FN 15

The entrance shaft is fairly vast, with a rocky ledge at -30 and a descent along a flow of speleothems and then between corroded walls: flutes, overhangs, erosion blades. Its floor (5 m by 1.5) is flat, made up of a clogging of clay and gravel. Above a small niche, a climb gains a joint intersection where the calcite covering the walls has its crystals exposed. In the middle of the small shaft, a fissure gives at the bottom of a spacious, speleothem-covered chimney, whose opening at the very top seems to communicate with the entrance shaft. The continuation is at the bottom of the small shaft, beneath a rock bridge separating two short conduits that join to become the top of the Ushuaia shaft; the descent is enlivened by the passage of rock bridges and by a very high and fine erosion blade, pointing upwards. Behind, a parallel speleothem-covered shaft, topped by a chimney, has been explored; its floor offers an impenetrable meandering start and, at mid-height, a decimetric skylight lets stones fall for a few metres.

Below the opening of the P15, a very steep squeeze would be the low point of an Entonnoir (funnel) formed by the great joint, a narrow Entonnoir coated with a mud hitherto rare in the cavity. After enlargement, a short slide pours into a fairly wide P8, with a crumbling floor; on the side, a small vertical conduit quickly pinches out. Opposite, one enters horizontally into a niche that overlooks a shaft of a diameter approaching one metre, fairly irregular, where the vestiges of an important speleothem deposition are noted; at -154, an impenetrable fissure had to be enlarged. Behind, a shaft splits in two over a few metres: one branch is quickly blocked, the other leads to a vertical squeeze followed by a small shaft. The verticals cut by narrowings then lead to a zone where the white rock appears in a small chamber cluttered with important blocks of calcite, remains of floors, and speleothems still in place but in the process of dismantling; one is at -185. A little higher, towards -170, vestiges of a stalagmitic floor strewn with sand were observed on the wall: one would therefore be crossing an ancient filling "cleaned" over nearly twenty metres. The bottom, at -188, is a vertical tube 1 m in diameter, its floor clogged with a very plastic clay; a sump allows one to see a little lower, on the side, but the digging out seems impossible.

Almost directly above the Ushuaia shaft awaited the P62; morphologically, the two shafts are but one, and only blocks wedged behind a rock bridge prevent one from entering the P62 directly without setting foot in the joint. A P97, almost a P100! The entrance of the shaft is vast, but 2 m below, a rocky floor is pierced by a narrower elliptical opening, the start of a straight vertical conduit with perfectly smooth walls, about ten metres long. Then the shaft widens to 4 to 5 m in diameter, showing on one wall the remains of large stalagmitic flows; a second ledge, 17 m from the bottom, is made up of a rock bridge masked by blocks. A fissure high up gives, after a few metres of climbing, onto a parallel shaft topped by a chimney, itself adjoining another impenetrable vertical conduit. At the bottom of this shaft, fossils are visible on the wall, as well as the trace of dormouse claws in a small clayey filling. The P62 originally stopped at an earthy clogging sloping gently down towards a concave wall, where a few tiny fissures left a little hope; the digging out showed that the earth was only a slight thickness, and beneath it blocks of fairly large size, many of them made of calcite, let through a motivating draught. The continuation, meandering, had to be notably enlarged: a very small skylight a few metres further on became the access to a step that opens onto a pretty incised meander, which itself gives onto a fairly wide shaft by successive ledges. At this level one leaves the breccia to find the white limestone again; the bottom of the shaft is a stepped meander descending towards the NE, as far as a small hole giving into a clogged flat-out passage, and on the wall an enlarged fissure has yielded the continuation. One arrives in a crushed zone where all the walls are corroded, often unstable. Just below the skylight, the traces of an ancient mud clogging are observed over a few metres; one is roughly at the altitude of the bottom of the other branch (same rock, clogging). Below, a fairly wide shaft is barred by an enormous block, then a small ledge, then another narrow and "rascagnous" shaft, and at -200 one lands in a chamber with a floor of unstable scree. On one side, a "lean" shaft descends, after a delicate narrowing, to a calcified bottom; above, a narrow chimney will flirt topographically with a -188 branch, at identical altitude, offset laterally by 3 m (stopping on blocks, with a fairly important trickle).

In the crumbling chamber, towards the NE, one follows the left wall to avoid a shaft almost entirely blocked by imposing crushed blocks, at the bottom of which a fissure surely communicates with the bottom of the chasm. One is at the top of a shaft with dangerously flaking walls that opens into the most vast place of this part of the cavity: a volume whose floor is punctured by several shafts separated by unstable blocks and rocky edges. One of them, in the middle, leads to the low point: a niche on the NW side where two full gour pools appear to be fed by a speleothem-covered forced conduit. This shaft communicates through a skylight with a step further to the W; behind it, a fissure in the wall descends a notch into the crystallized white limestone, found again just at this spot, all the rest being excavated in the breccia. Several narrow chimneys have been partially climbed. On the SE side, another shaft leads to the continuation; high up, opposite one of the possible accesses to this shaft, in a high joint, one is stopped after a climb by calcified blocks that let air filter through. At the bottom of the shaft, an incision 10 cm wide cut into the rocky floor (it has since been masked by the remains of the digging out); the enlargement of this incision allows one to enter a low passage, the threshold of a speleothem-covered niche.

The entrance, originally impenetrable, is between two subvertical fluted walls; four m lower, one moves away from it to gain a wider perpendicular fracture, at the bottom at -13. One can gain towards the NW a crumbling chamber where two descending passages are possible, one very narrow and speleothem-covered, the other between blocks. Below, one finds another small chamber, sloping. To the West, a low passage opens onto a third small chamber rising, with a ceiling made up of a cone of debris; the wall above the low passage is made of a beautiful dark grey limestone striped with parallel horizontal calcified fissures, visible only at this spot. At the top of the chamber, a digging out has allowed the opening of a small shaft in two parts separated by a narrowing; the bottom is cluttered with blocks with diverticula rising beneath cones of debris.

The Ushuaia shaft opens by narrowing into the great joint, a NS fracture strongly inclined towards the E, where the W wall offers a beautiful spectacle of underground lapiaz with deep flutes, so deep that one of them opens onto a pretty P17 whose bottom narrows seriously when one leaves the breccia to find a crystallized white limestone more reluctant, it seems, to cavern formation; the continuation is but a tiny descending crawl. A little higher in the fracture, a chimney appears "balcony-like" in the ceiling; it allows, by small conduits and a crumbling chamber, to climb back towards about -60.

The entrance shaft descends along a flow of speleothems. The small shaft behind the skylight is speleothem-covered, and the chimney above its median fissure is as well. The parallel shaft explored behind the erosion blade is speleothem-covered and topped by a chimney. In the shaft of a diameter approaching one metre, the vestiges of an important speleothem deposition are noted. In the small chamber at -185, important blocks of calcite, remains of floors, neighbour with speleothems still in place but in the process of dismantling; towards -170, vestiges of a stalagmitic floor strewn with sand were observed on the wall. The P62 shows on one wall the remains of large stalagmitic flows. In the niche on the NW side, two full gour pools appear to be fed by a speleothem-covered forced conduit.

a weak aspirating draught is perceptible through small centimetric openings in the wall, a few metres above the bottom at -188, despite the clay plug. In the sector of the "lean" shaft, the whole sector is well watered, and the stop on blocks is made with a fairly important trickle.

Back to the entrance shaft: a slide, too muddy, encourages going to rig the continuation by passing through a narrower zone of the joint, high up. Behind one of the erosion blades, a pendulum allowed spotting a fissure probably communicating with a chimney explored lower down. The continuation is towards the South, where the wall is adorned with erosion blades, via a short and rough downclimb that ends in front of an enlarged skylight passage, and behind which opens a small speleothem-covered shaft. The descent of the P62 is very pleasant. a fissure high up gives after a few metres of climbing onto a parallel shaft topped by a chimney. Each shaft descended "on the first go" in the crushed zone gave rise to a consequent purge. The enlargement of the incision allows one to enter a low passage, the threshold of a speleothem-covered niche.

The explorations of the deepest branch have allowed the discovery of a chimney that topographically comes very close to the terminus of -188: there are therefore nearby voids and a probable communication. During the ascent of the entrance shaft, at -40, a dormouse was seen trotting on a slightly overhanging wall. In the P62, fossils are visible on the wall at the bottom of the shaft, as well as the trace of dormouse claws in a small clayey filling. Despite the clay plug at -188, the digging out seems impossible (or else one must throw the clay onto the walls to stick it there, we tried!).