Shells and bones decay and disappear when left on the bottom of the sea, where sediment is not accumulating.

We probably take a quite erroneous view, when we assume that sediment is being deposited over nearly the whole bed of the sea, at a rate sufficiently quick to embed and preserve fossil remains.
Throughout an enormously large proportion of the ocean, the bright blue tint of the water bespeaks its purity.

The many cases on record of a formation conformably covered, after an immense interval of time, by another and later formation, without the underlying bed having suffered in the interval any wear and tear, seem explicable only on the view of the bottom of the sea not rarely lying for ages in an unaltered condition.

The remains which do become embedded, if in sand or gravel, will, when the beds are upraised, generally be dissolved by the percolation of rain water charged with carbonic acid.

Some of the many kinds of animals which live on the beach between high and low water mark seem to be rarely preserved.