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Trois Cavern

Andrea Balbo and Krish Seetah, ably assisted by Anwar Janoo of the University of Mauritius, undertook a daylong exploration of this underground cave system on the 10th of December 2009. Traces of human activity were recorded within some of those tunnels that may be connected to runaway slaves and/or later periods. Evidence of earlier human presence was not noted within these tunnels. A range of features were described and samples collected from the lava tunnel, including various animal bone remains (pig, dog), a human tooth, landsnails, possible temporary sleeping places along the tunnel walls (higher than the centre of the tunnel), and fireplaces along the tunnel walls. A test pit, dug in the tunnel in the 1990s, was also noted and served as a serendipitous occasion for stratigraphic recording.

The pit sequence included:

(a) 0-20 cm very dark brown clayey silt sheet flows with magnesium staining indicating sheet flow accumulation (possibly indicating more intense rain and erosion);

(b) 20-35 cm dark brown (7.5YR3/4) blocky silty clay;

(c) 35-65 cm clasts from a rockfall;

(d) 65 cm magnesium stains;

(e) 85 cm reduced yellowish green peds.

(c, d, e) 35-85 cm dark brown (7.5YR3/4) clayey silt;

The transition from (b) to (a) could coincide with clearing for sugar cane planting or with a transition to higher precipitation. The tunnel pavement is mostly made of angular basaltic clasts fallen from the tunnel roof (average 20 cm). Larger blocks (up to 150 cm) were present. Finer dark reddish brown (5YR3/2) sediment (silt and fine sand) was accumulated in the central part of the tunnel floor, along the tunnel axis, and includes animal footprints and charcoal. Channelling was observed on the finer sediment parallel to the tunnel axis, indicating the occasional presence of running water. Water and finer sediment are coming to the cave through the tunnel entrances as well as by percolation from the roof, as indicated by a clay film covering walls and blocks in the tunnel. Above the roof, land is cultivated with sugar cane. White spores were observed on the surface of the fine sediment. Occasional accumulation of finer sediment (clay) was observed within circular depressions along the tunnel axis.