In these two species, as well as in some others, these forests are like those on the higher lands of the Bahr El Ghazal province and parts of Southern Kordofan. The Bahr El Ghazal forests cover the larger portion of the ironstone deposits in that province, and, as far as quality goes, are probably the finest found in the Sudan, many trees of great height and girth being found there, one of them, the African mahogany (“Homraya,” _Khaya senegalensis_), having a beautiful timber, already known to commerce. It is in these forests that rubber-producing lianas are most abundant, the best of them being “Ndala” or “Odilo” (_Landolphia owariensis_), _vide_ Chapter VII. The forests on the Bahr El Jebel and the woodlands of the Bahr El Ghazal province are more like those on the Upper White Nile, but some other trees appear, and the forests are not only in belts, but cover large areas. Near Mongalla the ironstone appears, and the forests partake of the same character as those of the Upper Bahr El Ghazal. The forests on the Abyssinian and Eritrean frontiers have not yet been explored by an expert. All over the Sudan the forests suffer greatly from fires which are set alight by the natives either for purposes of sport, or to clear the paths, or for grazing after the rains. Owing to these fires numbers of trees get killed or mutilated, and it is hopeless to think of developing fine forests until they can be kept under control. [Sidenote: Fuel.] One of the great economic questions of the Sudan, which gives rise to a certain anxiety, is the future supply of fuel. Although the felling of trees is under control, those alongside the river necessarily suffer greatly from the demand for steamer fuel, and there is not an unlimited supply. So far, no coal or petroleum has been found in the Sudan; it is believed that there are beds of lignite in the Dongola Province, but up till now they have not been thoroughly explored. Imported coal now costs from £E.4 to £E.6, and petroleum £E.6, a ton at Khartoum. (_Vide_ also p. 20.) [Sidenote: Concessions.] A certain part of the Sudan—chiefly to the north and north-east and south-east—has been leased to concessionaires for the purpose of prospecting for minerals and exploiting them when found. There are traces of gold and other minerals in most of these areas. [Sidenote: Survey.] The Sudan is being surveyed (commenced in 1898) on a scale of 1/250000. So far, over 50 sheets out of 139 projected have been published, and the work of surveying is proceeding steadily. _Vide_ p. 349. [Sidenote: Sanitary.] The population is very gradually being trained in sanitary methods, but it is a slow process. Efforts are also being made to stamp out malaria,[16] etc., by the latest scientific methods, but the size of most of the malarial districts is vastly in excess of the means so far available to deal with them. At Khartoum and at some of the other chief towns the steps taken have proved most effectual.