16 THE HISTORY OF CREATION. 
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earth, the tertiary epoch, or era of Leafed Forests, is much 
shorter and less peculiar than the three first epochs. This 
epoch, which is also called the cznolithic or czenozoic 
epoch, extended from the end of the cretaceous system to 
the end of the pliocene system. The strata deposited 
during it amount only to a thickness of about 3000 feet, and 
consequently are much inferior to the three first great 
groups. The three systems also into which the tertiary 
period is subdivided are very difficult to distinguish from 
one another. The oldest of them is called eocene, or old 
tertiary; the newer miocene, or mid tertiary ; and the last 
is the pliocene, or later tertiary system. 
The whole population of the tertiary epoch approaches 
much nearer, on the whole as well as in detail, to that of 
the present time than is the case in the preceding epochs. 
From this time the class of J/ammals greatly predominates 
over all other vertebrate animals. In like manner, in the 
vegetable kingdom, the group—so rich in forms—of the 
Angiosperms, or plants with covered seeds, predominates, 
and its leafy forests constitute the characteristic feature 
of the tertiary epoch. The group of the Angiosperms con- 
sists of the two classes of single-seed-lobed plants, or Mono- 
cotyledons, and the double-seed-lobed plants, or Dicotyledons 
The Angiosperms of both classes had, it is true, made their 
appearance in the Cretaceous period, and mammals had 
already occurred in the Jurassic period, and even in the 
Triassic period; but both groups, the mammals and the 
plants with enclosed seeds, did not attain their peculiar 
development and supremacy until the tertiary epoch, so 
that it may justly be called after them. 
The fifth and last main division of the organic history 
