. The story of Africa and its explorers. )servations of Erwin von Bary, there is a dis-tinct volcanic crater in the isolated mountain * Floyer, Kriv Bullrtin, No. 72, p. 290. t Playfair, Travels in the Footsteps of Bruce, , ^-^^, 1!)1, 212, 22f;; and Playfair and Browns Biblio-t,raphy of Morocco (//. (L S.), Introduction, pp. 208-9. mass of Air, with a vast lava stream down its In short, all the geological and topographical features of the Sahara go to prove that, while it must, like a great portion of Africa, have been under water at one time, this period was probably not later th
. The story of Africa and its explorers. )servations of Erwin von Bary, there is a dis-tinct volcanic crater in the isolated mountain * Floyer, Kriv Bullrtin, No. 72, p. 290. t Playfair, Travels in the Footsteps of Bruce, , ^-^^, 1!)1, 212, 22f;; and Playfair and Browns Biblio-t,raphy of Morocco (//. (L S.), Introduction, pp. 208-9. mass of Air, with a vast lava stream down its In short, all the geological and topographical features of the Sahara go to prove that, while it must, like a great portion of Africa, have been under water at one time, this period was probably not later than the Cretaceous epoch. Even then there would have been isolated masses, or islands, above the surface of the sea. One of the most remarkable facts about the Sahara is the comparatively small depth at which water is found. In the „ , . Underground Algerian soui the water actually water: circulates close to the surface of ^° ^^^ the soil, so that a well can be sunk almost any-. SIB E. LAMBEET PLAYFAIR. {From a Pliotograph hy H. J. IVhUlock, Birmingham.) where with comparative ease by simply pene^trating the layer of gypsum that covers thesandy substratum in which the water is con-tained. In Algeria, indeed, all the way fromBiskra—an oasis in the Sahara—to Timassin,throughout the whole extent of the WadyGheir, and even to the south of it, de-pressions known to the natives as Bahr (sea,lake), and to the French as Goiifres, arefound full of water. They appear to be thespiracles of a vast subterranean sheet of of these apertures, Sir Lambert Playfairtells us, are inhabited by numbers of X /citxrhriff fih- Erdkundi; 18S0. 84 THE 8T0BY OF AFRICA. tislies (Cyprinodontidce and Ghromidit), whichlive freely exposed to the air and hght,and breed under normal conditions. Tiieirunderground life is merely an episode, and,as it were, an incident in the voyages whichthey undertake between one hcdir and they reach the neighbourhood of awell, they a
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