CENOZOIC ERA 



CHAPTER XVIII 



THE TERTIARY PERIOD 



Origin of Name, Subdivisions, etc. 



The Cenozoic era is often called the "Age of Mammals" be- 

 cause, for the first time, these most highly organized of all animals 

 became abundant and diversified and were masters of the land. 

 Plants and animals both took on a decidedly modern aspect, with 

 species of living organisms represented for the first time, some even 

 in the early Cenozoic and many during the later portion of the era. 



The name "Tertiary" has entirely lost its original significance, 

 but has, nevertheless, become thoroughly fixed in the literature of 

 geology. In the early days of the science, the whole known 

 geological column was divided into three groups of rocks, and later 

 into four groups, namely: Primary, Secondary, Tertiary, and 

 Quaternary. After the discovery of rocks still older than these, the 

 term Primary was replaced by Paleozoic ; Secondary by Mesozoic ; 

 while Tertiary and Quaternary have been retained as subdivisions 

 of the Cenozoic. 



Following are the subdivisions of the Tertiary system now 

 recognized as world-wide in application: 



Tertiary 

 System 



Pliocene series 



("More recent"). 

 Miocene series 



("Less recent"). 

 Oligocene series 



("Little recent"). 

 Eocene series 



("Dawn of recent"). 



Upper Tertiary. 



Lower Tertiary. 



Sir Charles Lyell first divided the Tertiary into Eocene, Miocene, 

 and Pliocene on the basis of percentage of living species repre- 

 sented in each series, there being very few in the earliest and a 



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