THE ANCIENT MAMMALS OF BRITAIN. 313 



ficial manure. Although its Molluscs are generally of a northern 

 type, this feature is less marked than in the Norwich Crag. 

 The lowest, or Coralline Crag, which is generally of a light 

 colour, takes its name from the number of species of Polyzoa 

 found in these beds ; its Molluscan Fauna indicating warmer 

 conditions than those prevailing during the deposition of the 

 upper members of the series. 



One of the features of the Mammalian Fauna of the crags 

 is the occurrence of remains of Mastodons, which are quite 

 unknown in the higher beds, and the comparative rarity of true 

 Elephants ; while still more noticeable is the abundance of the 

 remains of Cetaceans, referable to many species and genera. 

 Although some of the Crag Mammals belong to existing 

 species, the great majority are extinct, and a small propor- 

 tion belong to genera no longer existing. It is probable that 

 the greater number of the Mammals found in these beds belong 

 to species which were living during the time of their deposition, 

 although a few may have been derived from antecedent Miocene 

 beds. Certain specimens are, however, met with which have 

 clearly been washed out from the London clay cr other older 

 Tertiary formations ; and these, which may generally be recog- 

 nised by their water-worn condition, will be omitted from our 

 survey. Although the Mammals obtained from the different 

 crags are by no means always the same, it will be convenient 

 to treat of the whole series collectively. 



Among the most difficult fossils to determine specifically are 

 detached teeth of the Cats, and certain such specimens from 

 the Red Crag, which have been regarded as indicating an extinct 

 species, are so like the corresponding teeth of the Leopard that 

 it would be hazardous to say they do not belong to that animal, 

 although, on the other hand, it would be equally rash to say 

 positively that such was the case. Whether a Sabre-tooth occurs 

 in these deposits is uncertain ; but there is no doubt as to the 



