Section of the massif of TRABUC and location of the main galleries.
The underground system, departing from Grand Abîme – a justifiably chosen name – leads to the deeper areas in which the water flows freely, however we do not know its origin.
The various levels of the caves correspond to successive carving out works. Their direction was the subsidiary consequence of tectonic accidents, and the primary consequence, for all the large chambers, of low collapses caused by the dissolution of the materials to be found in the deeper layers which are often full of gypsum.
Empty spaces caused by dissolutions, the lack of horizontal cohesion of the rock coming from marly beds account for horizontal or terraced shapes of the roofs. This is the consequence of the lifting off of the stata and the huge mass of fallen rocks obstructing the chambers.
These characteristics appear both in the converted part and in the kilometres of galleries visitors cannot view.
The great Chamber of the Lac de Minuit to be found in the converted part has the false aspect of a great chamber related to a tectonic accident.
However the great wall is not a fault, but rather a great cataclysm. The slow extraction from the roofs had been continuing for thousands of years, and so had the splendid concretions of the upper parts.
In the deepest levels, the subterranean stream flowing into Le Gardon is probably a recent phenomenon that is partly using old systems.