RODENTS OF LIBYA 9 



black. The majority of these hamadas are usually flat and lack any 

 contrasting physical features. The coarser hamadas tend to have 

 more undulating; surfaces, and occasionally local mounds or rocky 

 outcroppings are present. In general, the hamadas show little change 

 in relief, being of comparable elevation throughout their full expanse. 

 Some of the larger hamadas stretch uniterruptedly for several hun- 

 dred kilometers and in this respect are remote and desolate. 



Sand Seas 



Although occupying a smaller total land area than the hamadas, 

 the sand seas or "ramleh" are one of the most distinctive physical 

 features of the Sahara. They occur sporadically in the interior of 

 Libya where they are contiguous with the hamadas and frequently 

 interdigitate with them. Small and localized sandy plains and dune 

 areas are present in the Libyan interior, but the principal sand seas 

 are represented by the Sand Sea of Calanscio of east-central Cy- 

 renaica; the Sand Sea of Rebianna, which is continuous with the 

 latter and extends to the northern outliers of the Tibesti Mountains 

 of extreme southern Cyrenaica; the great Idehan Murzuch of the south- 

 ern Fezzan and the Idehan Ubari of the southwestern Fezzan, which 

 includes virtually all of the region south of the Hamad a de Tinrhert 

 to the Wadi Irauen and Wadi el Agial and includes the area from 

 Sebha west to the Algerian border. The "Ramleh Zellaf," immediately 

 north of Sebha, is the easternmost portion of this immense sand sea. 



Normally these sand seas have gently undulating surfaces, but 

 frequently extensive dune areas occur. The individual dunes vary in 

 size, but some reach almost mountainous proportions, sometimes 

 exceeding 250 meters in height. Some of the dunes of the Sand Sea 

 of Calanscio are reputed to be even higher. In many areas the dunes 

 are relatively stable, but in others they are constantly changing 

 shape and shifting their positions. Firmness of the sand varies mark- 

 edly from place to place and according to the time of day, being 

 firmer during the cool, early morning hours than in the hotter periods 

 of midday. 



Serirs 



Occasionally, bedrock is covered with a veneer of sand and gravel 

 of varying depth. When these areas are quite extensive, they are 

 known as "serirs" and differ from typical sand seas by their more 

 uniform surfaces and the coarser, more heterogeneous nature of the 

 individual particles. The Serir of Calanscio, of central Cyrenaica, 

 typifies this physiographic type and includes the vast plain extending 

 from Gialo Oasis south to Tazerbo Oasis and extending from the 



285-134 — 68^—2 



