104 PROTOZOA. 



sentatives of this group are found in almost all formations 

 in which calcareous rocks are developed, and if we admit 

 Eozoon to be a member of this group, then the order dates 

 from the Laurentian, and has been continued throughout the 

 entire period represented by the known stratified rocks. The 

 Foraminifera have also contributed notably to the formation 

 of the solid crust of the earth, and have often built up mas- 

 sive and widely extended limestones. Well-known examples 

 of these foraminiferal limestones are the great Fusulina lime- 

 stones of Eussia and North America and the Saccammina lime- 

 stone of Britain, both of which belong to the Carboniferous 

 period ; the White Chalk of the Cretaceous period ; and the 

 Nummulitic limestone, Miliolite limestone, and Dactylopora 

 limestones of the Tertiary period. The Chalk has been 

 already alluded to (see p. 15), and we shall, have occasion 

 to briefly notice the others of the above-mentioned limestones 

 in speaking of the generic types which characterise them. 

 Besides having largely officiated as lime-makers, the Fora- 

 minifera have materially contributed to the formation of 

 deposits of greensand at various periods of the earth's his- 

 tory, and are known to be carrying on the same process at 

 the present day. The green grains in such green sands as 

 those of the Cretaceous period (as first shown by Professor 

 Ehrenberg for similar green grains in the Lower Silurian of 

 Kussia), seem to be often really casts of Foraminifera in glau- 

 conite (silicate of iron and potash), from which the calcareous 

 shell has been dissolved away. Similar green sands, similarly 

 composed in part of internal casts of Foraminifera, are now 

 being laid down in various of the warmer seas of the globe. 

 All the recent Foraminifera (with the exception of the chi- 

 tinous Gromidce) are exclusively marine in habit, and all the 

 extinct members of the group were doubtless inhabitants of 

 the sea. Like many other lowly organised forms, the Fora- 

 minifera have been very " persistent " types of life. Various 

 of the Palaeozoic genera have descended to us unchanged 

 from the Palaeozoic period ; and the prevalent forms in the 

 Chalk are hardly different from those of the Atlantic " ooze." 

 Upon the whole, Dr Carpenter concludes that " there is no 



