mingling of what appear 

 to be northern and southern animals. The land mammals of the 

 Nodule-bed include such sub-tropical genera as Hy^na, Ante- 

 lope, Tapir, Rhinoceros, Elephant, and Mastodon ; but with 

 these are a few which seem to indicate more temperate conditions, 

 and the Marine mammals may point to a still colder climate, for 

 some of the Cetacea are such as now inhabit the more northern 

 parts of this hemisphere. The fishes of the Nodule-bed again 

 point to a warmer climate. 



From the Coralline Crag Cetacean remains have been obtained 

 which seem to indicate a temperate climate, and the large number 

 of fish Otoliths from this horizon all belong to Gadoids which are 

 common in temperate and northern seas, but are rare so far south 

 as the Mediterranean. Ohrysophrys, Thynnus, and Platax, on 

 the other hand, may indicate warmer ccmditionB. 



