THE EOCENE PERIOD. 



241 



The Marine Life. 



The very name Eocene, founded upon the presence of a small per- 

 centage of living species, implies the stage reached by the marine inver- 

 tebrates. Not only were the existing orders, families, and genera 

 established, with some exceptions, but even the present species had 

 begun to appear. The changes that follow from this time on are valu- 

 able as criteria of correlation, climate, migration, and other elements 



a * 1 



Fig. 433.— Eocene Foraminifera: a, Nodosaria bacillum Defrance; b, N. communis 

 (d'Orbigny) ; c, Anomalina ammonoides (Reuss); <I, Cristellaria gibba d'Orbigny; 

 e, C. radiata (Bornemann); /, g, and h, Globigcrina bidloides d'Orbigny; i, Vagina- 

 Una legumen (Linne); j, Discorbina turbo (d'Orbigny); k, Truncatulina lobatula 

 (Walker and Jacob); I, Textnlaria subangulata d'Orbigny. Magnified 10 to 50 

 times. (Maryland Geological Survey.) 



of the later history, but they do not record any further profound bio- 

 logical transformations. They stand in striking contrast with the radical 

 and rapid evolution of the placental mammalians. 



Geologically, the most striking feature of the marine Eocene life 

 was the extraordinary abundance and size of the foraminifers. Mas- 

 sive beds of limestone in the Paris basin were largely made up of the 

 tests of Miliola. Other Eocene limestones were formed chiefly of Or- 

 bitolites, Orbitoides, Operciilina, and Alveolina, while the nummulitic lime- 

 stone, whose wide range and great importance has already been indi- 



