GEOLOGICAL FORMATIONS. 287 



out the open plain. They are all in the form of a crescent, the horns turning to the 

 south under the influence of the north wind. 



Geological Formations. 



Nearly all the sandstone rocks and dunes are destitute of vegetation ; but few 

 shrubs are found on tLe slopes of the crystalline mountains, which are embellished 

 by these verdant thickets. Hitherto no fossils of animals have been discovered 

 in the sands of the desert of Korosko, but only some petrified trees, like those in 

 the Bayuda steppe, in Egypt, and several other countries of Eastern Africa. 

 According to Russegger, these Nubian sandstones have been deposited since the 

 chalk period. One of the most extraordinary products of this geological formation 

 consists of spheroidal stones of all sizes, resembling balls, shot, and bullets. They 

 are so thickly scattered over the soil that travellers had seriously proposed to 

 Mohammed Ali that he should supply his artillery parks from this source. These 

 stone bullets, similar to those found in Hungary in the mountains near Koloszvar, 

 are formed of concentric beds of variously coloured sands, hollow in the middle, or 

 else filled with loose sand, and with a very hard ferruginous exterior. The cir- 

 cumference of the stone is frequently marked by a ridge similar to that which the 

 moulds leave on the bullets at their point of contact. 



The great caravan route which traverses the Nubian desert, to the east of the 

 Nile, from Abu-Hamed to Korosko, extends over a space of about 300 miles, which 

 comprises some of the most remarkable localities, offering examples of all the 

 geological formations of the country. This region is specially termed atmiir, a 

 name probably of Berber origin, for in the language of the Tuaregs temura means 

 a " tract of country." After having ascended the trachyte-crested hills, and 

 surmounted the granite escarpments, the caravan route winds from breach to 

 breach between the sandstone hills, and even crosses a plain which, according to 

 the Arabs, is an ancient lacustrine basin, the Bahr-belâ-mâ, or " Waterless River." 

 Nevertheless there are no indications which point to the presence of running or 

 still waters having ever been in this place. One well only, that of Morad, yields 

 a scanty supply of fresh water to travellers crossing the atmur. But there are 

 régions in this desert where the sand contains abundance of saline substances 

 which doubtless proceed from ancient evaporated lakes. In the vicinity of the 

 river the natives extract this salt and sell it to the caravans. 



The largest of the dry valleys which wind through the desert of Nubia is that 

 of Wady-Allaki. Taking its origin in the mountains of the Etbaï, it follows a 

 north-westerly course and falls into the Nile below Korosko ; its basin is more 

 than 10,000 square miles in extent. It has occasionally happened that the 

 Wady-Allaki, suddenly filled by heavy showers, has for some hours suddenly 

 become a powerful affluent of the Nile, the force of its current completely barring 

 the main- stream. But the valley of the wady and the tributary gorges are nearly 

 always dry ; nevertheless, the concealed moisture is revealed by the trees, under 

 which the Bisharin tribes are accustomed to encamp. 



