ORIGIN AND CHARACTERISTICS 5 



to the modern Divers) were discovered by 

 Barrett in the Upper Greensand of Cambridge- 

 shire ; others obtained from the chalk forma- 

 tion of South Sweden have been described by 

 Professor Dames. A much more extensive series 

 of Ornitholites (referable to no less than seven 

 genera) from the Cretaceous rocks of North 

 America have been described by Professor 

 Marsh. Two of these, from the shales of Kansas, 

 formed his distinct sub-class Odontornithes, but 

 as all Cretaceous birds are believed to have 

 been toothed the term has more recently been 

 employed to embrace all Ornitholites of that 

 epoch. The list of Pre-Tertiary Ornitholites is 

 comparatively a small one. As might naturally 

 be inferred Ornitholites become much more 

 numerous in Tertiary deposits. Avine evolution 

 must have been progressing upon a vast scale 

 during the closing ages of the Cretaceous and 

 the early eras of the Tertiary systems ; and not 

 only do we find a much greater and most 

 significant wealth of avine fossils, but a steady 

 progress towards those types which dwell upon 

 the earth in our own time, or which occupied 

 it in ages not very remotely preceding the 

 present. Some of the most remarkable Orni- 

 tholites of the early Tertiary Period relate to 



