Good description.

And for the land lovers - Travertine in riverbeds that have been flowing
across limestone - creating travertine (rock) calcareous limestone is on
the Shell building in Houston and other banks... beautiful history in it.
Naturally when heated by a local thermal event Marble might be obtained.
Considering the Gulf Coast - the coast was hundreds of miles (now out in
the Gulf of Texas/LA (mostly) out to sea before the great melt off and flooding of the oceans.
Various events of rivers and impacts are still visible even under the eons of droppings.
Out there dredging and such might bring up ancient land snails. Like examples
abound in the MED region - when the MED flooded and also the black sea.

Martin [ recreated from a list server bounce : > 250 lines. ]

Allen Aigen wrote:

> > Martin,
> > Geode was a poor term for Bob's hunk of limestone with a cavity in it.
> > Some geodes (as from Oregon?) do look like brown lumps of mud with silica
> > inside.  Geodes form in cavities in different types of rocks (mostly
> > basalts and tuffs but even some limestones) and usually have quartz
> > crystals lining the inside, but may have calcite and/or a number of
> > different minerals.  Bob's limestone formed as calcareous mud on an
> > ancient sea floor, which happened to have a marine snail trapped in the
> > mud.  The shell remained mostly empty when buried.  When the mud
> > consolidated as a rock, the fluids from the mud first dissolved the
> > shell, leaving a cavity ( a mold of the outside of the shell), then
> > precipitated some fine calcite crystals in the cavity.  A geode it is
> > not.  I have a BS in geology and a Master's degree in paleontology, if
> > that is supposed to help.
--
Martin H. Eastburn

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