ORIGIN OF EOLIC DEPOSITS 697 



cas(% there must be extensive areas to receive the \vind-l)orue dusts, Tor 

 the latter can not be all transported to the ocean by the through-flowing 

 rivers of the desert nor by the streams of the contiguous semi-arid and 

 moist belts. 



The possible formation of desert plains of southwestern United States 

 and the tremendous differential action of deflation upon hard and soft 

 rocks in the Great Basin and tlie Mexican tableland are by no means 

 exceptional occurrences.*^ To vast deflative action is now ascribed the 

 surface expression of so many of the arid tracts of the globe that there 

 seems to be no longer any question of the verity of the process. In addi- 

 tion to the references given, mention may also ])e made to the conclusions 

 of Petrie*^ in the Nile delta, La Touche** in the Indian peninsula, of 

 Berg"^" in Siberia, of Ivchenko*^ in central Asia, of Hundhausen*^ along 

 tlie southern coast of France, of Davis*^ in South Africa, of Hume*^ and 

 of Barron^^ in the country between the Nile and the Bed Sea, of HilP^ 

 in northern Mexico, and of Blackwelder^^ in central Wyoming. 



DISPOSITION OF EXPORTED DUSTS FROM DESERT TRACTS 



The part which exported desert dusts play in the formation of con- 

 tinental deposits is only beginning to receive the attention which it 

 merits. Premising extensive wind-scour in an arid tract, the subject of 

 the final lodgment of the fine materials removed demands adequate con- 

 sideration. Of the desert dusts borne through the air the volume set- 

 tling on bodies of water is doubtless very much greater than is generally 

 surmised. Off the west and north coasts of Africa the amounts of Sahara 

 dusts blown into the Atlantic Ocean and the Mediterranean Sea are 

 commented on by many observers.^^ Eucker,^* Meunier,^^ and Hellman 

 and Meinardus^'^ in particular describe certain of these dust-falls. In 

 bays and arms of the sea, especially when situated adjacent to desert 

 regions, accumulations of this kind must be enormous. The Gulf of 



*a Journal of Geology, vol. xvii, 1909, p. 31. 



*3Proc. Royal Geog. Soc, vol. xl, 1889, p. 648. 



" Mem. Geol. Surv. India, vol. xxxv, 1902, p. 10. 



*-• Pedologie, 1902, p. 37. 



*«Ann. G6ol. Min. Russie, vol. vii, 1904, p. 43. 



*' Globus, vol. xc, 1900, p. 40. 



*s Journal of Geology, vol. xiii, 1905, p. 381. 



*« Top. and Geol. Pen. Sinai, Cairo, 1906. 



^'"Top. bet. Cairo and Suez, 1907, p. 115. 



^■1 Eng. and Mining Jour., vol. Ixxxv, 1908, p. 688. 



t^a Journal of Geology, vol. vii, 1909, p. 429. 



f^a Nature, vol. Ixiii, 1001, p. 514. 



f^-' Comptes Rendus de I'Acad. des Sci., T. cxxxii, 1901, p. 894. 



55Abhandl. K. Preuss. Meteorol. Inst., 1901, ii Bd., No. 1. 



68 Trans. American Inst. Mining Eng., vol. xl, 1909, p. 709. 



XLVI— Bull. Geol. Soc. Am., Vol. 22, 1910. 



