GIANT BIRDS. 157 



had ^heir original home on the great Euro- Asiatic 

 continent, from whence they have gradually migrated 

 southwards till they reached regions free from the 

 large carnivorous mammals of the continents. 



Looking back through the Tertiary rocks of Europe 

 to see if we can find there traces of ancestral Giant 

 Birds, it is not till we come to the Lowest Eocene, or 

 period immediately below the London Clay, that our 

 search is rewarded. Here, however, both in England, 

 France, and Belgium, we meet with limb-bones and 

 other remains of Giant Birds, which, from their huge 

 size, must almost certainly have belonged to the group 

 under consideration. In this bird, which is known as 

 Gastornis, the lower end of the leg-bone has a bony 

 bridge, as in the Moas ; and since this is a feature com- 

 mon to the great majority of flying birds, it suggests 

 a community of origin between them and the Giant 

 Birds ; the loss of this bridge in the living members of 

 the latter thus being an acquired character. Although 

 we are still very much in the dark as to the real 

 affinities of the Gastornis, yet it appears to be more 

 nearly related to the Moas and the Dromornis than 

 to any other birds, and it might, therefore, have well 

 been one of the ancestors of the group. Another 

 closely allied bird is found in the Eocene of the 

 United States, while others have left their remains in 

 the Tertiary deposits of South America. 



This is at present the extent of our knowledge of 

 the former distribution of Giant Birds ; but it may be 

 confidently expected that whenever the Tertiary forma- 



