6 ( No. 98 GEOGRAPHY is the great volcanic massif of Jebel Marra ( 9,000 ft. ) . South and south -west of this the country is more fertile and better watered, while east of the Nile the soil is of a much richer type, being especially so near the fron tier ( Tokar, Kassala ) and in the rich alluvial tracts of the Gezira between the Blue and White Niles . The so - called Isle of Meroe , between the Atbara, Blue Nile, and White Nile , exhibits all the varying features of the transitional zone, while in the Gezira the Sudan reaches its highest point of potential fertility .

( 3 ) The tropical zone, between the 10th parallel and the Uganda frontier, consists of a wide and shallow depression, bordered to the west and south by the Dar Fertit hills, the plateau of the Nile-Congo watershed, and the mountains of the Uganda frontier , and to the east by the outlying south-westerly spurs of the Abyssinian highlands. The greater part is clothed with savannah, open forest, and bamboo jungle . The bottom of this basin, especially between the Bahr el-Ghazal and Bahr el- Jebel, is permanently water logged and forms a large swamp area . East of the Bahr el-Jebel, much of the Sobat-Pibor and Mongalla districts consists of marshy grass-land, forming a savannah swamp during the wet season, but parched and sterile in the dry months. On the Uganda border this gives place to a group of rugged granite moun tains rising in the Imatong rangeto over 9,000 ft. in height . This region is still imperfectly known.

Coast The coast line , from Bir Shalatein to Ras Kasar, is about 400 miles long. The only bays of importance are Dongonab or Dokhana (at about 21° N. ) and Akik, north-west of Ras Kasar. The shores are low , and consist mainly of coral furrowed by numerous streams ( khors ) . The coastal plain , varying in breadth from ten to twenty miles, rises gently to meet the well defined foothills of the Red Sea range. Twenty -seven miles south of Suakin the mountains approach the