ORIGIN OF THE OASES. 325 



for the most part thermal; other waters contain sulphur, while the so-called 

 fountain of the '' Sun," said to be alternately cool in the middle of the day and 

 warm at night, has really a nearly uniform temperature of from 84° to 85° F. 

 It has been identified with the spring still flowing at some distance from the 

 temple of Um-beidah. At the same time it is easy to understand that, in the 

 absence of precise measurements, the ancients may easily have been deceived as to 

 its real temperature, and thus suppose it cold by contrast under the burning sun, 

 and hot during the chilly nights. 



With the date groves of the oasis are intermingled the olive, the apricot, the 

 pomegranate, the plum, and the vine, while the clearings are planted with onions. 

 Although annexed to Egypt in 1820, Siwah is rather a geographical dependence 

 of Cyrenaica ; for it is connected with the slopes draining to the Gulf of Sidra 

 by the Faredgha oasis and by other verdant islets surrounded by rocky and sandy 

 wastes. 



Towards the north another depression in the plateau on the route to Alexan- 

 dria is occupied by the oasis of Grara, which is inhabited by some forty persons. 

 According to a local tradition this number of forty cannot be exceeded, death 

 inevitably re-establishing the equilibrium whenever disturbed by an excess of 

 births or by too great an inroad of immigrants. 



Origin of the Oases. 



At sight of the chain of oases diverging from the Nile, and winding through a 

 series of valleys and gorges seawards, it was only natural to regard these low-lying 

 and fertile tracts as the remains of some old watercourse, some western branch of 

 the Nile now partly obliterated by the invading sands. The natives have pre- 

 served legends recording the gradual desiccation of this waterless stream, and 

 down to a recent period most travellers still sought the traces of the Nile in the 

 oases of the Libyan desert. Even on some contemporary maps the channel of 

 the so-called Bahr-Belâ-mâ is drawn from valley to valley, as if its course had 

 actually been determined by local surveys. 



It is in any case highly probable that at some remote geological age fluvial 

 or marine waters, excavating straits and valleys, may have flowed through the 

 region now occupied by the oases. But during the present epoch no branch of 

 the Nile or inlet of the Mediterranean has penetrated into these depressions of the 

 desert, which contain neither alluvia of fluvial origin, nor marine deposits asso- 

 ciated with contemporary molluscs. Nevertheless the thermal waters of the oases 

 contain animal species belonging both to the Mediterranean and Red Sea fauna. 

 Such, for instance, are the two little fishes called cyprinodon dispar and cyprinodon 

 calaritanus* 



But if in their formation the oases are independent of the present Nile, they 

 may possibly be connected with it through the waters which feed their date 

 plantations. Certainly the copious springs serving to irrigate the oases of Dakhel 



* Zittal, " Die Sahara." 



