Thursday, July 2, 2009

Vegetal rock

My Antipodes blog contains so many references to rocks that I must pardon readers who might feel that the author has rocks in his head. Let us admit, in a scientific spirit, that it's a debatable point...

The precise geological name of the rocks that concern me today is calcareous tufa. Here's a specimen from a low wall at Gamone:

Once you scrape away the moss, it's pure calcium carbonate, of the kind that once blocked the ancient ceramic water pipes at Gamone:

Tufa rock forms rapidly in places where highly-calcareous water emerges into the open air and meets up with mossy vegetation, which enters into the production of the rock. That's why I refer to this tufa as vegetal rock. It's a soft substance, easily cut with a saw, which was often used in the construction of houses. Here's an example from the corner of my house at Gamone:

In this photo, you can see fragments of Gamone bluestone (ancient hard rock) interspersed among the blocks of tufa.

The calcareous tufa at Gamone came surely from the domain of the Carthusian monks at Val-Sainte-Marie, Bouvante (Drôme), known for such deposits. But the most famous source of calcareous tufa in the region happens to lie to the north, in Isère, at an equal distance from Choranche. I'm talking of the ancient village of La Sône, which I mentioned in recent blog articles entitled An old map talked to me of trees [display] and Weaving machines [display].

The name of the village, La Sône, comes from its Latin reference: aqua sonus, the sound of water. What a splendid name for a village! Here's an image of the place where that archaic sound was first heard:

Since time immemorial, water filled with 315 mg/liter of limestone (compared to 10 to 50 mg/liter for ordinary mineral water) has been tumbling into the Isère at La Sône, at the following magnificent spot:

And that's what the phenomenon of calcareous tufa is all about. Here's a close-up view of the formation of this vegetal rock:

Today, at La Sône, visitors can admire splendid gardens at the base of these water-falls. Before the calcareous waters disappear into the Isère, they are collected in a series of beautiful ponds.

It would appear that the vegetation and the frogs have had time to get adjusted to the high degree of calcium carbonate.

Needless to say, the hand of humans is omnipresent in these gardens, as it should be, just alongside the place where the hands of weavers once produced a century of silk.

The garden's attractions include weird hand-made inventions that use the falling waters to produce ethereal sounds.

Bamboo-lovers like me are equally enchanted. La Sône is a magic place!

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