Through a man-made tunnel with 220 steps, we come
to the 1st chamber, situated at a depth of 55 metres.
A faint light from the natural entrance greets us.
This is a pothole or aven in French. The pile of
debris, immediately visible, was formed by the collapse
of the natural entrance as well as stones and soil
that has fallen in due to the natural attrition
of wind and rain. Remains of animals that have either
fallen in or been thrown there in more recent times
have also been found.
To dig through this pile is to dig into time itself,
with domestic animals on top and remains of long
vanished species further down. Reindeer and bison
lived in this region during the last ice age that
ended more than 12,000 years ago. You can find out
more about them and the men who hunted them at the
Regional Museum of Prehistory.
It is through this hole that the
first explorers entered. They were led by Robert
de Joly and descended on 19th August 1935. The
pothole was of course well known to local people
but, due to its great depth, it had never been
explored.
The first great chamber is 125
metres long and 90 metres wide, a little more
than one hectare in area (2.5 acres). The numerous
crystallisations of stalagmites and stalactites
display a vast range of shapes, some of which
are extremely delicate.
About 6 million years ago, the lowest level of
the caves was formed by an underground river,
now long gone. During the last step of the visit,
you will be able to admire this remarkable gallery.
Limestone is slightly soluble in water and little
by little, rainwater, in combination with carbon
dioxide that naturally occurs in the soil, filters
through to become slightly acidic and corrosive.
This corrosive water then eats away at the small
fissures it passes through, enlarging and distorting
them.
The shape of the stalagmites often gives rise
to their name: "piles of plates" for
example. These particular shapes are found only
in caves with high roofs. Drops fall from the
roof and spread out in micro-droplets when contact
is made with the floor. Drops falling from a lower
height have less speed on impact and form different
shapes: fine "candles" result.
In this part of the cave beside the "piles
of plates", the "palm trees" have
grown. They can be as tall as 15 metres. There
is the 11-metre "pine cone", the symbol
of Orgnac. Similar to the "piles of plates",
the "palm trees" only exist where cave
roofs are high but where water drops regularly
and more abundantly. The many splash-outs of micro
droplets from numerous drops cause a build up
of "petals" on the sides of these extraordinary
stalagmites.
To the left, several metres in
front of the cave wall, a curtain of stalactites
has joined the stalagmites below to form the "organ
pipes". In the centre is the funeral urn
of the discoverer of these caves, Robert de Joly,
whose last wish, a short time before his death
in 1968, was that his remains should be placed
in the caves.
