INTRODUCTION 



41 



to the monumental researches of Gerard Paul Deshayes (1795-1875) on 

 the succession of the shells in the Paris Basin; he perceived that as we 

 pass from the older and lower to the higher and more recent geological 

 levels there is an increasing percentage of living types or species. To the 

 threefold division discovered by Deshayes, Charles Lyell in 1833 applied 

 the names Eocene, Miocene, and Pliocene. In 1854 Heinrich Ernst Bej-rich 

 (1815-1896) perceived that in many parts of Europe a fourth grand divi- 

 sion existed between Eocene and Miocene times, for which he proposed 

 the term Oligocene. Another step in this naming of the periods or sys- 

 temes was in 1839 when LyelP proposed the term "Pleistocene" for the 

 period succeeding the Pliocene and preceding the Recent or Holocene. 



Students of fossil shells also took the leadership in further dividing 

 the Age of Mammals into time periods by demonstrating that the epochs 

 can be subdivided into stages, or Stages. Thus the French invertebrate 

 palipontologist, Alcide Dessalines d'Orbigny (1802-1857), divided the Eocene 

 of France into a lower stage, or Suessonian, named from the deposits chiefly 

 north of Paris, and an upper stage, or Parisian, named from the deposits 

 around Paris. Successive proposals of D'Orbigny, Dumeril, Mayer-Eymar, 

 Suess, Deperet have finally led (1889) to the subdivision of all the Cseno- 

 zoic periods into a large number of Stages which receive their names from 

 the geographical localities in which they are most typically represented in 

 various parts of France, Belgium, Italy, and Sicily. It is now recognized 

 that each of these stages represents a long period of time. These stages and 

 their approximate parallels in North America are exhibited in the accom- 

 panying table. 



Preliminary Correlation 



1 Charles Lyell, Antiquity of Man, 1839, p. 6. 



