e of the waters of the Baltic, of
living Diatoms and _Radiolaria_ of the same species as those which, in a
fossil state, constitute extensive rocks of tertiary age at Caltanisetta,
Zante, and Oran, on the shores of the Mediterranean.

Moreover, in the fresh-water rotten-stone beds of Bilin, Ehrenberg had
traced out the metamorphosis, effected apparently by the action of
percolating water, of the primitively loose and friable deposit of
organized particles, in which the silex exists in the hydrated or soluble
condition. The silex, in fact, undergoes solution and slow redeposition,
until, in ultimate result, the excessively fine-grained sand, each
particle of which is a skeleton, becomes converted into a dense opaline
stone, with only here and there an indication of an organism.

From the consideration of these facts, Ehrenberg, as early as the year
1839, had arrived at the conclusion that rocks, altogether similar to
those which constitute a large part of the crust of the earth, must be
forming, at the present day, at the bottom of the sea; and he threw out
the suggestion that even where no trace of organic structure is to be
found in the older rocks, it may have been lost by metamorphosis.[4]

[Footnote 4: _Ueber die noch jetzt zahlreich lebende Thierarten der
Kreidebildung und den Organismus der Polythalamien. Abhandlungen der Koen.
Akad. der Wissenchaften._ 1839. _Berlin_. 1841. I am afraid that this
remarkable paper has been somewhat overlooked in the recent discussions
of the relation of ancient rocks to modern deposits.]

The results of the Antarctic exploration, as stated by Dr. Hooker in the
"Botany of the Antarctic Voyage," and in a paper which he read before
the British Association in 1847, are of the greatest importance in
connection with these views, and they are so clearly stated in the former
work, which is somewhat inaccessible, that I make no apology for quoting
them at length--

"The waters and the ice of the South Polar Ocean were alike found to
abound with microscopic vegetables belonging to the order _Diatomaceoe_.
Though much too small to be discernible by the naked eye, they occurred
in such countless myriads as to stain the berg and the pack ice wherever
they were washed by the swell of the sea; and, when enclosed in the
congealing surface of the water, they imparted to the brash and pancake
ice a pale ochreous colour. In the open ocean, northward of the frozen
zone, this order, though no doubt