THE CRETACEOUS PERIOD. 



263 



portant group of the Palms. It is thus a matter of interest to 

 reflect that plants closely related to those now inhabiting the 



186 — Cretaceous Angiosperms. a, Sassafras Cretaceuin ; b, Liriodeiidron 

 Meekii; c, Leguminosites Marcotianus ; d, Salix Meekii. (After Dana.) 



earth, were in existence at a time when the ocean was tenanted 

 by Ammonites and Belemnites, and when land and sea and 

 air were peopled by the extraordinary extinct Reptiles of the 

 Mesozoic period. 



As regards animal life, the Protozoans of the Cretaceous 

 period are exceedingly numerous, and are represented by Fora- 

 mifiifera and Sponges. As we have already seen, the White 

 Chalk itself is a deep-sea deposit, almost entirely composed 

 of the microscopic shells of Foraminifers, along with Sponge- 

 spicules, and organic ^^(^r/j- of different kinds (see p. 22, hg. 7). 

 The green grains which are so abundant in several minor sub- 

 divisions of the Cretaceous, are also in many instances really 

 casts in glauconite of the chambered shells of these minute 

 organisms. A great many species of Formninifera have been 

 recognised in the Chalk ; but the three principal genera are 



