CENOZOIC TIME. 505 



IV. CENOZOIC TIME. 



It has been observed that before the close of the Mesozoic the 

 medieval features of the era were already passing away. The 

 Cycads had begun to give place to Oaks, Willows, and Palms ; the 

 ancient type of Ganoids, to Salmon, Perch, and Herring ; and the 

 corals, Echini, and shells were in a great degree allied to those of 

 existing seas, though all of extinct species. But, notwithstanding 

 these progressing changes, the Mesozoic aspect continued on to the 

 end, appearing prominently in the multitudes of Ammonites and 

 Belemnites, in the predominance of Cestracionts and Ganoids 

 among fishes, and in the supremacy of the great class of Eeptiles. 

 Even the little Mammals which appeared among the Eeptiles bore 

 the mark of the age ; for the larger part, at least, approximated to 

 the oviparous Eeptiles and Birds in being themselves of a semi- 

 oviparous type, the Marsupial. 



But these Mammals were prophetic species ; and with the 

 opening of a new era the Eeptiles dwindled in numbers, variety, 

 and size, and Mammals in their turn became the dominant race. 

 At the same time, types much like those of the age of Man were 

 multiplied in all departments of nature. As the era advanced, the 

 first of living species appeared, — a few among multitudes that be- 

 came extinct, and afterwards a larger proportion; and before its 

 close, nearly all kinds of life, excepting Mammals, were identical 

 with those of the present era. As the Palaeozoic or ancient life was 

 followed by the Mesozoic or Medieval, so now there was as marked 

 a change to the Cenozoic or recent life and world. 



Cenozoic time embraces only a single age, the age of Mammals. 



MAMMALIAN AGE. 



The age of Mammals is divided into two periods : — 



1. The Tertiary, in which all the Mammalian species are extinct, 

 and the proportion of living Invertebrates — Eadiates, Mollusks, 

 Articulates — varies from none in the early part of the period to 

 90 per cent, in the latter part. 



2. The Post-Tertiary, in which nearly all the Mammalian species 

 are extinct, but the Invertebrates are nearly all living, not over 5 

 per cent, being extinct. 



The name Tertiary is a relic of early geological science. When 



