14 U.S. NATIONAL MUSEUM BULLETIN 2 75 



Near Murzuch the Cretaceous Nubian Sandstone outcrops, forming 

 the Murzuch Cuvette. The "Murzuch Limestones" (Cretaceous) form 

 a series of limestone plateaus of lacustrine origin and contain gastro- 

 pods. The plateaus are deeply eroded and are overlain by deep 

 Quaternary deposits. 



East of the basaltic Gebel el Harug el Asued, marine deposits are 

 covered by the "Continental Terminal," which contains the remains 

 of saurians, tortoises, fishes, and silicified woods. 



The Gebel Uweinat is a mountain massif located near the Libyan, 

 Egyptian, and Sudanese borders. Basally, it is formed of middle 

 Pre-Cambrian crystalline schists, which have been intruded by 

 granite, which forms the greater part of the Gebel. Following mag- 

 matic activity, a basal layer of Carboniferous sandstones was de- 

 posited, followed by several layers of continental sandstones containing 

 silicified wood. 



Volcanic Activity 



Volcanic activity occurred in three regions of Libya: the Gebel 

 Gharian (Gebel Nefusa) south of Tripoli, the Gebel es Soda south of 

 Socna, and the Gebel el Harug el Asued of southeastern Tripolitania 

 and the northeastern Fezzan. These eruptions began in the Oligocene 

 and continued until the Recent. Volcanic extrusions of the Gebel el 

 Harug el Asued cover an area of 25,000 square kilometers and are 

 represented by two major basaltic divisions. The first eruptions 

 inundated the Eocene Plateau and today form an extensive lava field. 

 A plateau of scoriaceous basalt of more recent origin occupies the 

 center of the massif. The most recent basaltic flows have been de- 

 posited by volcanic cones, which still persist but are inactive. At 

 present, there is no volcanic activity in any of these areas in Libya. 



Climate 

 Libyan Interior 



Two climatic subdivisions of the Libyan interior can be recognized: 

 an arid or desert type, and a semiarid or steppe type. 



Arid or Desert Type 



The Saharan portion of Libya is typical of the low latitude desert 

 as regarded by Trewartha (1937), and unless stated otherwise, the 

 following meteorological data relating to Libya was obtained from 

 this source. 



In the true Saharan portions of Libya, rainfall is always meager 

 and extremely variable from year to year. In these areas, the variabil- 

 ity of rainfall shows a 40+ percent departure from the normal, so 

 it is meaningless to speak of a "typical" rainfall curve for the Libyan 

 Sahara. Many areas in the interior of Libya receive less than one inch 



