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 for 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. 



2d ly. 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 lias 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". 



(T> 



4thly. These masses of submarine origin have, since their 

 formation, been raised to the height of two thousand or three 



(: .Sou vjl. ii. ; cliiiplurs v., vi., and vii. 



