Re: Meaning of the Geological Column

On Mar 4, 8:40 pm, Zoe <muz...@xxxxxxx> wrote:
On 4 Mar 2007 09:34:19 -0800, "jet" <jtr...@xxxxxxx> wrote:

snip>



Take a walk from Porthmadog, Wales to London. You will pass, in order:
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian,
Triassic, Jurassic Cretaceous and Tertiary layers. The reason you can
do this is because they are all stacked one on top of the other and
you are walking though the exposed areas.

my question remains: what is the basis for identifying these layers
you see in your walk, by names of dig sites that are physically widely
scattered over Europe? If it is not due to index fossils, and if it
is not due to the types of material that make up the rock layer, then
what is left?

I think you are trying to be obtuse here as this is not difficult.
Initially you describe a single formation. Then you go on and describe
the formations above and below them. Eventually the formations in that
area are described. You know that the lower ones are older and the
higher ones are younger. These are compared with formations in
another location. You find that some of the formations are similar. It
could be for any number of reasons: same composition, structure,
fossils, etc. Some are different. But you notice that the ones that
are similar are in the same relative order. You continue to do this at
different locations and eventually are able to reconstruct the
"geologic column".

.

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