322 NORTH-EAST AFRICA. 



penetrated much farther southwards than at present. But in that case it is difficult 

 to understand how these fossil woods could have been stranded in such a good state 

 of preservation, and, moreover, without being associated with any of those vegetable 

 or animal marine organisms which are always found adhering to driftwood. Nor 

 is any theory advanced to explain how this flotsam and jetsam could have been 

 borne over lofty mountains to the upland plateaux of Abyssinia. 



On the other hand it is impossible to suppose that these petrifications can have 

 been brought down by fluvial currents such as that of the Nile, because they are 

 nowhere associated with any alluvial deposits. Hence these sterculiaceaB of the 

 Nilotic basin must be regarded as still in situ, or at least in the immediate vicinity 

 of the places where they originally flourished. The opinion which finds greatest 

 favour with geologists is that the vegetable fibres were gradually petrified under 

 the action of thermal waters, such as still occur in various parts of Egypt, and 

 especially in the region of the oases. Becoming saturated with these waters, the 

 fallen trunks would be gradually changed to stone, just as they become converted 

 into peat or turf in the swampy districts of more northern latitudes. 



Doubtless the petrifications of herbs and other vegetation at present going on 

 round about the geysers of Iceland and of Montana in North America, differ from 

 those of the Egyptian deserts in their general appearance and process of formation, 

 for in these districts the plants are changed not into particles of quartz but into 

 amorphous flints. But allowance should, perhaps, be made for climatic dif- 

 ferences and for the long action of time. Close to the " petrified forest " of Cairo 

 is observed a dome-shaped sandstone hill, the Jebel-el-Ahmar, or " Red Mountain," 

 the interior of which is easily quarried, thanks to the softer character of the deeper 

 strata. May not this sandstone hill, isolated amid the surrounding nummulitic 

 limestones, have been gradually accumulated by the action of some ancient geyser ? 

 And to the similar action of thermal springs may we not attribute the preservation 

 of the trees on the neighbouring plain, which at that time was doubtless thickly 

 wooded ? 



The Western Oases. 



To the west of Egypt as well as to the west of Nubia a chain of oases is 

 developed which describes a curve almost parallel to the course of the Nile. The 

 first of these oases is that of Kurkur, which although scarcely more than 60 

 miles from Assuan, has never been inhabited. At about the same distance in a 

 north-westerly direction stretches the so-called "Great Oasis" of the ancients, now 

 known as that of Khargeh, from the name of its chief town. Including the palm- 

 groves of Beris, it occupies a depression stretching north and south for a distance of 

 90 miles. It does not, however, form one continuous oasis, but rather an archi- 

 pelago of small oases, a cluster of cultivated islands separated from each other by 

 intervening tracts destitute of vegetation. 



"West of Khargeh lies the oasis of Dakhel, or Dakleh, that is to say, the 

 "Interior," also known as the Wah-el-Grharbieh, or "Western Oasis." Dakhel is 



