;o THE STORY OF THE EARTH. 



ferns of the present clay are well repre- 



ted ill strata older than the chalk, by such 

 types as Pteris^ Asplcnium, Adiantum, Aspidtum, 

 and Gleichenia* Palms arc represented by Xipa. 

 are numerous representations of the oak, 

 willow, beech, fig, laurel, ebony, magnolia. Xoth- 

 IS known of the origin of this ancient cretace- 

 ous flora, but there is no ground for believing 

 that it suddenly came into existence in widely 



.rated parts of the world, where it is first met 

 with. 



In the oldest group of rocks every class of 

 animals is represented by many genera which 

 still live. Thus the Foraminifera, which fill so 

 large a place in the life of the open ocean at the 



sent day, are represented in the Silurian period 

 by the genera Dcntalina, Lagena^ Nodosaria, 7V/t- 

 tula rid. 



The existing genera of Echinoderms are not 

 known from so early a period ; but in the begin- 

 ning of the secondary time CidartS and many 

 <»ther genera are found, which abound at the pres- 

 ent day. 



Among shells the Brachiopods Liflgula and 



msa t Diseina y Rhyncontlla, Tcrebratula and oth- 

 i from the older primary time-. 



The Common bivalve shells, which have few 



ntatives in the Primary rocks, include such 

 familiar forms as Pecten % Pinna % Cardiun % Arca } 



tla. 



I be ' ommon Univalve shells begin with such 

 form Patella y maria % Chiton^ Natica^ 



. Dentalium y winch have never since 1" 



i irth. The A 'autilu s dates from 



period. 

 Tic. history of 



