Latitude 15° 1,525 feet (north of Tanout) 1,800 feet (Tanout). „ 18° 1,000 feet (desert west of Aïr) 1,600 feet (desert east of Aïr) 1,220 feet (Bilma Oasis. Longitude 13°) „ 20° 1,500 feet (Gara Tindi) 1,350 feet (In-Azaoua) „ 22° 3,100 feet (Zazir) } 3,700 feet (Tenacurt) }Land rising to the Ahaggar 4,200 feet (Tamanrasset)}Mountains. „ 30° 350 feet (Hassi Inifel) Land that falls gradually 600 feet (Messedli) away to a low basin in the El Erg region between the Ahaggar and Atlas Mountains. The widespread aspect of the Sahara is of vast desolate plains of rock and sand. But a fact which has been overlooked to an astonishing degree, by popular consent, is that the Great Desert is relieved by some very remarkable mountain groups, chief of which are Aïr, Ahaggar, and Tibesti—each in extent as large as the whole of England, and towering majestically to altitudes of 6,000 to 10,000 feet. They are mountains that are lost to the world; full of mystical silence, like the rest of the Sahara, and bleak and wild, yet they are vast and rich in rugged grandeur; and the greys and browns of their slopes are a feast to the eyes of traveller weary of scanning limitless plains of sand. [Illustration: A DEEP RAVINE IN THE TASSILI OF AHAGGAR WITH POTHOLES OF WATER IN THE BOWELS OF THE ROCK] Aïr and Ahaggar I know well; Tibesti I have not visited. The former are, in general, alike, particularly in rocky bareness and eerie desolation; but, of the two, Aïr is the more picturesque and fascinating. Both, accentuated by their desert surroundings, stand out in strong, clear relief, aggressively bold and dominant—majestic in every line, amid unrestricted space of earth and sky.