8 U.S. NATIONAL MUSEUM BULLETIN 2 75 



Saharan desert of the interior. These transitional deserts are generally 

 irregular in profile and are frequently dissected by numerous dry 

 watercourses (wadis) which drain northward into the Mediterranean. 

 Some of the larger wadis, such as the Wadi Bey, Wadi Soffegin, and 

 Wadi Zemzem of northern Tripoli t a nia, form characteristic topo- 

 graphic features with their deep canyons, boulder-strewn slopes and 

 broad, eroded bottoms. Gravel plains (hamadas) of small extent are 

 not uncommon in these marginal deserts and are frequently inter- 

 spersed with mud pans reminiscent of playas. Sandy plains and dune 

 areas are present also but are usually sporadic and localized. 



Farther southward, in the Sahara proper, these gravel plains and 

 sandy areas are of much greater extent and form discrete physio- 

 graphic entities which are known regionally by specific names, such 

 as the Hamada el Hamra of southwestern Tripolitania, the Idehan 

 Murzuch of the Fezzan, and the vast Sand Sea of Calanscio of eastern 

 Cyrenaica. 



Hamadas 



The terrain of most of the interior of Libya is typically Saharan, 

 being composed primarily of vast areas of pebble deserts or "hamadas" 

 interspersed among desolate sand seas or "ramleh." Mountainous 

 areas or "gebels" and rocky scarps frequently interrupt the otherwise 

 featureless landscape. Contrary to popular belief, these hamadas are 

 the dominant physical feature of the Sahara, the sandy plains (serirs) 

 and sand seas forming probably less than 20 percent of the total 

 land area. 



The hamada desert is a distinct physiographic type characterized 

 by extensive gravel plains formed of pebbles of various sizes lying 

 on top of a rather firm substrate. The size of the individual particles 

 varies considerably in the different types of hamada, ranging from 

 small pebbles to rather coarse rock-strewn surfaces. Regional differ- 

 ences in the character of the hamadas are sometimes striking. For 

 example, the Hamada cl Hamra of southwestern Tripolitania is of 

 the fine-grained type and provides probably the smoothest, most 

 featureless surface of any of the Libyan hamadas. The hamadas 

 farther south are much coarser in composition, especially those sur- 

 rounding the volcanic extrusions of the Gebel el Ilarug el Asued of 

 centra] Libya and the numerous localized hamadas which occur 

 between the oases of Traghen, Umm el Araneb, Meseguin, and 

 Zuila in the Fezzan. Some of these Fezzanese hamadas could be 

 likened to vast boulder fields. 



The overall coloration of these hamadas is generally gray, but 

 local variations of rod, yellow, and brown occur. The coarse hamadas 

 associated with volcanic extrusions are normally dark gray or even 



