Judging from the fossil shells, the marine inlet or the fluvial bed between the Mediterranean and the lacustrine basin of the Sahara, was definitely closed about the postpliocene period. Nevertheless, the riverain peoples of the shott, struck by the aspect of dried-up inlets presented by these basins, persistently maintained that communication formerly existed between the sea and the sebkhas, but that Alexander the "two horned" closed the outlet by his enchantments.
Before the geographical exploration of the country, the Isthmus of Cabes, between the sebkhas and the sea, was merely considered as one of those sandy
beaches such as are found on every shore before the mouths of rivers whose current, even when aided by the ebb and flow of the tides, is not sufficiently strong to clear a passage seawards.
It was supposed that sandhills had gradually raised the bar, which had itself probably been elevated above the sea-level by the effect of some inland disturbance. M. Fuchs, by measuring the height of the sill with a barometer, at last discovered the true state of the case.
From a mean elevation of 330 feet, the little chain of hills revealed two breaches from 190 to 200 feet high, whose geological formation he ascertained to
