10 U.S. NATIONAL MUSEUM BULLETIN 275 



western margins of the Sand Sea of Calanscio to the eastern limits 

 of the Gebel el Harug el Asued. 



Fesh-fesh 



In some areas of Libya, the surface layer is composed of extremely 

 soft and unstable materials similar in texture to silt or loess deposits. 

 These "fesh-fesh" deserts are usually restricted in size but occasionally 

 cover large areas. This type of desert is most abundant in areas of low 

 elevation and along the margins of depressions such as the Sebchet el 

 Gheneien, north of Gialo, and Giarabub Oasis. The hamadas and 

 serirs sometimes grade imperceptibly into local "pockets" of fesh-fesh. 

 This intercalation of serir and fesh-fesh occurs frequently in the 

 western part of the Serir of Calanscio near the eastern limits of the 

 Gebel el Harug el Asued. 



Depressions 



The depressions associated with Giarabub Oasis and Bahr el Tubat 

 and the Sebchet el Gheneien north of Gialo are physiographically 

 distinct from the surrounding terrain. These depressed areas are 

 located great distances from the sea but are below sea level. These 

 low-lying areas of Cyrenaica represent the westernmost limits of the 

 great east-west depression which links together Siwa Oasis, theQattara 

 Depression, and the Wadi Natroun of northern Egypt. Most of these 

 low-lying areas have extensive salt marshes in their lowest portions, 

 and the larger depressions frequently contain saline lakes of con- 

 siderable size. Bahr el Tubat, east of Giarabub, is typical of this type 

 of shallow salty lake, which has thick encrustations of salts along its 

 margins, which in some places extend several hundred meters from 

 the waters edge. Smaller saline lakes occur in the oases of Tazerbo, 

 Cufra and Bzema of southern Cyrenaica, and isolated pockets, con- 

 taining some open water with marginal encrustations of salt, are of 

 sporadic occurrence in the central Fezzan. 



Mountainous Areas of the Interior 



Scattered throughout the interior of Libya are numerous rocky 

 escarpments, large wadis with steep rocky margins, and extensive 

 desert mountain ranges (gebels). Most of the mountainous areas of 

 the Libyan hinterland are characteristically rugged with sharp con- 

 tours and have broad canyons with angular rock formations and 

 precipitous walls. Isolated rock formations, some of which reach huge 

 proportions, occur irregularly throughout the Fezzan and southern 

 Cyrenaica. 



The larger mountain complexes of Libya are volcanic extrusions 

 and are surrounded by great expanses of coarse, boulder-sized talus. 



