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dwell on them on this occasion. I shall conclude with noticing 
some of the changes which have been, and still are, going on 
in Africa and Asia. 
M. Charles Martins, of Montpellier, gives the following 
account of the physical characters of the great Sahara, or 
desert, in the province of Constantine : — 
“We entered a district composed of grey, blue, yellow, and red marles, 
associated with conglomerates and limestones, cut up into deep ravines by 
the torrents which, during the rainy season, descend from the rock-salt 
mountains. These ravines, from fifty to sixty yards in depth, were so close 
to each other that it would have required several days to reach the foot of the 
mountain, distant only a few miles in a straight line, through this labyrinth 
of gorges separated by sharp narrow ridges. Let those geologists who wish 
to describe the erosive action of pluvial waters set aside the "wretched 
examples they quote to illustrate their argument ; let them visit Algeria, and 
gain their inspirations from the ravined district of Djebel-el-Mela and the 
mountains of the Kabyle. There they will see how the erosive power of 
water is able, under our very eyes, to transform a level plain into a mass of 
mountains as varied and broken in their forms as those which have been 
caused by the elevation and fracture of strata.” 
The Sahara itself is a dried-up sea-bottom. No correct 
estimate can be made when the inland sea disappeared, but the 
indications presented by the marine deposits favour the idea 
that the event was not very remote. M. Martins observes : — 
“ When it took place, the Mediterranean existed as it is now, 
for we find in the Sahara the shells of the same mollusca which 
still live on its shores.” Indeed, a very large area of the 
Sahara is still below the level of the Mediterranean Sea, from 
which it is separated by an isthmus of sand and gravel. The 
communication having been thus closed, the inland sea-waters 
have been absorbed and evaporated. “Were this isthmus 
broken through, a large area of the Sahara would again 
become a sea.” These changes bordering the African coast 
appear to have been brought about more from the influence of 
prevalent winds and currents, tropical rains, and the sand- 
storms of the desert, than from any great upheavals. Drifted 
sands in eastern Africa have overwhelmed the temple . of 
Jupiter Ammon and the villages on the west side of the Nile, 
and have thus converted the scenes of habitation and cultivation 
into a barren, sandy desert during the last three thousand 
years. Look at Thebes and behold its colossal columns, 
statues, temples, obelisks, all desolated and dilapidated. Yet 
its hundred gates were celebrated by Homer, and its magnifi- 
cence praised during its decline even by the Romans. It and 
other great cities, including Carthage, flourished within the last 
