. The vast majority of fossils have been formed under water, and a
large proportional number of these--whether the animals were marine,
terrestrial, or inhabitants of fresh water--have been formed in
sedimentary deposits either of sand, gravel, or other porous material.
Now, where such deposits have been afterwards raised into the air for
any considerable time--and this has been more or less the case with all
deposits which are available for exploration--their fossiliferous
contents will have been, as a general rule, dissolved by the percolation
of rain-water charged with carbonic acid. Similarly, sea-water has
recently been found to be a surprisingly strong solvent of calcareous
material: hence, Saturn-like, the ocean devours her own progeny as far
as shells and bones of all kinds are concerned--and this to an extent of
which we have probably no adequate conception.

Of still greater destructive influence, however, than these solvent
agencies in earth and sea, are the erosive agencies of both. Any one who
watches the pounding of the waves upon the shore; who then observes the
effect of it upon the rocks broken into shingle, and on the shingle
reduced to sand; who, looking behind him at the cliffs, sees there the
evidence of the gradual advance of this all-pulverising power--an
advance so gradual that no yard of it is accomplished until within that
yard the "white teeth" have eaten well into the "bowels of the earth";
who then reflects that this process is going on simultaneously over
hundreds of thousands of miles of coast-lines throughout the world; and
who finally extends his mental vision from space to time, by trying
dimly to imagine what this ever-roaring monster must have consumed
during the hundreds of millions of years that slowly rising and slowly
sinking continents have exposed their whole areas to her jaws; whoever
thus observes and thus reflects must be a dull man, if he does not begin
to feel that in the presence of such a destroyer as this we have no
reason to wonder at a frequent silence in the testimony of the rocks.

But although the erosive agency of the sea is thus so inconceivably
great, it is positively small if compared with erosive agencies on land.
The constant action of rain, wind, and running water, in wearing down
the surfaces of all lands into "the dust of continents to be"; the
disintegrating effects on all but the very hardest rocks of winter
frosts alternating with summer heats; the grind