Geological Timescale |
Geological Tour |
Contents provided by courtesy of Eric Rowe, Master Potter, Geologist, Botanist and a fine fellow.
Sophia Antipolis was an industrial site long before the present technopole was dreamed of - possibily for more than two thousand years! A look at the geological map of the region and you will see marked the many abandoned clay mines that once pitted the area. A very refractory clay was dug here and taken to Biot or Vallauris (map q15) and the finished product exported to the old, and later, the new world. One of the larger mines is now the site of the open air theater but usually the mines were much smaller than this. The clay filled hollows in an earlier limestone formation and was laid down in irregular layers and colors - white, green and ochre yellow. After cleaning it throws well on the potters wheel. This same clay was used to make the large Jarres that made Biot so famous.
To better understand the origins of this clay and the whole underlying structure of the Beyond region one needs a good understanding of it's geology.
Africa has given this part of Europe some nasty jolts in the distant past; so much so that, standing on the Esterels and looking north, you are looking at the ancient sea! The massively thick strata of limestone deposited on the old sea floor has been lifted up (with pressure from Africa) into the mountains we see today. Tanneron, the Esterel and the Massif des Maures are indeed, even talking in geological terms, very old lands. They are also, for the same reason, acid; never having had the calcium (chalk) as an undersea deposit, which means a different 'flora' grows there from that found on limestone (hardened chalk). There are some flowers and trees that like one or the other and some not too much of either (neutral soils) and some that will grow anywhere.
The geology of a region also has a profound effect on the economy as we can see from the Sophia clay deposit. The following table should give a clearer idea of all this.
Simplified Geological Table
Lac St. Cassien
Cretaceous - Lower
Cretaceous - Upper
||Tertiary - Paleocene
Tertiary - Eocene
Tertiary - Oligocene
Tertiary - Miocene
Tertiary - Pliocene
Quaternary - Pleistocene
Quaternary - Holocene
Alps, Biot volcano
The two volcanos marked on the table are very far apart in time and nature. The Esterels were formed from the lava flow of a very early time (Palaeozoic era) that cooled to form a very enduring granite-like rock with small crystals - Rhyolite. You can find it used as a paving-stone in the older streets of Bagnols-en-Forêt. It also makes a most imposing landscape.
The Biot volcano is more 'recent' (Miocene) and is much more 'alkaline', ie., much less silica (quartz) and much more iron and other metal minerals. The low hill that is left is made up mostly of consolidated volcanic ash, but it must have been quite explosive to judge from the amount of volcanic 'bombs' imbedded in it. This consolidated volcanic ash was, until very recently, quarried and used to build some of best bread or pizza ovens in existence. Luckily, for those who appreciate good bread, some are still being used for baking in the old way - with wood!
Although the Alps are relatively young there has already been considerable erosion. Nearly all the deposits of the Cretacous era have all but vanished! Vestiges can still be found in the Caussols and St. Vallier area, with a few typically Cretaceous fossils and flints. The underlying Jurassic limestone is very resistant to erosion in the Alpes Maritimes. After the departure of the sea the limestone lay for a long time in shallow seas or lakes where the calcium crystals were infiltrated by magnesium. When this process is complete (half magnesium, half calcuim) the rock is then called 'Dolomite' - from the Dolomites in Italy. In the Alpes Maritimes the process is often incomplete and it is then called 'Dolomitic Limestone'. These rocks, when freshly broken, have a reddish-ochre color, due to the presence of magnesium. Going to the east of our region in the Alpilles around Les Baux the limestone has not undergone this process and remains white. The deep red scars one can see in this landscape are due to the extraction of Aluminium ore called 'Bauxite' after Les Baux where it was first discovered! The color is due to heavy iron staining of the ore and, now that purer deposits have been found in the world, the original Baux deposits are no longer mined or are in the process of closure.
Lac St. Cassien and around
Driving round the lake towards the Autoroute (map q15) and looking left after the bridge one can see the gray to black rocks by the roadside. These are the 'schists' of the 'Carboniferous Period'. A time of rich vegetation during which much of the world's coal deposits where formed. Under the severe pressures this region has undergone during it's geological history the coal deposits, never very thick, have been transformed to anthracite (hard coal). These deposits have been mined in the past - more especially at Boson, a little further down the autoroute towards Fréjus - but the quality was poor and the seams thin. The gray schists and shales are a kind of hardened clay and result from the earth on which the ancient forests grew. The dark color comes from the mixed-in 'Carbon'. In many coal-mines this clay is still soft and, as it will stand high temperatures, is used to make fire-bricks.
Driving over the autoroute and then turning left and under it, along a track, one can see large blocks of white stone that look, at first, like massive quartz, but, if you scratch it, you find that it is very soft! This is Flourite. Continuing along the rough road you will end up in front of one of the once largest mines in Europe of this mineral. Converted to flourine it is used in drinking water, toothpaste and in steel production.
Just ouside St. Paul-en-Fôret, towards Bagnols-en-Forêt, is a granite ridge, it's highest point being near the road, at right angles to it, plunging down at both ends. Granite is usually composed of (essentially) quartz, felspar and black and/or white mica, but in the case of the St. Paul granite, as it's called, the mica is replaced by tourmaline. Instead of the thin flakes of mica one can clearly see the tourmaline in the form of little black sticks. Here and there, where there have been a concentration of minerals on the ridge slopes, you can find larger crystals often attached to massive quartz. Finer, deep-green tourmaline is used in jewelry, but that of St. Paul is all opaque and black!
Continuing the road to Barjol one goes through a landscape of 'metamorphic' rocks which were formed in the surroundings by the heat and pressure from the granite intrusion. These rocks are called 'gneisses' (with felspar) or schists (no felspar, but bands of black mica). Gniesses are formed by pressure and heat, schists with pressure only. Schists will often easily split into layers like a kind of deformed slate. In some parts of France it is even used for roofing.
Broken Dam. Along the autoroute, about halfway to Fréjus, you can see on the right the remains of a dam, the Barrage de Maupasset. One night of heavy rain, on 2 Dec 1959, this dam gave way, causing death, injury and much damage on it's path to the sea. The rupture of the Barrage de Maupasset was basically caused by a non appreciation of this aptitude of schist, on which the dam rested, to give way along it's cleavage surfaces. The responsibilities have still not been officially determined.
(Moh's scale of Hardness or what scratches what.)
This scale is based on the fact that some rocks are much harder than others and can be identified in this way. For those who might wish to start to know minerals and rocks, with a pen-knife and a lump of granite you can already make a start. If it scratches everything it is not granite! The knife will not scratch the quartz, but will mark felspar and easily pick off flakes of mica. One has to be careful to see that it is the rock being scratched and not the knife. Use the point only. A lump of quartz will scratch about anything you are likely to find - except carburundum and diamonds! There are many interesting minerals to find and the job gets even more complicated the nearer you get to the Esterels. Their is even a unique rock to be searched for between Bouloris and Dromont, near St. Raphael - the beautiful dark blue 'Esterillite'.
Note: Minerals are what rocks are composed of. They, themselves, are made up of oxides or carbonates. For instance quartz is part of the make up granite and is composed of Silicium or SiO2 (Silicic acid + oxygen).
|| crystallized calcium
||Carborundum is 9+