TERTIARY AGE. 489 



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 Reptiles. 

 Even the little Mammals, which appeared among the Reptiles, bore 

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

 the oviparous Reptiles and Birds, in being themselves of a semi- 

 oviparous type, the Marsupial. 



But these Mammals were prophetic species : with the opening of 

 a new era, the Reptiles 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, species still living 

 appeared, — a few among multitudes that became extinct, and after- 

 ward a larger proportion ; and, before its close, nearly all kinds of 

 life, excepting Mammals, were identical with those of the present era. 

 As the Paleozoic or ancient life was followed by the Mesozoic or Medi- 

 aeval, so now there was as marked a change to the Cenozoic or recent 

 life and world. 



Cenozoic time embraces two ages : — 



I. The Tertiary, or age of Mammals. 



II. The Quaternary age, or age of Man. 



I. THE TERTIARY, OR MAMMALIAN AGE. 



Of the Tertiary age, all the Mammalian species are extinct ; and 

 the proportion of living Invertebrates — Radiates, Mollusks, Articu- 

 lates — varies from very few in the early part of the period to ninety- 

 five per cent, in the latter part ; while, in the Quaternary, nearly all 

 the Mammalian species are extinct, but the Invertebrates are nearly 

 all living, not over five per cent, being extinct. 



The name Tertiary is a relic of early geological science. When introduced, it was 

 preceded in the system of history by Primary and Secondary. The first of these terms 

 was thrown out when the crj'stalline rocks so called were proved to belong to no par- 

 ticular age, — though not without an ineffectual attempt to substitute it for. Paleozoic; 

 and the second, after use for a while under a restricted signification, has given way to 

 Mesozoic. Tertiary holds its place, simply because of the convenience of continuing 

 an accepted name. 



Epochs. — The earliest adopted subdivisions of the Tertiary were 

 the Lower, Middle, and Upper. For these, Lyell substituted the fol- 

 lowing, based on the proportions of the fossils that belonged to species 

 still living, namely, — 



1. Eocene, from ^ws, dawn, and ko.lv6<s, recent (the latter a root 

 also in the word Cenozoic) ; the species nearly all extinct. 



2. Miocene, from /xciW, less, etc. ; less than half the species living. 



