Gee, Andy;-
   ---and all this time, I thought it was, "Sic transit Gloria Maris."
    Anon
>
> From: Andy Rindsberg <[log in to unmask]>
> Date: 2004/07/16 Fri PM 01:12:50 EDT
> To: [log in to unmask]
> Subject: Re: Mystery fossil
>
> David Campbell wrote,
> > In the eastern U.S., most of the late Pleistocene (ice age) fossil shells
> are of living species.  Earlier in the Pleistocene, and especially before
> the mid-Pliocene (ca. 3.5 million), the proportion of extinct species is
> much higher.
>
> Ah yes. In 1833, Charles Lyell divided the Tertiary Period into "Newer
> Pliocene, Older Pliocene, Miocene, and Eocene" epochs based on percentage of
> living species among the fossil mollusks. The Newer Pliocene is now called
> the Pleistocene and is reassigned to the Quaternary Period. Lyell's Older
> Pliocene is our Pliocene. His Miocene and Eocene are now our Miocene,
> Oligocene, Eocene, and Paleocene.
>
> And the latest twist is to substitute Neogene and Paleogene Periods for the
> familiar Tertiary Period, but that hasn't caught on universally. Neogene =
> Pliocene + Miocene, and Paleogene = Oligocene + Eocene + Paleocene. These
> days, the epoch and period boundaries are all carved in stone: Instead of
> calculating molluscan percentages, committees of stratigraphers select exact
> levels at particular outcrops of strata ("stratotypes"). The outcrops are
> chosen for their excellence of fossil diversity and preservation; usually
> marine sections are preferred. For the Tertiary, microfossils are more
> important to stratigraphers than mollusks these days. Sic transit
> gloriamundi!
>
> Andrew K. Rindsberg
> Geological Survey of Alabama
>
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