Igue de Frau

The narrow entrance is vertical, in the form of a first shaft of about 5 m. At the base of the small shaft, on the left, a short dead-end gallery shelters the carcass of a dog, which certainly fell there by chance. a colony of bats has found refuge on the ceiling. On the right, after passing through a constriction, one finds oneself at the top of a non-vertical shaft. As the descent proceeds, the conduit becomes increasingly spacious; it intersects a dead-end shaft, then branches to the right. a few clayey offshoots lead nowhere. One thus arrives at the top of a new shaft, not vertical but steeply inclined. The diameter of this new section is 3 to 4 m. During the descent, two parallel dead-end shafts are encountered, totally covered in concretions. Finally, the large shaft breaks through the ceiling of a chamber about ten metres high and about twenty metres in diameter. At its centre is found the usual debris cone, here made up of enormous blocks and rubble of all kinds. It is in the left wall that one discovers the small window with its plunging fissure. If one crosses the chamber diagonally while keeping to the left, one notices a low conduit, about twenty metres long, cleared by the E.R.S. de Catus; this conduit ends in a clayey fill. At the other end of the chamber, we are at the low point of the cavity (-40 m). An impenetrable fissure cluttered with blocks, branches, etc., absorbs a small stream coming from the shaft and from the vaults of the chamber.

L'Igue du Frau develops in the Portlandian, which is formed of nodular limestones, topped by fine-textured limestones in small beds or in platelets. Here one has the typical example, especially where the shaft breaks through the chamber. The small beds and platelets are visible over several metres. Certain precautions are to be taken at this level during the visit, because of falling stones.

The walls of the new section are calcified and the stalagmitic flows numerous.

The cavity can be considered absorbing, because a small stream flows permanently in the shaft and disappears into the terminal fissure. During heavy precipitation, the igue absorbs several litres/second. Its waters, like those of its neighbour, the "Chateau de Crabilliers" pit, presumably head towards the Vert valley located only 3 km away. We have listed between Catus and Saint-Médard Catus, 5 km apart, 7 main springs of which several serve for the drinking water supply of several communes.

Topographic information: total surveyed development: 73 m; development of the main route: approx. 60 m; estimated total development: approx. 90 m.