FORAMINIFERA. 



they play in the formation of Chalk. The great formation of 

 the White Chalk forming the well-known chalk-cliffs of the 

 south of England, and attaining sometimes a thickness of not 

 less than 1000 feet is to a very large extent composed of the 

 debris of the microscopic shells of Foraminifera. As already 

 pointed out, therefore, the White Chalk is to some extent 

 comparable with the ooze of the deep Atlantic, which is also 

 largely made up of the skeletons of these minute organisms. 

 Amongst the Foraminifera of the Chalk are the genera Globi- 

 gerina (fig. 6, /), Rotalia (fig. 9), and Textularia (fig. 12), all 

 of which are represented by living species, no difference being 

 distinguishable in the case of 

 the first between the Creta- 

 ceous and the modern form. 

 In the Cretaceous formation 

 (Upper Greensand) we have 

 also the gigantic Arenaceous 

 Foraminifer which consti- 

 tutes the genus Parkeria, 

 the shell of which attains a 

 diameter of two and a quarter 

 inches. 



In the Kainozoic period the Foraminifera attained their 

 maximum of development, both as regards their size and the 

 number of generic types. The Eocene formation especially is 

 remarkable for the profusion of its Foraminiferous fauna. The 

 Middle Eocene in particular is characterised by the possession 

 of a very widely spread and easily recognised formation, known 

 as the Nummulitic Limestone, from the occurrence in it of a 

 large coin-shaped Foraminifer, the Nummulite (fig. 13). Num- 

 mulites attain a size of as much as three inches in circumference, 

 and their structure is very complex. According to Sir Charles 



Fig. 12. Textularia Meyetiana. 

 D'Orbigny. 



Fig. 13. Nummulites Icevigatus. Eocene. 



Lyell, " the Nummulitic Limestone, with its characteristic 

 fossils, plays a far more conspicuous part than any other 



E 



