116 
NEWER PLIOCENE PERIOD. 
[Ch. IX. 
of the land being often carried across the ocean, and the aquatic 
tribes over great continental spaces*. It is obviously expedient 
that the terrestrial and fluviatile species should not only befitted 
for the rivers, valleys, plains, and mountains which exist at the 
era of their creation, but for others that are destined to be formed 
before the species shall become extinct ; and, in like manner, the 
marine species are not only made for the deep or shallow 
regions of the ocean at the time when they are called into being, 
but for tracts that may be submerged or variously altered in 
depth during the time that is allotted fop their continuance on 
the globe. 
Recapitulation. — We may now briefly recapitulate some of 
the most striking results which we have deduced from our in- 
vestigation of a single district where the newer Pliocene strata 
are largely developed. 
In the first place, we have seen that a stratified mass of solid 
limestone, attaining sometimes a thickness of eight hundred feet 
and upwards, has been gradually deposited at the bottom of the 
sea, the imbedded fossil shells and corallines being almost all of 
recent species. Yet these fossils are frequently in the state of 
mere casts, so that in appearance they correspond very closely 
to organic remains found in limestones of very ancient date. 
2dly. In some localities the limestone above-mentioned 
alternates with volcanic rocks such as have been formed by 
submarine eruptions, recurring again and again at distant inter- 
vals of time. 
3dly. Argillaceous and sandy deposits have also been pro- 
duced during the same period, and their accumulation has also 
been accompanied by submarine eruptions. Masses of mixed 
sedimentary and igneous origin, at least two thousand feet in 
thickness, can thus be shown to have accumulated since the 
sea was peopled with the greater number of the aquatic species 
now living. 
4thly. These masses of submarine origin have, since their 
formation, been raised to the height of two thousand or three 
* See vol. ii. ; chapters v., vi., and vii. 
