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The Railway Cutting showing a cross section of Portland Stone
Swindon
Cockles Looking
closely at the rock face of Portland Stone see if you can spot the layer
of broken up shells, cockles and other bi-valves that lived in Swindon's
Jurassic sea.
Looking
closely at the layers below the sand, the Cockley Beds, you can spot cockles
whose modern day relatives now live off the coast of Australia.
The Cockley
Beds aren't actually cockle beds but death assemblages i.e. the shells
are not in their original life position. Instead what you're looking at
is piles of empty shell, all jumbled together, to form great shell banks
that coated the shallow tropical sea floor.
The Cockley Bed as it might have appeared
in Swindon's warm Jurassic Sea.
The broken
up shells again suggest a sea that was probably quite rough and stormy
at times.
It may even
have been the result of Jurassic hurricanes that came through the area
and stirred everything up leaving bits of broken shell all over the seabed.
Below
the Cockley beds are the Glauconitic Beds which are sandy limestone layers
containing glauconite. Glauconite gives a green colour to fresh surfaces
and cropped up in shallow warm seas about 155 million years ago. Although
there are no seashells in this layer the presence of glauconite shows
that it was still a marine environment.
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