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In one of the vols. of the Scientific Exploration of Algeria (a 
work published by the French Government), a tale is told of a 
caravan of one thousand camels crossing the Chott, when one of 
the animals wandered a little from the way, and, as is their wont, 
was followed by all behind, and all successively disappeared in a 
sort of quicksand. And Moula-Ahmed, the authority for this 
story, states that when he crossed it, a surface of one hundred and 
fifty feet in breadth suddenly gave way, engulfing the men and 
camels who happened to be upon it, and none of whom escaped. 
Such are the Chotts, obviously the relics of an ancient sea, 
from the shallow parts of which the water has already vanished, 
and whose less shallow parés are now in process of being dried up. 
The deep hollow in which these chotts lie, soon attracted the 
attention of the French after they became masters of Algiers, and 
the question arose, was it beneath the level of the Mediterranean ? 
Many facts pointed to the probability of this being the case; and 
at last the French Government, in 1876, entrusted to Captain 
Roudaire, who had drawn public attention to this subject, and its 
importance, in an able and interesting article in the Revue des 
Deux Mondes, in 1874., the determination of this problem: and it 
was the model of this district, based upon the levels he had just 
taken, which drew my attention to the matter this last summer. 
In his report to the Ministry of Public Instruction, he gives a 
most instructive account of the methods by which he conducted 
and verified his levels, and the difficulties with which his 
observations were beset, owing to the extraordinary and ever 
varying atmospheric movements taking place in the heated air of 
the desert, and which are familiar to us as the cause of mirage. 
Suffice it to say, that he found the Chott Djerid separated from the 
Gulf of Gabes by an isthmus about twenty-five miles across, the 
highest part of which was about one hundred and thirty feet above 
the sea. That the surface of the Chott Djerid was about sixty 
feet above the Mediterranean. That the isthmus of Kriz in its 
highest part was about one hundred and thirty feet above the 
Mediterranean. That the surface of the Chott Rharsa was about 
sixty feet de/ow the Mediterranean, as were the numerous Chotts 
