4 . (No. 98 GEOGRAPHY > of the Sudan, the boundary, as defined by the Anglo French Agreement of March 1899, and the supple mentary convention of September 8, 1919, continues to follow the watershed to 11° north latitude . From 11° to 15° north latitude it runs to the junctionof the Wadi Azum and the Wadi Kaja ; follows the latter to the Wadi Azunga, which it follows to a point north of Jebel Kudri to be fixed by the Boundary Commission ; then turns N.E. , N. and N.W. to a point about half -way between the 15th and 16th parallels, where it turnsdue E. until it reaches long . 24 °, which is the eastern limit of the French sphere; it then turns N. and follows that degree of longitude until its intersection with parallel 19° 30 ' of north latitude. It will be seen that the frontiers dividing the Sudan from Egypt in the north and Uganda in the south are purely artificial, corresponding with neither racial nor geographical divisions ; and their exact position is of little or no importance. The eastern frontier, on the other hand, is exposed to certain disadvantages, includ ing that of leaving the head -waters of the great Nile affluents outside Sudan territory .

(2) SURFACE, COAST , AND RIVER SYSTEM Surface Such unity of character as the Sudan possesses is given to it by theNile valley, which forms its chief natural feature. The country is best conceived as a great plain or shallow depression, extending north from the equatorial lakes to the Egyptian frontier, and comprising successive zones of swamp , steppe, and desert . This plain is bounded to the west by the hills of the Nile-Congo watershed and the highlands of Darfur ( 8,000–9,000 ft . ) , and to the east by the Abyssinian tableland and its continuation in the Red 1 The actual wording of the Agreement is self-contradictory : see Italian Libya, No. 127 of this series (cf. also below , pp . 34, 35) .