30 The Sahara. 
of the African continent, and consequently produced serious modifi- 
cations of the climate of Europe. ‘There was a general impression 
that the Desert of the Sahara was of recent formation; but the 
opinions of geologists were divided as to the period to which it 
should be assigned, some considering it of Tertiary and others of 
Quaternary age. Our observations resolve these doubts, and defi- 
nitely fix the age of the Sahara, by the help of a little shell, the 
Cardium edule. This shell was known to exist in the neighbour- 
hood of the Caravanserai of Om-Thiour, near Chott-Melrir, and it 
had been found at a depth of about 23 feet in the artesian wells of 
that place.* From this it might have been supposed that it belonged 
to the Chott (or Lake) Melrir. But, on the other hand, we met 
along with it a species of Buccinum, from stage to stage, at a great 
distanee from the Chott (even near Guemar in Souf), always in the 
same geological position, in a bed of sand distinctly stratified under- 
neath the superficial gypsum. It thus became evident that the shells 
did not belong to the Chott, but to a lower stratum indicating a sea 
far more extensive and older than the salt lakes. These shells, 
therefore, not only attest the existence of a sea in those regions, but 
also that that sea belonged to our own epoch. Further the Cardium 
edule is, in the Mediterranean, a species inhabiting brackish waters 
at the mouths of rivers ; and we may conclude that the Sahara, be- 
fore being dried up, was an inland sea—a kind of brackish Baltic— 
and this amongst other things explains the small number of the 
species ; for it is known that the faunas of inland seas are poor in 
number and debased.t 
To sum up, when all communication with the ocean had ceased, 
and the gulf became a lake, the saltness of the waters would by 
evaporation increase so much as almost to destroy all animal life ; 
the Chott-Melrir would become like the Dead Sea; and, in fact, it 
is affirmed that it is completely destitute of life. 
This idea of a slow but recent elevation of the Sahara had already 
been mooted as a theory by M. Escher, and it was a source of lively 
satisfaction to him to find his hypothesis confirmed on the spot. 
The presence of this sea was referred to by M. Escher to explain 
certain phenomena in our country (Switzerland) connected with the 
Glacial period which ended when this sea disappeared. Is it possible 
to form an idea of the climatal conditions imposed on Europe by this 
vast extent of water? We may do so when we consider the influ- 
ence exercised by the burning winds which come from the Sahara, 
and which are so justly’called ‘ snow-eaters’ and ‘ glacier-destroyers.’ 
While the Sahara was covered with water our mountains never felt 
the burning breath of the ‘foehn’ and the ‘sirocco ; the winters, 
never opposed by a lukewarm breeze, could accumulate their snows 
* See Memoir by M. Ch. Laurent, Bullet. Soc. Géol. France, vol. xiv. p. 615, 
1856-7.—A. C. R. 
+ See observations made by Rey. H. B. Tristram, M.A., F.L.8., &e., in his work 
on ‘The Great Sahara’ (1860, Murray); also Appendix to 3rd edition of Lyell’s 
‘Antiquity of Man’ (Dee. 1863), p. 28.—A. C. R. : 
