GEOLOGY. 275 



Though the Sahara lies at such an elvation, yet AVO hear of no very lofty 

 mountains there; in Air, however, we come upon a few single peaks (the 

 Baghtzen, Dodschen, and others), but these are only from 3000 to 5000 feet 

 in height. Nor are there any extensive mountain chains, unless we except 

 the line of hills between Air and Ghat, and the Uariat, which eastward of 

 the Ghat A'alley stretches north and south, though even this nowhere rises 

 to any great height. It would appear that the southern part of this quarter 

 of the desert is even more mountainous in its character than the northern, 

 while this in its turn, with its extensive plateaus whose scarped sides give 

 them the appearance of gigantic blocks that have been suddenly pushed up 

 through the ground, possesses a peculiar interest of its own. If we compare 

 these lofty plateaus with similar elevations in Europe, we may conceive of 

 the highest part of the Gharian as being at an equal level with the most 

 remarkable table-lands of Europe, those of Spain and the Morea. The 

 two other plateaus may be compared with the highest of the Swiss and South 

 German table-lands, while the deep-lying Wady (500 feet) is about the height 

 of the elevated plains of Bohemia. 



This portion of the desert is therefore not low, but lofty ; not a monotonous 

 dead-level, but a broken highland; in short, it is a series of table-lands of 

 different elevations. Neither is this portion of the Sahara by any means a 

 sea of sand; in fact, only a comparatively small part of it answers to such 

 a description. But though the Sahara, as far as our information extends, 

 proves to be a highland, it does not follow that it is so throughout. The 

 probabilities of the case, however, are in favor of this conclusion. The 

 measurements of Vogel, in the year 1853, on his route from Tripoli over 

 Sokna to Murzuk, and thence to Bilma, show that some of the eastern por- 

 tion of the desert is likewise a table-land. It is true that he found the tract 

 between the base of the Gharian and Sokna much lower than elsewhere 

 (Boudschem is only 200 feet above the level of the ocean), but to the south- 

 ward of Sokna he ascended a narrow pass of the Black Mountains to a 

 plateau of 2000 feet in altitude, which stretched away in an unbroken surface 

 of from 1360 to 1590 feet, as far as Murzuk, and hence it appeared probable 

 that the Murzuk plateau at its eastern extremity merges into the Hamadah. 

 From Aschenumma, in the neighborhood of Bilma, Vogel writes: " I have 

 ascertained that the Great Desert is one vast plateau formation, of the 

 general height of from 1200 to 1500 feet." 



"With these data before us, based as the}* are upon scientific research, we 

 are prepared to give credence to the reports of the natives respecting the 

 mountainous character of many portions of the Sahara. The whole south- 

 ern region of the Tibbus Desert (Libyan) appears from such reports to be 

 covered with high mountains and mountain ranges ; in fact, near its southern 

 border two remarkable mountain clusters have been discovered, the Borghu 

 and the Uadschunga, which arc so elevated that the natives dress in furs. 

 But the loftiest mountain in the region of the Tihbus is the Tibesty, to the 

 northeast of Bilma, which, according to our accounts, is visible at the dis- 

 tance of four days' journey; we know, moreover, that the Tibbus, even from 

 the remotest parts of the country, floe for refuge from the attacks of the 

 Tuareg to its solitary cliffs, which, with their precipitous sides, tower up 

 from the rocky abysses at their base. These rocks are so steep that the 

 Arabs say of them, " Your turban will fall off if you attempt to look up to 

 their summit; " and Vojcel has aptly compared them to the rock upon which 

 the fortress of Konristein, in Saxony, is built. In regard to the westernmost 



