Fig. 10. — ^Datb Palms (Jiiuwing in Artificial Depressions in Sand Dunes 

 AT El Wad, S. Algeria. {Photo : V. H. W. Dowson. July, 1922.) 



'£ 



Fig. 11. — Ridge of Cretaceous Limestone carved by Wind-driven Sand, 

 AT Umm Shersher, S. of Kharga Oasis, Libya. {Photo : F. W. Green, 

 Geol. Survey, of Egypt.) 



