Certain
fossils are common around Cabrières. Trilobites,
primitive sea-dwelling arthropods, can be found in
the sedimentary rocks of the Primary or Palaeozoic
period. The orthocone and goniatites are a species
of cephalopod which are now extinct.
The
orthocone developed during the Palaeozoic period and
disappeared at the end of the first era of the Secondary
(Mesozoic) geological period. The crinoides are fixed
echinoderms whose branched arms and stems are formed
from calcite crystals and are often found preserved
in limestone deposits.
For
the most part, the rocks around Cabrières are
from sea-bed deposits from the Primary geological
period : sandstone and quartzite ; siliceous sand
; chalk, silt carbonated with calcium, and dolomite
with added magnesium ; ancient siliceous silt rich
in actinopods and organic matter ; shale and clay.
These rocks were heavily deformed through folding when
the Hercynian mountain range developed. The faults which
resulted, filled with veins of quartz, became rich in
minerals and were later exploited (particularly for
copper and barite).
The travertines (a white calcareous rock), which form
the terrace of the Estabel overlooking the valley of
the river Boyne, are much younger. They were formed
from calcium carbonate deposited from springs over the
last million years of the Quaternary geological period.
