4 THE MIGRATION OF BRITISH BIRDS 



regard to Miocene and Eocene time it is still more 

 difficult, from the present state of our knowledge, to 

 derive even a general idea of its aspects. Of this, how- 

 ever, wc may rest assured, that it possessed many 

 dominant features which have long been entirely obli- 

 terated from existing types. Amongst these vanished 

 birds we may recall the giant Gastoriiis klaassein ; the 

 Accipitrine Lithornis vultiirinus ; the imposing Argillor- 

 nis and Odoiitopteryx — allied to the Gannets and the 

 Cormorants ; Halcyornis and Proheivdins, representing 

 our modern Gulls and Herons ; the Flamingo-like 

 Helornis, and the Ibis-like Ibidopsis. We need not, 

 however, speculate on the avifauna of so remote a past ; 

 it has little or nothing to do with the past emigrations 

 of existing species, or of the phenomenon of Migration 

 across what is now the liritish Archipelago, the philo- 

 sophy of those grand avian movements being amply 

 demonstrated by the forms inhabiting that area during 

 present time. 



For the purposes of the present volume it will not be 

 necessary to go back, geologically, to a very distant past. 

 On the ancient origin of Avian Season Flight I have 

 already dwelt at some length in the Migration of Birds. 

 The present work is more a study of the Post-Glacial 

 Emigrations of our avifauna and of Migration as under- 

 taken by birds in our own day, going on unceasingly 

 around us from year to )"ear, than a history of the phe- 

 nomenon of Migration in remoter ages. Nevertheless we 

 shall find in our investigation of the interesting subject 

 tliat it will be advisable not on!}' to go back at least to 

 late riiocciK^ and to Pleistocene or Quaternary time, 

 but to include the avifaunas of many areas more or less 



