356 REPORT— 1882. 



the Chinese, the haven of the great city which we know as Hangchow, 

 and which then lay on or near a delta-arm of the great Yangtse.' 



The chief works of which I have made use in the foregoing (besides 

 the original authorities named at the beginning, the Arabic ones in 

 published translations, chiefly French), are Richthofen's 'China,' Bd. i. 

 1877; the same author's papers 'Ueber den Seeverkehr nach und von 

 China in Alterthum und Mittelalter,' in the ' Transactions of the Berlin 

 Geog. Society ' for 1876 ; Sprenger, ' Post- und Reise-Routen des Orients,' 

 Leipzig, 1864; A. Maury, ' Des Anciens Rapports de I'Asie occidentale 

 avec rinde Transgangetique et la Chine,' in ' Bullet, de la Soc. de Geog. de 

 Paris,' 1846 ; Mr. Bunbury's work just quoted ; various notes of my own 

 in ' Cathay and the Way Thither,' ' Marco Polo,' and the text to my map 

 of Ancient India in Dr. W. Smith's ' Atlas of Ancient Geography.' 



The Deserts of Africa and Asia. By P. de Tchihatchef, Member 

 of the Academies of Sciences of Paris, Berlin, Munich, St. Peters- 

 burg, &c. 



[A communication ordered by the General Committee to be printed in extenso among 



the Reports.] 



The large sandy surfaces which occupy immense tracts on our globe 

 suggest naturally the belief of their being recently dried-up sea-bottoms, 

 an impression enhanced by the presence of salt efflorescence and shells 

 of still existing mollusks. It is therefore not surprising that the two 

 largest deserts of the world, viz., the Sahara in Africa and the Gobi in 

 Asia, have been, or are even sometimes now, considered as representa- 

 tives of recently raised-up sea-basins. But the latest explorations tend 

 to prove the contrary, at least as far as the Sahara is concerned, and the 

 little we know of the great Asiatic deserts seems to lead to a similar re- 

 sult. My intention is, therefore, to submit a few considerations on the 

 geological age of the following three deserts : the Sahara (the Lybian 

 Desert included), the deserts situated in Turkistan between the Jaxartes 

 and the Caspian Sea, and the Gobi of Central Asia. 



Before speaking of the Sahara, I must observe that this collective 

 name is applied to an immense region which forms a very broad strip 

 across the whole of Africa, from the Red Sea to the Atlantic, occupying 

 an area almost equal to the thii-d of the African continent. This desert, 

 the largest of the world, is dotted with oases, scattered on the sandy 

 surface like so many islands amidst the sea, and is known only in the parts 

 which belong to Algeria, Tunisia, and Tripoli (the last part being called 

 the Lybian Desert), whereas the western portion of the desert is still a 

 terra incognita ; therefore, I ask you to remember that by the name of 

 Sahara I mean only the more or less explored regions, adding, that what 

 we know of them is most probably applicable to the unknown or little 

 known tracts, the more so since they are almost exclusively composed of 

 sand accumulation, the origin and the formation of which we are able to 

 study in the Algerian and Lybian Deserts. 



Since Algeria (which I visited two years ago) has been annexed to 

 France, our knowledge of this country has made very rapid progress, so 



• See Marco Polo, 2nd ed. ii. 181, 182. 



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