If the decay of the soft parts of the sea-urchin; the attachment, growth
to maturity, and decay of the _Crania_; and the subsequent attachment
and growth of the coralline, took a year (which is a low-estimate
enough), the accumulation of the inch of chalk must have taken more than
a year: and the deposit of a thousand feet of chalk must, consequently,
have taken more than twelve thousand years.