THE MICROSCOPE IN MINERALOGY AND GEOLOGY. 95 



The lowest type of animal life, consisting of minute 

 portions of sarcode or animal jelly, having the power of 

 putting forth prolongations of the body at will, contain 

 some forms which cover themselves with shells, usually 

 many-chambered, of carbonate of lime. From the pores 

 in these shells, through which the root-like processes of 

 sarcode are protruded, they are called Foraminifera. 



FIG. 54. 



Fossil Polycystina, etc., from Barbadoes: a, Podocyrtis mitra; 6, Rhabdolithus scep- 

 trutn ; c, Lychnocanium falciferum; d, Encyrtidium tubulus; e, Flustrella concentrica; 

 /, Lychnocanium lucerna; g, Encyrtidium elegans; h, Dictyospyris clathrus; i, Encyr- 

 tidium mongolfieri; A;, Stephanolithis spinescens; /, S, nodosa; m, Lithocyclia ocellus; 

 n, Cephalolithis sylvina; o, Podocyrtis cothurnata; p, Rhabdolithes pipa. (From Car- 

 penter.) 



Another class, the Pofycystina, secrete a siliceous shell, 

 usually of one chamber. The accumulations of the Fo- 

 raminifera have formed our chalk beds, while the Polycys- 

 tina have contributed to siliceous strata, like the Diato- 

 macece (Fig. 54). 



The origin of white chalk strata has been illustrated 



